Page 1

SUSTAINABLE BUILDING ENVELOPES: DSC INTEGRATED GLASSBLOCKS. PERFORMANCE ANALYSIS INVOLUCRI EDILIZI SOSTENIBILI: INTEGRAZIONE DI CELLE SOLARI DI TERZA GENERAZIONE NEL VETROMATTONE. ANALISI PRESTAZIONALE Thesis by: Dario D’Anna

Università degli Studi di Palermo Facoltà di Ingegneria

Corso di Laurea Magistrale a Ciclo Unico in Ingegneria Edile-Architettura

Involucri edilizi sostenibili: Impiego di materiali tecnologicamente avanzati per l’ottimizzazione energetica e l’incremento prestazionale degli elementi di captazione della luce naturale

SUSTAINABLE BUILDING ENVELOPES: DSC INTEGRATED GLASSBLOCKS. PERFORMANCE ANALYSIS / INVOLUCRI EDILIZI SOSTENIBILI: INTEGRAZIONE DI CELLE SOLARI DI TERZA GENERAZIONE NEL VETROMATTONE. ANALISI PRESTAZIONALE Supervisor: Prof. Rossella Corrao

Thesis by: Dario D’Anna

Assistant Supervisor: Prof. Marco Beccali Tutor: Ing. Luisa Pastore

2011/2012


Università degli Studi di Palermo Facoltà di Ingegneria

Corso di Laurea Magistrale a Ciclo Unico in Ingegneria Edile-Architettura

Involucri edilizi sostenibili: Impiego di materiali tecnologicamente avanzati per l’ottimizzazione energetica e l’incremento prestazionale degli elementi di captazione della luce naturale

SUSTAINABLE BUILDING ENVELOPES: DSC INTEGRATED GLASSBLOCKS. PERFORMANCE ANALYSIS / INVOLUCRI EDILIZI SOSTENIBILI: INTEGRAZIONE DI CELLE SOLARI DI TERZA GENERAZIONE NEL VETROMATTONE. ANALISI PRESTAZIONALE Supervisor: Prof. Rossella Corrao

Thesis by: Dario D’Anna

Assistant Supervisor: Prof. Marco Beccali Tutor: Ing. Luisa Pastore

2011/2012


a Myriam


Abstract Il lavoro di tesi che qui si illustra è stato condotto nell’ambito del Laboratiorio di Tesi di Laurea dal titolo “Involucri edilizi sostenibili. Impiego di materiali tecnologicamente avanzati per l’ottimizzazzione energetica e l’incremento prestazionale degli elementi di captazione della luce naturale” coordinato dalla Prof.ssa Rossella Corrao. In particolare, il laboratorio è finalizzato ad individuare possibili strategie per l’incremento prestazionale del vetromattone, proponendo anche soluzioni sperimentali, da utilizzare per la costruzione di involucri traslucidi con elevate caratteristiche di sostenibilità. Sono state indagate le problematiche connesse alla definizione di pannelli traslucidi che impiegano moduli fotovoltaici DSC integrati in vetromattoni modificati, per la realizzazione di involucri edilizi efficienti dal punto di vista energetico (isolamento termico, trasmissione luminosa) ed in grado di sfruttare, al contempo, la radiazione solare per la produzione di energia. L’elemento ripetuto nella costruzione del pannello è un dispositivo fotovoltaico composto da un modulo DSC integrato nel vetromattone. Il presente lavoro di tesi illustra le analisi condotte sulle prestazioni ottiche di tale dispositivo fotovoltaico, studiato in relazione a differenti configurazioni. La tesi comprende, inoltre, una raccolta di brevetti riguardanti la tecnologia DSC, registrati dal 1998 al primo semestre del 2011 e che sono stati individuati attraverso una ricerca condotta sul web insieme ad alcune schede di approfondimento sugli stessi brevetti ritenuti più significativi ai fini della comprensione delle potenzialità di questa nuova tecnologia fotovoltaica.

VII


Table of contents


Foreword NoTes

CHAPTeR 1 Introduction

1.1 european framework on solar energy and photovoltaic technologies 1.2 PV and solar cell technologies 1.3 Dye-sensitized solar cells 1.4 Towards the design of BIPV glazed envelopes 1.5 The ecological matter of PV: the ePT, the recyclability and the LCA 1.6 DsC Possible applications: the “Photovoltaic luminous walls� NoTes

CHAPTeR 2 Trends in patents analysis 1998-2011

2.1 Introduction 2.2 Patents publication timeline 2.3 Current DsC state of art. Technical analysis of selected patents NoTes

CHAPTeR 3 Hypotheses of DSC integration into the glassblock NoTes

CHAPTeR 4 Optical performance analysis

4.1 Basic Theory 4.2 DssC optical modeling: a study on the state of art and the optical properties of the single layers composing the cell 4.3 Analysis method 4.4 Preliminary simulations results 4.5 simulations on Hyp. 1a, 2a, 3a and 4: results NoTes

1 3 7 12 15 21 32 40 46 51 54 58 104 109 117 122

136 143 145 155 175 XI


Conclusions

181

APPeNDIX B - List of the applicants

203

APPeNDIX A - excerpt of the patents database ATTACHMeNT 1 - Analysis on “CLEAR Q19 SMOOTH TRANSPARENT” by ssV for seves

ATTACHMeNT 2 - Verbal competition “For the design of a device that employs energy production technology based on photovoltaic materials made from organic materials”

ATTACHMeNT 3 - email correspondence with the optiCAD software developers Bibliography and sitography

XII

185 211

215

221

225


Foreword The use of sustainable energies and a controlled energy consumption lately became fundamental themes in architecture and civil constructions. Referring to what we call building envelopes, and in particular for glazed building envelopes, features of comfort such as thermal insulation, natural illumination, protection from direct sun rays are required. Quite often wide glazed surfaces in a building mean a great amount of heat loss during the winter season and great energy consumption for air-conditioning during summer. The control of the energy fluxes inside-out the buildings has central importance to achieve adequate levels of comfort in accordance to different climate conditions and to limitate the energy consumption. The international community has already come out with a specific regulation system for the evaluation and control of indoor climate and luminous and solar characteristics of the glazed buildings1,2. In this sense the glassblock, diffused by the end of the 19th century3, represents still today a valid alternative to float glass for the definition of glazed building envelopes4. When we talk about sustainable architecture, one more fundamental characteristic is the use of renewable energies. Solar radiation represents by far the largest and most available renewable energy source.

Fig.1 Potential of renewable energy sources in relation to the global primary energy consumption Source: Photovoltaics, Edition Detail, 2010 1


Although only a small portion of the solar radiation reaches the surface of the Earth, just a few hours of sunshine contain more energy than the entire population of the planet consumes in one year. If we could use just 0,04% of the available solar radiation effectively, the sun could meet our total energy needs worldwide5 (Fig. 1). The use of photovoltaics in order to convert the global irradiation into electricity already had diffusion with two generations of PV technology (respectively, crystalline silicon cells and thinfilm solar cells) and it is now moving forward to a third generation: the Dye-sensitized Solar Cells (DSCs). DSCs offer a low-cost alternative to traditional crystalline photovoltaic devices. In fact production and materials costs are significantly lower than the other photovoltaics technologies. The high efficiency of liquid DSCs, which have recently set a new benchmark of 12.3%, derives from molecular design and control of nanoarchitecture of the different layers they are composed of. The research counducted through this thesis examinates the possibilities of integration of DSC into the glassblock. The DSC integrated glassblock is presented in different configurations, which have been foreseen and already exposed in a previous degree thesis6. The present work is in fact part of a broader research, conducted in the Degree Theses Laboratoy named "Sustainable Building Envelopes: Use of advanced materials for energy optimization and increased uptake of the natural light (tr.)” coordinated by the Prof. Rossella Corrao. The laboratory was founded to study in particular the possibilities to achieve better performing glassblocks. The previous works presented during the laboratory represent the base for all the further studies here conducted7. More in particular a preliminary study of the DSC state of art based on the analysis of the patents published worldwide from 1998 to 2011 will be shown; subsequently the results of simulations conducted through OptiCAD® for the evaluation of the device luminous and solar characteristics in the different configurations will be described.

2


NOTES 1. UNI EN 673:2011 “Glass in building - Determination of thermal transmittance (U value) - Calculation method”. 2. UNI EN 410:2011 “Glass in building - Determination of luminous and solar characteristics of glazing”. 3. The very first glassblock as intended today was patented in France, 1886 by Gustave Falconnier. cfr. R. Corrao, Glassblock and Architecture, Florence: Alinea Editrice, 2010. 4. In particular for its light diffusing and light directioning properties together with lower thermal transmittance compared to float glass. 5. Weller, B., Hemmerle, C., Jakubetz, S., & Unnewehr, S. (2010). Photovoltaics, Technology Architecture Installation. Basilea: Edition Detail. 6. Morini M., “Involucri edilizi sostenibili: Integrazione di celle solari di terza generazione nel vetromattone per la realizzazione di pannelli traslucidi fotovoltaici”, Degree thesis in Building Engineering and Architecture, University of Palermo, A.Y. 2010/11. 7. - Cappello D., “Simulazioni dinamiche per la valutazione delle prestazioni ottiche e termiche di nuove configurazioni del vetromattone. Intercapedine ad una camera”, Degree thesis in Building Engineering and Architecture, University of Palermo, A.Y. 2009/10. - Mannino P., “Simulazioni dinamiche per la valutazione delle prestazioni ottiche e termiche di nuove configurazioni del vetromattone. Intercapedine a più camere”, Degree thesis in Building Engineering and Architecture, University of Palermo, A.Y. 2009/10. - Trapani G., “Indagine teorico-sperimentale per la caratterizzazione meccanica del sistema di incollaggio a freddo finalizzato alla riduzione del valore di trasmittanza del vetromattone, Prove di laboratorio”, Degree thesis in Building Engineering and Architecture, University of Palermo, A.Y. 2009/10. - Garraffa A., “Indagine teorico-sperimentale per la caratterizzazione meccanica del sistema di incollaggio a freddo finalizzato alla riduzione del valore di trasmittanza del vetromattone, Simulazioni numeriche”, Degree thesis in Building Engineering and Architecture, University of Palermo, A.Y. 2009/10. - Foderà C., “Analisi delle problematiche connesse all’isolamento termico degli involucri in vetromattone e valutazione sperimentale di nuovi sistemi di posa in opera”, Degree thesis in Building Engineering and Architecture, University of Palermo, A.Y. 2008/09. - Messina V., “Analisi delle problematiche connesse alla sicurezza degli involucri in vetromattone e valutazione sperimentale di nuovi sistemi di posa in opera”, Degree thesis in Building Engineering and Architecture, University of Palermo, A.Y. 2008/09. - Pastore L., “Sistemi di posa in opera e materiali innovativi per l’incremento prestazionale degli involucri edilizi in vetromattone”, Degree thesis in Building Engineering and Architecture, University of Palermo, A.Y. 2008/09.

3


CHAPTER 1

Introduction


Chapter 1 - Introduction

1.1 European framework on solar energy and photovoltaic technologies Reasons for putting efforts into the research of economically viable and renewable energy sources towards the development of a low-carbon society are evident. Solar energy has the potential to satisfy the future global need for energy consumption. In Europe, fitting the total surface of south-oriented roofs with PV equipment would enable full coverage of our electricity needs1. However its use is still today not very diffused especially if compared to other renewable energies. From the beginning of the 21st century the diffusion in Europe in use of renewable energies has shown slow but considerable growing, with exponential behaviour in the last years (see Chart 1.1). 700 600 500 400 300 200 100 0

19 18 17 16 15 14 13 12 1999

2000

2001

2002

2003

2004

2005

2006

2007

2008

2009

Biomass Biomass & rrenewable enewable w waste aste (T (TWh, Wh, left-hand left-hand scale) scale) W Wind ind tu turbines rbines (TWh, (TWh, left-hand left-hand scale) scale) left-hand scale) scale) Geothermal Geothermal (T (TWh, Wh, left-hand H Hydropower ydropower (T (TWh, Wh, left-hand left-hand scale) scale) Electricity from off c consumption, El ectricity fr om rrenewables enewables (% o onsumption, rright-hand ight-hand scale) scale) (1) (1)

Chart 1.1 Renewable energies production development in Europe during the years 1999-2009. Left scale Total TWh produced. Right scale: Share in total electricity production. Source: Eurostat

In 2009 the primary production of renewable energy within the 27 EU state members was 148.4 million tonnes of oil equivalent (TOE) an 18.3 % share of total primary energy production. Among renewable energies, the most important source was biomass and waste, accounting for 67.7 % of primary renewables production followed by hydropower (19.0 % of the total) and wind energy (7.7 %). The largest producer of renewable energy within the EU in 2009 was Germany, with an 18.7 % share of the EU-27 total; follows France (13.2 %) then Sweden (10.7 %) and Italy (9.9 %), which renewable energy production was coming mostly from geothermal energy sources.

7


Chapter 1 - Introduction

Only small percentages were producted with solar energy conversion, with average percentage production generally comprised within 1-5%. The only countries which made exception are Cyprus with 77.3% (such a high percentage has to be valuated in consideration of the small extension of the country) and Greece with 10.4%2. The present data, which refer to more than two years ago, show a general pejorative state compared to the sustainable energy produced today. In fact renewable energy share in total electricity consumption passed from 18,3% in 2009 to 19.8% in 20103, with a perspective of continue growth in 2011-2012, and the diffusion of PV systems has also intensively grown. We can say the main factor which still causes unpopularity of solar energy caption systems and slow diffusion of the same is probably their costs in comparison to others, mainly related to the production costs. Table 1.1 shows a comparison between different renewable energy types and the relative costs in 2011. Energy type

Cost

Wind

$0.038-$0.06/kWh

Biomass

Geothermal Hydro Solar

$0.029-$0.09/kWh $0.039-$0.30/kWh $0.051-$0.11/kWh $0.15-$0.30/kWh

Solar (nanotechnologies) $0.05/kWh (expected)

Table 1.1 Cost per kWh of electricity collected through different renewable energy use, May 2011 Data source: greenelectricityguide.com

It is evident that actually, the cost of solar energy producted with traditional photovoltaic systems is still significantly higher (up to three times) compared to others. By the way, even if PV still represents a minimal part in the total amount of renewable energies production, in 2010 it reached the first place surpassing any other renewable electricity sector in terms of installed power capacity in Europe during the year, with more than 13 GW installed. Leader in the sector was Germany again, with 7,4 GW installed followed by Italy with 2,3 GW. The energy production in the sector 8


Chapter 1 - Introduction

resulted nearly doubled, leading to a cumulated total capacity of 29 GW in the end of 20104. It also must be said that is unlikely for Europe to become price leader in the PV sector as by now Asia production is largely cheaper. Also, from the supply point of view, Europe is still importing the photovoltaic devices from eastern world countries. Governmental financial support is fundamental for a diffusion of a photovoltaic culture and in the last years the EU has set out many plans and strategies for a new energy production development based on a more secure, sustainable and low-carbon economy. In order to face to climate change through a reduction in gas emissions, the use of renewable energy provides security and diversity in energy supply and less air pollution. We now provide a brief in the main active programs of today as presented in the 26th EU PVSEC (Photovoltaic Science and Engineering Conference) which took place in Hamburg 5-9 September 2011. With reference to the European Photovoltaic Actions and Programmes 2011 document, from the European Commission, insights on the following communications and programmes will be given: I. Renewable Energy: Progressing towards the 2020 target, Communication from the European Commission published on 31st January 2011;

II. Directive 2009/28/EC, so called “RES (Renewable Energy Sources) Directive” from the European Parliament and Council, for the promotion of the use of energy from renewable sources; III. Energy Road Map 2050, from the European Commission, adopted on 15th December 2011;

IV. 7th Framework Programme, funding programme by the European Union running for seven years from 2007 to 2013 to develop research, growth, competitiveness and employment; V. IEE (Intelligence Energy Europe) giving support for collaborative actions of different countries in the European Union. The second IEE calls for proposal started in 2007 and will end in 2013;

VI. SEII (European Solar Industrial Initiative) launched in June 2010 for bringing together the industry, the research community, the Member States and the European Commission for rapid development of solar energy technologies. 9


Chapter 1 - Introduction

I. Renewable Energy: Progressing towards the 2020 target, Communication from the EC This communication provided a review on the development of renewable energies in Europe, putting in evidence what were the deficiencies in the european system and the target missed. In particular the Commission recognized that the limited growth of Europe's renewable energy industry resulted partly from the limited EU regulatory framework, so the EU introduced a supportive legislative framework, which challenge is to move to the national level, with concrete action on the ground. II. RES (Renewable Energy Sources) Directive The Directive sets the target for all the Member States to achieve by 2020 a 20% share from renewable energies, covering all the types of energy consumption (including also the heating sector for the first time). A key element of the Directive is the elaboration of National Renewable Action Plans (NREAPs) providing detailed road maps for the development and achievement of the targets for each Member State. III. Energy Road Map 2050 The Roadmap 2050 project is an initiative of the European Climate Foundation (ECF) and has been developed by a consortium of experts funded by the ECF. The mission of Roadmap 2050 is to provide a practical, independent and objective analysis of pathways to achieve a low-carbon economy in Europe, in line with the energy security, environmental and economic goals of the European Union5. The work of the consortium was published in three volumes: - Volume I: Technical and Economic Analysis. Undertaken by McKinsey & Company, KEMA, the Energy Futures Lab at Imperial College London, Oxford Economics and the ECF, 2010; - Volume II: Policy Report. Undertaken by E3G, the Energy Research Centre of the Netherlands, the Regulatory Assistance Project and the ECF, 2010; - Volume III: Graphic Narrative. Undertaken by the Office for Metropolitan Architecture and the ECF, 2010. Chart 1.2 shows the target set up by the Energy Road Map for CO2 emissions until 2050. 10


Chapter 1 - Introduction

Chart 1.2 Reduction of CO2 emissions in Europe as a target set up by the Energy Road Map 2050. The emissions in 2050 shall be reduced up to 80%. Source: Roadmap 2050 Technical Analysis

IV. 7th Framework Programme The Framework Programmes (FPs) have been the main financial tools through which the European Union supports research and development activities covering almost all scientific disciplines. Six calls for proposal have been already launched in the period going from 2007 to 2012. I. e., under the 7th Framework Programme (2010) and between the themes “Energy” and “Nanoscience. Nanotechnologies, materials and new production technologies”, three projects have been selected for negotiation of the EU contribution addressing the topic “Development and up-scaling of innovative photovoltaic cell processes and architectures...”6, exploring the issues related to the production of Dye-Sensitized Solar Cells (DSSCs), an emerging photovoltaic technology which detailed description will be given in the next chapters. 11


Chapter 1 - Introduction

V. IEE The Intelligent Energy Europe programme helps to achieve the EU’s 2020 targets by supporting collaborative action between different countries. The IEE projects contribute in particular to the improvements of EU policies and legal frameworks, in order to create better market conditions for the development of renewable energies technologies. An important field of the IEE Programme is on Building Skills and Capacities, which programs support the training and qualification of onsite construction workers and system installers on sustainable energy solutions in buildings. VI. SEII The European Solar Industrial Initiative was established with the aim of bringing together the industry, the research community, the Member States and the European Commission for rapid development of solar energy technologies. It deals both with PV and concentrating solar power.

1.2 PV and solar cell technologies

Availability of clean, safe and affordable energy to all citizens in sufficient quantities is a prerequisite for a sustainable society. Presently almost one-third of the world population does not have access to commercial energy (in particular, to an electricity grid). In spite of the recent success of renewable energies in some areas, the growing global energy consumption still causes an increase in the consumption of fossil fuels and associated CO2 emissions. The use of fossil resources has to be gradually replaced by the application of renewable energy technologies and the greenhouse gas emissions have to be decreased substantially. To ensure this, we need diversified and renewable energy sources. PV has the unique property that arrays can be built ranging in different proportion from a few milliwatts up to a multi-megawatt installation, depending on users needs. PV modules can be part of a consumer product, mounted on roofs of houses, integrated in a building skin or assembled into large power stations. PV is quiet and safe and it fits well in the existing infrastructure offering possibilities to make intelligent matches between electricity supply and demand7. 12


Chapter 1 - Introduction

Today there are basically two principal categories of solar cell types, to which we commonly refer as first and second generation solar cells, plus a new one that is emerging and showed so much potential to be already acclaimed as the third generation of solar cells. The first generation solar cell (the conventional solar cell of today) is the silicon-based, which rules on around 90% of the total current PV market. The second generation is referred as the thin film solar cells, and makes use of silicon (amorphous) thin films but also other materials, such as CdTe (Cadmium Telluride) and CIS (Copper-Indium-Selenium). An emerging technology, which can be considered between the second and the third generation is represented by the Dye-Sensitized Solar Cells (DSSC or DSC), which will be described further in this chapter, because of their unique features, which make them suitable for several new photovoltaic applications. Fig. 1.1 schematically resumes the three solar cells generations with respective subcategories. I

II

III

Fig. 1.1 Typology and features of the three solar cells generations. Monocrystalline cells have characteristic rounded corners, polycrystalline a distinct crystal structure, and thin film modules a stripy appearance Source: Photovoltaics, Edition Detail, 2010 13


Chapter 1 - Introduction

Another category of cells (but which has not commercial extents) is the so called multijunction cells. These cells have reached record efficiencies which are massively superior to all the other kind of PV cells (up to 41%), but their cost is estimated as one hundred times more expensive than the common crystalline silicon cells8. This is why this kind of cells, which architecture is based on multistrates of thin films particularly selected, and used in concentrators, has actually no market at all, and its use is still limited to extraordinary applications such as installations on spatial satellites, where no other energy sources are available. In Chart 1.4 the roadmap for PV technologies is shown by representing record efficiencies achieved over time for the different PV technologies.

Chart 1.3 Best research-cell efficiencies. Source: National Renewable Energy Laboratory (NREL), US 14


Chapter 1 - Introduction

1.3 Dye-sensitized solar cells Dye-sensitized solar cells, first invented in the early nineties by O’ Regan and Gratzel at the École Polytechnique Fédérale de Lausanne (EPFL), represent the most promising invention related to photovoltaics of the last 20 years. The DSC is a nanostructured electrochemical device which mimics the process of plant photosynthesis. These new solar cells are composed of a multi-layered structure in which several thin films are enclosed between two conductive transparent substrates in order to activate current in a regenerative cycle process. The transparent electrodes are generally glass or flexible plastic sheets in which a thin transparent conductive oxide (TCO) is deposited. Commonly the active layer consists of a mesoporous nanocrystalline titanium dioxide film (thickness 10μm ca. - particles diameter between 10 and 30nm) in which a sensitizing dye, responsible of the absorption of the incoming light, is deposited. The device is completed by a counter-electrode comprising a thin platinum catalyst. The two electrodes are sealed to ensure confinement of the electrolyte usually containing the iodide/triiodide redox couple. Fig 1.2 and 1.3 show examples of realized DSCs, while in Fig 1.4 the scheme of the cell structure is shown.

From left to right: Fig. 1.2 Hana Akari (literally "flower light") DSC module designed by Sony Fig. 1.3 Semitransparent DSC Module 60x100 cm, realized at Fraunhofer ISE (Institute for Solar Energy)

15


Chapter 1 - Introduction

Light

TiO2-coated electrode <

Transparent conducting coating

Light Magnified 1000= e<

e<

Counter electrode

Glass

e<

Dye and TiO2

Iodide Tri-iodide

Load e<

e<

e<

Electrolyte (iodide/tri-iodide) Glass Transparent conducting coating and catalyst

Light

Magnified 1 000000= e<

Electron injection

e<

Dye Electrolyte (iodide/tri-iodide)

TiO2 nanocrystals (diameter 5 20 nm)

< Iodide I

I3< Tri-iodide Cycle

Fig. 1.4 Schematic structure of the nanocrystalline dye-sensitized solar cell (DSSC) Source: Elsevier Science 16


Chapter 1 - Introduction

The regenerative process in the dye solar cell consists of five steps9: - 1. At the beginning, the sensitizer absorbs a photon from light and an electron is transferred from S° to a higher lying energy level. The sensitizer is in the excited state S*; - 2. Injection of the excited electron into the conduction band of the semiconductor occurs within a femtosecond timescale; - 3. The electron percolates through the porous TiO2 layer to the conductive support and passes the external load to reach the counter electrode; - 4. The electron is then transferred to triiodide to yield iodide; - 5. The iodide reduces the oxidized dye S+ to its original state S°. Usually, synthetic inorganic compounds such as ruthenium complexes are employed as molecular sensitizers. In order to replace the rare and expensive ruthenium compounds, many kinds of organic synthetic dyes have been actively studied and tested as low-cost materials. In nature, some fruits, flowers, leaves and so on show various colours and contain several pigments that can be easily extracted and then employed in DSSCs. Natural dyes are more available, easy to prepare, low in cost, non-toxic, environmentally friendly and fully biodegradable10. Unfortunately DSC made using organic compounds as synthetizer did not show yet efficiencies that could be considered competitive with those showed by the ruthenium based cells (Table 1.2, next page). “High conversion efficiency” and “low manufacturing cost” are the two key points for popularization of solar cells. A group of scientists in EPFL’s Laboratory of Photonics and Interfaces, under the leadership of EPFL professor Gratzel, has recently set the new record of 12.3% efficiency11. This performance is comparable to silicon-based solar panels while the costs of this technology are significantly lower. Last version Gratzel cells mimic the process of plant photosynthesis also in their colour, which corresponds to a greenish tint. This colour increases the efficiency of the process that converts light energy into electricity getting the most out of the energy coming from sunlight; the cell absorbs the colours of the spectrum with the highest energies and rejects the rest, which includes the green wavelengths. This new efficiency benchmark makes DSCs theoretically surpass crystal silicon-based cells: the theoretical maximum efficiency of Gratzel cells is 17


Chapter 1 - Introduction Natural dye

max e (nm)

Jsc(mA cmо 2 )

Voc(V)

FF(%)

(%)

Begonia

540

0.63

0.537

72.2

0.24

Tangerine peel

446

0.74

0.592

63.1

0.28

Rhododendron

540

1.61

0.585

60.9

0.57

447, 425

0.53

0.689

46.6

0.17

Marigold

487

0.51

0.542

83.1

0.23

Perilla

665

1.36

0.522

69.6

0.50

Herba artemisiae scopariae

669

1.03

0.484

68.2

0.34

China loropetal

665

0.84

0.518

62.6

0.27

Yellow rose

487

0.74

0.609

57.1

0.26

Flowery knotweed

435

0.60

0.554

62.7

0.21

Bauhinia tree

665

0.96

0.572

66.0

0.36

Petunia

665

0.85

0.616

60.5

0.32

Lithospermum

520

0.14

0.337

58.5

0.03

Violet

546

1.02

0.498

64.5

0.33

Chinese rose

516

0.90

0.483

61.9

0.27

Mangosteen pericarp

/

2.69

0.686

63.3

1.17

Rose

/

0.97

0.595

65.9

0.38

Lily

/

0.51

0.498

66.7

0.17

ŽīĞĞ

/

0.85

0.559

68.7

0.33

/

1.19

0.607

65.4

0.47

515

13.74

0.773

57.6

6.11

Fructus lycii

BroadleaĬ olly leaf N-719

18

/


Chapter 1 - Introduction

now 30%, compared with 26% for silicon12. Today the main challenges for development of the DSSCs and in order to achieve higher efficiencies are to increase absorption quantity of sun light, and to extend the lifetime of the cell, which is highly influenced by the presence of the organic dyes which are easily going bad and the liquid electrolytes used, because they are prone to evaporation13. Dye-sensitized solar cell technology have a wide range of advantages and features never seen in compared other PV systems, which make them suitable for multiple new kinds of application. This solar cells generation has the unique characteristic to be insusceptible to the incident angle and intensity of the sunlight. Despite traditional silicon based modules, DSSCs still work in weak light conditions, even when indoors. The traditional efficiency estimating methods, based on watt-peak-evaluation, only consider the behaviour of the cell in its maximum working condition and do not even take into account this peculiarity. Efficiency is a parameter calculated and referred to the Standard Test Conditions14 (STC) which actually never occur. The watt-peak-based evaluation commonly used to estimate traditional PV performances can lead to an underestimation of the performances of dye-sensitized solar cells. In fact, in DSSCs the production of electricity does not grow linearly with the intensity of the light. It has its own peak when the intensity of solar irradiation is about 200 W/sqm – 1/5 of 1000 W/sqm, corresponding to the STC – and decreases with the growing of the intensity of the radiation. This particular behaviour differences DSCs from the other photovoltaic technologies, but it is not to consider a disadvantage; in fact the average solar radiation on earth surface is far to the referential 1000 W/sqm and stands about 170 W/sqm. Since at the European average latitude the total solar radiation is formed by 50% of diffuse light15, it has been demonstrated that if we consider two photovoltaic systems, one based on DSC technology and one based on crystalline silicon, with the same peak power, the first produce in a year almost 10-15% more energy than the silicon-based system16. Moreover the capacity of diffuse light absorbing gives to this cell another unique feature of being active also when not south oriented and when vertically installed, i.e. in In the left page: Table 1.2 Photoelectrochemical parameters of the DSCs sensitized by natural dyes extracted with (a) ethanol, (b) water, and (c) 0.1 M HCl–ethanol. N719 was extracted with the mixture of (d) acetonitrile and tert-butyl alcohol; (e) λ max in the visible light range is shown. Source: “Dye-sensitized solar cells using 20 natural dyes as sensitizers”, Journal of Photochemistry and Photobiology A: Chemistry, 219, 2011

19


Chapter 1 - Introduction

building facades. DSCs are colourable, transparent and can assume almost any shape or form different patterns by selective area deposition of the active surface on the substrates. For this reason they have an enormous potential in terms of building integration (Building Integrated Photovoltaics, BIPV): modules total transparency can be graduated both in terms of area occupied by the active surface of the cell and transparency of the active area in itself, which can be calibrated by variation of the TiO2 layer thickness and the dye used. Their lighter weight which comes from the possibility of the cell to be deposited on every kind of transparent substrate (plastic included) increases their potential in building integration, by significantly reducing the actual loads carried by the building structure. Thanks to a particular nanostructure (which will described in the next chapter) DSCs have one more unique characteristic which is the possibility to be mounted on flexible substrates, opening never seen horizons to BIPV. Flexible DSCs are shown Fig 1.5 and 1.6.

