Beneficial effects of the aluminum alloy process as practiced in the photovoltaic device fabrication laboratory

摘要

The aluminum alloy process implemented in Sandia's Photovoltaic Device Fabrication Laboratory (PDFL) has major beneficial effects on the performance of commercial multicrystalline-silicon (mc-Si) substrates. Careful analysis of identically processed cells (except for the alloyed layer) in matched mc-Si substrates clearly indicates that the majority of the benefit arises from improved bulk minority carrier diffusion length. Based on spectral response measurements and PC-1D modeling the authors have observed improvements due to the alloy process of up to 400% in the average diffusion length in moderate-area cells and around 50% in large-area cells. The diffusion length is dramatically improved in the interior of the silicon grains in alloyed substrates, resulting in the majority of the recombination occurring at the grain boundaries and localized areas with high defect densities.