Microscopic investigations on surface-state dependent moisture stability of hybrid perovskite

Hybrid organic-inorganic perovskite (HOIP) materials have caught enormous attention in photovoltaics and photoelectronics for the outstanding photovoltaic properties. However, their instability to environment, such as illumination, temperature, moisture and oxygen, hinders the way to commercialization. To figure out the interaction mechanism of H2O and CH3NH3PbI3 (MAPbI3), massive theoretical researches have been done, while the experimental results are yet insufficient and inconsistent. Here, we systematically investigate and compare the influence of H2O on the MAPbI3 perovskite films with or without DMF post-annealing in dark or light condition. The reversible penetration of H2O into pristine MAPbI3 leads to the fusion of grain boundaries thus grain growth into micron level in short-time moisture exposure, and swelled crystalline whisker cracking into smaller grains in long-time exposure upon the release of H2O. However, no degradation occurs in dark condition. As DMF post-annealing treatment changes the surface states of MAPbI3, the interaction of exotic H2O and internal MAPbI3 significantly varies from pristine MAPbI3. Three different surface states with different topographies have influence on the interactions process and mechanism with H2O, leading to different decompositon rates, the striped surface which is the most rough in the three and experiencing the minimum change in SP with exposure to 80% humidity decomposes into PbI2 fastest. However, the addition of light will once again affect the aforementioned process.it is found that even ambient light could severely speed up the moisture-induced decomposition of MAPbI3, while DMF post-annealing significantly improves the stability of MAPbI3 films upon exposure to humidity and illumination, benefiting from the MAI-deficient thus H2O resistant surface.