Fig 1.5 and 1.6 Photovoltaic bus shelter designed with flexible DSC modules, designed by Konarka Technologies Inc. in San Francisco, USA

All of this potential is also supported by noticeably lower production costs, which make this technology promising also in order to achieve wide diffusion of PV systems, finally available for everybody at affordable price. These cells and panels can be produced in a simple way in open air, which means a significant cost reduction of 1/5 to 1/10 as compared to silicon solar cells17. 20


Chapter 1 - Introduction

1.4 Towards the design of BIPV glazed envelopes Between 1850-1851 the Crystal Palace was built in Hyde Park, London, for want of Queen Victoria to host the Great Exhibition of Great Britain and its colonies recent technological achievements. It was an enormous glazed warehouse (92000 m2) entirely built with standard iron, wood and glass elements. It was at the time the largest amount of glass ever seen in a building. Astonished visitors coming from all the British colonies found themselves in a huge open-space right under the day light and the trees of Hyde Park. The Crystal Palace represented an architecture developed by horticulturists and garden specialists in orangeries but brought to a sophisticated level and spectacular scale. Although the statics by its coevals (John Ruskin disparaged it as “a great cucumber frame”) it became the archetype for plenty of modern and contemporary buildings, defining the type that is today commonly referred as the glazed envelope. The history of glazed building envelopes continues into the 19th century when increasingly complex structures were built incorporating glass and iron industrial construction techniques. In the second half of nineteenth century, the early glassblocks and prismatic glass emerged as an alternative to float glass for their

From left to right: Fig. 1.7 Interior view of the Glas Pavilion by Bruno Taut for the Werkbund Exposition in Cologne, 1914 Fig. 1.8 Commercial advertisement by Luxfer Prism Company as appeared on Scribner’s Magazine

21


Chapter 1 - Introduction

particular light diffusing properties. At that time, when a slow transition from gas light to electric light was under way, there was also an increased desire for bringing in the interiors of the buildings as much as daylight as possible, in order to save energy and create healthier working environments especially in factories and offices. Glassblocks already existed in various shapes and sizes, designed in order to provide different light diffusion effects. The leadership in this sector was held by a Chicago-based industry, the Luxfer Prism Company (particularly well known for the association with Frank Lloyd Wright, who designed some of their prism tiles) which by the beginning of ‘900 rapidly expanded its market from the United States to all Europe, establishing new branches of the company in many countries i.e. Great Britain and Germany18. The contribution of innovators such as Paxton influenced the pioneers of 20th century architectural design such as Scheerbart and Taut, which based the paradigms for the modernist Glasarchitekur, in which the glassblock was already protagonist from the very beginning. Already in the 20th century several glazed luminous buildings, characterized by semitransparent, more discreet volumes were built exploiting the unique features of the glassblock (i.e. Glass pavilion for the Werkbund exposition in Cologne by Taut, 1914; Maison de verre in Paris by P. Chareu, 1932).

Fig. 1.9 Maison de Verre, designed by Pierre Chareau, Paris, 1932 22


Chapter 1 - Introduction

Together with the massive use of light transmitting elements in architecture the notion of luminous building was born. In fact that was the time in which designers started to think about the appearance of the architecture by night. Envelopes glowing from the inside started to diffuse, where the appearance of translucent rather than transparent played an important role in the formation of a new aesthetic19. Today transparency and its graduation still represent one of the main issues of contemporary architecture and new questions about living the glazed envelopes arose. In general when we refer to building envelopes, we indicate a technical element which rules the relationship between a part of the space in it included and a part from it excluded; in this definition there is not values like inside nor outside. In this question, a good point of view could be find in Junya Ishigami’s words, thinking about architecture as an environment itself: “Architecture has been formulated as a shelter [...] in order to separate us from the natural environment [...]. Such an image is unsuited to this newly emerging environment. To see architecture not a shelter but as environment itself” 20

From left to right: Fig. 1.10 ING Group Headquarters, Meyer & Van Schooten Architecten, Amsterdam, 2002 Fig. 1.11 Circle On Cavill, Sunland Group, Surfers Paradise, Australia, 2007 Fig. 1.12 Hanner Office Building 2, Audrius Ambrasas Architects, Vilnius, Lithuania, 2001

23


Chapter 1 - Introduction

The concept of architecture as environment let us consider the envelope as the frame in which different environments with different internal laws come in contact. The definition of building envelope has conceptual but also practical meaning. The boundaries of a building envelope, sometimes referred to as a skin, have in fact to provide a certain number of features related to the control of the fluxes which travel in both direction from the included space to the excluded space and vice versa. In this sense, every building could be defined a building envelope, but it is preferred to applicate this definition to those in which this filter function is more evident. The fluxes which cross the skin of an envelope can have different nature, i.e. they could be related to technical requirement connected to comfort and livability principles (i.e. light fluxes, heat fluxes). Trivially, if we think about lighting, it is evident that the light flux is subjected to an inversion during the day time, letting the natural light come inside during the day hours and glowing from the inside during the night (not for nothing, i.e. the Maison Hermes by R. Piano is called as “the lantern”). Glazed surfaces so wide also need particular design approaches, careful of the issues of excessive incoming solar radiation and thermal insulation. In addition, contemporary building envelopes can also carry out extra features such as being vector for informations (media buildings) or energy

From left to right: Fig. 1.13 Maison Hermes, Renzo Piano, Tokyo, 2001 Fig. 1.14 Example of BIPV using silicon based thin-film photovoltaics Shuco FT+ 24


Chapter 1 - Introduction

accumulators (BIPV). Sustainability in building construction is inherently related to the concept of building envelope, because the principle of energy conservation is deeply founded on the one of the fluxes control. In facts, no sustainable building exists without a proper thermal insulation and smart properties in captation of light.

From top to bottom and from left to right: Fig. 1.15 East Anglia Atrium and Facade, Solarnova, England Fig. 1.16 Swiss Pavilion at the Shanghai Expo 2010, Buchner Bründler Architects. The curtain in facade includes technological elements made of dye-sensitized cells and luminous leds Fig. 1.17 Studies for an office building, Olaf Gipser Architects, Amsterdam

25


Chapter 1 - Introduction

In particular, the glassblock is today competitive to other building elements, just for its capacity of light directing and light diffusing coupled with good properties of thermal insulation. Its lower thermal transmittance compared to float glass derives from the air chamber included within the two composing shells, which reduces the heat exchanges. These particular features make the glassblock suitable for the realization of wide glazed surfaces and for the definition of totally or partially glazed envelopes. Moreover it has been already introduced the well-know term of “building integrated photovoltaics” which interestingly add to the energy conservation principle in building envelopes the one of the use of renewable energies, which let us to speak properly of sustainable architecture. BIPV is considered as the most ecological application of photovoltaics, having impact only in the built environment and saving the natural landscapes from the massive diffusion of the photovoltaic fields. Although BIPV using first and second generations solar cells already exists in a wide range of possibilities (i.e. roof and facade integration, movable shutters and louvres) the combination of these kinds of solar active surface with other functions in building constructions usually comes out with a number of compromises. A distinction between proper integration and installation has to be done. The difference is substantial: PV modules properly integrated are those which substitute another element of the building (i.e. coverings, sunshades, windows) leading to a save in terms of materials and costs, but also, in general, to better architectural solution, avoiding the effect of the “later added” which characterize the most common photovoltaics installation in buildings. Roof installation is certainly the most diffuse typology of photovoltaics application on buildings, and also the cheapest. PV modules can be installed in pitched roofs with proper orientation and on flat roofs using particular mounting systems. However this kind of application comes with consequences which are both architectural (in some cases the installation really compromises the aesthetic of the building) and technical, because roof-installing includes interventions on the roof for the anchorage (with possible consequences in the waterproofing) and anyway, for free-standing systems, to significant higher loads. On the other hand, the integration of traditional PV systems in the facade, which has in general minor impact (it causes no substantial volumetric changes nor particular waterproofing problems) comes together with a loss in therms of energy collected, due to their vertical 26


Chapter 1 - Introduction

position. The enormous potential of DSC in terms of architectural integration was already introduced. Their non-oriented applicability, together with availability in diďŹ&#x20AC;erent colours and transparency degrees, possibility of having them in diďŹ&#x20AC;erent patterns and drawings, light weight are all characteristics which contribute to make this technology surely the most appropriate for the BIPV. For these reasons we have investigated the possibility of integration of a DSC system into the glassblock, combining their characteristics in a synergic component for the deďŹ nition of glazed photovoltaic integrated building envelopes. In Fig 1.28 the possible outlook of a DSC integrated glassblock is shown.

Fig. 1.18 DSC integrated glassblock, a possible outlook

In accordance with the calculations made in another work21, we here give by way of information a report on 11 buildings in which 19x19 cm glassblocks are widely used, for which we hypothesized the integration with DSC cells on half of the total number of glassblocks used. The partial and the total land save was calculated with reference to the square meters needed for equivalent energy production using crystalline silicon-based modules and amorphous silicon-based modules. As shown in Table 1.3 (next page), the integration on only half of the glassblocks would save 2024 or 5060 m2 of land if the same amount of energy would have to be produced respectively with monocrystalline and amorphous silicon based PV panels. 27


Chapter 1 - Introduction

name of the building, location

1

S-Bahn Station Expo 2000, Hannover

3

Puccini Theatre, Florence

25000

V, H

4500

V

Liege-Guillemin Station, Liegi

28000

H

Locarno Teleferic, Locarno

4500

V

Beck's Logistic Centre, Bremen

2 4

Santo Volto di Ges첫 Church, Rome

6

Pirelli Headquarter, Milan

5 7

glassposition of blocks installation used (19x19 cm)

25000 4750

28000

Technology Museum, 12000 Berlin

8 9

10 11

Reception Centre Up31000 down Court, Taichung Conbipel Shopping Centre, Florence Leipzig Airport, Leipzig

16000 8000

V

V

H V V V

H

total surface [m2]

glasskWp colland save compared to land save compared blocks lected by of monocrystalline silicon- amorphous siliconneeded half glassbased PV modules [m2] based PV modules [m2] for 1kWp* blocks

H1 H2 H1 902.5 H2 H1 162.5 H2 H1 171.5 H2 H1 1010.8 H2 H1 1010.8 H2 H1 162.5 H2 H1 433.2 H2 H1 1119.1 H2 H1 577.6 H2 H1 288.8 H2

902.5

369 428 369 428 369 428 369 428 369 428 369 428 369 428 369 428 369 428 369 428 369 428

33.88 29.21 33.88 29.21 6.10 5.26 6.44 5.55 37.94 32.71 37.94 32.71 6.10 5.26 16.26 14.02 42.01 36.21 21.68 18.69 10.84 9.35

271.00 233.64 271.00 233.64 48.78 42.06 51.49 44.39 303.52 261.68 303.52 261.68 48.78 42.06 130.08 112.15 336.04 289.72 173.44 149.53 86.72 74.77

677.51 584.11 677.51 584.11 121.95 105.14 128.73 110.98 758.81 654.21 758.81 654.21 121.95 105.14 325.20 280.37 840.11 724.30 433.60 373.83 216.80 186.92

TOT (referring to H1) TOT (referring to H1)

2024.39

5060.98

Table 1.3 Land save by integration of DSC modules in half of the glassblocks in 11 selected glassblock made envelopes

28


Chapter 1 - Introduction

H1 and H2 stand for “Hyp.1” and “Hyp.2” further described in Chapter 3, moreover in the table the position of installation vertical (V) such as in panels or walls or horizontal (H) such as in roofs and pavements is indicated. The total (TOT) in the land save is referred to the sum of the land saves related to an integration type according to the Hyp. 1 which in the table are put in evidence with grey colour. In the next pages, photographs of the 11 selected building are reported.

Fig. 1.19 Leipzig Airport (Leipzig)

29


Chapter 1 - Introduction

From left to right and top to bottom: Fig. 1.20 S-Bahn Station Expo 2000 (Hannover), Fig. 1.21 Beck's Logistic Centre (Bremen), Fig. 1.22 Santo Volto di Ges첫 Church (Rome), Fig. 1.23 Puccini Theatre (Florence), Fig. 1.24 Liege-Guillemins Station (Liegi), Fig. 1.25 Pirelli Headquarter (Milan)

30


Chapter 1 - Introduction

From left to right and top to bottom: Fig. 1.26 Locarno Teleferic (Locarno), Fig. 1.27 Technology Museum (Berlin), Fig. 1.28 Reception Centre Updown Court (Taichung), Fig. 1.29 Conbipel Shopping Centre (Florence)

31


Chapter 1 - Introduction

1.5 The ecological matter of PV: the EPT (Energy Payback Time), the recyclability and the LCA (Life Cycle Assesment)

Fig. 1.30 solar power plant (1 MW), Cabanillas, Spain

32

Photovoltaics is considered to be one of the most eco-friendly electricity production systems at all. When PV panels convert solar energy into electrical energy they do not consume fuel, do not produce toxic emissions nor noise. Nevertheless in the last years polemics around photovoltaic and argues about solar panels to be truly green arose. The reasons of the critics are mainly related to the energy consumption and pollution generated for their production, to the consume of raw materials, to the recyclability of the components at the end of the useful time. Another point in the critics is related to the land use (8÷20 m2 per kWp22) and the impact on natural environment of the photovoltaic fields, which cover potential agricultural fields for thousand square meters, with also a high perceptive impact in the landscapes. When producing PV panels energy is consumed and this of course cannot be avoided. By the way, if we compare the consumed energy for the production with the collected energy during a PV panel lifetime, the total energy balance is largely positive. A measurement of the proportion of the energy consumed for the production of a


Chapter 1 - Introduction

solar cell and the energy production of the same exists and it is named Energy Payback Time (EPT); it corresponds to the time interval in which the operating device returns as much energy as it was necessary for the production and assemblage of its components. The energy payback time in photovoltaics is of course different between the various PV technologies and it is direct function of the operating conditions, annual exposition to the light, weather etc. so it is usually calculated within certain geographical limits. In general, if the photovoltaic technology is building integrated (so modules replace other components) we can consider a shortening in the energy payback time, because the energy that would have been necessary to produce the substituted element can be subtracted from the total energy consumption. Moreover, if we think about e.g. photovoltaic sunshades, we can also consider the amount of energy saved i.e. for cooling systems. A second point could be whether or not the energy consumed was coming from sustainable or from unsustainable resources. In the case of sustainable energy collected to produce photovoltaics systems, the energy produced by the system itself could be considered totally in positive. Chart 1.4 shows the energy payback time of different PV systems. Due to high temperatures needed for production of silicon based solar cells, they actually show the highest energy input. C. Europe

Monocrystalline 14.0 %

Raw silicon

Southern Europe

Wafers

Central Europe Southern Europe

Polycrystalline 13.2 %

Cells Laminate

Central Europe Southern Europe

Ribbon of silicon 12.5 %

Frame System technology

Central Europe Southern Europe

CIS 11.5 %

Overall

Central Europe Southern Europe

CdTe 9.0 %

Central Europe Southern Europe

Amorphous Si 5.5 %

Northern Europe Southern Europe

DSSC* 8%

0

1

2

3

4

* DSSC Source: ECN Solar Energy Chart 1.4 EPT of the different PV technologies. Elaborated data from Source: Photovoltaics, Edition Detail, 2010 ŶĞƌŐLJƉĂLJďĂĐŬƟŵĞ΀LJĞĂƌƐ΁

33


Chapter 1 - Introduction

Despite the lower energy output, thin-film based photovoltaics shows on the other hand a shorter energy payback time because their production costs, in terms of energy, are lower. Absolute supremacy in the chart is shown by DSC technologies which energy payback time is estimated from 0.8 (glass-glass substrates), 0.7 (stainless steel) to 0.6 years (PET)23. Photovoltaic modules life cycle of the traditional systems lasts about 30 years24. So we expect to see significant numbers in return of the unusable and scrap modules 20-30 years after market growth, and so not before 2015, considering the fact that photovoltaics diffusion basically started in the nineteens. A wrong opinion on the recyclability of the PV modules is diffused that they cannot be recycled. All PV technologies available today, being silicon-based or non-silicon based are recyclable. What has to be considered is that silicon is an abundant material on Earth but i. e. indium and tellurium are not, and this is one more reason to get into their recycling. Even if recycling of PV solar modules is still a young industry many innovations have been made in the past years to make recycling systems effective and cost-efficient. Industrial recycling methods of crystalline traditional PV panels methods are already well advanced25. When a PV module expires its use time it is treated in special furnaces (at temperatures of about 500°C) in order to separate glass, metals, intact cells and cell fragments. Before this treatment the module frame has to be

Fig 1.31 Scraps of PV panels, PV Cycle, Germany 34


Chapter 1 - Introduction

removed and it can be sold i.e. for scrap or reused. The cell fragments are melted and processed to form new wafers while the intact cells are treated chemically to remove the contacts and coatings, then they can be used again as new. Thanks to new production technologies, these can achieve conversion eďŹ&#x192;ciencies even higher than the original solar cells. The glass (about 80% in weight of the module26) can be recycled with traditional glass recycling industrial methods. Plastics are currently thermally treated. Chart 1.5 shows the scheme of recycling process of a crystalline silicon based PV module. PV Module

Muffle furnace o temp. >500 C

Module components separation

Al, Cu, Steel

PV Cells

Glass Recycling

Metal Recycling

Hazardous gas emission

Glass

Chemical Processes

PV Cells

New PV Cells Production

Silicon Plates

Cell Quality Control

Use of silicon powder as a technological component

Silicon

Silicon Powder Production

Fig 1.32 Scheme of the recycling process of a crystalline silicon based PV module Source: Gdansk University of Technology 35


Chapter 1 - Introduction

Thin film modules can also be recycled. The best results so far have been achieved with amorphous silicon modules. Placed in acid bath the silicon and TCO layers become detached from the glass so they both can be used to produce new solar cells, with the same efficiency. One alternative without any pretreatment is the direct use of the coated glasses as an ingredient for glass melts, the final product quality is adequate for reuse in insulating materials for the building industry or as a raw material for glass bottles. For what concerns CIS and CdTe technologies it is today possible to recycle 95%27 of the materials used which can be recovered for the use in new materials. The recycling process starts by crushing the module, which results in a subsequent separation of the different fractions. This recycling process is designed to recover up to 90 % of the glass and 95 % of the semiconductor material contained in the modules, which is very important because indium and tellurium are rare. The module frames can be sold for scrap or reuse. The recycling process of CIS and CdTe solar panels is simple and can be briefly described as follows28: 1. Removing of frame and junction box (preparation step) 2. Shredding 3. Removal of the semiconductor layer with alkaline solution 4. Processing of glass in traditional flat glass recycling line Output fractions of this process are ferrous and non-ferrous metals, glass and plastics with a recycling average quota close to 80% (input weight). The glass resulting from PV modules is mixed with standard glass to be reintroduced in the glass fibre or insulation industry. In Fig. 1.33-34-35 the products of a CdTe module recycling process are shown.

Fig. 1.33-34-35 Output fractions of CIS and CdTe recycling process 36


Chapter 1 - Introduction

Still not so much has been studied for what concerns recyclability of DSC modules, but as well as recycling of other PV technologies, materials can be filtered and easily separated for reutilization. The TCO layers in the glass can be removed through thermal or chemical processes so the glass can be recycled with traditional methods. In order to quantify a product or system environmental impact over its life cycle, the standard ISO 1404029 provides the instructions to build up a so called LCA (Life Cycle Assessment). In brief LCA is a tool to analyse the total environmental impact of a product or system from cradle to grave. In Table 1.4 the materials and the process energy needed for the production of a nanocrystalline dye sensitized solar cell system per m2 of active area (a.a.) are shown.

Table 1.4 Components of a nanocrystalline DSC system and respective masses per m2 of a.a. and energy needed for the production of 1 m2. Source: “Environmental aspects of electricity generation from a nanocrystalline dye sensitized solar cell system”, Renewable Energy, 23, 2001 37


Chapter 1 - Introduction

The energy needed for the production of 1 m2 of active area is identified in the range within 100-280 kWh. Since the module area per 1 m2 active solar cell area is estimated 1.43 m2 the module process energy per module area results 70-200 kWh/m2 module. The remaining part of the impact of the entire LCA deals with emission produced during the cell life time, in particular during production and end of life processes. A LCA of a nanocrystalline DSC30 showed a comparison in the CO2 emissions in atmosphere in relation with the electricity generation for a DSC system and a natural gas/combined cycle power plant under the hypothesis of 30 years life time31. The gas power plant resulted in 450 g CO2/kWh while the DSC system in between 19–47 g CO2/kWh. For what concerns the end of life processes the following assumptions were made: metals and glass were recycled, inorganics and silicone rubber were disposed into a landfill and the rest of the polymers were incinerated. Table 1.5 shows the emissions and resource used for a kWh during a DSC life cycle.

38

Table 1.5 Ranking procedure for the significant emissions and resources in a DSC life cycle Source: “Environmental aspects of electricity generation...”, Renewable Energy, 23, 2001


Chapter 1 - Introduction

In the same table, the relative significances, calculated trough different methods are shown. In column 2 the significant emission or resource resulting in the highest environmental impact was given the value 1, the emission or resource showing the second highest impact was given the value 2 etc. In column 3, as a next step, value 1 was given a score of 10, value 2 score 8, value 3 score 6, value 4 score 4 and value 5 score 2 and the scores were summarized. The significant emission or resource with the highest score, i.e. highest significance was given the weighed significance 1 (column 4) and the second highest score was given the weighed significance 2 etc. The activities and system components resulting as major contributing on environmental impact over the life cycle are: the energy needed for producing the solar cell module; the emissions in the recycling of the glass. Frames and junction boxes recycling also showed significant impact. As can be seen from the weighed significance in Table 1.5, the most significant emissions and resources according to all weighing methods are sulphur dioxide and carbon dioxide emission. This is the basis for the selection of carbon dioxide emission as a relevant environmental indicator in the comparison of different solar cell scenarios and with a conventional electricity generating systems. The environmental impact assessment from the use of some scarce material resources, in this case ruthenium, is weak. As a confirmation, Andersson et al.32 have calculated the ratio between the total ruthenium requirements and the maximum ruthenium resource on Earth, based on a very large scale production of DSC systems. If produced systems of DSC would supply 100,000 TWh/year, i.e. 11400 GW (500 GWp supports Europe), the ruthenium requirement to resource ratio would be between 0.3–3% of the total amount of ruthenium available on Earth.

39


Chapter 1 - Introduction

1.6 DSC possible applications: the “Photovoltaic luminous walls” As previously stated, possible applications of dye sensitized solar cells are multiple. Here follows a brief description of a design developed in occasion of the competition “For the design of a device that employs energy production technology based on photovoltaic materials made from organic materials”, organized in 2012 by the Community of Messina Foundation, in conjunction with The Horcynus Orca Foundation, The Mediterranean University of Reggio Calabria and The Institute of Chemical Physical Processes of CNR, which we called “Photovoltaic luminous walls” (Fig 1.36 and 1.37). The present work received the mention of the exanimating commission. Photovoltaic luminous walls are based on the idea of a urban design element, that could transform the sunlight (considered a public resource) and give it back to the community. A photovoltaic luminous wall is stand-alone device that can be used to furnish and bring light to urban spaces such as plazas, boulevards, bus stops, without any further cost after the installation on site. It includes two aluminim frames containing 20 photovoltaic DSC modules each, which estimated power in standard illumination conditions is about 5 W (100 W in total in the entire wall); the aluminim frames are joined to the two sides of another aluminim frame “C” section in which a number of luminous leds take place. The three-frames package is mounted apart then inserted

From left to right: Fig. 1.36 Photovoltaic luminous walls Fig. 1.37 Photovoltaic luminous walls with led screen integration for public transport stops use 40


Chapter 1 - Introduction

inside a steel “C” section structure. On the two extremities there are two cavities protected with perforated steel sheet, designed to include counters, batteries and charge controllers. Fig. 1.38 and 1.39 show cross-sectional views of the edges of the walls. 2

2 5

5 3 7

6 6 2 3

4 4

1 1 Fig. 1.38-39 Detailed cross sections at the edges of the walls. Scale 1:5 1. Laminated glass 4+8 mm including the DSCs 2. Extruded steel profiles 3. Aluminium frame with glass holder for easy maintenance 4. Led 5. Bended perforated sheet 6. Cables 7. Electrical box

The perforated sheet is used in order to provide natural ventilation inside the wall, avoiding the insurgence of moisture-related phenomena. The wall is designed as a modular and modulable element and it can be installed both vertically and horizontally on its side, creating different urban 41


Chapter 1 - Introduction

spaces. Its installation and maintenance are easy and quick. Fig. 1.40 and 1.41 show respectively the assembly method of the wall and a method for fixing the same to the ground in vertical or horizontal position, using a metal plate.

From left to right: Fig. 1.40 Assembly scheme of the wall. Numbers indicate the chronological order of the operations Fig. 1.41 Scheme for fixing the photovoltaic luminous wall to the ground using a metal plate

Of course the DSC modules may assume different colours by changing the type of dye and different transparency by changing the thickness of the TiO2 paste deposited. The device collects the sun energy during the day in one or more batteries located inside the lateral cavities, then consumes it during the night with its glowing. The number of the leds inside the frame comes out from an estimation conducted in the hypothesis that the cells work in condition similar to the standard conditions. The limit was to let the cells charge the batteries enough to be glowing all night long. The calculation was made considering that, on the average, in southern Europe there are 12 hours of light and 12 hours of darkness. In order to be more restrictive, it was considered a worse condition of 10 hours of light and 14 hours of darkness, moreover it has not be included 42


Chapter 1 - Introduction

in the calculation the amount (little) of energy that device can produce also thanks to the artiďŹ cial light generated and received by the device itself during the night. So the calculation can be expressed through the following equation, considering an average consumption of 3W for each led: day collected energy = night consumed energy 5 W x number of modules x 10 h = 3 W x number of leds x 14 h In the proposed design, 20 modules were used so, out from the equations, the number of led that can be installed is in this case 24. The cost of the single wall was estimated â&#x201A;Ź 387533. In the next pages the two tables presented for the competition (respectively in Fig. 1.42 and 1.43) are shown.

43


Chapter 1 - Introduction

MURI SUL LUNGOMARE

MURI SUL LUNGOMARE

A

B

S

T

R

A

C

T

Il dispositivo presentato di artiene alla seguito appartiene categoria degli elementi di arredo urbano e si tratta in particolare di un muro fotovoltaico luminoso minoso delle dimensioni totali di 250x96x30 cm. de rispondere L’oggetto intende ad un tempo alla ll duplice esigenza di arredare ed illuminare spazii urbani quali piazze, viali ed aree di attesa dei mezzi zi di trasporto pubblico, al solo costo dell’installazione, e, essendo concepito come e dispositivo interamente stand-alone

autosufficiente. Esso è costituito da una coppia di telai in alluminio sui quali trovano alloggia alloggia-mento complessivamente 20 moduli delle dimensioni di 19x76 cm per una potenza complessiva di circa 100 W in condizioni standard; i telai in alluminio sono alloggiati all’interno di un profilo a “C” in acciaio a formare una camera interna, entro la quale è collocata un’ulteriore cornice dotata di led luminosi. Sulle due estremità del muro sono presenti due cavità protette da piastre metallimetalliche forate all’interno delle

quali è possibile alloggiare contatori, batterie chimiche, regolatori di carica. Le piastre forate permettono un’adeguata ventilazione naturale, riducendo la possipossibilità che si manifestino fenomeni di condensa. Il muro è concepito come elemento modulare e modu modu-labile, posizionabile in verti verti-cale o orizzontalmente su un fianco a formare ambiti urbani diversificati. E’ di semplice realizzazione e manutenzione e fa uso di materiali ad alto contenuto riciclabile (metalli e leghe) e di facile reperimento. Le lastre possono assumere

colori diversi sulla base del tipo di colorante scelto e diversi gradi di opacità sulla base dello spessore di pasta di ossido di titanio deposi deposi-tata (e dunque di colorante a s s o r b i t o ) . Ciò permette di poter ottenere non soltanto muri in colori diversi ma anche ad esempio muri che presenpresensfuma-tano un gradiente di sfuma tura dello stesso colore. degli Infine applicando stamp adesivi su supporto trasparente è possibile usare i muri anche come affissione superficie di af ffissione ffissione per pubblicità (sostenibilità economica) info e manifesti.

NE A-A 1:10

SEZIONE B-B 1:10

MURI MU RI F FOT FOTOVOLTAICI TOVOLTAICI AIC CI LUMINOSI LUMIINO OSI CONCORSO PER LA PROGETTAZIONE PROGETT TAZIONE AZIONE DI UN DISPOSITIVO CHE UTILIZZI TECNOLOGIE DI PRODUZIONE ENERGETICA BASATE BASATE SU MATERIALI MATERIALI FOTOVOLTAICI FOTOVOLTAICI RICAVATI RICA CAVATI DA MATERIALI MATERIALI ORGANICI

44

Fig. 1.42 Table n.1 as presented for the competition “For the design of a device that employs energy production technology based on photovoltaic materials made from organic materials”


Chapter 1 - Introduction

MURO ALLA FERMATA DEL TRAM

MURI DELLA MEMORIA

2

2

5

5 3 7

6 6 2 3 PARTICOLARE DELLA LASTRA 1:5 Ciascuna delle 20 lastre incluse nel muro può contenere 44 moduli di 6 celle ciascuno per una superficie attiva complessiva di 67320 mm2. I moduli hanno dimensioni di 170 x 11 mm (rettangolo interno) e sono incapsulati in guarnizioni in Surlyn dello spessore di 2 mm. Le celle sono collegate per mezzo di contatti in pasta d’argento. La potenza prodotta in condizioni standard AM 1.5 e 100 mW/cm2 è di circa 5 W.

