High power, commercial Silicon-FilmTM solar cells

Silicon-Film^TM wafers are cut from continuous sheets of solar cell quality silicon grown on low cost substrates. The original Silicon-Film^TM solar cells, the AP-225, were squares cut 15.4 cm on a side for an area of 236 cm². The 15.4 cm dimension was the largest width that could be cut from the sheet while maintaining reasonable uniformity. Improvements in process control provided the opportunity to cut wafers that are 17.8 cm on a side for an area of 316 cm². This larger area has led to a new solar cell, the AP-300, with a power of 3.5 W. This power is the highest available for any commercial polycrystalline silicon solar cell. Increased power, while maintaining the cost of handling a single unit, results in enhanced value in the final product. A unique gettering process that utilizes a front surface aluminum layer has been developed to enhance solar cell performance. Prior to the work presented here, this process had achieved a 2.82 W solar cell for an area of 239 cm². Present process development and optimization efforts are concentrated on fine-tuning the silicon growth process and improving post-growth processing techniques. Post-growth improvement of minority carrier lifetime is accomplished through external gettering and bulk defect passivation techniques. This paper presents the solar cell process development that led to the demonstration of a 3.5 W large area AP-300 solar cell