Lead Vacancy Can Explain the Suppressed Nonradiative Electron–Hole Recombination in FAPbI3 Perovskite under Iodine-Rich Conditions: A Time-Domain Ab Initio Study

Experiments show that the excited-state lifetime of hybrid organic–inorganic perovskites, synthesized under iodine-rich conditions, can be greatly enhanced. Ab initio nonadiabatic (NA) molecular dynamics demonstrates that a single lead vacancy, which constitutes a major defect within the iodine-rich environment, significantly suppresses the nonradiative electron–hole recombination in HC(NH2)2PbI3 (FAPbI3) perovskite. The simulations show that electron–hole recombination in pristine FAPbI3 occurs within one nanosecond. Introduction of a single lead vacancy weakens the NA electron–phonon coupling and prolongs the coherence time simultaneously. The weaker NA coupling competes successfully with the longer coherence time, extending the lifetime over tens of nanoseconds. The calculated recombination time scales show excellent agreement with experiment. Our study rationalizes the microscopic mechanism responsible for experimental observations, suggesting a rational choice of defect can modulate perovskite excited-state lifetimes and improve solar cell performance.