Abdelilah SLAOUI by L'ambassade de France en Israël

Silicon Thin Film Solar Cells: Potential & Challenges" Abdelilah SLAOUI Institut d’Electronique du Solide et des Systèmes InESS CNRS – Univ. Strasbourg Strasbourg, France Costel-Sorin.Cojocaru@polytechnique.edu ECOLE

POLYTECHNIQUE

Pere Roca i Caboroccas

LPICM UMR 7647

InESS (PHASE) active in PV Since 1975 …

… more than 300 publications

Photovoltaic research at InESS 1) High efficiency cells on mc-Si & ribbons (< 100Âľm)

2) TF-Si cells on foreign substrates contact

contact base

emetteur

substrat

InESS

3) Advanced concepts (QDs, plasmonics , RE-TCOs)

4) Polymer based organic cells (+LIPHT) QD cell 2 : Eg=2 eV

QD cell 1 : Eg=1.5 eV

Bulk Si : Eg=1.1 eV

Outline 

Thin Film Solar Cells Market



Silicon thin film technologies:  Polymorphous Si/µc-Si  Polycrystalline Si * Direct deposition approach * Seed layer approach  Si nanostructures (Si-NWs, Si-nps)

Photovoltaic Techn.in 2009: Market shares

• Progress in PV modules production • Si wafer based PV modules still dominant: 84% in 2009 • Schipments of TFs ~14% in 2008 & 16% in 2009 Source: Paula Mints, Navigant Consulting

Learning Curve for PV modules Historical and Projected Experience Curve for PV Modules

Source: GreenTech/Prometheus

TF Silicon based Modules

a-Si, amorphous,

Âľc-Si, microcrystalline,

polymorphous

TF c-Si Crystalline

polycrystalline

From Amorphous to Polymorphous Si Hydrogenated amorphous Silicon (a-Si:H) at Ts < 250°C - Most widely-used deposition method – PECVD - Strong degradation of efficiency  unstable Si-H bonding Layers deposited from SiHx radicals H2

RF electrode

SiH4 GeH4 PH3 TMB

Costel-Sorin.Cojocaru@polytechnique.edu ECOLE

POLYTECHNIQUE

Plasma

Pumping

Substrate Low Ts ~ 200 °C Scale up demonstrated LPICM UMR 7647

From Amorphous to Polymorphous Si Plasma-formed nanocrystals/clusters contribute to deposition ď&#x192;¨ polymorphous silicon(pm-Si:H) Nanostructured material Silicon nanocrystals in an amorphous matrix

4 nm 100 cm2 mini-module

Medium Range Order Improved transport properties and stability Costel-Sorin.Cojocaru@polytechnique.edu ECOLE

POLYTECHNIQUE

LPICM UMR 7647

Towards Micromorph Si solar cells µc-Si:H PIN solar cells 1,0

pm-Si:H

µc-Si

Réponse Spectrale

0,9

LitD4_C

0,8 0,7 0,6 0,5 0,4 0,3

Jsc = 24.5 mA/cm2

0,2 0,1 0,0

400

500

600

700

800

900

1000

Longueur d'onde (nm)

Potential micromorph η =15% Costel-Sorin.Cojocaru@polytechnique.edu ECOLE

POLYTECHNIQUE

Voc

Jsc

η(%)

67.3

0.520 V

24.5 mA/cm2

8.6% LPICM UMR 7647

From polymorphous to Crystalline-Si -Growth from nanocrystals leading to unusually large crystalline domains - Manifests as epitaxy or very-large grain fraction

Si Si

Towards high efficiency solar cells through Low Pressure Plasma Processes E.V. Johnson et.al. Appl. Phys. Lett. 92 (2008) 103108 Costel-Sorin.Cojocaru@polytechnique.edu ECOLE

POLYTECHNIQUE

LPICM UMR 7647

t LT a lm i f i -S c k ic h t m ~1 Âľ

c-Si transferred onto a PI film (or on a metal foil) Costel-Sorin.Cojocaru@polytechnique.edu ECOLE

POLYTECHNIQUE

LPICM UMR 7647

Outline 

Thin Film Solar Cells Market



Silicon thin film technologies:  Polymorphous Si  Polycrystalline Si * Direct deposition approach * Seed layer approach  Si nanostructures (Si-NWs, Si-QDs)

TF- Crystalline Si solar cells ? Potential:  2-3 µm Si to reach reasonable efficiency  Similar technology than bulk Si  No hazardous nor rare elements

Challenges Fast deposition/formation High quality material (Leff >> W) Good surface passivation Efficient light confinment