4 4

1

1

PARTICOLARI 1:5 1. Vetro stratificato 4+8 mm contenente le celle 2. Profili in acciaio estrusi 3. Telaio in alluminio con fermavetro per facile manutenzione 4. Led 5. Lamiera forata piegata 6. Cavi elettrici 7. Scatola elettrica

1

3

4

5

2 SCHEMA CIRCUITO 1. Lastra 2. Junction-box 3. Regolatore di carica 4. Accumulatore chimico 5. Circuito di led

2 3

1 3

COMPONENTI IMPIEGATI

SCHEMA DI MONTAGGIO I numeri indicano l’ordine delle operazioni

Fig. 1.43 Table n.2 as presented for the competition “For the design of a device that employs energy production technology based on photovoltaic materials made from organic materials”

1. DSSC

2. PROFILI ESTRUSI

3. TELAIO IN ALLUMINIO

4. LED

5. LAMIERA FORATA

MURI FOTOVOLTAICI LUMINOSI CONCORSO PER LA PROGETTAZIONE DI UN DISPOSITIVO CHE UTILIZZI TECNOLOGIE DI PRODUZIONE ENERGETICA BASATE SU MATERIALI FOTOVOLTAICI RICAVATI DA MATERIALI ORGANICI

45


Chapter 1 - Introduction

NOTES 1. Photovoltaic Technology Research Advisory Council. (2005). A Vision for Photovoltaic Technology: EU Commission. 2. Renewable energy statistics from Eurostat available on: http://epp.eurostat.ec.europa.eu/statistics_explained/index.php/Renewable_energy_statistics. 3. EurObserv’ER. (2011). The State of Renewable Energies in Europe (11th ed.). Paris. 4. Ibidem. 5. European Climate Foundation, & Office for Metropolitan Architecture, Roadmap 2050: a practical guide to a prosperous low-carbon Europe (Vol. 3: Graphic Narrative), 2010. 6. For an overall EU contribution of € 24,5 million. 7. Photovoltaic Technology Research Advisory Council. A Vision for Photovoltaic Technology, op. cit. 8. www.solclima.it/le_celle_multigiunzione.html. 9. D. Martineau, Dye Solar Cells for Real: The Assembly Guide for Making Your Own Solar Cells, Solaronix, 2010. 10. G. Calogero, G. Di Marco, Red Sicilian orange and purple eggplant fruits as natural sensitizers for dye-sensitized solar cells, Solar Energy Materials & Solar Cells, 92, 2008, pp. 1341– 1346. 11. N. Guerin, Dye-sensitized solar cells break a new record, 2011 from http://actu.epfl.ch/news/dye-sensitized-solarcells-break-a-new-record/ 12. Ibidem. 13. T. W. Lin, J. Lin, S. Y. Tsai, J. N. Lee, C. C. Ting, Absorption Spectra Analysis of Natural Dyes for Applications in DyeSensitized Nano Solar Cells, 31st National Conference on Theoretical and Applied Mechanics, Kaohsiung, Taiwan, 2007. 14. T = 25°C ; I = 1000 W/m2 ; AM 1.5 spectrum. 15. R. Ciriminna, P. Pagliaro, G. Palmisano, BIPV, Il fotovoltaico integrato nell’edilizia, Dario Flaccovio Editore, Giugno 2009, Palermo. 16. Toyota’s exihibition at Aichi 2005 Expo. 17. J. Kawakita, Trends of Research and Development of Dye-Sensitized Solar Cells, Quarterly Review, 35, 2010. 18. cfr. R. Corrao, Glassblock and Architecture, op cit. 19. cfr. D. Neumann (2010). Translucent vs. transparent: Glassblocks and Prism Glass at the beginning of Modern Architecture in Glassblock and Architecture, op cit. 20. J. Ishigami, Another scale of architecture, Kyoto, Japan: Seigensha, 2011. 22. http://www.pragmanet.eu/solar/tipi_di_celle.aspx 23. M. J. De Wild-Scholten, A. C. Veltkamp, Environmental life cycle analysis of dye sensitized solar devices; status and outlook: ECN Solar Energy, 2007. 24. B. Weller , et al., Photovoltaics, Technology Architecture Installation, op. cit. 25. Ibidem. 26. Ibidem. 46


Chapter 1 - Introduction

27. http://www.pvcycle.org/ 28. Ibidem. 29. ISO 14040:2006 “Environmental management - Life cycle assessment - Principles and framework”. 30. H. Greijer, L. Karlson, S. E. Lindquist, A. Hagfeldt, Environmental aspects of electricity generation from a nanocrystalline dye sensitized solar cell system, Renewable Energy, 23, 2001, pp.27–39. 31. Ibidem. 32. B. Andersson, C. Azar, J. Holmberg, S. Karlson, Material constrains for thin-film solar cells, Energy, 23(5), 1998. 33. The summary costs calculation was made for taking part to the competition.

47


CHAPTER 2

1998-2011 trends in patents analysis


Chapter 2 - 1998-2011 trends in patents analysis

2.1 Introduction The interest on promising dye-sensitized solar cell technology is massively pushing the research in this field from all over the world with a fast increasing number of scientific publications and patent applications. A preliminary study on the current state of art is considered to be necessary before to start the study of a new application of this type of device. The DSSCs published patents situation is complex, and today continously developing. In the present work an analysis of the patents published worldwide has been conducted, by searching in the worldwide patents archive of the EPO (European Patent Office)1 and using the following keywords “dye sensitized solar cell”. With the results of this research a database including a number of 1625 patents families (patents applications that originate from the same priority document) was built. The DSCs history is relatively recent. First patents that deal with dye-sensitized solar cells appear at the end of 20th century and the patents publication is still actively going on. The very first published patents on DSSCs started from 1988 (EP0333641 Basic M. Gratzel and P. Liska patent “Photoelectrochemical cell, process for making such a cell and use of this cell”) even if the explicit definition of “Dye-sensitized solar cells”, which later came is not in their titles. For this reason some patents do not appear in the database. Since new patents are published almost day by day and there are patents filed in 2011 but today not published online yet by the EPO, the database includes the patents filed up to the date of 30th June 2011 (first semester of 2011). Until this date, the publications number is supposed not to grow anymore because all the patents presented seem to be already published2. Many of the patents only exists in the native language of the applicants (i.e. Japanese, Korean, Chinese) and this makes prior-art investigations difficult. An excerpt of the database is reported in Appendix A.

51


Chapter 2 - 1998-2011 trends in patents analysis

In Fig. 2.1 the analysis methodology used is schematically shown: the patents are sorted by filing date (which we consider more relevant than the publication date to describe the trend of the scientific research), then grouped once by the country in which the patent has been published, and then once by the particulary object/field of the patent. Moreover the analysis on the nature of the applicants (public or private) was conducted. In Fig. 2.2 a schematic evolution of dye-sensitized solar cell technology, before Gratzel invention, is shown in its most relevant steps. 1625 Patents database

Analysis over time

Organizational

Geografical

Technical Fig. 2.1 Graphical patents analysis scheme

J. Moser & H. Rigollot

Gerischer & Tributsch

M. Graetzel Tsubomura et al.

First sensitization of photoelectrode

ZnO electrode sensitized by organic dyes

Multi-crystalline ZnO electrode

Mesoporous TiO2 electrode and ruthenium based dyes

1887-1893

1968

1976

1991

52

Fig. 2.2 Main steps in the evolution of dye-sensitized solar cell technology until M. Gratzel invention


Chapter 2 - 1998-2011 trends in patents analysis

The history of the sensitization of semiconductors started farely before M. Gratzel’s experiments. It is an interesting convergence of photography and photo-electrochemistry, both of which rely on photo-induced charge separation at a liquid-solid interface. In 1887 it was observed by Moser3 (and then confirmed by Rigollot4 in1893) that the sensitivity of silver halides (used in photographic films) could be increased by coatings made with dye stuff. Sensitization of semiconductor materials (such as TiO2, ZnO, and SnO2) with photosensitizers (such as organic dyes that can absorb visible light) has been extensively studied in relation to the development of photography technology since the late 19th century. Gerischer and Tributsch published in 19685 and 19696 the results of their studies on a ZnO electrode used in electrochemical energy converting cells and sensitized by organic dyes including rose bengal, fluorescein, and rhodamine B. During the first years of the sensitized solar cell research, most studies were made with single crystal oxide samples, with very low power conversion efficiencies (< 1%). Tsubomura et al.7 reported a breakthrough in the conversion efficiency (2,5%) in 1976 by using the powdered high porosity multi-crystalline ZnO instead of single crystal semiconductor, resulting in a significant increase of the surface area of the electrode. The most significant advance in the field of dye-sensitized solar cells was introduced by Gratzel and coworkers in 19918. They greatly improved the power energy conversion efficiency from lower than 2,5 to 7%. The main reasons for the improvement were as follows: (1) the preparation of nanostructured TiO2 film, (2) the use of ruthenium complex that was adequately bonded to TiO2 nanoparticles, (3) the selected organic liquid electrolyte based on iodide/triiodide.

53


Chapter 2 - 1998-2011 trends in patents analysis

2.2 Patents publication timeline During the last two decades over 1600 patents about dye sensitized solar cells were published worldwide, a number which confirms the interest of the scientific community in this subject. In this sense, the most active countries were, and still are: Japan, the Republic of Korea and China; a relevant number of publications belongs to Taiwan and United States too. At present, Japanese research achievements provide the world's highest records both in the cell and module conversion efficiencies and Japan is also leading the world in developing quasi-solid electrolytes and plastic substrates. Because Gratzel's basic patent (Switzerland) expired on April 12, 2008, efforts toward commercialization and practical use are expected to be in the next years more active. In regard to commercialization, there are already companies such as G24 Innovations (U.K.) Solaronix SA (Switzerland) and Dyesol (Australia) which are “active” in the market and have already released 1998

140

1999

2000

2001

2002

2003

2004

120 100

95

80 61

60 39

40

54

11

321

3

10 4

Switzerland

United States China Republic p of Korea JJapan

United States

53

Taiwan United States China Republic p of Korea JJapan

Japan

2

Germanyy N th l Netherlands

1

Australia

1

United States China Republic p of Korea JJapan

1

United States

Netherlands

0

1

Japan

19

20

Chart 2.1 Trends in patents with reference to the country of issue (Part I)


Chapter 2 - 1998-2011 trends in patents analysis

commercial products. Prototype models have been released by companies such as Aisin Seiki Co. Ltd., Toyota Central R&D Labs. Inc., Fujikura Ltd., Sony Corporation, TDK Corporation, Rohm Co. Ltd., Hitachi Maxwell Ltd. and Peccell Technologies Inc.. For what concerns flexible DSC Konarka Technologies (US) is ready to release its products on the market. It is possible to notice that in this list also small industries and firms with little PV history are included, which now have the possibility to enter in a new market segment9. Thus the development for practical use is expected to continue. In Chart 2.1 the trend in patents publications worldwide is shown. After an exponential growth in the first decade of the 21st century, publications in this field are now slightly going down. In fact, the number of patents published in 2011 (first semester) results slightly lower than the half of the total number of patents published in 2010. The massive growth registered in 2000 decade has been justified by the worldwide increasing expectations for renewable energies which resulted in numerous governmental and industrial programs providing funds and financial support for the research (already exposed in Chapter 1). The database includes 2005

2006

2007

2008

2009

127

2010

2011 ;ĮƌƐƚƐĞŵĞƐƚĞƌͿ

122 109

100

8

76

80

75 6

60

5 3

35 29

40

2

22 2

13

Chart 2.1 Trends in patents with reference to the country of issue (Part II)

14 788

20 0

Australia Taiwan United States China Republic p of Korea Japan J

Australia Taiwan United States China Republic p of Korea Japan J

Sweden

United Kingdom

13

1 Taiwan United States China Republic p of Korea J Japan

2

3

United Kingdom A t li Australia Taiwan United States China Republic p of Korea J Japan

1

Australia Taiwan United States China Republic p of Korea Japan J

Switzerland

15

Taiwan United States China Republic p of Korea Japan J

1 Taiwan United States China Republic p of Korea Japan J

1

Germany

18 1

120

105

83

2

140

55


Chapter 2 - 1998-2011 trends in patents analysis

only 11 different publishing countries, which is an extremely low number depicting that the DSC research community is still geographically very limited. With regards to applicants/assignees, we have found a total number of 310 applicants, which is also quite a small number (it means that on the average each of the 310 applicants published approximately 5 patents). As found by Petterson et al.10 and shown in Chart 2.2, approximately 80% of the patent families are filed by companies, i.e. approximately 20% have universities or research institutes as applicants/assignees. This ratio has remained just about constant for the past ten years. However, there are substantial differences between different nations. For Japan 90% of the patent families have industrial applicants/assignees. The corresponding values for Korea and U.S. are 80%. Taiwan and China, on the other hand, display an opposite trend, with 50% and 40%, respectively, as industrial applicants/assignees, i.e. the most of the patent families from China have universities or research institutes as applicants/assignees. $!!"# ,!"# +!"# *!"# )!"# (!"# '!"# &!"# %!"# $!"# !"#

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Chart 2.2 Ratio of patents published by companies in respect to those published by universities or research institutes 56


Chapter 2 - 1998-2011 trends in patents analysis

Chart 2.3 shows the number of patents published by companies or privates, by universities or research institutes and those in which private and public bodies collaborated.

''%#

("#

!"# )**+,-./0123#/40#2*5-,657# **+,-./0123#/40#2*5-,657# )

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Chart 2.3 Ratio of patents published by companies in respect to those published by universities or research institutes

In Appendix B the complete list of the 310 applicants, in which is also indicated the country of origin, is reported.

57


Chapter 2 - 1998-2011 trends in patents analysis

2.3 Current DSC state of art. Technical analysis of selected patents In Chart 2.4 the progress in the number of publications with reference to the particular object or field of the patent is shown. The patents are sorted in 12 categories further described: 1) DSSC Manufacturing methods; 2) DSSC Modules; 3) Photoelectrode configuration and TiO2 pastes; 4) Organic and inorganic dyes or absorption methods; 5) Counter electrodes; 6) Electrolyte type and composition; 7) Transparent conductive substrates; 140

1998

1999

2000

8) Encapsulation methods and spacers; 9) Flexible DSSC; 10) Solid-state DSSC; 11) Apparatus for manufacture or control; 12) Applications.

2001

2002

2003

2004

120 100 80 58

60 29

58

10 2

35221

Manufacturing method Modules Photoelectrode Dyes y Counter electrode Count Electrolyte y Substrates S b t t Sealings g DSSC Flexible D

54

Manufacturing method Photoelectrode Dyes

2

Dyes

Manufacturing method

0

9 1

Solid-state

20

29

25

889

4 1 23 113 Manufacturing method Modules Photoelectrode Dyes y Counter electrode Count Electrolyte Substrates Sealings Solid-state Apparatus pp Application Applications

25

1 1 Manufacturing method Manufac Modules Photoelectrode Dyes y Counter C t electrode Electrolyte y Substrates S b t t Sealings Solid-state Applications

40

Chart 2.4 Trends in patents with reference to the object/field of the inventions (Part I)


Chapter 2 - 1998-2011 trends in patents analysis

From a technical perspective, the majority of the DSC patent applications deal with DSC manufacturing methods and semiconductor materials, but also dyes, electrolytes, substrates and DSC modules. The remaining part deals with particular applications and instruments used for the manufacture and control. In particular what is investigated the most is definitely the nature of the semiconductor photoactive layer (also the patents categorized as DSSC manufacturing methods, very often deal with configurations of the photoelectrode) and this is a trend that is in line with the trend in scientific licterature publications. The reasons of the disproportion of such a dominant trend is of course related to the strong influence that the photoelectrodes design has on the efficiency of the cells, which is the main factor leading to possibilities of commercialization.

2005

2006

2007

2008

2009

2010

140

2011 ;ĮƌƐƚƐĞŵĞƐƚĞƌͿ

107

100

90 78

80

78 65

65 57

80 64

60

54 41

1 12 6 88 3

1 15 16 2 3

67

11 9 8

20 13

Chart 2.4 Trends in patents with reference to the object/field of the inventions (Part II)

23

0

Apparatus pp A li ti Applications

4

8

Manufacturing method Modules Photoelectrode Dyes y Counter electrode Count Electrolyte

14

Manufacturing method Modules Photoelectrode Dyes y Counter C t electrode Electrolyte y Substrates Sealings g Fl ibl D Flexible DSSC Solid-state Apparatus A li ti Applications

1321

Manufacturing method Modules M d l Photoelectrode Dyes y Counter electrode Count Electrolyte y Substrates Sealings g Flexible Fl ibl D DSSC Solid-state Apparatus pp Applications Application

11 2

Manufacturing method Manufac M d l Modules Photoelectrode Dyes y Counter C t electrode Electrolyte y Substrates Sealings g Flexible Fl ibl D DSSC Solid-state Applications

6

0 12 8

Manufacturing method M d l Modules Photoelectrode Dyes y Counter C t electrode Electrolyte y Substrates Sealings Fl ibl D Flexible DSSC Apparatus pp A li ti Applications

13

Manufacturing method Modules Photoelectrode Dyes y Counter C t electrode Electrolyte y S b t t Substrates Sealings g Flexible Fl ibl D DSSC Solid-state Apparatus pp Applications Application

19

Manufacturing method Modules Photoelectrode Dyes y Count Counter electrode Electrolyte y S b t t Substrates Sealings g Flexible D DSSC Apparatus pp Applications Application

40

4 35

29 11 7 5 3 23

120

59


Chapter 2 - 1998-2011 trends in patents analysis

Chart 2.5 schematically shows the relative magnitudo of each of the 12 categories identified, in which is evident that putting together the two categories called DSSC manufacturing method and Photoelectrode configuration and TiO2 pastes, more than half of the total number of publications is reached. In the following pages we will be going deeper in details in the analysis of the patents, trying to trace a line in what is for each of the 12 categories the evolution of the state of art according also to the scientific publications in this field11. During this part of the research the support of scientific literature was fundamental due to a lack in english published patents. In fact what was found during this analysis is that a high proportion of Asian patents (more than 70%) strangely do not proceed after the national phase, so they are available only in native language of the applicants. Their applications lead only to a local patent protection.

Substrates

Organic and Counter inorganic dyes and electrode absorption methods Apparatus Sealings

Flexible

DSSC Modules

Solid-state

DSSC Manufacturing methods

Applications

Electrolyte type and composition Photoelectrode configuration and TiO2 pastes

60

Chart 2.5 Relative magnitudo of the 12 objects/fields identified through the technical analysis of the patents in the database


Chapter 2 - 1998-2011 trends in patents analysis

2.3.1 A brief overview on the 12 categories 1) DSSC Manufacturing methods The original concept of DSCs is based on a semiconductor film of TiO2 nanoparticles, in which a ruthenium based dye is absorbed, a iodide-triiodide based electrolyte and a platinum counter electrode, stacked in between two electrically conductor transparent substrates. It was published by O’ Regan and Gratzel in 1991 in the magazine Nature12. More than 20 years after the O’ Regan and Gratzel publication, as the present work confirms, thousands of alternative configurations and alternative components have been investigated and it is difficult to identify a DSC patent that is actually the base for all the other invented configurations. By the way we can refer to two main DSC concepts. The first one, conventionally referred to as double-substrate sandwich, is today the most diffused and it is the one previously described in Chapter 1. The second concept, introduced by Kay et al.13 is referred to as single substrate or monolithic. It is based on the combination of conductive graphite and catalyzing carbon black powders and it is particularly suitable for serial connected modules. The two patents related to the aforesaid inventions are US5084365 (Photo-electrochemical cell and process of making same, 1990) and DE19540712 (Monolithic, series-connected photovoltaic modules and processes for their preparation, 1995). Other interesting informations on the manufacturing methods of DSCs can be found i.e. in patents US2011155223 (Dye-sensitized solar cell and a method of manufacturing the same, 2009) and EP2407985 (Dye-sensitized solar cell, 2011).

From top to bottom: Fig. 2.3 Andreas and Toby Meyer, founders of the Switzerland-based company Solaronix, holding their developed PICTO and MIMO type dye sensitized solar cells Fig. 2.4 A sony developed dyesensitized solar cell according to the patent US2011155223 61


Chapter 2 - 1998-2011 trends in patents analysis

Fig. 2.5 A 3600 cm2 panel consisting of 12 serial-connected current-collecting glass based sandwich DSC modules developed by the Institute of Plasma Physics in Hefei, China 62

2) DSSC Modules The reliability of a DSC module is definitely more complex compared to the one of a single cell. First of all, when we refer to a DSC module we indicate a device with significantly increased size both in x and y directions in relation to a laboratory cell (usually few centimeters wide). Cells with large active areas cannot be made by simply scaling up the dimensions of the components and a serie of new issues has to be considered. The main issue in the passage from laboratory to large scale dimensions cells is the resistance of the TCO layer, which thickness should be considerably increased in order to achieve acceptable efficiencies but causing, on the other hand, a significant loss in the transparency of the substrate to which corresponds a loss in light absorption. Moreover particular attention has to be given to the sealing method of the electrolyte (primary sealing) which is highly corrosive towards the metallic connection grids. Also the contact between separate cells must be avoided. In addition to this, the system must also be sealed from the outside environment (secondary sealing) in order to use organic solvents which are highly volatile. To seal the modules, an inert material such as silossanic resins or glass frit has been used. The complexity in the actual realization of highly efficient modules is also evident in the relatively low number of published patent applications in comparison with those describing a single cell manufacturing method. Publications related to DSSC modules are farely low than those on DSC materials or manufacturing method and very few publications deal with modules manufactured on flexible sub-


Chapter 2 - 1998-2011 trends in patents analysis

strate. The DSC modules are made differently in dependance of the substrates types. For the monolithic structure, where only one substrate is needed, a TCO glass is commonly used. For the sandwich structures, different substrates combinations are used, such as: two pieces of TCO glass; one TCO glass and one metal foil; two TCO coated polymer sheets; one TCO polymer sheet and one metal foil. The architecture of the modules is mainly referable to the five categories further presented below14 and schematically reported in Fig. 2.6: (a) Sandwich Z-interconnected modules The DSC module is based upon a sandwich construction with the working electrodes deposited on a first substrate and the counter electrodes on a second substrate. A conducting material is used to build the electrical connections between the substrates and the adjacent cells (connected in series). These conductors must be efficiently insulated from the electrolyte to avoid corrosion. Moreover, the electrolytes of adjacent cells must be separated from each other to avoid unwanted mass transport. The Z-interconnection device has been applied on both rigid and flexible substrates. An example of sandwich Z-interconnected module is given in patent EP2337041 (Dye sensitized solar cell module and method of fabricating the same, 2010). (b) Sandwich W-interconnected modules This sandwich module design carries cells with alternating working and counter electrodes on each substrate, consequently every

(a)

(b)

(c)

(d)

(e) Substrate TCO TiOЇнĚLJĞ ůĞĐƚƌŽůLJƚĞ ŽƵŶƚĞƌĞůĞĐƚƌŽĚĞ Conductor Graphite

Fig. 2.6 Schematic cross sections of the five types of DSC modules: (a) sandwich Z-interconnection; (b) sandwich W-interconnection; (c) sandwich current collection; (d) monolithic serial connection; (e) monolithic current collection. The proportion of the module schemes are not reported to scale 63


Chapter 2 - 1998-2011 trends in patents analysis

second cell in the module is illuminated through the counter electrode. In this way interconnections are avoided but the cells must anyway be separated by a seal to avoid mass transport between adjacent cells. The design allows a high ratio of active area in the device but requires a good cell matching: the cells illuminated through the working electrode should generate as much current and voltage as the ones illuminated through the counter electrode, this can be obtained by using different widths of the cells or by matching the performances through optimizing the cell parameters. An example of sandwich W-interconnected module is given in patent EP2043191 (Dye sensitized solar cell module and method of fabricating the same, 2007).

Fig. 2.7 A glass based module (the so called meander type) consisting of six serial connected current collecting parts, developed by Fraunhofer ISE, Germany

64

(c) Sandwich current-collecting modules This sandwich model design is based on increasing the cell size through the use of current collectors in the TCO glass to reduce the sheet resistance. The most common solution in literature has been to place silver current collectors on top of the TCO layer. Since silver corrodes in contact with the conventional iodide/triiodide redox couple in the DSC, the silver lines must be thoroughly insulated. An alternative design for current collection modules is the so called “meander-type”, which driving force is to have fewer holes in the substrate for electrolyte filling compared to the Z-interconnected modules where each cell requires two holes. The patent related to the invention of the meander-type DSC module is WO2005096391 (Photo-electrochemical solar cell module, 2005).


Chapter 2 - 1998-2011 trends in patents analysis

(d) Monolithic serial-connection modules The monolithic connection requires only one substrate, upon which three porous layers are disposed, namely a photoelectrode of dye sensitized nanocrystalline TiO2 (in anatase form) a spacer of electrically insulating and light reflecting particles of TiO2 (in rutile form) and a counter electrode made of graphite powder and carbon black. The pores of the three layers are filled with iodide-based electrolyte. The monolithic series connection is achieved by overlapping each carbon counterelectrode with the back contact of the adjacent photoelectrode. (e) Monolithic current-collecting modules The monolithic current-collecting modules (no efficiency of such a device was still shown) consists in the application of current collectors in the monolithic concept. 3) Photoelectrode configuration and TiO2 pastes Compared to bulk materials, semiconductor nanomaterials used as photoanodes can offer a larger surface area for dye adsorption (more than one thousand times if compared to an equal wide plane surface) contributing to optical absorption and leading to an improvement in the solar cell conversion efficiency. The semiconductor nanostructures can be classified in15: 1. nanoparticles pastes; 2. one-dimensional nanostructures (nano wires and nanotubes). Photoelectrodes made of materials such as Si, GaAs, InP, and CdS decompose under irradiation owing to photocorrosion. In contrast, oxide semiconductor materials, especially TiO2, have

Fig. 2.8 A sandwich W-interconnected glass based DSC module developed by Sharp, Japan

65


Chapter 2 - 1998-2011 trends in patents analysis

From top to bottom: Fig. 2.9 SEM microphotographs. A) anatase, B) rutile. Source: “Photocatalityc degradation of acridine dyes...” in Journal of Environmental Management, 101, 2012 Fig. 2.10 SEM microphotographs of TiO2 nanotubes. Source: “TiO2 nanotubes...”, Nanoscale, 1, 2010 66

good chemical stability under visible irradiation in solution; and additionally, they are nontoxic and inexpensive. The TiO2 thin-film photoelectrode is prepared by a very simple process. TiO2 colloidal solution (or paste) is coated on a TCO substrate and then sintered at 450° to 500°C, producing a TiO2 film about 10 μm in thickness. The porosity of the film is also important because the electrolyte, which contains the redox ions, must be able to penetrate the film effectively. Fig. 2.9 shows a scanning electron microscope (SEM) photograph of a nanocrystalline TiO2 film in anatase e rutile forms. To date, nanocrystalline TiO2 electrodes have been used predominantly as the photoelectrode in DSSCs, but other oxide semiconductor materials, ZnO, SnO2, Nb2O5, In2O3,SrTiO3 and NiO, have been also analysed. Nevertheless, nanocrystalline TiO2 electrodes have the best performance, and oxide semiconductor materials better performing than TiO2 have not been found16. Recently, combined photoelectrodes consisting of two oxide semiconductor materials have also been investigated, obtaining better performances compared to that of ZnO or SnO2 electrodes17. On the other hand, nanotubes (especially carbon nanotubes) resulted advantageous in providing direct pathways for electron transport, which results faster than in the nanoparticle films. However they showed relatively low conversion efficiency probably because of the smaller internal surface area in the photoelectrode films they are used in18. An example of a photoelectrode built using ZnO nanoparticles is given in patent US20110162708 (Dye-sensitized solar cell employing zinc oxide aggregates grown in the presence of lithium,


Chapter 2 - 1998-2011 trends in patents analysis

2011). Examples of photoelectrodes built using carbon nanotubes are given in patent KR20110021362 (Carbon nanotubes electrodes, solar cells rechargeable batteries, manufacturing method for selfluminous body, 2009) and patent KR20090107851 (Dye sensitized solar cell using carbon nanotube based ďŹ lms and the fabrication method thereof, 2008). 4) Organic and inorganic dyes and absorption methods In DSCs the dye as sensitizer plays a key role in absorbing the sunlight and transforming the solar energy in electrical energy. Both metallic and organic complexes have been used as sensitizers. By far, the highest eďŹ&#x192;cient cells have been produced with Ru (ruthenium) containing compounds, which have carboxyl groups to anchor to the TiO2 surface. Typical Ru complex photosensitizers are: - the N3 dye (or red dye) which can absorb over a wide range of the visible regions from 400 to 800 nm; - the black dye, absorbing in the near-IR region up to 900 nm. Metal complexes having metal centers other than Ru have also been synthesized and their performance have been investigated. These include Fe complexes, Os complexes, Re complexes, and Pt. However, highly eďŹ&#x192;cient performance exceeding that of the Ru complex photosensitizers has not been obtained. Porphyrin and phthalocyanine derivatives have also been employed as photosensitizers in the DSSC19. Organic dyes can also be utilized as photosensitizers. They have several advantages as photosensitizers: (1) variety of structures for molecular design, (2) they are cheaper than metal com-

Fig. 2.11-12-13-14 showing respectively red berries and red berries extract obtained by grinding of the same; a photoelectrode appearance before and after the absorption of the dye. Source: Solaronix Products Catalogue 2011 67


Chapter 2 - 1998-2011 trends in patents analysis

plexes, and (3) they have larger absorption coefficients. Aggregates of the merocyanine dye formed on the TiO2 surface result in expansion of the absorption area, especially in the long-wavelength region, resulting in improvement of light-harvesting performance20. In addition to organic dyes, natural dyes extracted from plants can also be used as photosensitizers. Dyes obtained from flowers, leaves, fruits, etc. can be used as sensitizers in DSCs. The dyes extracted from these materials contain cyanine, carotene, chlorophyll, etc. The highest conversion efficiency recorded by this kind of dyes is of 1.17%21. Overall, natural dyes as sensitizers of DSCs are promising because of their environmental friendliness, low-cost production, and designable polychrome modules.

Fig. 2.15 Comparative graphs of graphene, ITO and single walled carbon nanotubes (SWNT) used in the formation of DSC counter electrodes. Source: “Continuous, highly flexible and transparent graphene films...” in ACS Nano, 5, 2010

68

5) Counter electrodes Counter electrodes play the role of returning back electrons to the electrolyte. Since the electrolyte is corrosive, the counter electrode requires high corrosion resistance. At the same time a high reaction rate is needed to quickly reduce iodine to a iodide ion in the electrolyte. Considering the balance between these factors, a conductive glass electrode coated with platinum is generally used. As alternatives to platinum, polymeric or carbon nanotubes counter electrodes have been proposed. Sputtered Pt on a TCO substrate has been usually employed as a counter electrode. When Pt is sputtered producing a mirror like effect, the photocurrent is slightly increased due to the light-reflection effect. In addition, the electrocatalytic activity of the Ptsputtered TCO electrode for the reduction of tri-iodide ions is


Chapter 2 - 1998-2011 trends in patents analysis

improved by the formation of Pt colloids on its surface. Small amounts of an alcoholic solution of H2PtCl6 are dropped on the surface of the Pt-sputtered TCO substrate, followed by drying and heating at 385° C for 10 min, resulting in the formation of Pt colloids on the surface. The properties of the Pt counter electrode directly affect the fill factor of the solar cell22. 6) Electrolyte type and composition The electrolyte used in the DSSC usually contains I−/I3− redox ions, which mediate electrons between the TiO2 photoelectrode and the counter electrode. Mixtures of iodides such as LiI, NaI, KI, tetraalkylammonium iodide (R4NI), and imidazolium-derivative iodides dissolved in nonprotonic solvents (e.g. acetonitrile, propionitrile, methoxyacetonitrile, propylene carbonate, and their mixture) can be employed23. Viscosity of solvents directly affects ion conductivity in the electrolyte and, consequently, the cell performance. The iodine redox electrolyte gives the best performance24. Organic solutions containing iodine redox ions have been used as redox electrolyte too. Volatility of the electrode represents a critical point for the long term stability of a DSC. Roomtemperature ionic liquids used i.e. in electrochemical devices such as batteries have also been utilized and studied in DSSCs to replace of liquid electrolytes25. Ionic liquids used in DSSCs include imidazolium derivatives. If the viscosity of these ionic liquids can be decreased similarly to that of organic solvents, the solar cell performance will be improved as a result of increased ionic mobility of the electrolyte26.

Fig. 2.16 Bottles of iodine based electrolytes commercially released by Solaronix 69


Chapter 2 - 1998-2011 trends in patents analysis

7) Transparent conductive substrates Usually Transparent Conducting Oxide (TCO) coated glass is used as the substrate for the TiO2 photoelectrode. For high solar cell performance, the substrate must have low sheet resistance and high transparency. In addition, sheet resistance should be nearly independent of the temperature up to 500°C because sintering of the TiO2. Indium–Tin Oxide (ITO) is one of the most famous TCO materials, but Fluorine doped Tin Oxide (FTO) is also commonly used. In spite of having low resistance at room temperature, ITO resistance increases significantly at high temperature in air. Usually, fluorine-doped SnO2 is used as the TCO substrate for DSSCs. 8) Encapsulation methods, spacers, sealings A sealing material is needed to prevent the leakage of the electrolyte and the evaporation of the solvent. Chemical and photochemical stability of the sealing material against the electrolyte component iodine and the solvent is required also in order to prevent corrosion of the metallic connection grids27.

