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.