Photos: KLA-Tencor Corporation
Industry & Suppliers
KLA-Tencor’s ICOS PVI-6 inspection modules provide high speed, automated, optical inline inspection of monocrystalline and polycrystalline solar wafers and cells.
Take control Process control: Important tools to reduce the balance of system costs in PV manufacturing are the use of advanced optical defect inspection systems and surface metrology systems, in combination with a comprehensive process control methodology, explains Pieter Vandewalle of KLATencor Corporation.
Government incentives are not sustainable in the long run, because they are subject to policy shifts that can potentially cause disruptions in the deployment process. Therefore the PV industry must drive down the overall cost of solar energy deployment. Key factors to reduce the balance of system costs in PV manufacturing include the use of technologies and processes enabling the production of high-efficiency cells; a much higher degree of automation; comprehensive tightly-integrated process control; and high-volume yield improvements. The average price per kilowatt-hour of electricity from traditional generation is projected to continue to rise over the next decade, while the price for solar generated electricity is projected to fall significantly. As the curves approach convergence, “grid parity” will be achieved, with timeframes varying by region. Solar cell manufacturers need to lay the foundation today in order to respond to the impending upswing in market demand over the next few years. Deployment of comprehensive process control methodologies will be a key enabling factor not only in manufacturers’ ability to profitably meet the solar energy industry’s need for high volumes and consistent quality at ever-lower prices, but also to enable production of higherefficiency cells. Increasing productivity through improvements to manufacturing processes that result in greater yields is a key contributor to lower costs. Experience has shown that for every onepercent increase in yield, there is a corresponding five-percent cost reduction. The ability to drive up production volumes while maintaining quality will lead directly to a lower cost per device. For example, doubling the production output will typically result in a 22 percent decrease in the overall unit cost.
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Evidence from research at leading laboratories and academic institutions indicate that there are a range of significant opportunities for improving the manufacturing processes used in solar cell production. However, the advanced lab-proven techniques that enable greater efficiencies have not yet been implemented on a widespread basis in real-world production environments. Other improvements in manufacturing technologies, such as reducing wafer thickness or Kerf loss during sawing processes, result in efficiency gains that offer significant cost reduction. For example, a one-percent improvement in efficiency can deliver up to ten-percent cell manufacturing cost savings. In addition, a 20 micron (μ) reduction in wafer thickness (from 200μ to 180μ) can provide a seven-percent cost saving. It can be expected that significant cost reductions can be achieved by deploying comprehensive process control solutions within volume production photovoltaic manufacturing environments to leverage the disciplines and methods that have already been modeled in the labs. Process control modeling initiatives at institutions such as University of Maine, University of South Florida, Georgia Tech, Stuttgart University and Stanford, as well as corporate labs such as the laboratories of Boeing, RCA, Sharp and United Solar, have demonstrated the ability to achieve dramatically higher yields and efficiencies.
Deploying process control Bare Wafer Test: Wafers come into the line (upper left in the graphic on page 85) and undergo dimensional measurement and checks for thickness variation, surface defects, microcracks, saw marks, chipping, etc. Texture inspection: Wafers are weighed and reflectivity is checked offline. Sheet resistance is measured and offline sam-
06 / 2011 | www.pv-magazine.com