F. Llopis, I. Tobıas, SOLMAT 87, (2005), pp.481-492.

Polycrystalline Si by Direct CVD • HT-CVD at T>900°C • HT substrates : Alumina, SiSiC, SiN, mullite • High Dep. Rate ~1-5µm/min

15s

120s

10µm

30 sec

60 sec

180 sec

Polycrystalline Si by Diect CVD pp+-Si//Fox/ADS09 CVD @1200°C

1 2

• small grains  large density of GBs  many defects • large distribution  depletion of grains • Preferentiel grains orientation  (110) Enlarging grains  CVD-OVL, seed layer approach Neutralizing defects  TREBLE, hydrogenation A. Slaoui, et al., SOLMAT, 71/2, 245 (2001)

Polycrystalline Si by CVD-OLL CVD-OLL  Si deposition on Flowable oxides (DC)  increased adatom mobility  reduce nucleation density

Bare mullite

Mullite + PSG A.Focsa, A. Slaoui et al., Renewable Energy 33 (2008) 267–272 EU-LATECS project: IMEC, Dow-Corning, FhgISE, InESS

Mullite + BSG

Polycrystalline Si: Seed Layer Approach VPE / SPE Si Absorbing layer Si Seed layer

substrate

Aluminium induced Crys. Zone (lamps) melting induced Rx Laser induced Crys. BS Glass, Ceramics Glass, HT Glass Alumina, Mullite, SiSiC, Metal foils contact

contact

base

emetteur

Si < 2µm substrat

Polycrystalline Si by AIC Aluminum Induced Crystalization of a-Si before anneal

anneal 5min / 500°C

anneal 10min / 500°C

anneal 60min / 500°C

Source: Nast et al. E. Pihan , A. Slaoui, Thin Solid Films 511 – 512 (2006) 15 – 20

Poly-Si by AIC vs substrate Fox/Mullit e

Fox/Alumin a

thSiO2

Glass

Fox/Silic on

500°C

475°C

100 450°C

crystallized fraction (%)

AIC poly-Si layer on glass-ceramic substrate

50 µm E. Pihan et A. Slaoui., J. Crystal Growth 305, 2007, pp. 88-98

Growth Kinetics

0 0

100

150 200 250 annealing time (min)

300

350

Polycrystalline Si by AIC on Glass Ceramics 475°C/3h

EBSD analysis: grains size & grains orientation

Defect analysis using EBSD Technique

black lines→high angle red lines → Σ3 twin green lines → Σ9 twin ANR project - Polysiverre: InESS, Corning, TOTAL, AET, LPICM, INL, EMSE

Polycrystalline Si by AIC on Metal Foils

• Metal (FeNi) as a back contact • development of a conducting barrier layer against metallic imp.

CSL boundaries

P. Pathi/A. Slaoui., Applied Physics A, 97 (2009) 45. A. Pathi/A. Slaoui, 24th European PVSEC 2009, 2533.

ANR project - CRISILAL: CEA, InESS, ArcelorMital, AnealSys

Polycrystalline Si solar cells by AIC Homojunction - Mesa Base contact Emitter contacts

Heterojunction - IDC Emitter contacts Base contacts ITO

SiNx Emitter (n+)

a-Si

Absorber layer (p) Absorber layer (p / n)

BSF layer (p+) AIC layer (p+)

AIC layer (p+ / n+)

substrate

Emitter n+

Ln Lcol

• large charge collection  high Isc • large SCR  low Voc

AIC + epi-CVD (2.1µm) Voc ~ 450-530 mV Efficiency ~ 8 – 10% Limited by intragrains defects • Higher Voc • Lower series resistance

O. Tuzun , A. Slaoui et al. , 23 EUPVSEC SOLMAT 2010, in press

Polycrystalline Si by LIC Laser Induced Crystalization of a-Si anneal

445nm 110nmSi Silayer layer

experiments Epi-layer r by LIC e y la d e e S strate Glass sub

EU project -HIGH-Ef: IPJ, Horiba, CSG, Bookam, EMPA, InESS ANR project -SiLaSol: InESS, ArcelorMital, CEA, Excico, IREPA-laser

Polycrystalline Si by ZMR Current density [mA/cm²]

Si by CVD + Zone Melting recrystallization 30

pc-Si on mullite substrate Ellipsoidal reflector

after ZMR

CCD-camera

Linear halogen lamp

Sample

no ZMR

Ar, O2

Elongated grains Size: 1-20 mm S. Bourdais, S. Reber, A. Slaoui, 16th EU-PVSEC, (Glasgow, Ecosse, 2000) p. 1492

