Probing the microscopic mechanisms in photovoltaic degradation behaviors of CH3NH3PbI3 perovskite films via photoconductive atomic force microscopy

Halide perovskite CH3NH3PbI3 (MAPbI(3)) is a promising candidate material for future high efficiency solar cells, while suffering from low stability that hinders their commercial applications. Here, we investigated the microscopic mechanisms underlying the photovoltaic degradation behaviors in MAPbI(3) based solar cells, by using a time sequence photoconductive atomic force microscope spectroscopic (pcAFMs) in a moist environment. From the evolution of pcAFM maps, one can see two distinguished different evolution stages, the initial inter-diffusion stage that increases the overall photocurrent at the first few hours, which is followed by a decomposition stage that leads to the continuous decline of photocurrents with elongated durations. Moreover, an estimated lifetime map was also derived, which offers an overview insight into the different microscopic degradation mechanisms. In particular, some major decomposition mechanisms have been revealed, including an overall slow decomposition in all the grains, fast spreading of initial failure region, as well as newly formed failure regions occurring at grain junctions. The unveiling of these mechanisms might help improve the performance of halide perovskite solar cells, and provides a paradigmatic example for probing the microscopic photovoltaic mechanisms by using the powerful pcAFM technique.