From top to bottom: Fig. 2.17 Top view AFM image of ITO films. Source: “Deposition of ITO films on SiO2 substrates” in Applied Surface Science, 248, 2005 Fig. 2.18 Typical 3D AFM image of an ITO film. Source: “Deposition of ITO films on SiO2 substrates” in Applied Surface Science, 248, 2005 70

9) Flexible DSSC The standard fabrication process of DSSC includes sintering of nanoparticles for the formation of the photoactive electrode, which requires temperatures up to ≈450°C. This process restricts the fabrication of these type of cells only on non flexible substrates28. In fact the main issues in forming flexible DSSC are forming flexible electrodes and counter electrodes. Low temperatures annealing methods have been studied but it has been ob-


Chapter 2 - 1998-2011 trends in patents analysis

served that the cell efficiency decreases with the decrease of TiO2 annealing temperature29. It is also possible, as an alternative, to form the photoactive electrode on a metal foil used as substrate (e.g. stainless steel, tungsten, titanium, zinc). This solution however has also shown low-efficiency energy conversion30. A flexible electrode may be formed by a structure of conductive fibres (for example glass fibres) coated with FTO or ITO. This kind of electrode substitutes the common titania paste based DSSC photoelectrode and it can be immersed in electrolyte as usual. A flexible counter electrode may be formed on a polymeric cathode layer (eg. PET or PEN) in which a carbon-nanotube layer is posed as cathode. In this case, the photoactive layer should be sintered before the formation of the counter electrode. The patents US2009126784 (Dye-sensitized solar cell using conductive fibre electrode, 2008) and US2010051101 (Electrode of flexible dye-sensitized solar cell, manufacturing method and flexible dye-sensitized solar cell, 2009) show respectively fabrication methods for a flexible electrode and a flexible counter electrode. 10) Solid-state DSSC In standard DSSCs the electrolyte is generally a solution of acetonitrile in which iodine ions and iodine are dissolved. This solution has very low evaporating pressure, acetonitrile is prone to evaporation and drops in conversion efficiency at high temperature or with long-term use. To prevent leaking and degradation of the electrolyte a special attention is given to sealing methods of the cells and alternatives to liquid electrolyte have been proposed. These alternatives consist in solid-state or gel form elec-

From top to bottom: Fig. 2.19 Sandwich Z-interconnected flexible DSC module developed by G24i Innovations, United Kingdom Fig. 2.20 Different coloured solidstate DSCs developed within the MOLYCELL project financed by the European Commission 71


Chapter 2 - 1998-2011 trends in patents analysis

From top to bottom: Fig. 2.21 “Lumixo” the light engine developed by Solaronix to supply accurate test and DSC devices. Source: Solaronix Products Catalogue 2011 Fig. 2.22 The Test Cell Assembly Machine (TCAM) developed by Dyesol which provides the user with a rapid, reliable and repeatable method for the assembly and permanent thermoplastic sealing of DSC test cells.Source: Dyesol Products Catalogue 2011 72

trolytes. Solid-state dye-sensitized solar cells (SDSCs) have recently set an efficiency record of 5.1%31. Moreover, they allow easier interconnections of the cells into a monolithic module. Quasi-solidification of the electrolyte using a gelator is another method for replacing liquid electrolytes. Gelation can be accomplished by adding a gelator in the electrolyte without other changes in the other components of the cells. It has been verified that the efficiency of DSSCs using a gel electrolyte is almost the same as that using a liquid electrolyte while better long-term stability is obtained32. P-type semiconductors are the most common hole-transporting materials to fabricate solid- state DSCs. Several aspects are essential for any p-type semiconductor in a DSC: (a) it must be able to transfer holes from the oxidized dye; (b) it must be able to be deposited within the porous TiO2 nanocrystal layer; (c) a method must be available for depositing the p-type semiconductors without dissolving or degrading the dye on TiO2 nanocrystal; (d) it must be transparent in the visible spectrum, otherwise, it must be as efficient in electron injection as the dye. Copper-based materials, especially CuI and CuSCN are found to meet all these requirements33. In summary, compared to a liquid electrolyte DSC, the solid-state counterpart presents a relatively low conversion efficiency, so it is necessary to make further efforts to design new and more efficient inorganic nanomaterial electrolytes for DSCs34. An example of solid-state dye-sensitized solar cell is described in patent US20050006714 (Solid state heterojunction and solid state sensitized photovoltaic cell, 2004). 11) Apparatus for manufacture and control


Chapter 2 - 1998-2011 trends in patents analysis

The apparatus for manufacture and control includes i.e. solar simulators, used for testing the cells and which are able to reproduce i.e. the solar spectrum; screen printers used for the deposition of semiconductor nanoparticles layers, laser scribing machine, which use a CO2 to make incisions into the conductive oxide layer of the substrates in order to form the modules; holedrilling machines used to create electrolyte ďŹ ll holes in glass substrates; furnaces used i.e. for glass conductor activation and the ďŹ ring of working electrode and counter electrode pastes. 12) Applications Thanks to their peculiar characteristics, such as transparency, colourability, low weight, DSCs have a wider range of possible applications than any other photovoltaic system. Those that were found through the analysis of the patents (again, mainly from Japan) are listed below: -windows; -lamps; -led screens; -vehicles; -road signs; -sidewalk blocks; -interior panels; -ventilation systems; -decorations.

From top to bottom: Fig. 2.23 Smart Forvision, a project developed by Smart and BASF, Germany based research institute. 129 mini-DSC panels are integrated in the top of a car providing energy for air-cooling and multimedia service installed in the vehicle Fig. 2.24 Hana Hakari, DSC integrated lamp developed by Sony Corp

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2.3.2 Analysis of selected patents In the following pages a selection of 13 patents will be described more in details in order to investigate more on the main issues related to the fabrication of DSCs. With the analysis of these selected patents we will try to explain which are some of the alternative technical options available for diďŹ&#x20AC;erent components of the DSSCs. Each of the patents is presented in form of a summary, including a brief description of the invention and extracts of the drawings. The summaries are numbered and identiďŹ ed with the labels from S1 to S13 and the respective category, identiďŹ ed among the 12 categories already exposed is indicated. Included in the selection are the Gratzel basic patent US5084365 (Photo-electrochemical cell and process of making same, 1990) and the Kay basic patent DE19540712 (Monolithic, series-connected photovoltaic modules and processes for their preparation, 1995) even if published before 1998 and not included in the database. Table 2.1 resumes the identifying data for the 13 selected patents.

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Chapter 2 - 1998-2011 trends in patents analysis

Label

Publication Number

S2

DE19540712

S1

US5084365

S3

US2011155223

S5

EP2337041

S7

WO2005096391

S4

S6 S8 S9

S10 S11 S12 S13

EP2407985

EP2043191

US20110162708

Title

Photo-electrochemical cell and process of making same

Category -

Monolithic, series-connected photovoltaic modules and processes for their preparation Dye-sensitized solar cell and a method of manufacturing Manufacturing method the same Manufacturing method Dye-sensitized solar cell

Dye sensitized solar cell module and method of fabricating the same Dye sensitized solar cell module and method for fabricating same Photo-electrochemical solar cell module

DSSC modules DSSC modules DSSC modules

Dye-sensitized solar cell employing zinc oxide aggrePhotoelecrode configugates grown in the presence of lithium rations and TiO2 pastes KR20110021362 Carbon nanotubes electrodes, solar cells rechargeable Photoelecrode configubatteries, manufacturing method for self-luminous body rations and TiO2 pastes KR20090107851 Dye sensitized solar cell using carbon nanotube based Photoelecrode configufilms and the fabrication method thereof rations and TiO2 pastes US2009126784 Dye-sensitized solar cell using conductive fibre elecFlexible DSSC trode Flexible DSSC US2010051101 Electrode of flexible dye-sensitized solar cell, manufacturing method and flexible dye-sensitized solar cell US20050006714 Solid state heterojunction and solid state sensitized Solid-state DSSC photovoltaic cell Table 2.1 Resuming table with the identifying data for the 13 selected patents

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Chapter 2 - 1998-2011 trends in patents analysis

PHOTO-ELECTROCHEMICAL CELL AND PROCESS OF MAKING SAME Publication number: Filing date: Inventor(s): Applicant(s): Applicant(s) nationality:

Gratzel basic patent

S1

US5084365 05/02/1990 M. Gratzel, P. Liska M. Gratzel, P. Liska Switzerland [CH]

A regenerative photo-electrochemical cell comprising a metal oxide semiconductor layer and a monomolecular chromophore (dye) layer is disclosed. In this patent the framework for the definition of dye-sensitized solar cells is described; it contains all the fundamental and innovative elements of a DSC, namely a porous metal oxide semiconductor, where TiO2 is already indicated as preferable, in which a rutheniumbased dye is absorbed and an electrolyte layer which uses a iodides or bromides redox couples. The patent tackles the problem of corrosion under light irradiation of the materials used in traditional photovoltaic systems (such as silicon, gallium-arsenide, and cadmium suphide) when they come in contact with electrolytes, and introduces metal oxide semiconductors as an alternative for the manufacture of solar cells. In fact, metal oxide semiconductors are transparent and chemically stable when subjected to light irradiation using electrolytes. The sensitivity of the metal oxide can be then increased with the addition of chromophores (or dyes) used as charge carriers. The innovative architecture in this kind of solar cells, separates the two function of light absorption and charge carrier, which are respectively fulfilled by the semiconductor layer and the dye. Another fundamental aspect is the semiconductor surface factor of roughness (the ratio of actual/effective surface to the projected area of the surface of a body) which is indicated to be preferably more than 20 and i.e. 150. Moreover, the patent description reports: “Different chromophores have different spectral sensivities. The choice of chromophores can thus be adapted to the spectral composition of the light of the source in order to increase the yield as far as

76


Chapter 2 - 1998-2011 trends in patents analysis

possible. Particularly suitable metal oxide semiconductors are oxides of the transitions metals [...] of titanium, zirconium, niobium, tantalum, chromium, molybdenum, tungsten or alternatively oxides of zinc, iron, nickel or silver [...]. Example of suitable chromophores, i.e., sensitizers, are complexes of transition metals of the type metal of ruthenium and osmium...â&#x20AC;?

The invention also indicates the process for the production of the metal oxide semiconductor layer, identiďŹ ed with the so called SOL-GEL process35. Extracts of the drawings:

Gratzel basic patent

From top to bottom: Fig. S1.1 Cross section view of a Photoelectrochemical cell (1) with a chromophore coated metal oxide semiconductor layer according to the invention under light irradiation (10). it comprises a metal support (11) to which there is applied a metal oxide semiconductor layer (12). A monomolecular layer of sensitizer (13) is disposed on the surface of the semiconductor layer (12) and adjoins an electrolyte layer (14) which on the other side adjoins a conductive electrode (15) consisting i.e. of conductive glass or plastic. The cell (1) is closed by an insulating layer at the top (16) and bottom (17) Fig.S1.2 Section through a metal oxide semiconductor (212) with a monomolecular dye layer (213)

S1

77


Chapter 2 - 1998-2011 trends in patents analysis

MONOLITHIC, SERIES-CONNECTED PHOTOVOLTAIC MODULES AND PROCESSES FOR THEIR PREPARATION (tr.)

Publication number: Filing date: Inventor(s): Applicant(s): Applicant(s) nationality:

Monolithic DSSC

S2

78

DE19540712 02/11/1995 A. Kay École Polytechnique Fédérale de Lausanne Switzerland [CH]

In this patent a series-connected monolithic DSC module is disclosed. The present invention is based on the same concept of connection of traditional thin-film solar cells. The configuration of this new solar cell consists in three porous layers on a transparent conductive substrate, namely a photoelectrode of dye sensitized nanocrystalline TiO2 (in anatase form) a spacer of electrically insulating and light reflecting particles of TiO2 (in rutile form) and a counter electrode made of graphite powder and carbon black, in which the function of the graphite is the electronic conduction combined with catalytic activity, while the carbon black is used in order to increase the catalytic effect. The pores of the three layers are filled with iodide-based electrolyte. The monolithic series connections on the transparent conductive substrate (i.e. FTO coated glass) is achieved by overlap of each carbon counterelectrode with the back contact of the adjacent photoelectrode.


Chapter 2 - 1998-2011 trends in patents analysis

Extracts of the drawings:

Monolithic DSSC

From top to bottom: Fig. S2.1 Cross section of a monolithic DSC module. According to the invention more porous semiconductor layers (4) are posed in parallel strips on a common transparent substrate (1) which conductive coatings (2) are interrupted (3) as shown. The photo-electrodes (4) are possibly separated by a porous, light reďŹ&#x201A;ective insulating layer (5). The counter electrode (6) are electrically insulated from each other through gaps (7) containing a non-porous insulator or gas. The pores of the layers (4-6) are ďŹ lled with an electron transferring electrolyte. The module is sealed with a cover layer (8). The module external contacts are connected to the ďŹ rst counter electrode (9) and the last photo-electrode (10) of the series electric system circuit Fig. S2.2 shows a closer view of the monolithic DSC module. In red the particular disposition of the conductive coatings is put in evidence

S2

79


Chapter 2 - 1998-2011 trends in patents analysis

DYE-SENSITIZED SOLAR CELL AND A METHOD OF MANUFACTURING THE SAME

Publication number: Filing date: Inventor(s): Applicant(s): Applicant(s) nationality:

DSC designed by Sony Corporation

S3

US2011155223 17/06/2009 M. Morooka, R. Yoneya, M. Orihashi, C. Zhu, Y. Suzuki, K. Noda et al. Sony Corporation Japan [JP]

The patent provides a description of a dye-sensitized solar cell which is presented as “low cost and superior in appearance and design”. The inventors exhibit explicitely their intention in creating a solar cell which is good looking in aesthetical terms. Firstly in the patents a general description of the invention is given, then two practical examples of produced dye-sensitized solar cells are described in details. According to the present patent a dye sensitized solar cell has: a transparent conductive substrate, one or multiple porous titanium oxide layers supporting a sensitizing dye or a combination of dyes; a counter electrode provided on a second transparent substrate and an electrolyte layer. A sealing material is used to seal the region included between the two substrates. In order to display predetermined colours and patterns, different thickness, lamination structure and particles diameter of the titanium oxide layer are used, moreover the combination of two or more kind of titanium oxide different pastes is mentioned.In the stack, the transparent substrates are shifted to each other by the two directions in plane, in order to form a region outside the sealed area where metal power collecting layers can be placed. The metal power collecting layers are needed for the connection of the cells one to each other and for the connection with the terminals. For each of the layer in the stack, the following specific indications are given: Transparent substrates

80

Suitable transparent inorganic substrates given are made of quartz, sapphire, glass or similar and plastic substrates made i.e. of polyethylene, polycarbonate, polystyrene. Sug-


Chapter 2 - 1998-2011 trends in patents analysis

DSC designed by Sony Corporation

gested coating to make the substrate conductive are i.e. ITO, FTO, ATO (antimony doped SnO2). Titanium oxide layers The patterns are formed by screenprinting of the titanium oxide layer(s). The titanium oxide layer is suggested to be thick in the range within 3 and 30 μm, and the particles diameter within the range of 5 to 100 nm. It is also suggested to mix particles with different diameter in order to increase the cell efficiency. For best photocatalytic activity an anatase type crystalline titanium oxide is preferably used. Sensitizing dye Dyes having a carboxy group or phosphoric acid group are preferable i.e. Rhodamine B, rose bengal, porphyrines. Of them, those that are made of at least one kind of metal complex selected from the group consisting of Ru, Os, Ir, Pt, Co, Fe and Cu are preferable. Two or more of the dyes can be mixed with each other. Counter electrode Platinum, gold, carbon or conductive polimers can be used because they are electrochemically stable. For the purpose of enhancing the catalyst effect the side facing the porous titanium oxide ha preferably fine structure so as to increase the surface area. Electrolyte Combinations of iodine (I) and a metal iodide or organic iodide or combinations of bromine (Bi2) and a metal bromide or organic bromide in different solvents can be used as electrolyte. The possibility to have a gel-type or totally solid electrolyte by addition of a gelatizing agent is mentioned. In the patent a description for a paper-covered night light type made with DSCs is also given.

S3

81


Chapter 2 - 1998-2011 trends in patents analysis

Extracts of the drawings:

DSC designed by Sony Corporation

S3

82

From top to bottom: Fig. S3.1 Cross section of a dye-sensitized solar cell according to the ďŹ rst embodiment presented in the patent. Dye supporting porous titanium oxide layers (2a) to (2d) are formed on a transparent conductive substrate (1). A transparent conductive substrate (3) has a counter electrode (4) formed thereon. The cell is enclosed with sealing material (5) and ďŹ lled with electrolyte (6). The power collecting layers (7) are used when connecting two or more cells one to each other Fig. S3.2 Top plan view of a dye-sensitized solar cell according to the ďŹ rst embodiment presented in the patent


Chapter 2 - 1998-2011 trends in patents analysis

DSC designed by Sony Corporation

S3 From top to bottom and from left to right: Fig. S3.3-4-5-6 Top plan view of screens used in order to form a dye-sensitized titanium oxide layer by screen printing Fig. S3.7 Top plan view of a dyesensitized solar cell manufactured in accordance with the present invention, seen from a light receiving surface side

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Chapter 2 - 1998-2011 trends in patents analysis

DYE-SENSITIZED SOLAR CELL Publication number: Filing date: Inventor(s): Applicant(s): Applicant(s) nationality:

DSC designed by Samsung SDI Co.

S4

84

EP2407985 11/05/2011 H.C. Kim, J.T. Park, J.K. Lee, N.C. Yang Samsung SDI Co., Ltd. Japan [JP]

According to the present patent a dye-sensitized solar cell includes a plurality of unit cells posed in between of two substrates and separated with a sealing material. The unit cell includes first and second conductive transparent electrodes positioned on the internal surfaces of the first and of the second substrate, respectively. The first electrode is composed by an oxide semiconductor layer including an absorbed dye, the second electrode (counter electrode) is composed by a carbon nanotubes layer. Moreover the unit cell includes an electrolyte disposed between the first and the second electrodes, thus the DSC includes a plurality of electrolytes. In regard to the single stacks composing the cells the following specific indications are given: The substrates may be formed in glass or resin films, when flexibility is required and made electrically conductive by coating, for example, with an indium tin oxide (ITO), a fluorine-doped tin oxide (FTO), or antimony-doped tin oxide (ATO). The first conductive transparent electrode may further include a metal electrode formed of i.e. gold (Au), silver (Ag), aluminium (AI). Titanium oxide layers The oxide semi-conductor layer may include i.e. an oxide of cadmium (Cd), zinc (Zn), indium (In), lead (Pb), molybdenum (Mo), tungsten (W), antimony (Sb), titanium (Ti), silver (Ag), manganese (Mn), tin (Sn), zirconium (Zr), strontium (Sr), gallium (Ga), silicon (Si), or chromium (Cr) which

Transparent substrates


Chapter 2 - 1998-2011 trends in patents analysis

DSC designed by Samsung SDI Co.

particles have a size within the range of 5 to 1000 nm. Counter electrode The second electrode has to be made of a material providing electrons and performing a reduction catalyst function. For example, metal such as Pt, Au, Ag, AI, or metal oxide such as tin oxide,or a carbon-based material such as graphite can be used. Alternatively, the counter electrode may be formed of a carbon nanotube sheet. Sensitizing dye The sensitizing dye may include a ruthenium based dye. Electrolyte The type of electrolytes may be solid, gel or liquid type. Moreover in the patent an investigation on light transmittance of diďŹ&#x20AC;erent proposed embodiments, in accordance with the aperture ratio (a ratio of the area of the openings respect to the entire area of the counter electrode) is presented. Best results considering both light transmittance and eďŹ&#x192;ciency of the device are achieved with aperture ratio not exceeding 50%.

S4

85


Chapter 2 - 1998-2011 trends in patents analysis

Extracts of the drawings:

Manufacturing DSC designed by method Samsung SDI Co.

S4

86

From top to bottom: Fig. S4.1 Schematic exploded axonometry view illustrating a dye-sensitized solar cell (100), according to an embodiment of this patent. The cell includes a first substrate (110), a second substrate (120), a sealing material (130) and a plurality of electrolytes (140) Fig. S4.2 Schematic partial cross-sectional view taken along the line II-II of Fig. S4.1 illustrating the dye-sensitized solar cell. The cell includes a first, second, and third unit cells, respectively (100A), (100B), and (100C). The first unit cell (100A) includes i.e. the functional layers (11A) and (12A). The first functional layer (11A) includes a conductive transparent electrode (111A) and a first electrode (112A). The second functional layer (12A) includes a second conductive transparent electrode (121A) and a second electrode (122A). The same definitions correspond for unit cells (100B) and (100C)


Chapter 2 - 1998-2011 trends in patents analysis

DYE SENSITIZED SOLAR CELL MODULE AND METHOD OF FABRICATING THE SAME

Publication number: Filing date: Inventor(s): Applicant(s): Applicant(s) nationality:

EP2337041 06/12/2010 S.H. Joo, S. K. Park, S.H. Ryu, N.J. Myung, S.M. Jeong LG Display Corporation, Ltd. Republic of Korea [KR]

As a first substrate, a glass, quartz or plastic substrate can be employed. The plastic substrate can be formed from PET, PEN, PC, PP, etc and include i.e. an indium-tin-oxide (ITO) or fluorine-tin-oxide (FTO) coating layer. Moreover the first substrate can be doped with titanium,indium, gallium, and aluminium. Semiconductor oxide layer The first electrode can be formed including an electrically conductive metal oxide film (i.e. titanium oxide) in order to improve the contacts with the nano-particles which will be formed later and thus increasing the module efficiency. The nano-particles can be formed from one material selected from a material group which includes a semiconducTransparent substrates

DSSC modules z-connection modules

The dye-sensitized solar cell module here presented (a so called z-type module) includes several unit cells connected in series. Each of the cells comprises a first electrode, a blocking film (titanium dioxide), a light absorption layer, then a second electrode, a sealant and a metal electrical conductivity line stacked within two parallel substrates and separated by a sealing material. The light absorption layer includes a dye, nano-particles, a film and an electrolyte. The present invention also provides a solution capable of selectively print on only a desired region the nanoparticles of a metal oxide film. In regards to the components of the module, the following specific indications are given:

S5

87


Chapter 2 - 1998-2011 trends in patents analysis

DSSC modules z-connection modules

S5

88

tor -making silicone its representative- and a semiconductor compound including a metal oxide among titanium oxide, tin oxide, zinc oxide, niobium oxide, titanium strontium oxide,and their mixtures. More preferably, the titanium oxide is used in anatase form which particles diameter is within the range of about 1 nm to 510 nm. Electrolyte The redox electrolyte can be used or provided in the shape of a solution including an electrochemically inactive solvent (i.e. ethylene glycol or acetylene). It is possible for the electrolyte to use a redox electrolyte, more speciďŹ cally, one material selected from the material group, which includes a halogen redox-based electrolyte, a metal redox-based electrolyte, an organic redox-based electrolyte, or others. The second electrode (counter electrode) can be conďŹ gured to include a catalytic electrode and a transparent electrode. Counter electrode The catalytic electrode is used to activate the redox couple in the electrolyte. This catalytic electrode can be formed from an electrically conductive material such as platinum, gold, ruthenium, palladium, rhodium, iridium, osmium, carbon, titan oxide, an electrically conductive macromolecular material, and others.


Chapter 2 - 1998-2011 trends in patents analysis

Extracts of the drawings:

DSSC modules z-connection modules

From top to bottom: Fig. S5.1 Cross-sectional view showing a dye-sensitized solar cell module according to the present invention. It includes a first substrate (100), a first electrode (200), a blocking film (210), a light absorption layer (300), a second electrode (400), a second substrate (500), a sealant (600), and a metal electrical conductivity line (700). The light absorption layer (300) includes a dye (310), nano-particles (320), a film (350) and an electrolyte (330). The second electrode (400) includes a catalytic electrode (410) and a transparent electrode (420) Fig. S5.22 Cross-sectional view showing a unit cell included in the dye-sensitized solar cell module according to the present invention

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DYE SENSITIZED SOLAR CELL MODULE AND METHOD FOR FABRICATING SAME

Publication number: Filing date: Inventor(s): Applicant(s): Applicant(s) nationality: DSSC modules w-connections module

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EP2043191 03/07/2007 A. Fukui, R. Yamanaka, N. Fuke Sharp Kabushiki Kaisha Japan [JP]

In accordance with the present invention a dye-sensitized solar cell module, a so called â&#x20AC;&#x153;W-type moduleâ&#x20AC;? comprises a pair of opposed conductive substrates, in which at least one of the substrates is transparent and a plurality of conductive stripes parallel one another, disposed alternatively on internal surfaces of two opposite substrates. The photoelectric conversion stripes are composed by a porous semiconductor layer adsorbing a dye, an electrolyte layer and a catalyst layer and they are separated by an insulating layer. Such photoelectric conversion devices are electrically connected in series one with each adjacent.


Chapter 2 - 1998-2011 trends in patents analysis

Extracts of the drawings:

DSSC modules w-connections module

From top to bottom: Fig. S6.1 Cross Sectional view of a dye-sensitized solar cell manufactured in accordance with the present invention. The photoelectric conversion devices (1a) and (1b) are disposed alternatively on two substrates (10) and (17) coated respectively with conductive layers (11) and (18). The devices (1a) and (1b) include a porous semiconductor layer (12), an electrolyte layer (13), a catalyst layer (14). An insulating layer (16)â&#x20AC;&#x2C6;separate the devices (1a) and (1b) each other Fig. S6.2 Top plan view of a dye-sensitized solar cell module manufactured in accordance with the method presented in the invention, seen from a light receiving surface side (on the left) and a non light receiving surface side (on the right)

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PHOTO-ELECTROCHEMICAL SOLAR CELL MODULE Publication number: Filing date: Inventor(s): Applicant(s): Applicant(s) nationality:

DSSC modules Current collecting modules

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WO2005096391 31/03/2005 A. Hinsch, U. Belledin, R. Sastrawan, A. Georg Fraunhofer-Gesellschaft zur Förderung der angewandten Forschung e.V. Germany [DE]

In this patent a photo-electrochemical solar cell module, which is commonly referred in literature as a “mender-type” module, is disclosed. An electroconductive transparent layer, a porous chromatophore (dye) layer and a second electroconductive layer are disposed between two substrates. The solar cells are separated from each other by an insulating web comprising, in at least some areas, a conductor strip, and each solar cell presents at least one filling orifice (for dye and/or electrolyte). The second electroconductive layer presents on the side opposite to the separating layer, a channel and/or spacer shaped profile for forming cavities used for receiving and transmitting the dye and/or the electrolyte. This module design is based on increasing the cell size through the use of current collectors in the TCO glass, which reduce the sheet resistance. The driving force behind this solution was to have fewer holes in the glass substrate for electrolyte filling in relation to the Z-interconnection, where each cell required individual holes.


Chapter 2 - 1998-2011 trends in patents analysis

Extracts of the drawings:

DSSC modules Current collecting modules

From top to bottom: Fig. S7.1 Cross sectional view of the solar cell module which is limited at the top and bottom by a substrate (1). On the first substrate made i.e. of glass, a transparent conductive layer (2) i.e fluorine-doped Tin oxide includes an interrupting incision (9) is made by laser cutting. The solar cell module further comprises a carrier layer (3) separated by a film (4) from a counter electrode (5) made i.e. of graphite. The film (4) separates the individual chambers (8) from each other. The layers (3), (4), (5) and (8) are porous and filled with liquid electrolyte. The Illumination of the solar module comes from the bottom Fig. S7.2 Variant of a meandering arrangement where only the conductors (6), the separators (7) and the incisions (9) in the transparent conductive layer are shown Fig. S7.3 Plan view of the meander-shaped structures of the solar cell module

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DYE-SENSITIZED SOLAR CELL EMPLOYING ZINC OXIDE AGGREGATES GROWN IN THE PRESENCE OF LITHIUM

Publication number: Filing date: Inventor(s): Applicant(s): Applicant(s) nationality: Photoelectrode Photoelectrode and TiO2 pastes ZnO nanoparticle

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US20110162708 04/02/2011 Z. Qifeng, C. Guozhong University of Washington United States [US]

In this patent a ZnO nanoparticles photoelectrode based dye-sensitized solar cell and method of fabricating the same are described. Lithium ions are used to mediate the growth of the ZnO nanoparticles comprised in the photoelectrode. In fact, the use of lithium provides ZnO aggregates that have advantageous microstructure, crystallinity and operational characteristics, resulting from enhanced light scattering properties and better attitude in dyes adsorbing. The procedures developed and disclosed in this patent ensure the formation of an aggregate film that has a high homogeneity of thickness, a high density and a high specific surface area, together with good electrical contact between the film and the fluorine-doped tin oxide electrode.


Chapter 2 - 1998-2011 trends in patents analysis

Extracts of the drawings:

Photoelectrode Photoelectrode and TiO2 pastes ZnO nanoparticle

Fig. S8.1 (a) (b) (c) and (d) SEM images showing differences between “pure ZnO” and “Li-ZnO” films after dye sensitization according to the principles of the present invention

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CARBON NANOTUBES ELECTRODES, SOLAR CELLS RECHARGEABLE BATTERIES, MANUFACTURING METHOD FOR SELF-LUMINOUS BODY

Publication number: Filing date: Inventor(s): Applicant(s): Applicant(s) nationality: Photoelectrode Carbon and TiO2 pastes nanotubes

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KR20110021362 26/08/2009 S.W. Youn S.W. Youn Republic of Korea [KR]

A carbon nanotubes formed electrode and a dye-sensitized solar cell using the same are de-

scribed in this patent. Well-ordered mesoporous TiO2 structures with a narrow pore size dis-

tribution can be used in DSCs to achieve better conversion efficiencies compared to standard

mesoporous films with the same thickness. Ordered arrays of vertically orientated TiO2 nanotubes can be grown out of Ti metal in fluoride-based electrolytes. The length of the nanotubes (<1000 μm), wall thickness (5-34 nm), pore diameter (12-240 nm), and tube-to-tube spacing (0-10 nm) can be controlled by the preparation conditions, i.e. anodization potential, time, temperature and electrolyte composition. Initially, TiO2 nanotubes are usually amor-

phous, and crystallize upon heat treatment. Also carbon nanotubes (CNTs) can be used in order to form the electrodes in a DSC as described in the present patent. CNTs are remarkable

materials, which are being widely studied because of their extraordinary electronic and mechanical properties. They can pictured as rolled-up individual layers of graphite, relatively long, very narrow, hollow cylinders, whose walls are made of hexagonal carbon structures. When

irradiated by light they act as electron acceptors absorbing the electrons released by the dye36.

