While organic-inorganic hybrid perovskites are emerging as promising materials for next-generation photovoltaic applications, the origins and the pathways of the instability of perovskites remain speculative, mainly due to the difficulty in preparing well-defined experimental conditions for atomic-scale characterization. Herein, we employ ambient-pressure atomic force microscopy (AP-AFM) and ambient-pressure x-ray photoelectron spectroscopy (AP-XPS) to carry out surface characterization and atomic-scale analysis of the reaction mechanisms for methylammonium lead bromide (MA(CH3NH3)PbBr3) single-crystal surfaces in environments ranging from ultra-high vacuum (UHV) to ambient pressure. MAPbBr3 single-crystals grown in a solution process are mechanically cleaved at UHV to obtain an atomically clean surface. We observe surface inhomogeneity on the freshly cleaved MAPbBr3 surface: the coexistence of MA-terminated layers with cubic layer heights, and full and partial coverage of PbBr2-terminated defective layers with lower layer heights. Exposure of water to the freshly cleaved perovskite surface induces surface degradation of the MAPbBr3, which leads to the formation of clusters surrounded by pits. Guided by density functional theory (DFT) calculations, we propose the pathway for atomic scale degradation that leads to the formation of PbBr2 species.

Atomic-scale study of the degradation process on single-crystal perovskite surfaces: From ultra-high vacuum to ambient pressures

2019 Fall National Meeting

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