Polysilicon thin-film solar cells: Influence of the deposition rate upon enhanced diffusion and on cell performance

We study the diffusion of phosphorus in polysilicon layers deposited with thermal CVD and the impact on the performance of thin-film solar cells. Faster diffusion is observed both within grains and along grain boundaries when the deposition rate becomes very high. This is probably linked with the presence of < 110 > oriented grains, striated with microtwins, which tend to dominate during competitive growth. A high deposition rate is beneficial for the solar cells' red response and short-circuit current because of the deeper grain boundary diffusion peaks. However, lowering the deposition rate is required for a high open-circuit voltage. This suggests that lower deposition rates lead to lower defect densities at grain boundaries.