EFFICIENCY-LIMITING DEFECTS IN SILICON SOLAR-CELL MATERIAL

The precipitation rate of intentionally introduced iron during low-tem perature heating is studied among a variety of single-crystal and poly crystalline silicon solar cell materials. A correlation exists between the iron precipitation rate and the carrier recombination rate in dis location-free as-grown material, suggesting that diffusion-length-limi ting defects in as-grown material are structural defects which acceler ate iron precipitation. Phosphorous diffusion gettering was found to b e particularly ineffective at improving diffusion length after intenti onal iron contamination in materials with high iron precipitation rate s. We propose that intragranular structural defects in solar cell sili con greatly enhance transition metal precipitation during cooling from the melt and become highly recombination-active when decorated with t hese impurities. The defects then greatly impair diffusion length impr ovement during phosphorus gettering and limit carrier lifetimes in as- grown material.