High Power, Commercial Silicon-Film(TM) 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 the process control provided theopportunity 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 watts. 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 processthat 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 watt 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 ofminority carrier lifetime is accomplished through external gettering and bulk defect passivation techniques. This document will present the solar cell process development that led to the demonstration of a 3.5 watt large area AP-300 solar cell.