Modeling the Interaction of Molecular Iodine with MAPbI3: A Probe of Lead-Halide Perovskites Defect Chemistry

Understanding the defect chemistry of lead-halide perovskites is of paramount importance to further progress toward exploitation of these materials. Here, we combine recent experimental observations on the behavior of MAPbI3 upon exposure to I2 vapor with first-principles calculations to extract a global picture of defect chemistry in lead-halide perovskites. By matching the reported experimental observables we disclose the origin of the p-doping observed upon exposing MAPbI3 to I2 and highlight its consequences on the charge and ion transport and trapping activity. Electron/hole traps related to positive/negative interstitial iodine dominate the defect chemistry in intrinsic conditions, while in p-doped MAPbI3, electrons are mainly trapped by positive interstitial iodine and neutral lead vacancies. I2 spontaneously dissociates on iodine vacancies, leading to vacancy passivation and to the formation of positive interstitial iodine. I2 spontaneously dissociates on nondefective MAPbI3(001) surfaces to form pairs of negative/positive interstitial iodine. Upon trapping a hole/electron pair at negative/positive interstitial iodine, I2 release becomes thermodynamically favored, possibly representing a photoinduced trap-curing mechanism.