Degradation of co-evaporated perovskite thin film in air

Methylammonium lead halide perovskites as highly promising photovoltaic materials have been found unstable in air. We investigated the degradation of CH3NH3PbI3 by air exposure using X-ray diffraction (XRD), X-ray photoelectron spectroscopy (XPS), and atomic force microscopy (AFM). The stoichiometric sample was grown with co-evaporation of PbI2 and CH3NH3I on an Au coated Si wafer. It was found that the perovskite thin film gradually turned to PbI2 in air, accompanied with complete removal of N and substantial reduction of I. It was also observed that PbI2 crystallization roughened the film and resulted in a partial exposure of the Au substrate. (C) 2015 Published by Elsevier B.V.