Extracts of the drawings:

Fig. S9.1 Cross section (not to scale) of dyesensitized cell whose photoelectrode is formed by carbon nanotubes web, according to the present invention 96


Chapter 2 - 1998-2011 trends in patents analysis

DYE-SENSITIZED SOLAR CELL USING CARBON NANOTUBE BASED FILMS AND THE FABRICATION METHOD THEREOF

Publication number: Filing date: Inventor(s): Applicant(s): Applicant(s) nationality:

KR20090107851 10/04/2008 S.C. Yang, H.J. Park et al. Korea Institute of Science and Technology Republic of Korea [KR]

scribed in this patent. The carbon nanotubes provides direct pathways for electron transport, which results faster than in nanoparticles formed electrodes37.

Extracts of the drawings:

Photoelectrode Carbon and TiO2 pastes nanotubes

A carbon nanotubes formed electrode and a dye-sensitized solar cell using the same are de-

S10 From top to bottom: Fig. S10.1 Typical geometry of carbon nanotubes composed by cylinders whose walls are built up of hexagonal honeycombs of carbon atoms Fig. S10.2 SEM image of the carbon nanotubes used in order to form a photoelectrode according to the present invention 97


Chapter 2 - 1998-2011 trends in patents analysis

DYE-SENSITIZED SOLAR CELL USING CONDUCTIVE FIBER ELECTRODE Publication number: Filing date: Inventor(s): Applicant(s): Applicant(s) nationality: Flexible DSSC Flexible electrode

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US2009126784 26/06/2008 Pak H., Lee S. et al. Korea Electronics and Telecommunications Republic of Korea [KR]

The present patent describes a flexible dye-sensitized solar cell, including a flexible photoelectrode. The dye-sensitized solar cell includes: first and second electrodes facing each other, an electrolyte layer interposed between the first and second electrodes, wherein the first electrode comprises a structure formed of conductive fibres and a nano-particle semiconductor oxide layer formed upon it, where dye molecules are adsorbed in the nano-particle semiconductor oxide. The conductive fibres (for example glass fibres) are coated with FTO or ITO. This kind of electrode comprising conductive fibres and an oxide nanoparticles layer substitutes the common paste used in DSSC photoelectrodes and it can be immersed in electrolyte as usual.


Chapter 2 - 1998-2011 trends in patents analysis

Extracts of the drawings:

Flexible DSSC Flexible electrode

From top to bottom: Fig. S11.1 Schematic view of the structure of a semiconductor electrode according to an embodiment of the present invention Fig. S11.2 Schematic view of a stack structure made of ďŹ bres (220) with conductive coating (210) according to this invention

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ELECTRODE OF FLEXIBLE DYE-SENSITIZED SOLAR CELL, MANUFACTURING METHOD THEREOF AND FLEXIBLE DYE-SENSITIZED SOLAR CELL

Publication number: Filing date: Inventor(s): Applicant(s): Applicant(s) nationality: Flexible DSSC Flexible counterelectrode

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US2010051101 31/08/2009 H.J. Kim, S. S. Park, S.Y. Ji, Y. S. Won Samsung SDI Co., Ltd. Republic of Korea [KR]

The present patent describes a flexible dye-sensitized solar cell, including a flexible counter electrode. The method of manufacturing the flexible dye-sensitized solar cell in accordance with the present invention includes: 1. forming a separation layer on a carrier; 2. forming a dye-absorption layer on the separation layer; 3. forming a carbon-nanotube layer on the dye-absorption layer; 4. forming a cathode polymer layer on the carbon-nanotube layer, in which the cathode polymer layer is flexible; 5. separating the carrier by removing the separation layer. High temperature annealing process are usually associated with the dye-sensitized solar cell making of. A flexible counter electrode may be formed on a polymeric cathode layer (eg. PET or PEN) in which a carbon-nanotube layer is posed as cathode. In this case, the photoactive layer can be sintered before the formation of the counter electrode.


Chapter 2 - 1998-2011 trends in patents analysis

Extracts of the drawings:

Flexible DSSC Flexible counterelectrode

From top to bottom: Fig. S12.1 is a cross sectional view illustrating a flexible dye-sensitized solar cell in accordance the present invention, including: a dyeabsorption layer (30), a carbon nanotube layer (40), a cathode polymer layer (50), an electrolyte layer (60), a conductive substance layer (70) and an anode polymer layer (80) Fig. S12.2 is part of flow diagrams illustrating the method of manufacturing a flexible dye-sensitized solar cell in accordance with the present invention and it represents an intermediate status of the cell before completion. A carrier layer (10) is used in order to build the photosensitive layer (30) then is removed from the cell and replaced by an anode polymer layer coated with a conductive substance layer

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SOLID STATE HETEROJUNCTION AND SOLID STATE SENSITIZED PHOTOVOLTAIC CELL

Publication number: Filing date: Inventor(s): Applicant(s): Applicant(s) nationality:

Solid-state DSSC Solid-state heterojunction

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US20050006714 06/07/2004 M. Gratzel, R. Plass, U. Bach M. Gratzel, R. Plass, U. Bach Switzerland [CH]

In this patent a solid-state sensitized photovoltaic cell is presented. The cell includes a solid state p-n heterojunction comprising an electron conductor and a hole conductor. A sensitizing semiconductor in form of quantum dots38 (Q-dots) is located at the interface between the electron conductor and the hole conductor. The use of quantum dots permits to achieve high contact areas in the junction, which is prerequisite for efficient solar light harvesting. Light is absorbed by the Q-dots and produces electron-hole pairs. The electrons are injected from the Q-dots into the electron conducting solid (p) while the holes are injected in the hole conducting side (n) of the junction. In this way electric power is produced from light. Based on the invention by Gratzel et al. the present invention proposes to solve the issues related to the SDSCs (Solid Dye Sensitized Cells) dealing with the choice of an appropriate dye, stable against photodegradation and providing a working p-n heterojunction that includes both of the semiconductors (p and n type). The inventors found out the deposition of a sufficient amount of absorber material and further annealing treatment for forming continuous films at the surface of an n-type semiconductor in order to increase the light absorption also causes an obstruction in the permeation of the mesoporous structure by the p-type semiconductor, thus causing a loss in charge transport. In the present invention the molecular sensitizing dye is thus replaced by small individual semiconductor particles, named quantum dots. The term "individual particles" refers to particles of various sizes, in the nanometer range within 1 and 10 nm. The term does not refer to single discrete molecules on one hand but excludes larger clusters and continuous film portions on the


Chapter 2 - 1998-2011 trends in patents analysis

Extracts of the drawings:

Fig. S13.1 Schematic view of a solid-state sensitized photovoltaic cell. From bottom to top there are an ITO transparent glass support (1); the glass support (1) is coated by a transparent conducting layer (2) made of F doped SnO2, thereby the coated glass acts as a working electrode, which collects charge and current. A dense TiO2 layer (3) for avoiding direct contact between the organic hole conductor and the SnO2, which would short circuit the cell; a quantum dot sensitized nanocrystalline layer (4), forming a heterojunction; the back contact (5) of the cell is made of a fine gold layer of 10 nm covered by a thick nickel layer for a better current collection. Then it is showed a magnified schematic view of the microscopic structure of the p-n heterojunction: at the surface of TiO2 particles (6), are adsorbed Q-dots (7); the spaces are filled with particles (8) of an organic hole conductor

Solid-state DSSC Solid-state heterojunction

other hand. According to the invention, the average size of the sensitizing particles shall be smaller than the average size of the pores of the mesoporous structure formed by the n-type semiconductor material in order to avoid the penetration of the p-type semiconductor into the pores. The quantum dots are adsorbed at the surface of the n-type semiconductor where each dot forms a kind of point-contact junction between the n-type semiconductor and the p-type semiconductor material. As quantum dots, particles consisting of CdS, Bi2S3, Sb2S3, or Ag2S may be used, whereas PbS is preferred. For the formation of n-type semiconductor the use of nanocrystalline TiO2 (anatase) is preferred. The hole conductor may be selected from hole transporting inorganic solids like copper iodide or copper thiocyanate. Typically, the hole conductor may be an organic charge transport material, generally selected from the group consisting of spiro-and hetero spiro compounds. A preferred quantum dots sensitized nanocrystalline hetero junction is constituted of sintered particles of nanocrystalline TiO2 into which PbS particles in the nanometer range are adsorbed as sensitizers, and the pores between the particles are being filled with amorphous OMeTAD.

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NOTES 1. The EPO provides a free online service called Espacenet which includes an online archive of all the patents published in Europe and worldwide. 2. As confirmed by further researches made periodically within the online archive, which did not show any new patent published reporting a filing date preceding 30th June 2011. 3. Moser, J. (1887). Monatsch. Chem.(8), 373. 4. Rigollot, H. C. R. (1893). Acad. Sci.(116), 561. 5. Gerischer, H., & Tributsch, H. (1968). Ber. Bunsen-Ges. in Phys. Chem.(72), 437–445. 6. Gerischer, H., & Tributsch, H. (1969). Ber. Bunsen-Ges. in Phys. Chem.(73), 251–260. 7. Whose invention was identified in patent JP51151272 “A wet type photocell”, 1976. 8. O' Regan, B., & Gratzel, M. (1991). A low-cost, high-efficiency solar cell based on dye-sensitized colloidal TiO2 films. Nature(353), 737-740. 9. See Morini M., “Involucri edilizi sostenibili: Integrazione di celle solari...” op.cit. for a complete list of the companies active in the DSC production sector. 10. Pettersson, H., Nonomura, K., Kloo, L., & Hagfeldt, A. (2012). Trends in patent applications for dye-sensitized solar cells. Energy Environ. Sci.(5), 7376–7380. 11. Further notes will indicate the data reference sources. 12. O' Regan, B., & Gratzel, M. in Nature op. cit. 13. Gratzel, M., & Kay, A. (1996). Low cost photovoltaic modules based on dye sensitized nanocristalline titanium dioxide and carbon powder. Solar Energy Materials and Solar Cells(44), 99-117. 14. For the description of the five modules categories cfr. Hagfeldt, A., Boschloo, G., Sun, L., Kloo, L., & Pettersson, H. (2010). Dye-Sensitized Solar Cells. Chem. Rev.(110), 6595–6663. 15. As reported in Chen, Z., Tian, Q., Tang, M., & Hu, J. (2011). The Application of Inorganic Nanomaterials in DyeSensitized Solar Cells. In L. A. Kosyachenko (Ed.), Solar Cells - Dye-Sensitized Devices: Intech. 16. Luque, A., & Hegedus, S. (2003). Handbook of Photovoltaic Science and Engineering. Chichester, U.K.: Wiley. 17. Ibidem. 18. Chen, Z., et al., in Solar Cells - Dye-Sensitized Devices, op. cit. 19. Hagfeldt, A., et al., Dye-Sensitized Solar Cells, op.cit. 20. Luque, A., et al., Handbook of photovoltaic science and engineering, op. cit. 21. Zhou, H., et al., Dye-sensitized solar cells using 20 natural dyes as sensitizers, op. cit. 22. Luque, A., et al., Handbook of photovoltaic science and engineering, op. cit. 23. Ibidem. 24. Ibidem. 25. Ibidem. 104


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26. Ibidem. 27. Surlyn (Du Pont), a copolymer of ethylene and acrilic acid, meets these requirements. 28. Tiwari, A. (2010). Recent trends in Dye-Sensitized Solar Cell Technology. from www.azonano.com. 29. As reported in the Background section of the patent US2010051101 (Electrode of flexible dye-sensitized solar cell, manufacturing method and flexible dye-sensitized solar cell, 2009) 30. Ibidem. 31. Moulé, A. J., Snaith, H. J., Kaiser, M., Klesper, H., Huang, D. M., Grätzel, M., & Meerholz, K. (2009). Optical description of solid-state dye-sensitized solar cells. I. Measurement of layer optical properties. Journal Of Applied Physics(106). 32. Luque, A., et al., Handbook of photovoltaic science and engineering, op. cit. 33. Chen, Z., et al., in Solar Cells - Dye-Sensitized Devices, op. cit. 34. Ibidem. 35. The SOL-GEL process, described in the same patent, is a method for the production of titanium dioxide from pure titanium (99,5% purity), which includes a firing at 450°C. It is a process that has to be repeated from 10 to 15 times in order to obtain a thickness of 20 μm ca., then the substrate has to be heated again at about 550°C. 36. The present patent is available only in native language (Korean). The description reported is a comment taken out from Hagfeldt, A., et al., Dye-Sensitized Solar Cells, op.cit. 37. Ibidem. 38. Quantum dots were discovered at the beginning of the 1980s. They are extremely tiny (few millionths of a millimetre) specks of matter used in microelectronics in order to form superconductors. These superconductors electronic characteristics are closely related to the size and shape of the individual crystal where excitons are confined in all three spatial dimensions.

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CHAPTER 3

Hypotheses of DSC integration into the glassblock


Chapter 3 - Hypotheses of DSC integration into the glassblock

In the present chapter a brief description of the hypotheses of DSC integration into the glassblock previously studied1 is reported. The hypotheses show four possibilities of integration, in which the size and position of the DSC module is different. For the hypotheses numbered 1, 2, 3, a correspondent hypothesis 1a, 2a and 3a is presented, which consider for each case the possibility to use pre-assembled DSC modules in order to separate the production process of the cells from the production process of the glassblock. This means in therms of industrial production, a possibility for glassblocks producers to expand their market in photovoltaic devices without any significant change in their production structures, just by buying the DSC modules for the assemblage from external suppliers and by modifying the shape of the glass shells.

Fig. 3.1 A possible outlook of a DSC integrated glassblock 109


Chapter 3 - Hypotheses of DSC integration into the glassblock

Hypothesis 1 It consists in the modification of one of the two shells of the glassblock, redesigned to contain the deposition of the cells in a plain surface encircled with a glass protecting frame and a covered with a glass sheet.

Fig. Hyp. 1 - Axonometric scheme

Description Hypothesis 1 (Fig. Hyp1.1) includes the modification of the shape of one of the shells composing the glassblock (0) in particular the one that will be exposed to the sunlight. The external face (2) of the modified shell presents a protective perimetrical glass frame that is 10 mm wide and approximately 2,2 mm thick (1). This frame, already present in the standard shells but thinner, it is designed thicker to insert a glass sheet 2,2 mm thick (4) that is the transparent counter electrode of the cell. The glass sheet (4) protects the cells (3) interposed between, and it is previously coated with a TCO layer and a platinum (catalyst) layer. The external face (2) of the shell is previously coated with TCO too. The electrolyte can be injected through two openings (5) diameter = 1 mm on the glass sheet (4) that will be immediately sealed after the injection. In order to achieve the maximum efficiency the PV module is composed with 16 rectangular cells 10 mm wide and 170 mm high, separated by sealing stripes 1 mm wide. 110


Chapter 3 - Hypotheses of DSC integration into the glassblock

Hypothesis 1a It consists in the modification of one of the two shells of the glassblock, redesigned to contain the deposition glass on glass of a complete DSC module in a plain surface encircled with a protecting glass frame.

Fig. Hyp 1a - Axonometric scheme

Description Hypothesis 1a (Fig. Hyp1.7) includes the modification of the shape of one of the shells composing the glassblock (0) in particular the one that will be exposed to the sunlight. The external face (2) of the modified shell presents a protective perimetrical glass frame that is 10 mm wide but in this case approximately 4,4 mm thick (1) to insert a complete pre-assembled DSC module (3) composed in a sandwich structure between two conductive glass sheets each 2,2 mm thick. This solution involves larger quantity of glass used and larger loads for the device, but in the same time simplifies its production (the module can be assembled apart without complications on the production of the glassblock). In order to achieve the maximum efficiency the PV module is composed with 16 rectangular cells 10 mm wide and 170 mm high, separated by sealing stripes 1 mm wide. 111


Chapter 3 - Hypotheses of DSC integration into the glassblock

Hypothesis 2 It consists in the modification of one of the two shells of the glassblock, redesigned externally completely plane for the deposition of the cells. The electrode is the plane surface itself while the counter electrode is applied together with an additional plastic protective frame.

Fig. Hyp. 2 - Axonometric scheme

Description Hypothesis 2 (Fig. Hyp2.1) includes the modification of the shape of one of the shells composing the glassblock (0) in particular the one that will be exposed to the sunlight, which external face (1) is redesigned completely plane for the deposition of the cells. A glass sheet 2,2 mm thick (3) previously coated with a TCO layer and a platinum (catalyst) layer is applied on top of it. The external face (1) of the shell is previously coated with TCO too. The electrolyte can be injected through the sides where the electrodes come in contact, so no openings are needed. May be necessary the addition of a frame (in plastic material) with the function of protection from the effects of the weather (it avoids water infiltrations) and mechanical protection of the boundary. In order to achieve the maximum efficiency the PV module is composed with 17 rectangular cells 10 mm wide and 182 mm high, separated by sealing stripes 1 mm wide. 112


Chapter 3 - Hypotheses of DSC integration into the glassblock

Hypothesis 2a It consists in the modification of one of the two shells of the glassblock, redesigned externally completely plane for the deposition glass on glass of a complete DSC module applied together with an additional plastic protective frame.

Fig. Hyp. 2a - Axonometric scheme

Description Hypothesis 2a (Fig. Hyp2.2) consists in the application of a complete DSC module (2) on the external surface (1) of the glassblock in which the external of the two shells (0) is designed completely plane the same as in hypothesis 2. May be necessary the addition of a frame (in plastic material) with the function of protection from the effects of the weather (it avoids water infiltrations) and mechanical protection of the boundary. In order to achieve the maximum efficiency the PV module is composed with 17 rectangular cells 10 mm wide and 182 mm high, separated by sealing stripes 1 mm wide.

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Chapter 3 - Hypotheses of DSC integration into the glassblock

Hypothesis 3 It consists in the application of DSCs in the internal face of a glassblock, without modifying the shape of the shells. The shells must be glued (cold assembly) in order to avoid the damaging of the cells which are not resistant to high temperatures.

Fig. Hyp. 3 - Axonometric scheme

Description In the hypothesis 3 (Fig. Hyp3.1) no modifications in the shells (0) occur. In particular, the internal surface of the external shell (1) previously coated with a TCO layer, is used as substrate for the deposition of the cells (2). A glass sheet 2,2 mm thick (3) previously coated with a TCO layer and a platinum (catalyst) layer is the transparent counter electrode of the cell. The electrolyte can be injected before the assembly of the other shell through two openings (4) diameter = 1 mm on the glass sheet (3) that will be immediately sealed after the injection. In order to achieve the maximum efficiency the PV module is composed with 13 rectangular cells 10 mm wide and 145 mm high, separated by sealing stripes 1 mm wide.

114


Chapter 3 - Hypotheses of DSC integration into the glassblock

Hypothesis 3a It consists in the application of a complete DSC module, glass on glass, in the internal face of a glassblock, without modifying the shape of the shells. The shells must be glued (cold assembly) in order to avoid the damaging of the cells which are not resistant to high temperatures.

Fig. Hyp. 3a - Axonometric scheme

Description In the hypothesis 3a (Fig. Hyp3.2) no modiďŹ cations in the shells (0) occur. In particular, a complete DSC module (2) is applied glass on glass on the internal surface of the external shell (1). This solution involves larger quantity of glass used and larger loads for the device in comparison with hypothesis 3, but in the same time simpliďŹ es the production of the same. The module in fact can be assembled apart without interfering on the glassblock production methods, except that in this case the shells must be glued (cold assembly) in order to avoid the damaging of the cells which are not resistant to high temperatures. In order to achieve the maximum eďŹ&#x192;ciency the PV module is composed with 13 rectangular cells 10 mm wide and 145 mm high, separated by sealing stripes 1 mm wide.

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Chapter 3 - Hypotheses of DSC integration into the glassblock

Hypothesis 4 It consists in the insertion of a complete DSC module inside a “thermal belt” in plastic material to which the two shells are glued (cold assembly). The module divides the internal volume of the glassblock into two chambers, contributing in diminishing the thermal transmittance.

Fig. Hyp. 4 - Axonometric scheme

Description The hypothesis 4 (Fig. Hyp4.1) involves a configuration previously studied through other 2,3,4 to obtain better thermal performances of glassblocks. This configuration includes the works insertion of a plastic belt containing a complete DSC module (composed by 14 rectangular cells 10 mm wide and 154 mm high, separated by sealing stripes 1 mm wide; comprehensive thickness 4,4 mm) and to which the two shells are glued. The plastic belt is formed by a “U” shaped part (2a) and a cover top (2b) for the insertion of the DSC module. The plastic belt and the insertion of the DSC module as separator both contribute to the reduction of the thermal transmittance of the glassblock, moreover the energy production feature is given. The thermal belt presents two openings diameter = 1 mm for the cable connections. 116


Chapter 3 - Hypotheses of DSC integration into the glassblock

NOTES 1. Morini M., “Involucri edilizi sostenibili: Integrazione di celle solari...” op.cit. 2. Trapani G., “Indagine teorico-sperimentale per la caratterizzazione meccanica...” op. cit. 3. Garraffa A., “Indagine teorico-sperimentale per la caratterizzazione meccanica...” op. cit. 4. Foderà C., “Analisi delle problematiche connesse all’isolamento termico...” op. cit.

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CHAPTER 4

Op3cal performance analysis


Chapter 4 - Optical performance analysis

Introduction In this chapter the results of the op3cal analysis conducted on the hypotheses 1a, 2a, 3a and 4 are presented1. The study of the op3cal performance of the different hypotheses of the device becomes significant for at least two aspects: the first one refers to the quan3ty of luminous energy that reaches the ac3ve surface of the cells; the second one relates to the quan3ty of visible light that passes through the device, in other words, its transparency. In regard to transparency, this is in fact a phenomenon related to the sensi3vity of the human eye only to certain wavelength of light spectrum, comprised in the range within 390 and 750 nm2. The parameters used in order to describe the op3cal behaviour of the device in accordance to UNI EN 4103 are: - the solar factor; - the light transmi4ance; - the shading coefficient. In order to calculate these op3cal parameters and the cell energy absorp3on too, an analysis was conducted through numerical simula3ons, using Op3CAD® so$ware4. The first point in the analysis was to understand how to create an op3cal model of the device, with a main ques3on in how to model the DSSC.

121


Chapter 4 -Optical performance analysis

4.1 Basic Theory The sun emits energy within a range of wavelengths extended over what is the visible light interval, from ultraviolet to infrared. Its spectral behaviour is theore3cally defined equal to a blackbody at a temperature of 5760 K with a peak in the visible range, around the wavelength of 550 nm. When encountering the terrestrial atmosphere, the sunlight is filtered by the ozone and water and CO2, which cause in its spectrum a number of dips mainly located in the infrared region. The pathlength before a ray hits the earth surface is called Air Mass (AM) approximately defined as: AM = 1/ cos { where φ is the angle of eleva3on of the sun. The standard solar spectrum used for efficiency measurements of solar cells is defined at AM φ 1.5 G (global) giving φ=42°. This spectrum is usually given as normalized, so that the integral of the irradiance (the amount of radiant energy received from the sun per unit area and unit 3me) is 1000 W m-2. The efficiency of a photovoltaic device is deeply related to its capacity in absorbing the most from the solar radia3on spectrum. Due to the selec3ve absorp3on proper3es of the materials composing the cells, different technologies exploit different parts of the solar spectrum, as shown in Chart 4.1.

122


Chapter 4 - Optical performance analysis

100 80

absorptance

60 40 20

300

500

700

900

1100

1300 1500 wavelength [nm]

Crystalline silicon (Si)

Amorphous (triple) micromorphous SI

DSC*

Back-contact cell

Cadmium telluride (CdTe)

Solar spectrum AM 1.5

Amorphous Si (one layer)

Copper-indium diselenide (CIS)

*DSC producted by Sony Ltd. which exploits the “concerto effect” obtained by mixing dyes with different absorption spectra Chart 4.1 Absorption spectra of different solar cell types. Elaborated data from Source: Photovoltaics, Edition Detail, 2010

The main absorp3on spectrum of silicon solar cells (crystalline and amorphous) is located below the infrared, mostly in the violet and ultraviolet. This means that even best efficiency tradi3onal cells do not exploit the full spectrum of the sun light, thus a relevant part of the energy remains unused. This fact is pushing the research on considering the developing direc3on of solar cells in the study of the possibili3es to expand their absorp3on spectra. Dye-sensi3zed solar cells absorp3on can be calibrated precisely to cover almost the total sun light spectrum, so that theore3cal maximum DSC efficiency is already considered higher than tradi3onal PV cells. This is done by a careful selec3on of the compounds composing the dye and their propor3on in the mix. The solar irradia3on exists in three forms: direct, diffuse and reflected. Solar cells can func3on with all three forms of light although direct irradia3on is the form richest in energy. Diffuse light arises with scat123


Chapter 4 -Optical performance analysis

tering of light in the atmosphere for a frac3on of about 15% (see Chart 4.2) growing larger for regions at higher la3tude and in rela3on of the amount of clouds present in the sky.

Chart 4.2 Reference direct normal (black) and global (red, direct normal plus diffuse) terrestrial solar power spectra. The direct normal spectrum is attenuated, primarily in the visible part of the spectrum, by atmospheric scattering Source: “Utilization of Direct and Diffuse Sunlight in a Dye-Sensitized Solar Cell...”, J. Phys. Chem. Lett., 2, 2011

DSCs showed extremely lower dependance to the direc3on of incident light if compared to tradi3onal photovoltaic systems, resul3ng be4er suited for diffuse light condi3ons. When a radiant flux is incident upon a surface or medium, three processes occur: transmission, absorp3on, and reflec3on5. Fig 4.1 shows the ideal case, where the transmi4ed and reflected components are specular or perfectly diffused. Retroreflection Incident beam

Diff use transmission

Diff use reflection

Specular reflection

124

Specular ( regular) transmission

Fig 4.1 Idealized reflection and transmission. Source: Handbook of optics, Third Edition, Mc-Graw Hill, 2009


Chapter 4 - Optical performance analysis

4.1.1 Transmittance Transmission is the term used to describe the process by which incident radiant flux leaves a surface or medium from a side other than the incident side, usually the opposite side. The spectral transmi4ance x(m) of a medium is the ra3o of the transmi4ed spectral flux Umt to the incident spectral flux Umi , or U x (m) = mt U mi The transmi4ance x is the ra3o of the transmi4ed flux Ut , to the incident flux Ui , or x=

#

0

3

x (m) U mi dm

#

0

3

U mi dm

!

# x (m) dm

Note that the integrated transmi4ance is not the integral over wavelength of the spectral transmi4ance, but must be weighted by a source func3on Um as shown. Geometrically, transmi4ance can be classified as specular, diffuse, or total, depending upon whether the specular (regular) direc3on, all direc3ons other than the specular, or all direc3ons are considered. Fig 4.2 shows actual transmission and reflec3on.

Reflection, strong diffuse component

Reflection, strong specular component

Reflection, strong retroreflective component

Regular transmission

Diff use transmission

Fig 4.2 Actual reflection and transmission. Source: Handbook of optics, Third Edition, Mc-Graw Hill, 2009

125


Chapter 4 -Optical performance analysis

4.1.2 Absorptance Light appears due to energy emission. According to the quantum theory, the energy par3cles jump from lower energy levels to higher when absorbing energy. On the other side, the energy par3cles jump from higher energy levels to lower with energy emission by the par3cles. Fig.4.3 details the absorp3on and the emission processes of the energy par3cles.

Fig 4.3 Schematic absorption description

Absorp3on is the process by which the incident radiant flux is converted to another form of energy, usually heat. Absorptance is the frac3on of the incident flux that is absorbed. The absorptance of an element is defined by a = Ua / Ui . Similarly, the spectral absorptance a(m) is the ra3o of spectral power absorbed Uma to the incident spectral power Umi , a=

#

0

3

a (m) U mi dm

#

0

3

U mi dm

!

# a (m) dm

When a beam of light (photons) is incident on a material, the extent of the op3cal intensity of the light wave is reduced exponen3ally as expressed by the Lambert-Beer-Bouguer law: I = I 0 $ e - a'd 126


Chapter 4 - Optical performance analysis

where: I [J] is the transmi4ed intensity of light that leaves the medium; [J] is the incident intensity of light; I0 d [L] is the op3cal thickness; α’ [L]-1 is the absorp3on coefficient (cm−1 or km−1) Vice versa it is possible to express the Beer-Lambert absorp3on law in respect of the absorp3on coefficient as follows: 1 I a' =- d ln ( I 0 ) 4.1.3 Reflectance

Reflec3on is the process where a frac3on of the radiant flux incident on a surface is returned into the same hemisphere whose the surface base is and which contains the incident radia3on. The reflec3on can be specular (in the mirror direc3on), diffuse (sca4ered into the en3re hemisphere), or a combina3on of both. The most general defini3on for reflectance t is the ra3o of the radiant flux reflected Ur to the incident radiant flux Ui , or t=

Ur Ui

Spectral reflectance is similarly defined at a specified wavelength m as: t (m) =

U mr U mi

Moreover spectral reflectance factor (R) is defined as the ra3o of the spectral flux reflected from a sample to the spectral flux which would be reflected by a perfect diffuse lamber3an reflector. Reflec3on in nature occurs in a wide range of possible geometries (see Fig. 4.4). The fundamental geometric descriptor of reflectance is the bidirec3onal reflectance distribu3on func3on (BRDF) 127


Chapter 4 -Optical performance analysis

used to quan3fy reflected light from a surface considering the incident ray angle and the reflected ray angle both in respect to the normal direc3on at the surface in the point of incidence. In accordance with the energy conserva3on principle, the spectral and total transmi4ance, absorptance and reflectance are related by the following equa3on:

/x+/a+/t = 1

q1

q1

qr

q1

wr

2x f1 Dir ectional incident

f1

fr Dir ectional collected

Dir ectional incident

Bidir ectional reflectance

Dir ectional-hemispherical reflectance

w1

fr Dir ectional collected

Conical incident

Conical-directional reflectance

Conical collected

w1

2x

Conical incident

Hemispherical collected

Biconical reflectance

2x

Conical-hemispherical reflectance

wr

qr 2x fr Dir ectional collected

Hemispherical-directional reflectance

Hemispherical collected

wr

qr

Hemispherical incident

Dir ectional incident

Dir ectional-conical reflectance

w1

Conical incident

f1 Conical collected

Hemispherical incident

Conical collected

Hemispherical-conical reflectance

2x

2x

Hemispherical incident

Hemispherical collected

Bihemispherical reflectance

Fig 4.4 Nine geometrical definitions of reflectance. Source: Handbook of optics, Third Edition, Mc-Graw Hill, 2009 128


Chapter 4 - Optical performance analysis

4.1.4 Fresnel reflection Fresnel equa3ons are used in order to describe reflec3on of light when moving between media of different refrac3ve indices. They are used to predict the reflec3on and transmission coefficients for waves parallel and perpendicular to the plane of incidence calculated using the indices of refrac3on on both sides of the surface (see Fig 4.5). Incident lig

ht

Plane of inci

dence ZĞŇĞĐƚĞĚůŝ ŐŚƚ

Interface

dƌĂŶƐŵŝƩĞĚ ůŝ

ŐŚƚ

Fig 4.5 Fresnel reflection scheme. By knowing the refractive indices on both sides of the interface it is possible to calculate the transmission and reflection coefficients for waves parallel (in black) and perpendicular (in blue) to the plane of incidence

The Fresnel reflec3on for non-polarized light is related to the refrac3ve indeces by the following equa3on: R=

(n 1 - n 2) 2 (n 1 + n 2) 2

where R is the reflectance factor and n1 and n2 are the refrac3ve indices of the two media at a certain wavelength λ. In general, the greater is the angle of incidence with respect to the normal, the greater is the Fresnel reflec3on coefficient. 129


Chapter 4 -Optical performance analysis

4.1.5 Solar factor (Total solar energy transmittance) The solar factor (or total solar energy transmi4ance) is defined as the ra3o between the total solar energy that reach the internal surface of a medium and the energy that hit the external one. It includes the energy carried by the transmission of direct light and the energy -defined secondary- which reach the inside surface through thermal transmission in the medium as heat.

