Degradation of CH3NH3PbI3 perovskite materials by localized charges and its polarity dependency†
Despite the excellent performance of organic–inorganic hybrid perovskite materials in recent years, the mechanism of their decomposition under actual operating conditions has not yet been elucidated. Herein, we elucidated the breakdown process of CH3NH3PbI3 perovskite crystals and identified the polarity-dependent degradation pathway via localized charges by performing time-evolution measurements of the absorption spectra of perovskite films with different underlying charge transport layers and ab initio molecular dynamics calculations. It was found that the carrier polarity (hole-rich or electron-rich) inside the perovskite films played a critical role in the degradation rate, and the polarity-dependent degradation pathway strongly depended on the combination of the surrounding gaseous molecules. The hole-rich perovskite films degraded more rapidly than the electron-rich ones in the presence of H2O, while this degradation trend was reversed in oxygen-only ambient environments. Interestingly, the hole-rich film is extremely unstable in atmospheric air containing both H2O and O2, whereas the MAPbI3 film with excessive electrons was stable in air. An ab initio molecular dynamics simulation was performed to obtain the detailed degradation pathway of MAPbI3 under atmospheric conditions for different polarities of the localized charge. The simulation results are in good agreement with experimental results, and the production of Pb(OH)I predicted in our simulations is confirmed by X-ray-assisted spectroscopic measurements.