Array of halogen lamps

0 0,0

0,1

0,2

0,3

0,4

0,5

0,6

Voltage (V)

11,5% with 10 µm Si 15,4% with 20 µm Si

EU project -COMPOSIT: ISE, IMEC, InESS, RWE EU project-POLYSIMODE: IMEC, InESS, CSG, Helmoltz, ISE

Silicon based nanostructures solar cells Nanostructured Silicon: * SiNWs: light trapping * Si-nps: photon energy shifter (DC ?) * Si-nps: New wide BG absorbing Si (tandem)

Si nanostructure tandem cell

Vertical SiNWs Step 4: complete i-n layers on top i-layer

n-layer

Eg1

p-type

p-type SiNW

Glass or flexible sub

Eg2 SnO2

Strong light trapping Radial junction

Eg3

Eg=2eV

Si-nps

Eg=1,5eV

Si-nps

c-Si

Eg1> Eg2> Eg3 A. Slaoui, R.T. Collins, MRS Bulletin V32 (2007) N째3

Eg=1,1eV

Vertical Si–NWs based solar cells One pump down “all-in-situ” fabrication of SiNWs on TCO substrates Nano-scaled In or Sn drops produced on ITO or SnO2 by H2 plasma superficial reduction at 200oC~350oC. H+

SnO2 or ITO Cg (a) SiHx Diffusion of Si in catalyst drops

Dissolve & absorption Deposition interface

Sn or In drops <1 10>

H+

(b)

SiHx (or SiHx +H+)

(c)

a-Si

(c)

(a)

(b)

P.-J. Alet, P. Roca i- Cabaroccas et. al. Journal of Materials Chemistry 18 (2008) 5187 Costel-Sorin.Cojocaru@polytechnique.edu ECOLE

POLYTECHNIQUE

LPICM UMR 7647

Vertical Si–NWs based solar cells World record efficiency for a bottom up Silicon Wire Radial Junction Solar cell

Challenges - Control catalyst size - Density, position - Transport, doping,… Costel-Sorin.Cojocaru@polytechnique.edu ECOLE

POLYTECHNIQUE

LPICM UMR 7647

Silicon nanostructure wide Eg material

Energy PL (eV)

â&#x20AC;˘ Engineer a wider band gap material using Si nanostructures â&#x20AC;˘ Si QDs-relaxed size constraint cf QW, for given a quantum confinement

Si Nanoparticules size (nm)

Si nanostructure tandem cells MW-PECVD : NH3 + SiH4ď&#x192;¨ Si rich SiNx:H (Si-RSN) * Single layer anneal

20 nm

* Multilayers anneal

Delachat, Carrada, Slaoui; Nanotechnology 20 (2009) 415608_1-5 Keita, Delachat, Slaoui, J. Appl. Phys. 107 (2010) 093516

Si nanostructure tandem cells Bandgap value depends on SiNx thickness and on Si excess in SiNx BG 1 nm 3 nm

29% -

33% -

37% -

44% ? 1,85

50% ? 2,05

4 nm

2,05

5 nm

1,37

Si-nps

c-Si

• Potential : Efficiency ~35% • Chalenges: * Tunneling distance between layers & QDs * Doping * Extraction of carriers * Cost

The Future of TF-Si based PV Technologies • Better Control and rational use of materials - Better plasma control - Gas recycling - Faster high-quality TCO’s - Higher deposition/crystallization rates • New materials - Si-nanowires / Si-nanops - p-type TCO’s - Printable TCO’s - Nanocrystalline diamond, SiC

Long Term Objectives: -Concepts for stable cells with η >17% Costs <0.4 Euros/Wp at 500 MW, η = 15% (rigid) < 0.3 Euros/Wp at 500MW, η = 13% (flexible)

• Better light management - Improved TCO’s ( Lower IR absorption = lower N; Textured) - Random texture (texture glass; back reflector) - Periodic Structures (Grating, photonic crystals, plasmonics) - Conversion spectrum

Acknowledgements

From InESS/Strasbourg: C. Chatterjee; A. Chowdhury; F. Delachat; A. Focsa; P. Prathap; S. Roques, O. Tuzun; … ANR–HABISOL projects: CRISILAL, POLYSIVERRE, SILASOL EU Projects: LATECS, CRYSTALCLEAR; HIGH EF, POLYSIMODE From LPICM/Ecole Polytechnique/Palaiseau: P. Roca i-Cabarocas

Bilateral Conference on Energy

9 â&#x20AC;&#x201C; 13 May 2011; Nice / France

http://www.emrs-strasbourg.com/

Bilateral Conference on Energy Symposia: