Effective diffusion length of minority carriers in polycrystalline silicon

A new relation is presented for the effective minority-carrier diffusion length in polycrystalline silicon under solar illumination. It is found that effective diffusion length is controlled by the grain size d and the space-charge potential barrier height at the grain boundary. The dependence of effective minority-carrier diffusion length and space-charge potential barrier height on the grain size is also investigated theoretically. The theory predicts that, for large grain sizes, the effective diffusion length is approximately proportional to d1/2, while for small grain sizes it is proportional to d. The available experimental data are found to be in good agreement with the theoretical predictions.