CH3NH3PbI3-based solar cells were characterized with electron beam-induced current (EBIC) and compared to CH 3NH3PbI3-xClx ones. A spatial map of charge separation efficiency in working cells shows p-i-n structures for both thin film cells. Effective diffusion lengths, LD, (from EBIC profile) show that holes are extracted significantly more efficiently than electrons in CH3NH3PbI3, explaining why CH 3NH3PbI3-based cells require mesoporous electron conductors, while CH3NH3PbI3-xCl x ones, where LD values are comparable for both charge types, do not. © 2014 American Chemical Society.