Ɍe

ʌe·Ɍe



ɲe·Ɍe qe·Ɍe

ʏe·Ɍe qi·Ɍe

&ν &ξ

Fig. 4.6 Scheme for the determination of the solar factor

Fig. 4.6 shows the scheme of the solar flux repar33on when the solar radia3on hits a medium: the flux is first reflected, then a part of energy is absorbed and reparted inside and outside as heat, the remaining part is transmi4ed. In Fig 4.6: - te∙ Ue is the reflected part (te, reflec3on coefficient); - ae∙ Ue is the absorbed part (ae, absorp3on coefficient); - xe∙ Ue is the transmi4ed part (xe, transmission coefficient); - qe∙ Ue is the part of energy that goes backwards to the external environment as heat transfer through the medium, (qe, secondary external heat transfer factor); - qi∙ Ue is the part that gets to the internal environment as heat transfer through the medium, (qi, secondary internal heat transfer factor). 130


Chapter 4 - Optical performance analysis

According to the standard UNI EN 410, the solar factor (g) can be calculated as follows: g = xe + qi wherein: xe is the solar transmi4ance; qi is the secondary internal heat transfer factor In par3cular: xe is the solar direct transmittance, determined as follows: xe =

m = 2500 nm

/

S x (m) $ Dm

m m = 300 nm m = 2500 nm

/

S m $ Dm

where: Sm is the rela3ve spectral distribu3on of solar radia3on; Dm is the wavelength interval; x(m) is the spectral transmi4ance; m = 300 nm

qi is the secondary internal heat transfer factor. For the calcula3on of the secondary internal heat transfer factor qi, it is necessary to calculate the internal and external heat transfer coeďŹ&#x192;cients, respec3vely hi and he. For ver3cal glazed surfaces, when external wind speed is equal to 4m/s ca. and internal heat transmission occurring through only natural convec3on phenomena and internal chambers non ven3lated: hi= 8 W/m2K he= 23 W/m2K

(internal heat transfer coeďŹ&#x192;cient); (external heat transfer coeďŹ&#x192;cient).

These values are valid for standard soda-lime glass. 131


Chapter 4 -Optical performance analysis

Different calcula3on methods are used in order to calculate the secondary internal heat transfer factor qi, with reference to single, double and triple glasses. For single glasses:

h q i = a e $ h +i h e i

where: he, hi are respec3vely the internal and external heat transfer coefficients; ae is the solar direct absorptance of the glass sheet. For double glasses:

` a e1 h+ a e2 + a e2 j K qi = 1 e 1 1 ah + h + k i e K

where: he, hi are respec3vely the internal and external heat transfer coefficients; ae1 is the solar direct absorptance of the first glass sheet; ae2 is the solar direct absorptance of the second glass sheet; K is the thermal conductance within the external surface of the first glass sheet and internal surface of the second glass sheet. For triple glasses:

qi =

a a e3 + a e3 + a e2 + a e3 + ahe2 + a e1 k e K 23

K 12 1 a h + h1 + 1 + 1 k i e K 12 K 23

where: he, hi are respec3vely the internal and external heat transfer coefficients; ae1 is the solar direct absorptance of the first glass sheet; ae2 is the solar direct absorptance of the second glass sheet; 132


Chapter 4 - Optical performance analysis

ae3 is the solar direct absorptance of the third glass sheet; KWX is the thermal conductance within the external surface of the first glass sheet and the middle of the second glass sheet; KXY is the thermal conductance within the middle of the second glass sheet and the internal surface of the third glass sheet. The determina3on of the solar factor is used later in this chapter, in par3cular, for the evalua3on of the total solar energy which can be absorbed by a DSC module in different presented configura3ons of DSC-integrated glassblocks. According to the standard UNI EN 410, for its calcula3on, has to be considered the range between 300 nm and 2500 nm in wavelength.

133


Chapter 4 -Optical performance analysis

4.1.6 Light transmittance The light transmi4ance is defined as the ra3o between the transmi4ed light flux and the incident light flux. Fig 4.7 shows the scheme of the light flux repar33on when the sun light hits a transparent medium: the flux is first reflected, then a part of light is absorbed, the remaining part is transmi4ed.

incident light

ƌĞŇĞĐƚĞĚůŝŐŚƚ

ƚƌĂŶƐŵŝƩĞĚ absorbed light light &μ &ν &ξ

Fig. 4.7 Scheme for the determination of the light transmittance

According to the standard UNI EN 410, the light transmi4ance xV can be calculated as follows: xV =

m = 780nm

/

D $ x (m) $ V (m) $ Dm

m m = 380nm m = 780nm

/

m = 380nm

D m $ V (m) $ Dm

wherein: Dm is the rela3ve spectral distribu3on of illuminant D656; x(m) is the spectral transmi4ance; V(m) is the spectral luminous efficiency; Dm is the wavelength interval. 134


Chapter 4 - Optical performance analysis

The light transmi4ance calcula3on includes V(m) as weigh3ng func3on, which is needed to quan3fy the human eye different response at different wavelengths. The human eye, in fact, not only perceives light in the light visible range, but it does so differently within the range. The sensi3vity factor of the human eye is shown in Chart 4.3.

Chart 4.3 V(λ) Sensitivity factor of the human eye

The determina3on of the light transmi4ance is used later in this chapter, in par3cular, for an evalua3on of the total light transmi4ance of different configura3ons of presented DSC-integrated glassblocks. According to the standard UNI EN 410, for its calcula3on, has to be considered the range between 380 nm and 780 nm in wavelength. 4.1.7 Shading coefficient According to the standard UNI EN 410 the shading coefficient is calculated through the following formula: g SC = 0, 87

where: g is the solar factor; 0,87 is the typical transmi4ed energy of a transparent sheet of float glass with nominal thickness within 3 and 4 mm. 135


Chapter 4 -Optical performance analysis

4.2 DSSC optical modelling: a study on the state of art and the optical properties of the single layers composing the cell The design and development of dye-sensi3zed solar cells is currently o$en realized on empirical basis. An omni-comprehensive model which could es3mate the behaviour of the cell before its actual realiza3on both in terms of energy produc3on and op3cal features, s3ll does not exist. In view of assis3ng in the op3miza3on process, such a model is actually indispensable and this is the reason why the scien3fic community is now pu5ng efforts into its crea3on7. In the present work, par3cular a4en3on is given to the defini3on of an op3cal model. The complexity in the op3cal modelling of a DSSC is primarily due to: a) the nanometric thicknesses of the oxide coa3ngs of the substrates and catalyst; b) the micrometric thicknesses of the three absorbing layers composing the mesoporous medium (TiO2 , dye, electrolyte); c) the unclear boundaries between the three absorbing layers which in the DSSC assemblage are mixed and penetrate each other; d) light sca4ering in TiO2. Fig. 4.8 SEM and TEM images of TiO2 layers having different dimension nanoparticles, in particular (a) hollow anatase-TiO2 spheres, (b) and (c) surface and cross-section SEM images of hollow anatase -TiO2 films coated on FTO annealed at 600°C for 2 h, (d) cross-section SEM images of P25 (TiO2 Degussa commercial product) films coated on FTO glass and annealed at 600°C for 2 h Source: “Dye-sensitized solar cells based on hollow anatase TiO2 spheres...”, Electrochimica Acta, 55, 2010

136


Chapter 4 - Optical performance analysis

In par3cular, the thin layers, which thickness is in the range of the sunlight coherence length (≈ 600 nm) must be treated using coherent op3cs (transfer matrix approach8). Moreover, because of the mixed state of TiO2 , dye and electrolyte in the mesoporous medium, this has to be treated with the Bruggerman effec3ve medium approxima3on9. The TiO2 , usually considered in its anatase form, has a high refrac3ve index (≈3,1 at 400 nm) and weak, but s3ll significant light mul3 sca4ering proper3es, which are difficult to simulate accurately. Anyway the op3cs of the photoac3ve layer in the device are o$en calculated using a simplified Lambert-Beer type exponen3al absorp3on10. This approach does not account for mul3ple reflec3on occurring at the thin films interfaces and neglects coherence effects. S. Wenger et al.11 have proposed the framework for a coupled op3cal and electronic model of DSSCs, in which the output of the op3cal model (the dye absorp3on rate) is used as input for the electrical one in order to calculate the external quantum efficiency of the device, an important parameter which is not easily es3mated. As shown in Fig. 4.9 they es3mated that a DSC converts in electrical power only about 10% of the incident irradia3on on the average, due to op3cal and electrical losses. The op3cal model, experimentally validated, takes into account the par3cular op3cal behaviour of the thin films and calculates the transmi4ance and reflectance coefficients of the thin layers with a transfer matrix approach. Nevertheless the model neglects light sca4ering in TiO2 and the effects of the presence of the thin nanometric layer of pla3num par3cles, which are considered to be lowly influent. In conclusion, comparing the data coming out from the applica3on of this model with the ones which came out from tradi3onal Lambert-Beer type based Fig. 4.9 Schematic view of the various optical and electrical losses in a DSC. A large fraction of the incident irradiation is lost due to reflection, absorption of components -other than dye- and transmittance. At maximum operating point a good DSC is estimated to convert in electrical power only about 10% of the incident irradiation Source: “Coupled Optical and Electronic Modelling of Dye-Sensitized Solar Cells...”, Journal of Physical Chemistry C, 115, 2011

137


Chapter 4 -Optical performance analysis

analyses, it is possible to affirm that commonly used simplified methods are approximately valid12. In accordance with these results, during a first phase of the present work, it was tried to model the DSSC in its main layers considered as separate with the applica3on of the simplified approach. In order to study the op3cal behaviour of a DSC, the same can be schema3zed in 5 main layers (as shown in Fig. 4.10) which op3cal behaviour is considered to be approximately homogenous: 1) First substrate FTO coated glass (2,2 mm); 2) TiO2 + dye adsorbed layer (12 μm); 3) Electrolyte layer (16 μm); 4) Pla3num catalyst layer (350 nm); 5) Second substrate FTO coated glass (3,3 mm). Refrac3ve index, transmi4ance, reflectance and absorptance of each of the 5 elements was inves3gated. In the next pages follows the descrip3on of the op3cal proper3es of each of the 5 main layers.

3,3 mm FTO coated glass

ϯϱϬŶŵWůĂƟŶƵŵ

ϭϲʅŵůĞĐƚƌŽůLJƚĞ

2,2 mm FTO coated glass

ϭϮෆʅŵdŝK2 + Dye

Fig. 4.10 DSSC stack in its 5 main layers determining the optics of the device. The relative thicknesses are indicative of a possible embodiment of a DSSC

138


Chapter 4 - Optical performance analysis

The op3cal data of the transparent substrates shown in Chart 4.4 and 4.5 were directly taken from Solaronix13 commercial products in par3cular TCO22-15 and TCO30-8 (conduc3ve layers made of fluorine-doped 3n oxide coated glass, sold in squares 5x5, 10x10 and 30x30 cm and o$en used in experimental applica3ons) TCO22-15 is 2,2 mm thick while TCO30-8 is 3,3 mm thick.

Chart 4.4 Solaronix TCO 30-8 transmittance

Chart 4.5 Solaronix TCO 2215 transmittance

Between the two substrates the photoac3ve medium comprises, as previously said, three adsorbing layers with indis3nct boundaries. If we take a look at the photoac3ve medium in micrometric scale, although there is a region in which almost pure electrolyte is present, in the remaining por3on TiO2, dye and electrolyte result mixed and the respec3ve boundaries are unclear. In the present work an approxima3on was made and the photoac3ve medium was schema3zed in two separate layers: the first one 12 μm thick, consis3ng in the TiO2 sensi3zed with dye, and the second layer, 16 μm thick, considered as pure electrolyte. DSSCs with various transparencies are usually produced by controlling the dye type and the thickness of TiO2 photoelectrodes. Different dyes have different absorp3on spectra and in general, the dyes used are highly adsorbent in the visible range, to achieve the best conversion efficiencies (the biggest part of energy of the sun rays is within the visible light range). For example Sony has developed a method to improve the cell efficiency (the so called concerto effect14) in which different dyes are put in a mixture in order to expand the range of adsorp3on (see Chart 4.6). The quan3ta3ve rela3onship between the transparency and the efficiency of DSSC has to be considered case by case. 139


Chapter 4 -Optical performance analysis

Chart 4.6 Sony developed “concerto effect” by mixing black dye and D131

Chart 4.7 shows the rela3onship between light absorptance of N71915 dye with different thickness which SEM images are also shown in Fig. 4.11. Chart 4.8 shows the transmi4ance of DSSCs in dependance of the thickness of the TiO2 films16. Charts 4.9 and 4.10 show, i.e., the absorp3on spectra of organic dyes extracted from red sicilian orange juice and aubergine17. 1.5

50 8.13 +m 16.5 +m 26.7 +m 32.2 +m

0.9

0.6



30 20

0 300

400

500

600

Wavelength (nm) (nm)

140

8

10

0.3

0.0

8.13 + m 16.5 + m  + m 32.2 +

40

Transmittance (%)

Absorbance (a.u.)

1.2

700

800

Chart 4.7 Absorptance of N719 dye with different thickness. Source: “Application of transparent...”, Building and Environment, 46, 2011

300

400

500

600

Wavelength (nm)

700

(nm)

800

Chart 4.8 Transmittance of DSSCs with different TiO2 thickness films. Source: “Application of transparent...”, Building and Environment, 46, 2011


Chapter 4 - Optical performance analysis

400

a

450

500

Absorbance (a.u)

Absorbance (a.u)

Fig. 4.11 SEM images of different thickness of TiO2 films. Source: “Application of transparent dye-sensitized solar cells...”, Building and Environment, 46, 2011

b

550

600

650

Wavelength (nm)

700

750

800

Chart 4.9 Absorption spectra of red Sicilian orange juice, in water solution (a) (black line) and (b) absorbed in TiO2 photoanode (red line). Source: “Red Sicilian orange and purple eggplant...”, Solar Energy Materials & Solar Cells, 92, 2008

400

b a

450

500

550 600 650 Wavelength (nm)

700

750

800

Chart 4.10 Absorption spectra of aubergine extract, in water solution (a) (black line) and (b) absorbed in TiO2 photoanode (green line). Source: “Red Sicilian orange and purple eggplant...”, Solar Energy Materials & Solar Cells, 92, 2008

Recent studies have evaluated the advantages in the overall energy balance which come from the use of DSSCs as BIPV in windows system i.e. in an office building18. The ra3o between cell transparency and efficiency has to be accurately selected considering mul3ple factors; in fact more efficient cells, which means in general less transparent, do not always come with be4er performance in the overall energy balance. A window that is less transparent is more efficient both in terms of light absorp3on and energy saving related, i.e., to energy consump3on of cooling systems. By the way it causes, at the same 3me, a major quan3ty of energy needed for ar3ficial ligh3ng. 141


Chapter 4 -Optical performance analysis

For what concerns the electrolyte (basically acetonitrile) in this study it was firstly considered equal to water in adsorp3on and so prac3cally transparent19. This approxima3on was later abandoned, as far as the triiodides dissolved in it are par3ally light adsorbent20. The data on the platinum layer was deduced from an online database21 considering the values of elemental pla3num (Table 4.1 and 4.2). λ [nm] 300 360 580 800

1050 1300 1550 1650 1800 2050

2200

2500

Refrac3ve index (n)

Absorp3on coefficient (α') [m-1]

λ [nm]

1.61105

9036.2

450

1.46297 2.20672 2.83783

3.60667 4.48077 5.31000 5.56093 5.68212 5.16429

4.77139

3.77475

9113.4

430

8367.0

470

7778.4

7157.4 6533.0 5707.6 5347.5 4729.3 4132.7

3980.7

3960.8

Table 4.1 Spectral values of refractive index (n) and absorption coefficient (α’) in elemental platinum (full spectrum range). Source: www.refractiveindex.info

142

510 530 550 570 600 630 650 690 720

Refrac3ve index (n)

Absorp3on coefficient (α') [m-1]

1.84756

8779.4

1.79654 1.89441 2.00768 2.07187 2.13130 2.18433 2.25278 2.32479 2.37387 2.51356 2.60244

8839.4 8719.0 8628.3 8577.8 8487.4 8390.4 8312.3 8235.7 8207.6 8078.8 8000.7

Table 4.2 Spectral values of refractive index (n) and absorption coefficient (α’) in elemental platinum (visible spectrum range). Source: www.refractiveindex.info


Chapter 4 - Optical performance analysis

4.3 Analysis method The op3cal analysis was conducted by using Op3CAD so$ware. In order to validate the results of the simula3ons on the analysed hypotheses, preliminary tes3ng simula3ons were made separately on a 6 mm float glass sheet, on a glassblock, and on a complete DSSC. The results of the tests were compared to the literature data22,23,24. Then, for each of the selected hypotheses, referring to the UNI EN 410, solar factor, light transmittance and shading coefficient were calculated. Moreover, the effects of varia3on of the angle of the incidence of light beams at 30°, 45°, 60° were calculated. The solar factor was calculated actually notwithstanding fully the standard, which requests a calcula3on in the full range from 300 to 2500 nm. Due to the lack of informa3ons on op3cal performances of the DSSC in the far infrared field the solar factor was calculated in the range between 400 and 1400 nm. This approxima3on is considered not to interfere significantly in the final results because the energy distribu3on of the sunshine beyond 1400 nm includes only about 10% of the total energy (see Chart 4.11).

2,00

Spectral Irradiance W m-2 nm -1

1,75

1,50

1,25

1,00

0,75

0,50

0,25

0,00 250

500

750

1000

1250

1500

1750

2000

2250

2500

2750

3000

3250

3500

3750

4000

Wavelength nm

Chart 4.11 Normalized solar radiation spectrum at sea level

143


Chapter 4 -Optical performance analysis

Since the so$ware allows the user to put a maximum of 12 wavelengths, the simula3ons for the solar factor calcula3on were made by assigning to each of the 12 chosen wavelengths a weight propor3onal to the quan3ty of energy carried by the ray at each wavelength (see Paragraph 4.1 Basic theory for further details) as indicated in Table 4.3. λ (nm) weight

400 0.53

490 0.50

550 1.00

670 0.93

760 0.76

850 0.65

940 0.39

1030 0.48

1120 0.23

1210 0.32

Table 4.3 Wavelengths and weights used for the calculation of the solar factor

1300 0.22

1400 0.00

The light transmi4ance was calculated in the range between 430 and 720 nm according to the standard. The 12 weights assigned to the 12 chosen wavelength are propor3onal to the product of the energy carried by the ray at each wavelength (Illuminant D65) and the sensi3vity factor of the human eye at the same wavelength, as indicated in Table 4.4. λ (nm) weight

430 0.00

450 0.04

470 0.10

510 0.52

530 0.89

550 1.00

570 0.88

600 0.54

630 0.21

650 0.08

690 0.005

Table 4.4 Wavelengths and weights used for the calculation of the light transmittance

720 0.00

For each of the hypotheses a total of 35 simula3ons were made: - 1 for the determina3on of the solar factor; - 12 to determinate the spectral response of the device in the range within 400-1400 nm; - 1 for the determina3on of the light transmi4ance; - 12 to determinate the spectral response of the device in the range within 430-720 nm; - 9 for the determina3on of the response of the device to 30° - 45° - 60° angles of incident light, considering for each case 3 different materials used at the lateral boundary surfaces of the glassblock.

144


Chapter 4 - Optical performance analysis

4.4 Preliminary simulations results 4.4.1 Simulations on a 6 mm float glass sheet

Solar factor - The results of the simula3ons on a 6 mm float glass sheet are here presented. In Table 4.5 the values of transmi4ance (τ) absorptance (α) and reflectance (ρ) registered at 12 different wavelength are shown. The results of the complete simula3on, considering the combina3on of the weights assigned at each wavelengths are reported in Table 4.6. λ (nm)

τ

α

ρ

400

0.8939

0.0288

0.0772

550

0.8848

0.0384

0.0769

490 670 760 850 940

1030 1120

1210

1300

0.8848 0.8386 0.7833 0.7281 0.7188

0.7004 0.7004

0.7096

0.7373

0.0384 0.0864 0.1440 0.2016 0.2112

0.2304 0.2304

0.2208

0.1920

0.0769 0.0749 0.0726 0.0703 0.0700

0.0692 0.0692

0.0696

0.0707

1400

0.7465

0.1824

0.0711

complete simula3on

0.8014

0.1252

0.0734

Table 4.5 Spectral transmittance, absorptance and reflectance of a 6 mm float glass sheet

Table 4.6 Total transmittance, absorptance and reflectance of a 6 mm float glass sheet

145


Chapter 4 -Optical performance analysis

The solar factor (g) calculated according to the formula contained in the standard UNI EN 410 is: g = τe + q i We subs3tuted the τe in the formula with the τ determined through the Op3CAD complete simula3on, with the following result: g = τe + qi = 0,8337= 83,37 % We compared this result with the solar factor of a 6 mm float glass sheet calculated in a previous work25, which confirmed its reliability. In addi3on in Chart 4.12 a comparison between the spectral data extracted from the 12 simula3on at 12 different wavelengths and the literature data26 for transmi4ance and reflectance of a 6 mm float glass sheet is shown. The results of the simula3ons found are in perfect agreement with those extracted from literature. 1.0 0.9

dƌĂŶƐŵŝƩĂŶĐĞ͕ZĞŇĞĐƚĂŶĐĞ

0.8 0.7 0.6 0.5

dƌĂŶƐŵŝƩĂŶĐĞ ZĞŇĞĐƚĂŶĐĞ KƉƟĐĂĚƐŝŵƵůĂƚĞĚƚƌĂŶƐŵŝƩĂŶĐĞ KƉƟĐĂĚƐŝŵƵůĂƚĞĚƌĞŇĞĐƚĂŶĐĞ

0.4 0.3 0.2 0.1

500

750

Chart 4.12 Float glass (6 mm): comparison of the spectral data 146

1000 wavelength (nm)

1250


Chapter 4 - Optical performance analysis

Light transmittance - In Table 4.7 transmi4ance (τ) absorptance (α) and reflectance (ρ) registered at 12 different wavelengths are shown. The results of the complete simula3on, considering the combina3on of the weights assigned at each wavelength are shown in Table 4.8. λ (nm)

τ

α

ρ

430

0.8755

0.0480

0.0765

470

0.8848

0.0384

0.0769

450 510 530 550 570 600 630 650 690 720

0.8848 0.8848 0.8848 0.8848 0.8755 0.8571 0.8479 0.8386 0.8202 0.8110

0.0384 0.0384 0.0384 0.0384 0.0480 0.0672 0.0768 0.0864 0.1056 0.1152

0.0769 0.0769 0.0769 0.0769 0.0765 0.0757 0.0753 0.0749 0.0742 0.0738

Table 4.7 Spectral transmittance, absorptance and reflectance of a 6 mm float glass sheet complete simula3on

0.8766

0.0469

0.0765

Table 4.8 Total transmittance, absorptance and reflectance of a 6 mm float glass sheet

The complete simula3on gives as result:

τv = 87,66 %

We compared this result with the light transmi4ance of a 6 mm float glass sheet calculated in a previous work27, which confirmed its reliability. 147


Chapter 4 -Optical performance analysis

4.4.2 Simulations on the standard glassblock

Solar factor - The results of the simula3ons on the standard glassblock28 are presented. Table 4.9 shows the values of transmi4ance (τ) absorptance (α) and reflectance (ρ) registered at 12 different wavelengths. The results of the complete simula3on, considering the combina3on of the weights assigned at each wavelength are shown in Table 4.10. λ (nm)

τ

α

ρ

400

0.7992

0.0683

0.1326

550

0.7828

0.0894

0.1278

490 670 760 850 940

1030 1120 1210 1300 1400

0.7828 0.7034 0.6137 0.5301 0.5168

0.4906 0.4906 0.5036 0.5436 0.5573

0.0894 0.1855 0.2882 0.3806 0.3951

0.4237 0.4237 0.4095 0.3658 0.3508

0.1278 0.1111 0.0981 0.0893 0.0881

0.0858 0.0858 0.0869 0.0906 0.0920

Table 4.9 Spectral transmittance, absorptance and reflectance of the standard glassblock complete simula3on

0.6478

0.2455

0.1067

Table 4.10 Total transmittance, absorptance and reflectance of the standard glassblock

Considering the glassblock as a double glass with reference to UNI EN 410: g = τe + qi = 73,41 % 29 We compared this result with the solar factor calculated by the SSV (Stazione Sperimentale del Vetro, see Attachment 1)30, which confirmed its reliability. 148


Chapter 4 - Optical performance analysis

Light transmittance - In Table 4.11 the transmi4ance (τ) absorptance (α) and reflectance (ρ) registered at 12 different wavelengths are shown. The results of the complete simula3on, considering the combina3on of the weights assigned at each wavelength are shown in Table 4.12. λ (nm)

τ

α

ρ

430

0.7665

0.1099

0.1235

470

0.7828

0.0894

0.1278

450 510 530 550 570 600 630 650 690 720

0.7828 0.7828 0.7828 0.7828 0.7665 0.7346 0.7189 0.7034 0.6727 0.6577

0.0894 0.0894 0.0894 0.0894 0.1099 0.1491 0.1680 0.1855 0.2212 0.2384

0.1278 0.1278 0.1278 0.1278 0.1235 0.1163 0.1131 0.1111 0.1061 0.1039

Table 4.11 Spectral transmittance, absorptance and reflectance of the standard glassblock complete simula3on

0.7686

0.1070

0.1244

Table 4.12 Total transmittance, absorptance and reflectance of the standard glassblock

The complete simula3on gives as result: τv = 0,7685 = 76,85 % We compared this result with the light transmi4ance calculated by the SSV (see Attachment 1)31, which confirmed its reliability. Shading coefficient - The shading coefficient calculated in accordance with UNI EN 410: SC = 84,38 % 149


Chapter 4 -Optical performance analysis

4.4.3 Simulations on a complete DSC Due to problems encountered in the modeliza3on of thin films in Op3CAD32 and in order to avoid the treatment of the op3cal proper3es of thin layers -which does not meet the aim of the current study- the DSC was modelled as a simple lens, which proper3es correspond to the proper3es of the composing layers assembled together. The simula3ons conducted in the present work take into account a par3cular DSC assembled at the Ecole Polytechnique Federale de Lausanne, deeply described by S. Wenger et al.33 in order to build a theory on op3cal and electronical modelling of DSC. The precise thicknesses used in the assemblage are shown in Fig 4.12.

Fig 4.12 DSSC structure depicting the six layers composing the cell. Source: “Coupled Optical and Electronic Modelling of Dye-Sensitized Solar Cells...”, Journal of Physical Chemistry C, 115, 2011

Ruthenium based Z90734 (reddish-brownish colour) dye and acetonitrile based electrolyte were used. The other components used are commercial FTO coated glass electrode and pla3nized FTO counter electrode35. This simplifica3on, which became necessary during the development of the present work, actually excluded the possibility to directly inves3gate the hypotheses 1, 2, and 3, in which the cell assemblage misses one substrate, subs3tuted by the glassblock itself. However, we think that the considera3ons which came out from the study of the correspondent hypotheses 1a, 2a and 3a, in which a complete DSSC module is integrated into the glassblock are approximately extendable to the first ones, because the elimina3on of one of the glass substrates (which from the op3cal point of view consists in the elimina3on of an absorp3on component and a reflec3on component) can be considered lowly influent in the overall behaviour of the device.

150


Chapter 4 - Optical performance analysis

Anyway, further study should be considered for a more detailed evalua3on of the changes on op3cal behaviour in the excluded configura3ons. To understand on a quality level the spectral absorp3on of each of the components of the cell, we report detailed charts showing the dependance of the op3cal proper3es of the layers with the wavelength and their influence on the total op3cal behaviour of the DSC (Chart 4.13 and 4.14 illuminated respec3vely from the photoelectrode side and the counter electrode side). In the two charts the energy conserva3on principle is respected ( / x + / a + / t = 1 ). Moreover it is possible to no3ce that the total transmi4ance is independent from the illumina3on side and the reflec3on losses are slightly larger when the illumina3ng source is located on the electrolyte side. With regards to the photoac3ve layer 3 (TiO2/dye/electrolyte) a considerable absorp3on loss is evident for illumina3on coming from the electrolyte side, in addi3on the absorp3on of the electrolyte in itself grows (the absorp3on is mainly related to the absorp3on of triodides in the solu3on), subtrac3ng poten3al energy to the proper photoelectrode.

