Self-passivation of\nHalide Interstitial Defects by\nOrganic Cations in Hybrid Lead-Halide Perovskites: Ab Initio Quantum\nDynamics

Halide interstitial defects severely hinder the optoelectronic\nperformance of metal halide perovskites, making research on their\npassivation crucial. We demonstrate, using ab initio nonadiabatic\nmolecular dynamics simulations, that hydrogen vacancies (H<sub>v</sub>) at both N and C atoms of the methylammonium (MA) cation in MAPbI<sub>3</sub> efficiently passivate iodine interstitials (I<sub>i</sub>), providing a self-passivation strategy for dealing with the H<sub>v</sub> and I<sub>i</sub> defects simultaneously. H<sub>v</sub> at\nthe N site (H<sub>v‑N</sub>) introduces a defect state into\nthe valence band, while the state contributed by H<sub>v</sub> at\nthe C site (H<sub>v‑C</sub>) evolves from a shallow level at\n0 K to a deep midgap state at ambient temperature, exhibiting a high\nenvironmental activity. Both H<sub>v‑N</sub> and H<sub>v‑C</sub> are strong Lewis bases, capable of capturing and passivating I<sub>i</sub> defects. H<sub>v‑C</sub> is a stronger Lewis base,\nbonds with I<sub>i</sub> better, and exhibits a more pronounced passivation\neffect. The charge carrier lifetimes in the passivated systems are\nsignificantly longer than in those containing either H<sub>v</sub> or I<sub>i</sub>, and even in pristine MAPbI<sub>3</sub>. Our demonstration\nof the H<sub>v</sub> and I<sub>i</sub> defect self-passivation in\nMAPbI<sub>3</sub> suggests that systematic control of the relative\nconcentrations of H<sub>v</sub> and I<sub>i</sub> can simultaneously\neliminate both types of defects, thereby minimizing charge and energy\nlosses. The demonstrated defect self-passivation strategy provides\na promising means for defect control in organic–inorganic halide\nperovskites and related materials and deepens our atomistic understanding\nof defect chemistry and charge carrier dynamics in solar energy and\noptoelectronic materials.