Diffusion length of photo-generated charge carriers in layers and powders of CH₃NH₃PbI₃ perovskite

The diffusion or transport lengths of photo-generated charge carriers in CH₃NH₃PbI₃ layers (thickness up to 1 μm) and powders have been directly measured with high accuracy by modulated surface photovoltage after Goodman. The values of the diffusion lengths of photo-generated charge carriers ranged from 200 nm to tenths of μm. In thin CH₃NH₃PbI₃ layers, the transport lengths corresponded to the layer thickness whereas in thicker layers and in crystallites of CH₃NH₃PbI₃ powders the grain size limited the diffusion length. For grains, the diffusion length of photo-generated charge carriers depended on the measurement conditions.