Evaluation of the diffusion length of gettered multicrystalline silicon using solar cells - cross-sectional LBIC scan

摘要

The effective bulk diffusion length (L) in multicrystalline silicon was evaluated using the light-beam-induced-current (LBIC) technique using a geometrical configuration in which the front and back metallic contacts cover the entire front surfaces. The latter technique was performed on solar cells in cross section. We employed this particular configuration in order to evaluate the diffusion length independently of the recombination velocity at the front surface. For this purpose, we propose a new theoretical expression of the LBIC current. The diffusion length was found to be enhanced from 33 μm to 65 μm after gettering of undesired impurities from the bulk of the multicrystalline silicon. The gettering procedure used in this work is based on the formation of sacrificial porous silicon (PS) layers on both sides of the samples and heat treatments at different temperatures. This gettering method seems to concentrate some of the unwanted impurities close to the PS regions and to remove them by dissolving the PS layers.