Role of surface terminations in the chemical stability of CH3NH3PbI3 perovskite in combined light, H2O, and O2 environments: DFT/AIMD calculations and experimental validation

A deep understanding of the relationship between the surface termination of organic-inorganic metal halide perovskites and their structural degradation caused by environmental stimuli is critical for increasing the practicability of perovskite-based photovoltaic devices. In this work, the role of different surface termination on the degradation of CH3NH3PbI3 (MAPbI3) perovskite upon simultaneous exposure to water and oxygen in the presence of light is systematically investigated using density functional theory (DFT) and ab initio molecular dynamics (AIMD) simulations methods. Our results show that photogenerated electrons increase the interaction of H2O and O2 molecules on the MAPbI3 perovskite and the coexistence of H2O and O2 molecules degrade the MAPbI3 perovskite surface faster than the presence of either monomer on the surface. AIMD results indicate that the PbI2-terminated MAPbI3 surface undergoes significant structural degradation upon simultaneous exposure to light, H2O, and O2, whereas the MAI-terminated surface is stable. Furthermore, a series of MAPbI3-based perovskite solar cells (PSCs) with different concentrations of MAI precursor are fabricated, and their photovoltaic performance is studied. Our experimental results show that the PSC treated with 3 mg mL−1 of MAI has achieved a maximum PCE of 16.16% and a larger VOC of 1.02 V, with correspondingly improved stability. The finding presented here provides a strategy for improving the quality of the MAPbI3 perovskite layer and its photovoltaic performance.