  CH3NH3PbI3-based solar cells were characterized with electron beam-induced
current (EBIC), and compared to CH3NH3PbI3-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 CH3NH3PbI3-based cells require mesoporous electron
conductors, while CH3NH3PbI3-xClx ones, where LD values are comparable for both
charge types, do not.
