Humidity-Induced Grain Boundaries in MAPbI3 Perovskite Films

Methylammonium lead halide perovskites (MAPbI(3)) are very sensitive to humid environments. We performed in situ scanning force microscopy and in situ X-ray diffraction measurements on MAPbI(3) films to track changes in the film morphology and crystal structure upon repeated exposure to a high relative humidity environment (80%). We found that the appearance of monohydrate (MAPbI(3)center dot H2O) Bragg reflections coincided with the appearance of additional grain boundaries. Prolonging the exposure time to humidity induced more grain boundaries and steps in the MAPbI(3) films, and the peak intensities of the monohydrate MAPbI(3)center dot H2O increased. The monohydrate was not stable under dry atmosphere and could be reversed to MAPbI(3). However, the humidity-induced grain boundaries persisted. The presence of these additional grain boundaries was most likely the reason for an increase in hysteresis in JV behavior upon humidity exposure. Morphological changes were not observed for exposure to humidity <= 50% for a duration of 144 h.