Critical Role of Grain Boundaries for Ion Migration in Formamidinium and Methylammonium Lead Halide Perovskite Solar Cells

The critical role of grain boundaries for (CH(NH2)2PbI3)0.85(CH3NH3PbBr3)0.15 perovskite solar cells studied by Kelvin probe force microscopy under bias voltage and illumination is reported. Ion migration is enhanced at the grain boundaries. Under illumination, the light-induced potential causes ion migration leading to a rearranged ion distribution. Such a distribution favors photogenerated charge-carrier collection at the grain boundaries.