Chart 4.13 and 4.14 Detailed optical loss analysis of a the DSC stack. Source: Fig 4.12 DSSC structure depicting the six layers composing the cell. Source: “Coupled Optical and Electronic...”, Journal of Physical Chemistry C, 115, 2011

151


Chapter 4 -Optical performance analysis

Solar factor - The results of the simula3ons on the DSSC stack are here presented. Table 4.13 shows the values of transmi4ance (τ) absorptance (α) and reflectance (ρ) registered at 12 different wavelength. The results of the complete simula3on, considering the combina3on of the weights assigned at each wavelength are shown in Table 4.14. λ (nm)

τ

α

ρ

400

0.0645

0.8928

0.0427

550

0.1014

0.8544

0.0442

490 670 760 850 940

1030 1120 1210 1300 1400

0.0737 0.5530 0.7373 0.7281 0.6912

0.6543 0.6082 0.5622 0.5161 0.4424

0.8832 0.3840 0.1920 0.2016 0.2400

0.2784 0.3264 0.3744 0.4224 0.4992

0.0431 0.0630 0.0707 0.0703 0.0688

0.0673 0.0653 0.0634 0.0615 0.0584

Table 4.13 Spectral transmittance, absorptance and reflectance of the DSSC complete simula3on

0.4555

0.4856

0.0590

Table 4.14 Total transmittance, absorptance and reflectance of the DSSC

The complete simula3on gives as result: g = τe + qi = 58,08 %

152


Chapter 4 - Optical performance analysis

In Chart 4.15 a comparison between the spectral data extracted from the 12 simula3ons at 12 different wavelengths and the literature data36 for transmi4ance and reflectance of the complete DSSC stack is shown. The results of the simula3ons found are in good agreement with those extracted from literature data. 1.0 0.9

dƌĂŶƐŵŝƩĂŶĐĞ͕ZĞŇĞĐƚĂŶĐĞ

0.8 0.7 0.6 0.5

dƌĂŶƐŵŝƩĂŶĐĞ ZĞŇĞĐƚĂŶĐĞ KƉƟĐĂĚƐŝŵƵůĂƚĞĚƚƌĂŶƐŵŝƩĂŶĐĞ KƉƟĐĂĚƐŝŵƵůĂƚĞĚƌĞŇĞĐƚĂŶĐĞ

0.4 0.3 0.2 0.1

500

750

1000 wavelength (nm)

1250

Chart 4.15 - Complete DSC: spectral data

153


Chapter 4 -Optical performance analysis

Light transmittance - In Table 4.15 the transmi4ance (τ) absorptance (α) and reflectance (ρ) registered at 12 different wavelengths are shown. The results of the complete simula3on, considering the combina3on of the weights assigned at each wavelength are shown in Table 4.16. λ (nm)

τ

α

ρ

430

0.0829

0.8736

0.0435

470

0.0922

0.8640

0.0438

450 510 530 550 570 600 630 650 690 720

0.0922 0.0829 0.0829 0.1014 0.1751 0.3041 0.4239 0.4884 0.5990 0.6820

0.8640 0.8736 0.8736 0.8544 0.7776 0.6432 0.5184 0.4512 0.3360 0.2496

0.0438 0.0435 0.0435 0.0442 0.0473 0.0527 0.0577 0.0604 0.0650 0.0684

Table 4.15 Spectral transmittance, absorptance and reflectance of the DSSC complete simula3on

0.1596

0.7938

0.0466

Table 4.16 Total transmittance, absorptance and reflectance of the DSSC

The complete simula3on gives as result: τv = 0,1595 = 15,95 %

154


Chapter 4 - Optical performance analysis

Please note that the results are referred to a single cell, not to a module. When evalua3ng the solar factor and the light transmi4ance of a module the gaps (sealing) between the cells must be taken into account. Since in the next simula3ons DSSC modules are assembled with the glassblock, an improvement in transmi4ance of 10%37 which refers to the area not covered by the ac3ve surface in a module can be considered.

4.5 Simulations on Hyp. 1a, 2a, 3a, and 4: results

We now report the results of the simula3ons conducted on the hypotheses 1a, 2a, 3a and 4 of the device together with a brief descrip3on. In Fig. 4.13 the simula3on scheme used in the analysis of each hypothesis is shown.

Hyp. 1a

Hyp. 2a

Hyp. 3a

Hyp. 4

Fig. 4.13 Simulation schemes used in the analysis of Hyp. 1a, Hyp. 2a, Hyp. 3a and Hyp. 4 are shown by putting in evidence the position of the DSSC module (in red) and of a total adsorbing ďŹ lm (in green) used in order to estimate the the total transmittance of the device. The collimated light source (red arrows) is perpendicular to the plane surface of the glassblock and always extended to the same region as schematically shown

The collimated light source is perpendicular to the plane surface of the glassblock and always extended to the same region as schema3cally shown. The results are reported exactly as the output of the simula3ons and then commented. As it will be further described, the simula3ons on the Hyp. 3a and 4 showed some contradic3ons38, describing a behaviour of the device diďŹ&#x192;cult to compare with reality. Further simula3ons were conducted to put in evidence the cri3cal points iden3ďŹ ed in the results related to Hyp. 3a and 4, in order to take out values physically acceptable. 155


Chapter 4 -Optical performance analysis

4.5.1 Hypothesis 1a

Solar factor - The results of the simula3ons on the Hyp. 1a are presented. Table 4.17 shows the values of total transmi4ance (τ) absorptance of the glassblock (αgb), absorptance of the DSC (αdsc), total absorptance (αTOT), and total reflectance (ρ) registered at 12 different wavelengths. The results of the complete simula3on, considering the combina3on of the weights assigned at each wavelength are shown in Table 4.18. λ (nm)

τ

α gb

α dsc

α TOT

400 490 550 670 760 850 940 1030 1120 1210 1300 1400

0.0000 0.0000 0.0141 0.2840 0.4453 0.4046 0.3638 0.3211 0.2816 0.2476 0.2205 0.1692

0.0546 0.0614 0.0813 0.2181 0.2203 0.2567 0.2658 0.2770 0.2760 0.2669 0.2527 0.2299

0.8928 0.8832 0.8544 0.3945 0.2044 0.2161 0.2548 0.2912 0.2816 0.3870 0.4344 0.5085

0.9474 0.9446 0.9357 0.6125 0.4247 0.4727 0.5207 0.5682 0.5576 0.6539 0.6871 0.7385

0.0526 0.0554 0.0502 0.1034 0.1300 0.1227 0.1155 0.1106 0.1608 0.0985 0.0924 0.0923

complete simula3on

0.2277

0.1862

0.4939

0.6801

0.0922

Table 4.17 Spectral transmittance, absorptance and reflectance of Hyp. 1a

Table 4.18 Total transmittance, absorptance and reflectance of the Hyp. 1a

Considering the glassblock as a double glass with reference to UNI EN 410: g = 31,25 % 39 156

ρ


Chapter 4 - Optical performance analysis

In Chart 4.16 the repar33on of the incident radiant flux in total transmi4ance (τ) total reflectance (ρ) together with the rela3ve absorptance of the glassblock (αgb) and the rela3ve absorptance of the DSC (αdsc) are shown in respect of the energy conserva3on law and in dependance of the wavelength. 1,00

ďƐŽƌƉƚĂŶĐĞ͕ZĞŇĞĐƚĂŶĐĞ͕dƌĂŶƐŵŝƩĂŶĐĞ

0,90

ʏ

0,80 0,70 0,60

ʌ

0,50 0,40

ɲdsc

0,30 0,20

ɲgb

0,10 0,00

400

490

550

670

760

850

940

1030

1120

1210

1300

1400

ǁĂǀĞůĞŶŐƚŚ;ŶŵͿ Chart 4.16 Hyp. 1a: spectral data

The device behaves as an almost opaque body (with very low transmi4ance in the visible range) showing maximum transmi4ance (about 55%) at 760 nm ca. This result is very much influenced by the DSC type selected. In fact the selected DSC is more designed for high conversion efficiency to the detriment of total transmi4ance: the cell absorbs the most within the visible range, which is also the most energe3c, leading by consequence to a very low transmi4ance in the same range. We want to remember that in this simula3on an improvement in transmi4ance of about 10% can be considered in order to take in account the area not covered by the ac3ve surface in a module, which is not included in the simula3on. 157


Chapter 4 -Optical performance analysis

Light transmittance The results of the simula3ons on the Hyp. 1a are presented. Table 4.19 shows the values of total transmi4ance (τ) absorptance of the glassblock (αgb), absorptance of the DSC (αdsc), total absorptance (αTOT) and total reflectance (ρ) registered at 12 different wavelengths. The results of the complete simula3on, considering the combina3on of the weights assigned at each wavelength are shown in Table 4.20. λ (nm)

τ

α gb

α dsc

α TOT

ρ

430 450 470 510 530 550 570 600 630 650 690 720

0.0000 0.0119 0.0119 0.0000 0.0000 0.0141 0.0374 0.0990 0.1780 0.2272 0.3208 0.4006

0.0686 0.0750 0.0750 0.0685 0.0685 0.0813 0.1256 0.1795 0.2044 0.2180 0.2227 0.2152

0.8736 0.8640 0.8640 0.8736 0.8736 0.8544 0.7776 0.6514 0.5277 0.4617 0.3479 0.2614

0.9422 0.9390 0.9390 0.9421 0.9421 0.9357 0.9032 0.8309 0.7321 0.6797 0.5707 0.4766

0.0578 0.0491 0.0491 0.0579 0.0579 0.0502 0.0593 0.0702 0.0899 0.0932 0.1085 0.1228

complete simula3on

0.0374

0.1072

0.7955

0.9027

0.0600

Table 4.19 Spectral transmittance, absorptance and reflectance of Hyp. 1a

Table 4.20 Total transmittance, absorptance and reflectance of Hyp. 1a

The complete simula3on gives as result: τv = 0,0373 = 3,73 % We want to remember that in this simula3on an improvement in transmi4ance of about 10% can be considered in order to take in account the area not covered by the ac3ve surface in a module, which is not included in the simula3on. 158


Chapter 4 - Optical performance analysis

Shading coefficient - The shading coefficient calculated in accordance with UNI EN 410 gives as result: SC = 35,92 % In Table 4.21 the op3cal proper3es of the device in dependance of the angle of incidence of the radiant flux are shown. In par3cular the simula3ons were conducted assuming an inclina3on of 30°, 45°, 60° of the light rays measured from the perpendicular to the glassblock plane surface. R

30° 45° 60°

1 0.5 0 1 0.5 0 1 0.5 0

A

0 0.5 1 0 0.5 1 0 0.5 1

τ

0.1966 0.1907 0.1851 0.1443 0.1282 0.1126 0.0787 0.0561 0.0415

α gb

0.1816 0.1787 0.1769 0.1840 0.1731 0.1654 0.1760 0.1485 0.1306

α dsc

0.5076 0.5068 0.5064 0.5221 0.5199 0.5182 0.5215 0.5204 0.5194

α bou

0.0071 0.0071 0.0071 0.0190 0.0178 0.0171 0.0305 0.0278 0.0256

α TOT

0.6963 0.6926 0.6905 0.7252 0.7108 0.7007 0.7281 0.6967 0.6756

ρ

0.1071 0.1167 0.1245 0.1305 0.1609 0.1867 0.1933 0.2472 0.2829

Table 4.21 Optical properties of the device in dependance of the angle of the incident radiant flux (measured with the perpendicular to the glassblock plane surface). The values of total transmittance (τ) absorptance of the glassblock (αgb), absorptance of the DSC (αdsc), absorptance of the boundary (αbou) and total absorptance (αTOT), total reflectance (ρ) taken out from the complete simulation are showed. The values in column R and A indicate respectively the surface reflectance and surface absorptance of the material used at the boundary surfaces of the glassblock

For each of the inclina3ons the table shows also the dependence of the op3cal proper3es of the device to the nature of the material used at the lateral boundary surfaces of the glassblock. It is evident that when using a totally reflec3ve material the best transmi4ances are achieved, with a gap of 1 percentual point ca. when passing from a totally absorbent material to a totally reflec3ve one. The DSC absorptance does not seem to be really influenced by the type of material used at the boundary surfaces. 159


Chapter 4 -Optical performance analysis

4.5.2 Hypothesis 2a

Solar factor - The results of the simula3ons on the Hyp. 2a are presented. Table 4.22 shows the values of total transmi4ance (τ) absorptance of the glassblock (αgb), absorptance of the DSC (αdsc), total absorptance (αTOT), and total reflectance (ρ) registered at 12 different wavelengths. The results of the complete simula3on, considering the combina3on of the weights assigned at each wavelength are shown in Table 4.23. λ (nm)

τ

α gb

α dsc

α TOT

400 490 550 670 760 850 940 1030 1120 1210 1300 1400

0.0000 0.0000 0.0135 0.2812 0.4433 0.4027 0.3617 0.3190 0.2793 0.2452 0.2180 0.1668

0.0549 0.0619 0.0820 0.2212 0.2225 0.2588 0.2682 0.2794 0.2786 0.2695 0.2555 0.2327

0.8928 0.8832 0.8544 0.3944 0.2044 0.2160 0.2522 0.2912 0.3393 0.3870 0.4344 0.5085

0.9477 0.9450 0.9364 0.6157 0.4269 0.4748 0.5203 0.5706 0.6178 0.6565 0.6898 0.7413

0.0523 0.0550 0.0501 0.1031 0.1298 0.1225 0.1179 0.1104 0.1029 0.0983 0.0921 0.0920

complete simula3on

0.2261

0.1881

0.4937

0.6818

0.0922

Table 4.22 Spectral transmittance, absorptance and reflectance of Hyp. 2a

Table 4.23 Total transmittance, absorptance and reflectance of Hyp. 2a

Considering the glassblock as a double glass with reference to UNI EN 410: g = 31,24 % 40 160

ρ


Chapter 4 - Optical performance analysis

In Chart 4.17 the repar33on of the incident radiant flux in total transmi4ance (τ) total reflectance (ρ) together with the rela3ve absorptance of the glassblock (αgb) and the rela3ve absorptance of the DSC (αdsc) are shown in respect of the energy conserva3on law and in dependance of the wavelength. 1,00

ďƐŽƌƉƚĂŶĐĞ͕ZĞŇĞĐƚĂŶĐĞ͕dƌĂŶƐŵŝƩĂŶĐĞ

0,90

ʏ

0,80 0,70 0,60

ʌ

0,50 0,40

ɲdsc

0,30 0,20

ɲgb

0,10 0,00

400

490

550

670

760

850

940

1030

1120

1210

1300

1400

ǁĂǀĞůĞŶŐƚŚ;ŶŵͿ Chart 4.17 Hyp. 2a: spectral data

The considera3ons made when analysing the hypothesis 1a are here s3ll valid. Again, we want to remember that in this simula3on an improvement in transmi4ance of about 10% can be considered in order to take in account the area not covered by the ac3ve surface in a module, which is not included in the simula3on.

161


Chapter 4 -Optical performance analysis

Light transmittance - The results of the simula3ons on the Hyp. 2a are presented. Table 4.24 shows the values of total transmi4ance (τ) absorptance of the glassblock (αgb), absorptance of the DSC (αdsc) and total absorptance (αTOT), total reflectance (ρ) registered at 12 different wavelengths. The results of the complete simula3on, considering the combina3on of the weights assigned at each wavelength are shown in Table 4.25. λ (nm)

τ

α gb

α dsc

α TOT

ρ

430 450 470 510 530 550 570 600 630 650 690 720

0.0000 0.0114 0.0114 0.0000 0.0000 0.0135 0.0362 0.0968 0.1753 0.2244 0.3181 0.3982

0.0691 0.0756 0.0756 0.0691 0.0690 0.0820 0.1270 0.1819 0.2075 0.2211 0.2257 0.2178

0.8736 0.8640 0.8640 0.8736 0.8736 0.8544 0.7776 0.6514 0.5277 0.4617 0.3479 0.2614

0.9427 0.9396 0.9396 0.9427 0.9426 0.9364 0.9046 0.8333 0.7352 0.6828 0.5736 0.4792

0.0573 0.0491 0.0491 0.0573 0.0574 0.0501 0.0592 0.0699 0.0895 0.0929 0.1083 0.1225

complete simula3on

0.0365

0.1084

0.7955

0.9038

0.0597

Table 4.24 Spectral transmittance, absorptance and reflectance of Hyp. 2a

Table 4.25 Total transmittance, absorptance and reflectance of Hyp. 2a

The complete simula3on gives as result: τv = 0,0364 = 3,64 % We want to remember that in this simula3on an improvement in transmi4ance of about 10% can be considered in order to take in account the area not covered by the ac3ve surface in a module, which is not included in the simula3on. 162


Chapter 4 - Optical performance analysis

Shading coefficient - The shading coefficient calculated in accordance with UNI EN 410 gives as result: SC = 35,91 % In Table 4.26 the op3cal proper3es of the device in dependance of the angle of incidence of the radiant flux are shown. In par3cular the simula3ons were conducted assuming an inclina3on of 30°, 45°, 60° of the light rays measured from the perpendicular to the glassblock plane surface. R

30° 45° 60°

1 0.5 0 1 0.5 0 1 0.5 0

A

0 0.5 1 0 0.5 1 0 0.5 1

τ

0.1765 0.1765 0.1765 0.1315 0.1098 0.0887 0.0730 0.0505 0.0349

α gb

0.2047 0.2022 0.2001 0.2083 0.1906 0.1775 0.1954 0.1722 0.1539

α dsc

0.5076 0.5073 0.5070 0.5188 0.5180 0.5178 0.5194 0.5194 0.5194

α bou

0.0003 0.0003 0.0003 0.0109 0.0108 0.0108 0.0185 0.0185 0.0185

α TOT

0.7126 0.7098 0.7074 0.7380 0.7194 0.7061 0.7333 0.7101 0.6917

ρ

0.1110 0.1137 0.1161 0.1305 0.1708 0.2052 0.1937 0.2395 0.2733

Table 4.26 Optical properties of the device in dependance of the angle of the incident radiant flux (measured with the perpendicular to the glassblock plane surface). The values of total transmittance (τ) absorptance of the glassblock (αgb), absorptance of the DSC (αdsc), absorptance of the boundary (αbou) and total absorptance (αTOT), total reflectance (ρ) taken out from the complete simulation are showed. The values in column R and A indicate respectively the surface reflectance and surface absorptance of the material used at the boundary surfaces of the glassblock

For each of the inclina3ons the table shows also the dependence of the op3cal proper3es of the device to the nature of the material used at the lateral boundary surfaces of the glassblock. It is evident that when using a totally reflec3ve material the best transmi4ances are achieved. The DSSC absorptance does not seem to be really influenced by the type of material used at the boundary surfaces. 163


Chapter 4 -Optical performance analysis

4.5.3 Hypothesis 3a

As previously stated the simula3ons on Hyp. 3a showed contradictory results. Further informa3ons and the alterna3ve method adopted for the calcula3on of the luminous and solar characteris3cs of the device are reported further in this paragraph.

Solar factor - The results of the simula3ons on the Hyp. 3a are presented. Table 4.27 shows the values of total transmi4ance (τ) absorptance of the glassblock (αgb), absorptance of the DSC (αdsc) total absorptance (αTOT), and total reflectance (ρ) registered at 12 different wavelengths. The results of the complete simula3on, considering the combina3on of the weights assigned at each wavelength are shown in Table 4.28. λ (nm)

τ

α gb

α dsc

α TOT

400 490 550 670 760 850 940 1030 1120 1210 1300 1400

0.1394* 0.0902* 0.1171* 0.4177* 0.4545* 0.3824* 0.3562* 0.3214* 0.3028* 0.2922* 0.2965* 0.2687*

0.7330* 0.7169* 0.6877* 0.3297* 0.2504* 0.2986* 0.3210* 0.3509* 0.3711* 0.3863* 0.3942* 0.4290*

0.0630* 0.0723* 0.0723* 0.1166* 0.1595* 0.1966* 0.2025* 0.2127* 0.2128* 0.2079* 0.1920* 0.1861*

0.7960* 0.7891* 0.7600* 0.4463* 0.4099* 0.4952* 0.5235* 0.5636* 0.5839* 0.5943* 0.5862* 0.6150*

0.0645* 0.1207* 0.1229* 0.1360* 0.1356* 0.1225* 0.1203* 0.1150* 0.1133* 0.1135* 0.1173* 0.1163*

complete simula3on

0.2845*

0.4517*

0.1394*

0.5912*

0.1243*

Table 4.27 Spectral transmittance, absorptance and reflectance of Hyp. 3a * The values as resulting from the simulations are considered lowly reliable

164

ρ

Table 4.28 Total transmittance, absorptance and reflectance of Hyp. 3a * The values as resulting from the simulations are considered lowly reliable


Chapter 4 - Optical performance analysis

In Chart 4.18 the repar33on of the incident radiant flux in total transmi4ance (τ) total reflectance (ρ) together with the rela3ve absorptance of the glassblock (αgb) and the rela3ve absorptance of the DSC (αdsc) are shown in respect of the energy conserva3on law and in dependance of the wavelength. 1,00

ďƐŽƌƉƚĂŶĐĞ͕ZĞŇĞĐƚĂŶĐĞ͕dƌĂŶƐŵŝƩĂŶĐĞ

0,90

ʏΎ

0,80 0,70 0,60

ʌΎ

0,50 0,40

ɲdsc*

0,30 0,20

ɲgb*

0,10 0,00

400

490

550

670

760

850

940

1030

1120

1210

1300

1400

ǁĂǀĞůĞŶŐƚŚ;ŶŵͿ Chart 4.18 Hyp. 3a: spectral data * The values as resulting from the simulations are considered lowly reliable

The values resul3ng from the simula3ons on Hyp. 3a are considered lowly reliable. The simula3ons reveal, in facts, an anomalous behaviour of the device, with the glassblock becoming the most adsorbent component and the DSC absorbing a very narrow part of the incident flux (between 5 and 20%). Moreover, the transmi4ance of the device compared to the Hyp. 1a and Hyp. 2a has considerably changed, going against expecta3ons41. This behaviour is difficult to explain physically, so we decided to proceed with further simula3ons in order to verify the reliability of these data obtained. 165


Chapter 4 -Optical performance analysis

A new simula3on scheme was introduced, including a totally adsorbing film disposed in place of the DSC to evaluate the quan3ty of the luminous energy effec3vely reaching the cell, as shown in Fig. 4.14. ĚƐŽƌďŝŶŐĮůŵ

DSC ĂƐĞƐĐŚĞŵĞ

ĚƐŽƌďŝŶŐĮůŵ EĞǁƐĐŚĞŵĞ Fig. 4.14 New simulation scheme for the evaluation of the radiant flux reaching the surface of the DSC

The absorbing film recorded an absorp3on value equal to 80,1% (complete simula3on), which is the part of the radiant flux reaching the surface of the cell. A simple mul3plica3on shows an internal contradic3on: in facts, if we consider the absorp3on registered by the cell when placed on the external surface of the glassblock, in direct contact with light, it absorbs α dsc = 49,39%42 , in respect of the 100% incident flux. When placed inside, the cell should reasonably absorb a part of the total radia3on equal to 80,1 × 49,39% = 39,58% and not 13,94% as from the simula3ons results. Anyway, the significant factors that we want to find in this research are the total transmittance, needed to es3mate the device transparency and the por3on of light adsorbed by the cell, because it is propor3onal to its efficiency. For what concerns the total transmi4ance, considering the extent of the region hit by the 166


Chapter 4 - Optical performance analysis

rays of the light source when placed frontally (which, as already explained, is always the same in the analysis of the four hypotheses), the only difference among the four is the order in which glass or cell are intercepted. This means that for a frontal light source the total transmi4ance should be approximately the same for all the hypotheses, because the order of the components in the assembly stra3graphy is supposed not to influence the total transparency of the device. So, for the transmi4ances (spectral and total) it is possible to approximately refer to the ones registered in the analysis of Hyp. 1a. On the other hand, the DSC absorbances (spectral and total) are calculated by using the new simula3on scheme, as result of the product of the absorptances registered by the totally absorbing film disposed in place of the DSC (reported in Table 4.29-4.30 and indicated with the symbol I0*) and the correspondent absorptances registered by the DSC in the analysis of the Hyp 1a (reported in Table 4.17-4.18). In Table 4.31 the “corrected” spectral transmi4ance and absorptance of the DSC are reported. Table 4.32 reports the values referred to the complete simula3on. λ (nm) 400 490 550 670 760 850 940 1030 1120 1210 1300 1400

I0* 0.8940 0.8848 0.8848 0.8387 0.7834 0.7281 0.7189 0.7004 0.7004 0.7096 0.7373 0.7465

complete simula3on

0.8014

Table 4.29 Spectral absorptance of a totally adsorbing film (I0*) disposed in place of the DSC in Hyp. 3a Table 4.30 Total absorptance of a totally adsorbing film disposed in place of the DSC in Hyp. 3a

λ (nm) 400 490 550 670 760 850 940 1030 1120 1210 1300 1400

τ 0.0000 0.0000 0.0141 0.2840 0.4453 0.4046 0.3638 0.3211 0.2816 0.2476 0.2205 0.1692

α dsc 0.7981 0.7814 0.7559 0.3308 0.1601 0.1573 0.1832 0.2040 0.1972 0.2747 0.3203 0.3796

complete simula3on

0.2277

0.3958

Table 4.31 “Corrected” spectral transmittance and DSSC module spectral absorptance of Hyp. 3a Table 4.32 “Corrected” total transmittance and DSSC module total absorptance of Hyp. 3a

167


Chapter 4 -Optical performance analysis

Then, considering the glassblock as a double glass with reference to UNI EN 410: g = 31,25 % 43 Light transmittance - The results of the simula3ons on the Hyp. 3a are presented by way of informa3on. Table 4.33 shows the values of total transmi4ance (τ) absorptance of the glassblock (αgb), absorptance of the DSC (αdsc) and total absorptance (αTOT), total reflectance (ρ) registered at 12 different wavelengths. The results of the complete simula3on, considering the combina3on of the weights assigned at each wavelength are shown in Table 4.34. λ (nm)

τ

α gb

α dsc

α TOT

430 450 470 510 530 550 570 600 630 650 690 720

0.0970* 0.1083* 0.1083* 0.0993* 0.0993* 0.1171* 0.1791* 0.2685* 0.3442* 0.3773* 0.4245* 0.4604*

0.7016* 0.6972* 0.6972* 0.7070* 0.7070* 0.6877* 0.6128* 0.5009* 0.4169* 0.3737* 0.3084* 0.2624*

0.0813* 0.0723* 0.0723* 0.0723* 0.0723* 0.0723* 0.0813* 0.0995* 0.1082* 0.1166* 0.1324* 0.1393*

0.7829* 0.7695* 0.7695* 0.7792* 0.7792* 0.7600* 0.6941* 0.6004* 0.5252* 0.4903* 0.4408* 0.4017*

0.1200* 0.1222* 0.1222* 0.1214* 0.1214* 0.1229* 0.1269* 0.1311* 0.1307* 0.1324* 0.1347* 0.1379*

complete simula3on

0.1593*

0.6356*

0.0803*

0.7159*

0.1248*

Table 4.33 Spectral transmittance, absorptance and reflectance of Hyp. 3a * The values as resulting from the simulations are considered lowly reliable Table 4.34 Total transmittance, absorptance and reflectance of Hyp. 3a * The values as resulting from the simulations are considered lowly reliable

168

ρ


Chapter 4 - Optical performance analysis

The results showed the same contradic3ons as those of the simula3ons conducted for the calcula3on of the solar factor. Since the evalua3on of the light transmi4ance is conducted with the purpose of measuring the transparency of the device to the human eye, it is possible, approximately, to refer to the values of transmi4ance found during the analysis of Hyp. 1a. (Table 4.19 and 4.20), since, as already said, the absorptance of the single elements is considered to be not significant in the understananding of the total behaviour of the device and the swop in the order of the components in its stra3graphy is supposed not to interfere with the total transmi4ance of the device. Shading coefficient - The shading coefficient calculated in accordance with UNI EN 410 gives as result: SC = 35,92 % The results of the simula3ons conducted with different radiant flux inclina3ons are omi4ed.

169


Chapter 4 -Optical performance analysis

4.5.4 Hypothesis 4

As previously stated the simula3ons on Hyp. 4 also showed contradictory results. Further informa3ons and the alterna3ve method adopted for the calcula3on of the luminous and solar characteris3cs of the device are reported further in this paragraph.

Solar factor - The results of the simula3ons on the Hyp. 4 are presented by way of informa3on. Table 4.35 shows the values of total transmi4ance (τ) absorptance of the glassblock (αgb), absorptance of the DSC (αdsc) total absorptance (αTOT), and total reflectance (ρ) registered at 12 different wavelengths. The results of the complete simula3on, considering the combina3on of the weights assigned at each wavelength are shown in Table 4.36. λ (nm)

τ

α gb

α dsc

α TOT

400 490 550 670 760 850 940 1030 1120 1210 1300 1400

0.0827* 0.0902* 0.1171* 0.4177* 0.4545* 0.3824* 0.3562* 0.3214* 0.3028* 0.2922* 0.2965* 0.2687*

0.7409* 0.7268* 0.6977* 0.3463* 0.2688* 0.3171* 0.3393* 0.3688* 0.3890* 0.4044* 0.4128* 0.4477*

0.0630* 0.0723* 0.0723* 0.1160* 0.1570* 0.1945* 0.2009* 0.2116* 0.2120* 0.2074* 0.1917* 0.1859*

0.8039* 0.7991* 0.7700* 0.4623* 0.4258* 0.5116* 0.5402* 0.5803* 0.6010* 0.6119* 0.6045* 0.6336*

0.1133* 0.1107* 0.1130* 0.1200* 0.1197* 0.1060* 0.1036* 0.0982* 0.0962* 0.0959* 0.0990* 0.0977*

complete simula3on

0.2845*

0.4668*

0.1385*

0.6053*

0.1102*

Table 4.35 Spectral transmittance, absorptance and reflectance of Hyp. 3a * The values as resulting from the simulations are considered lowly reliable

170

ρ

Table 4.36 Total transmittance, absorptance and reflectance of Hyp. 3a * The values as resulting from the simulations are considered lowly reliable


Chapter 4 - Optical performance analysis

In Chart 4.19 the repar33on of the incident radiant flux in total transmi4ance (τ) total reflectance (ρ) together with the rela3ve absorptance of the glassblock (αgb) and the rela3ve absorptance of the DSC (αdsc) are shown in respect of the energy conserva3on law and in dependance of the wavelength. 1,00

ďƐŽƌƉƚĂŶĐĞ͕ZĞŇĞĐƚĂŶĐĞ͕dƌĂŶƐŵŝƩĂŶĐĞ

0,90

ʏΎ

0,80 0,70 0,60

ʌΎ

0,50 0,40

ɲdsc*

0,30 0,20

ɲgb*

0,10 0,00

400

490

550

670

760

850

940

1030

1120

1210

1300

1400

ǁĂǀĞůĞŶŐƚŚ;ŶŵͿ Chart 4.19 Hyp. 4: spectral data * The values as resulting from the simulations are considered lowly reliable

The considera3ons made when analysing the hypothesis 3a are here s3ll valid, so again we had to subs3tute the DSC with a totally adsorbing film. For an exactly frontal light source not even the posi3on of the DSC inside the glassblock resulted relevant, so the “corrected” values correspond to the value found for Hyp. 3a and are showed in Table 4.31 and 4.32. Considering this configura3on of the device as triple glass with reference to UNI EN 410: g = 45,72 % 44 171


Chapter 4 -Optical performance analysis

Light transmittance - In Table 4.37 the values of transmi4ance (τ) absorptance (α) and reflectance (ρ) registered at 12 different wavelengths are shown by way of informa3on. The results of the complete simula3on, considering the combina3on of the weights assigned at each wavelength are shown in Table 4.38. λ (nm)

τ

α gb

α dsc

α TOT

ρ

430 450 470 510 530 550 570 600 630 650 690 720

0.0970* 0.1083* 0.1083* 0.0993* 0.0993* 0.1171* 0.1791* 0.2685* 0.3442* 0.3773* 0.4245* 0.4604*

0.7133* 0.7072* 0.7072* 0.7169* 0.7169* 0.6977* 0.6245* 0.5155* 0.4326* 0.3904* 0.3265* 0.2810*

0.0813* 0.0723* 0.0723* 0.0723* 0.0723* 0.0723* 0.0813* 0.0995* 0.1081* 0.1163* 0.1314* 0.1374*

0.7947* 0.7795* 0.7795* 0.7892* 0.7892* 0.7700* 0.7058* 0.6149* 0.5408* 0.5067* 0.4579* 0.4183*

0.1083* 0.1122* 0.1122* 0.1115* 0.1115* 0.1130* 0.1151* 0.1165* 0.1151* 0.1160* 0.1176* 0.1212*

complete simula3on

0.1593*

0.6469*

0.0824*

0.7294*

0.1113*

Table 4.37 Spectral transmittance, absorptance and reflectance of Hyp. 3a * The values as resulting from the simulations are considered lowly reliable

Table 4.38 Total transmittance, absorptance and reflectance of Hyp. 3a * The values as resulting from the simulations are considered lowly reliable

Shading coefficient - The shading coefficient calculated in accordance with UNI EN 410 gives as result: SC = 52,55 % The results of the simula3ons conducted with different radiant flux inclina3ons are omi4ed. 172


Chapter 4 - Optical performance analysis

4.5.5 Results: summary In Chart 4.20 the total transmi4ance of the hypotheses 1a and 2a in dependance of the incident angle of the radiant flux is shown. The lines converge to 0 when the angle between the incident radiant flux and the perpendicular to the plane surface of the glassblock reaches 90°. 0,35 0,30 0,25 0,23 0,2 0,20

1a

0,2 0 0,20 ,20 0,18 0,1

0,15

2a 0,14 0, , 0,13 0, 0 13 1

ʏ΀й΁

0,10

0,08 0,07 0, 0,0 7

0,05 0,00

30°

45°

60°

90°

Chart 4.20 Total transmittance of the hypotheses 1a and 2a in dependance of the incident angle

A summary of the results achieved in this chapter is shown in Table 4.39 and 4.40 (next page) including simula3on schemes used, and solar factor, light transmi4ance, shading coefficient and DSC absorptance calculated for Hyp. 1a, 2a, 3a, 4.

