Efficiency-limiting defects in polycrystalline silicon

Efficiency-limiting defects in polycrystalline silicon were studied using intentional metal contamination and various thermal and gettering treatments. Recently we have determined that regions of polysilicon material with the highest as-grown diffusion length are found to contain dissolved iron after growth, indicating retarded iron precipitation during post-growth cooling in these regions. Intragranular structural defects are responsible for low diffusion length previous results. In order to better understand the interaction of metallic impurities with these structural defects, phosphorus and aluminum gettering and P/Al co-gettering, have been performed on a variety of silicon solar cell materials after identical transition metal contamination. Our results show that polysilicon is more resistant to diffusion length increase than single crystal material. A model is proposed in which the predominant diffusion-length limiting factors in low diffusion length material are structural defects, whose recombination activity depends upon their density and degree of transition metal decoration