173


Chapter 4 -Optical performance analysis

Simula3on scheme

Solar factor g [%]

Light transmi4ance Shading coefficient DSC Absorptance τv SC [%] [%] [%]

Standard glassblock

73,41

76,85

84,38

-

Hyp. 1a

31,25

3,73

35,92

49,39

Hyp. 2a

31,24

3,64

35,91

49,37

Table 4.39 Summary table showing solar factor, light transmittance, shading coefficient and DSSC absorptance, calculated for a standard glassblock, Hyp. 1a, Hyp. 2a, according to the results of the simulations Simula3on Scheme

Solar factor g [%]

Light transmi4ance Shading coefficient DSC Absorptance τv SC [%] [%] [%]

Hyp. 3a

31,25

3,73

35,92

39,58

Hyp. 4

45,72

3,73

52,55

39,58

Table 4.40 Summary table showing solar factor, light transmittance, shading coefficient and DSC absorptance, calculated for Hyp. 3a and Hyp. 4, according to the values “corrected” with the new simulation schemes

174


Chapter 4 - Optical performance analysis

NOTES

1. The hypotheses were already presented in Chapter 3, together with the hypotheses 1-2-3 which remained excluded from the op3cal analysis for the reasons that will be further described.

2. Bochnicek, Z. (2007). Why can we see visible light? Physics Education, 42, 37-40. 3. UNI EN 410:2011 “Glass in building...” op. cit.

4. Op3CAD is a geometric ray-tracing program for the layout and analysis of three-dimensional op3cal systems in which path rays are calculated un3l the intensity of the ray falls below a preset threshold value.

5. For the descrip3on of transmi4ance, absorptance and reflectance cfr. Bass, M., & Mahayan, V. N. (2009). Handbook of optics (Third ed.): Mc-Graw Hill.

6. CIE Standard Illuminant D65 is a commonly-used standard illuminant defined by the Interna3onal Commission on

Illumina3on (CIE). D65 corresponds roughly to a midday sun in Western Europe / Northern Europe and it is also called a daylight illuminant.

7. The nonexistance of such omni-comprehensive model is stated by Wenger S. et al. in Wenger, S., Schmid, M., Rothenberger, G., Gentsch, A., Gratzel, M., & Schumacher, J. O. (2011). Coupled Optical and Electronic Modeling of Dye-Sensitized Solar Cells for Steady-State Parameter Extraction. J. Phys. Chem. C, 115, 10218–10229.

8. The transfer-matrix method is a general technique for solving problems in sta3s3cal mechanics. It is used when

the total system can be broken into a sequence of subsystems that interact only with adjacent subsystems. For more details see Born M., Wolf E., Principles of optics: electromagnetic theory of propagation, interference and diffraction

of light, 7th ed., Cambridge University Press: Cambridge, U.K., 1999. and Centurioni, in E. Appl. Opt., 2005, 44, pp. 7532–7539.

9. Effec3ve medium approxima3ons or effec3ve medium theory are physical models that describe the macroscopic proper3es of a medium based on the proper3es and the rela3ve frac3ons of its components. For more details see Bruggeman, D. A. G. (1935). Ann. Phys., 24, 636-664.

10. The Beer–Lambert–Bouguer law is an exponen3al law that relates the absorp3on of light to the proper3es of the material through which the light is travelling. It was already presented in Paragraph 4.1.2 Absorptance. 11. Wenger S., et al., “Coupled Optical and Electronic Modeling of Dye-Sensitized Solar Cells...” op. cit.

12. This conclusion is explicit in Wenger S., et al., “Coupled Optical and Electronic Modeling of Dye-Sensitized Solar Cells...” op. cit.

175


Chapter 4 -Optical performance analysis

13. Solaronix is a well-known DSC and DSC components supplier based in Switzerland.

14. In August 2010 a prototype module based on Sony "Concerto Effect" dye-mixing technology set a world record for a dye- sensi3zed solar cell by achieving energy conversion efficiency of 9.9%.

15. Ruthenium-based dye o$en considered as reference for the design of other dyes for DSC.

16. Yoon, S., Tak, S., Kim, J., Jun, Y., Kang, K., & Park, J. (2011). Application of transparent dye-sensitized solar cells to building integrated photovoltaic systems. Building and Environment, 46, 1899-1904. 17. Calogero G., et al., “Red Sicilian Orange...” op. cit.

18. Yoon S., et al., “Applica3on of transparent dye-sensi3zed solar cells...” op. cit.

19. Murray A., (2006). A Comparison of Acetonitriles, Technical Report, Romil Ltd., Cambridge, U.K.

20. Wenger S., et al., “Coupled Optical and Electronic Modeling of Dye-Sensitized Solar Cells...” op. cit.

21. www.refrac3veindex.info. The inbuilt research engine shows the refrac3ve index and other informa3ons (such as the absorp3on coefficient) by selec3ng a material and typing a specific wavelength.

22. The results of the simula3ons conducted on the 6mm float glass sheet were compared to the results obtained by Cappello D., Mannino P., in “Simulazioni dinamiche...” op.cit.

23. The results of the simula3ons conducted on the glassblock were compared to the results obtained by the SSV (Stazione Sperimentale del Vetro) for SEVES S.p.A.

24. The results of the simula3ons conducted on the DSC were compared to the results obtained by Wenger S., et al., “Coupled Optical and Electronic Modeling of Dye-Sensitized Solar Cells...” op. cit. 25. Cappello D., Mannino P., in “Simulazioni dinamiche...” op.cit.

26. www.electroyou.it

27. Cappello D., Mannino P., in “Simulazioni dinamiche...” op.cit.

28. A standard glass block was iden3fied in SEVES made “CLEAR Q19 SMOOTH TRANSPARENT”. 29. he = 23 W/m2K ; hi = 8 W/m2K ; ae1 = 0,1510 ; ae2 = 0,0950 ; K = 2,13 W/m2K.

30. The analysis conducted by the SSV (Stazione Sperimentale del Vetro) for SEVES S.p.A. on a CLEAR Q19 SMOOTH

TRANSPARENT type glassblock gave as result a solar factor g = 79,7%. The percentual points which are missing in our

simula3on are related to the solar energy beyond the 1400 nm limit which had to be excluded because of the lack of informa3ons in the op3cal behaviour of DSC systems over this range, as already explained.

176


Chapter 4 - Optical performance analysis

31. The analysis conducted by the SSV (Stazione Sperimentale del Vetro) for SEVES S.p.A. on a CLEAR Q19 SMOOTH TRANSPARENT type glassblock gave as result a light transmi4ance τV = 79,5%.

32. The so$ware showed results which were considered unrealible when dealing with thin films. An e-mail correspondence with the so$ware developers (reported in Attachment 3) showed that it is possible to obtain different result with the so$ware last release as confirmed by the developers.

33. Wenger S., et al., “Coupled Optical and Electronic Modeling of Dye-Sensitized Solar Cells...” op. cit.

34. Ruthenium-based dye well-known for its prominent thermal stability when combinated with other addi3ves.

35. Wenger S., et al., “Coupled Optical and Electronic Modeling of Dye-Sensitized Solar Cells...” op. cit. See the Experimental Section of the ar3cle for more details.

36. Wenger S., et al., “Coupled Optical and Electronic Modeling of Dye-Sensitized Solar Cells...” op. cit.

37. This approxima3on is based on the calcula3on of the ra3o between the area which is not covered by the ac3ve cells in respect of the total area of the module. The effects of the presence of a sealing material and of the coated glasses in the area not covered by the ac3ve cells are not taken into account.

38. The so$ware showed anomalous results for all the simula3ons on which the rays of the light source hit first an el-

ement with lower refrac3ve index and then an element with higher refrac3ve index (namely, simula3ons on Hyp. 3a

and 4). As reported from an e-mail correspondence with the so$ware developers (reported in Attachment 3): “[...] It does look like a bug. On rare occasions when a new feature is added a bug is created [...]”. 39. he = 23 W/m2K ; hi = 8 W/m2K ; ae1 = 0,1340 ; ae2 = 0,0522 ; K = 2,13 W/m2K. 40. he = 23 W/m2K ; hi = 8 W/m2K ; ae1 = 0,1362 ; ae2 = 0,0519 ; K = 2,13 W/m2K.

41. As will be further repeated, the total transmi4ance of the device is supposed not to change considerably in the

four hypotheses. In facts, considering the extent of the region hit by the rays of the light source when placed frontally, in the different hypotheses the only difference among the four is the order in which glass or cell are intercepted. This means that for an exactly frontal light source the total transmi4ance remains more or less the same for all the four hypotheses, because the order of the components in the assembly does not influence the total transparency. 42. As reported in the simula3ons on the Hyp. 1a, complete simula3on.

43. he = 23 W/m2K ; hi = 8 W/m2K ; ae1 = 0,1510 ; ae2 = 0,0522 ; K = 2,13 W/m2K.

44. he = 23 W/m2K ; hi = 8 W/m2K ; ae1 = 0,1510 ; ae2 = 0,3956 ; ae3 = 0,0522 ; K12 = 3,26 W/m2K ; K23 = 3,26 W/m2K.

177


Conclusions


Conclusions

Conclusions The analysis of the optical behaviour of the presented hypotheses put in evidence some potentialities and critical points in the integration of third generation photovoltaics into the glassblock, especially considering the application of this type of device in order to build photovoltaics glazed envelopes. First of all transparency, which is one of the features which make DSCs unique in comparison to other photovoltaic technologies, has been considerated as truly the main property making the integration worth. Unfortunately it was already showed how transparency and conversion efficiency are collateral one to the other, meaning the best conversion efficiencies are reached when the most of the light is adsorbed. Moreover the solar radiation spectrum includes the most of the solar energy just within the visible light range. This means as a consequence that cells which aim is to reach higher conversion efficiency inevitably have to cover the visible range, causing the drop in human eye perception of light. So we think the way of integration should head more to smart design in the shape of the cells, made by choosing appropriately the ratio between the covered and uncovered area by the active layers. Another alternative could be i.e. the study of a smart facade system, in which fullfilled or partially filled glassblocks are mixed together with clear glassblocks. In the hypotheses analysed the total light transmittance resulted stationary, since the order in which the components are assembled in the device does not particulary influence its behaviour in total in therms of total transparency. So this feature did not make any of the four alternatives really preferable to the others. What so became determinant is of course the conversion efficiency. Conversion efficiency was here considered as the second parameter in the assessment of the performance of the device, but somebody could actually consider it the first, since this parameter is directly related to the economical reliability. The growth in the photovoltaic market, especially in therms of research and innovations is, in fact, deeply linked to the capitals of the investors (public or private), which must have guarantees of profit for their investments in this technology. Thus, to be really competitive, the best conversion efficiency is enormously important. 181


Conclusions

Among the studied hypotheses, the best conversion efficiencies where shown by Hyp. 1a and Hyp. 2a (the adsorbed light in the range between 400 and 1400 nm was found respectively equal to 49,39 % and 49,37 %). Between the two, which efficiency is practically equal (in both cases the cell is positioned outside the glassblock) the Hyp. 2a is the best, because it provides a larger area for the deposition of the cells. Anyway the Hyp. 1a and 2a were already presented as the best in a previous thesis1, also because of the advantages related to easier assembly methods. On the other hand the Hyp.3a and 4 shall be considered as a second choice, because the positioning of the cell (whether complete or not) behind a glass -so not under direct solar radiation- causes significant losses in therms of light that is absorbed and converted by the cell itself. From the optical point of view these losses can be quantified around the 10% and are due to additional reflection and absorption of the glassblock shell which results interposed between the cell and the sun light. Anyway particular considerations can be made upon Hyp.4 because of its increased thermal insulation properties compared to the others. This special feature could result determinant in the balance between energy producted by the DSC integrated modules and the saving in energy consumption related to air-conditioning (heating and cooling). Further studies in this thesis laboratory should consider the possibility of experimental analysis on a built device in order to study its actual behaviour. For what concerns the software simulations, a step forward could be the analysis of the DSC considering the constituent layers separated one from the other, and the investigation of the excluded hypotheses 1, 2 ,3. Moreover a study of the electrical connections for the creation of DSC solar panels has to be taken, together with strategies for improve protection of the device from the weather. The creation of the patents database revealed fundamental importance in this work. It constituted not only the base for the studies here conducted but it represents a contribute for the knowledge and the information in the emerging field of dye-sensitized solar cells. It will also represent a good starting point for further studies. 1

Morini M., “Involucri edilizi sostenibili: Integrazione di celle solari...” op.cit.

182


APPENDIX A

Excerpt of the patents database


Appendix A - Excerpt of the patents database

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Appendix A - Excerpt of the patents database

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Appendix A - Excerpt of the patents database

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KJFH@AJ+CH]H

K-CJ+KJF-CH KHBJ]-CJ+C-S@EAJCH

197


Appendix A - Excerpt of the patents database

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Appendix A - Excerpt of the patents database

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Q)IR1S/(/-T/I/J)-NOMP )RK)-IR1KG)-NOMP S)D/Q/IR1-J/1LR1-NOMP IUG1TUE/-J/S/QUS1-NOMP 1(/DULR1-Q)IR1K)E1-NOMP IR11K)-)I/TU-NOMP IUG1Q/T/-R1FH)-NOMP R)E1S/(/-Q/IU)-NOMP J)Q)I/(/-IR1K1LR1-NOMP

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%+#!$#%!!&

**#!&#%!!'

()%!!'!%*,!&-./*0

I7BAB89-C5235>?9?58-:54-;<7= >78>?9?@7;->5AB4-C7AA

JREHH-D)KF-L)-\JF-NOMP S/(/1-J)IR1)-NOMP S1IR1-S/JIUR1S)-NOMP

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%$#!$#%!!&

%'#!&#%!!,

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HA7C945;7->Z]>94B97X-3W5957A7C94?CC58674>?58-7A72789X-B8;-;<7= >78>?9?@7;->5AB4-C7AA

YUO1SUE/-\JF

T/JIU1-R1E)IR1 )S/F/-SHK1LR1 S/(/IR1T/-J/SUQ/ H^UEH-JHJIUQ/ J/K/DH-K)DU)

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199


APPENDIX B

List of the applicants


Appendix B - List of the applicants

3M Innovative Properties Co.

[US]

Choi Hong Duck

[KR]

Academia Sinica

[TW]

Citizen Holdings Co. Ltd.

[JP]

Adeka Corp.

[JP]

CTCI Foundation

[TW]

Advance Design Technology Inc.

[TW]

Daegu Gyeongbuk Inst. Science

[KR]

Agency Industrial Science Technology

[JP]

Dai Ichi Kogyo Seiyaku Co. Ltd.

[JP]

Aisin Seiki

[JP]

Daikin Industrial Ltd.

[JP]

Ajou University Industrial Academie Coop. Found.

[KR]

Daimler Chrysler Ag.

[DE]

Amao Yutaka

[JP]

Dainippon Printing Co. Ltd.

[JP]

Applied Carbon Nono Technology

[KR]

Dalian Chemical Physics Inst.

[CN]

Araume Kazuma

[JP]

Dc Solar Corp.

[TW]

Aruze Corp.

[JP]

Dms Co. Ltd.

[KR]

Asahi Glass Co. Ltd.

[JP]

Do Corp. Ltd.

[KR]

Aurotek Corp.

[TW]

Dongfang Electric Group Dongfa

[CN]

Basf

[DE]

Dongil Engineering Consulants Co. Ltd.

[KR]

Beijing Inst. Technology

[CN]

Dongjin Semichem Co. Ltd.

[KR]

Bexel Corp.

[KR]

Doshisha

[JP]

Bridgestone Corp.

[JP]

Dow Corning Toray Co. Ltd.

[JP]

Brother Industrial Ltd.

[JP]

Dye Sensitized Solar Cell

[US]

Byd Co. Ltd.

[CN]

Eagon Windows & Doors Co. Ltd.

[KR]

Canon

[JP]

Eastman Kodak Co.

[US]

Casio Computer Co. Ltd.

[JP]

Ecole Polytechnique Federale De Lausanne (Epfl)

[CH]

Central Glass Co. Ltd.

[JP]

Elachem Co. Ltd.

[KR]

Cera Co. Ltd.

[KR]

Electric Power Dev. Co.

[JP]

Chang Ho

[TW]

Electronics and Telecomunication

[KR]

Changchun Applied Chemistry

[CN]

Emerging Display Technologies Corp.

[TW]

Chem. Well. Tech. Co. Ltd.

[KR]

ENN Technologies Co. Ltd.

[CN]

Chery Automobile Co. Ltd.

[CN]

Enplas Corp.

[JP]

Chicago State University

[US]

Erekuseru

[JP]

China Lucky Film Group Corp.

[CN]

Eternal Chemical Co. Ltd.

[CN]

Chinese Academie

[CN]

Eun Sung Co. Ltd.

[KR]

Chisso Corp.

[JP]

Everlight Chem. Industrial Corp.

[TW]

203


Appendix B - List of the applicants

FC Micro Electronics Co. Ltd.

[KR]

Institute of Research & Innovation

[JP]

FDK Corp.

[JP]

Institute of Science & Tech. Kwangju

[KR]

Flypower Internat. Co. Ltd.

[TW]

Internat Semiconductor Technology Ltd.

[TW]

Fuji Photo Film Co. Ltd.

[JP]

IPB

[JP]

Fujifilm Corp.

[JP]

Iricd Group Elecrtronics Comp.

[CN]

Fujikura Ltd.

[JP]

Irico Group

[CN]

Fujimori Kogyo Co.

[JP]

ITM Power [Gb]

[UK]

Furukawa Electric Co. Ltd.

[JP]

IUCF Hyu

[KR]

General Electric Company

[US]

Japan Carlit Co. Ltd.

[JP]

General Electric Company

[US]

Japan Science & Tech. Corp.

[JP]

Gunze

[JP]

Japan Vilene Co. Ltd.

[JP]

Han Kyu Sung

[KR]

Jinex Corp. Ltd.

[TW]

Hayashi Engineering Inc.

[JP]

JSR Corp.

[JP]

Hitachi Ltd.

[JP]

Jung On Yu

[KR]

Hodogaya Chemical Co. Ltd.

[JP]

Kabushiki Kaisha Toshiba

[US]

Hon Hai Prec. Industry Co. Ltd.

[JP]

Kaneko Masaharu

[JP]

Hongfujin Prec. Industry

[CN]

Kangnung National University

[KR]

Hsiuping Inst. Technology

[TW]

Kansai Pipe Kogyo

[JP]

Hydis Tech. Co. Ltd.

[KR]

Kim Hwan Kyu

[KR]

Hyogo Prefecture

[JP]

Kim Sun Jae , Lee Hee Gyun

[KR]

Hyundai Motor Co. Ltd.

[KR]

Kitamura Hiroshi

[JP]

Ind Academic Coop.

[KR]

KNT Science

[JP]

Industrial Technology Research Institute

[CN]

Koa Corp.

[JP]

Industry Foundation of Chonnam National University

[US]

Koga Kazuki

[JP]

Iner Aec Executive Yuan

[TW]

Koito MFG Co. Ltd.

[JP]

Inha Industrial Partnership Inst.

[KR]

Kolon Inc.

[KR]

Inst. Nagoya Industrial Science Res.

[JP]

Konica Minolta Holdings Inc.

[JP]

Inst. National Colleges Tech. Japan

[JP]

Korea Advanced Inst. Sci. & Tech.

[KR]

Institute of Biophotochemonics Co. Ltd.

[JP]

Korea Electro Tech. Res. Inst.

[KR]

Institute of Nuclear Energy Research

[US]

Korea Electronics Telecommunications

[KR]

Institute of Plasma Physics Cas.

[CN]

Korea Industrial Tech. Inst.

[KR]

204


Appendix B - List of the applicants

Korea Inst. Ceramic Eng & Tech.

[KR]

National University Yunlin Sci. & Tech.

[TW]

Korea Inst. Sci. & Tech.

[KR]

Ngk Spark Plug Co.

[JP]

Korea Institute of Energy Research

[KR]

Nichiban

[JP]

Kyocera Corp.

[JP]

Ningbo Inst. Mat. Tech. & Eng. Cas.

[CN]

Kyodo Printing Co. Ltd.

[JP]

Nippon Aerosil Co. Ltd.

[JP]

Kyungpook National University Industrial Academie

[KR]

Nippon Catalytic Chem. Ind.

[JP]

Kyungsung University Industry Cooperation Foundation

[KR]

Nippon Electric Glass Co.

[JP]

Kyushu Inst. of Technology

[JP]

Nippon Kayaku

[JP]

Lee Jun

[KR]

Nippon Oil Corp.

[JP]

Lee Yun Je

[KR]

Nippon Steel Chemical Co.

[JP]

Lg Display Co. Ltd.

[JP]

Nissan Chemical Industrial Ltd.

[JP]

Lin Chong-Ren

[TW]

Nissha Printing

[JP]

Manac Inc.

[JP]

Nisshin Steel Co. Ltd.

[JP]

Matsushita Electric Works Ltd.

[JP]

Nissin Electric Co. Ltd.

[JP]

Mazda Motor

[JP]

Nitto Denko Corp.

[JP]

Meidensha Electric Mfg Co. Ltd.

[JP]

Nlab Solar Ab

[SE]

Metal Industrial Res. & Dev. Ct

[TW]

Nof Corp.

[JP]

Minghsin University of Science and Technology

[TW]

Nok Corp.

[JP]

Mitsubishi Electric Corp.

[JP]

Oike Kogyo

[JP]

Mitsui Du Pont Polychemical

[JP]

Oki Electric Industrial Co. Ltd.

[JP]

Miwoo Industrial Co. Ltd.

[KR]

Optrex

[JP]

Mjsmart Technology

[KR]

Panasonic Corp.

[JP]

MST Korea

[KR]

Paru Co. Ltd.

[KR]

National Inst. For Materials Science

[JP]

Peccell Technologies Inc

[JP]

National Inst. of Adv Industrial & Technol

[JP]

Phoenix Materials Co. Ltd.

[KR]

National Inst. of Advance Industrial Science

[JP]

Pioneer Corp.

[JP]

National Taipei University of Technology

[TW]

Plasmag Technology Inc.

[CN]

National University Chonbuk Industrial Coop. Found.

[KR]

Polymers Crc Ltd.

[AU]

National University Chonnam Industrial Found.

[KR]

Posco

[KR]

National University Taipei Technology

[TW]

Prodisc Technology Inc.

[TW]

National University Tsinghua

[TW]

Pusan National University Industrial Coop. Found.

[KR]

205


Appendix B - List of the applicants

Rainbow Group Company

[CN]

SPD Lab. Inc.

[JP]

Rich Power Technologies Ltd.

[TW]

Stichting Energie

[NL]

Rihui Zeng

[CN]

Sumitomo Chemical Co.

[JP]

Sambomotors Co. Ltd.

[KR]

Taiwan Textile Res. Inst.

[TW]

Samsung Electronics Co. Ltd.

[JP]

Taiyo Yuden

[JP]

Sanyo Electric Co.

[JP]

Tatsumo

[JP]

Seiko Epson Corp.

[JP]

Tdk Corp.

[JP]

Sekisui Chemical Co. Ltd.

[JP]

Teijin Dupont Films Japan Ltd.

[JP]

Seoul National University Industrial Foundation

[KR]

Teijin Dupont Films Japan Ltd.

[JP]

SFC Co. Ltd.

[KR]

Tera Korea Co. Ltd.

[KR]

Shanghai Inst. Ceramics

[CN]

Tg Energy Inc.

[KR]

Shanghai Inst. Tech. Physics

[CN]

Three Bond Co. Ltd.

[JP]

Shanghai Lianfu New Energy Technology Co. Ltd.

[CN]

Tianjin Lishen Battery

[CN]

Shanghai Toyou Digital Tech. Co. Ltd.

[CN]

Timo Technology Co. Ltd.

[KR]

Sharp

[JP]

Toda Kogyo Corp.

[JP]

Sharp Kabushiki Kaisha

[US]

Tokai Rubber Industrial Ltd.

[JP]

Shimane Prefecture

[JP]

Tokyo Inst. Tech.

[JP]

Shimizu Norio

[JP]

Tomiyama Pure Chemical Industrial Ltd.

[JP]

Shinetsu Chemical Co

[JP]

Tomoegawa Paper Co. Ltd.

[JP]

Shinko Electric Industrial Co

[JP]

Toppan Printing Co. Ltd.

[JP]

Shinonzu

[JP]

Toray Industries

[JP]

Showa Denko

[JP]

Toshiba Corp.

[JP]

SI N G Co. Ltd.

[KR]

Toyo Seikan Kaisha Ltd.

[JP]

SK Energy Co. Ltd.

[KR]

Toyota Central Res. & Dev.

[JP]

SNT Co.

[JP]

Tripod Technology Corp.

[JP]

SNU Foundation

[KR]

Uchida Satoshi

[JP]

Soken Kagaku

[JP]

Ulvac Inc.

[JP]

Solaris Nanosciences Inc.

[US]

Unist. Academy Industry Res. Corp.

[KR]

Solchem Co. Ltd.

[KR]

University of Beijing

[CN]

Son Sung Cheul, Lee Jae Hyun

[KR]

University of Braunschweig Tech.

[DE]

Sony Corp.

[JP]

University of Chungju National Industrial Academie Coop. [KR]

206


Appendix B - List of the applicants

University of Dalian Fisheries

[CN]

University of Sejong Industrial Academie Coop. Gr .

[KR]

University of Dalian Tech

[CN]

University of Seoul Industry Coop. Found.

[KR]

University of Donghua

[CN]

University of Shanghai

[CN]

University of East China Normal

[CN]

University of Shinshu

[JP]

University of Electro Communications

[JP]

University of Shu Te

[TW]

University of Electronic Science & Tech

[CN]

University of Sogang Industrial University Coop. Found.

[KR]

University of Fuzhou

[CN]

University of Soongsil Res. Consortium

[KR]

University of Gifu

[JP]

University of South China Tech.

[CN]

University of Guangdong Technology

[CN]

University of Southeast

[CN]

University of Guilin Tech.

[CN]

University of Southern California

[US]

University of Gunma

[JP]

University of Sungkyunkwan Found.

[KR]

University of Hebei Technology

[CN]

University of Suzhou

[CN]

University of Hefei Technology

[CN]

University of Tianjin

[CN]

University of Huaqiao

[CN]

University of Tokyo

[JP]

University of Huazhong Science Tech

[CN]

University of Tsinghua

[CN]

University of Industrial & Academie Collaboration

[KR]

University of Washington

[US]

University of Inje Industrial Academie Cooperation

[KR]

University of Wuhan

[CN]

University of Jiaotong Southwest

[CN]

University of Xi An Jiaotong

[CN]

University of Jinan

[CN]

University of Xiangtan

[CN]

University of Kagawa

[JP]

University of Yeungnam IACF

[KR]

University of Konkuk Industrial Coop. Corp.

[KR]

University of Yonsei IACF

[KR]

University of Kookmin Industrial Academie Coop.

[KR]

Ushio Electric Inc.

[JP]

University of Korea Industrial & Academie Coop.

[KR]

Wang Yu

[CN]

University of Kyoto

[JP]

Woongjin Chemical Co. Ltd.

[KR]

University of Kyung Hee University Industrial Coop.

[KR]

Yamaguchi Prefecture

[JP]

University of Nanjing

[CN]

Yang Ru-Yuan

[TW]

University of Nankai

[CN]

Yokohama Rubber Co. Ltd.

[JP]

University of Niigata

[JP]

Yoshida Masahiko

[JP]

University of Osaka

[JP]

Yoshino Katsumi

[JP]

University of Osaka

[JP]

Yuen Foong Yu Paper Co. Ltd.

[TW]

University of Qingdao Science & Tech.

[CN]

Zichen Zhao

[CN]

207


ATTACHMENT 1

Analysis on “CLEAR Q19 SMOOTH TRANSPARENT” by SSV for Seves


Attachment 1 - Analysis on “CLEAR Q19 SMOOTH TRANSPARENT” by SSV

211


Attachment 1 - Analysis on “CLEAR Q19 SMOOTH TRANSPARENT” by SSV

212


ATTACHMENT 2

Verbal of the competition â&#x20AC;&#x153;For the design of a device that employs energy production technology based on photovoltaic materials made from organic materialsâ&#x20AC;?


Attachment 2 - Verbal of the competition

Downloadable at: http://www.unirc.it/documentazione/media/ďŹ les/comunicazione/Articoli/2012/120608_concorso_ecologico/dispositivo/Verbale_concorso_dispositivo.pdf

215


Attachment 2 - Verbal of the competition

Downloadable at: http://www.unirc.it/documentazione/media/ďŹ les/comunicazione/Articoli/2012/120608_concorso_ecologico/dispositivo/Verbale_concorso_dispositivo.pdf

216


Attachment 2 - Verbal of the competition

Downloadable at: http://www.unirc.it/documentazione/media/ďŹ les/comunicazione/Articoli/2012/120608_concorso_ecologico/dispositivo/Verbale_concorso_dispositivo.pdf

217


ATTACHMENT 3

Email correspondence with the OptiCAD software developers


Attachment 3 - Email correspondence with the OptiCAD software developers

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DSC INTEGRATED GLASSBLOCKS  

SUSTAINABLE BUILDING ENVELOPES: DSC INTEGRATED GLASSBLOCKS. PERFORMANCE ANALYSIS / INVOLUCRI EDILIZI SOSTENIBILI: INTEGRAZIONE DI CELLE SOLA...

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