Hybrid organic–inorganic perovskites are currently considered the most promising next-generation photovoltaic material. However, poor stability, arising from structural degradation under exposure to moisture, heat, and strong current, remains a critical challenge for their device applications. Using ab initio nonadiabatic molecular dynamics, we demonstrate that methylamine fragments deriving from the dissociation of the methylammonium cation can undermine structural stability, produce deep hole traps, and decrease charge carrier lifetimes by 1–3 orders of magnitude. Both stability and charge lifetime can be restored by methylamine passivation with chlorines, which withdraw electrons from the lone electron pair of methylamine and bring the trap levels down into the valence band. The charge lifetime of the passivated system is even longer than that of the pristine perovskite. The simulations reveal the detailed microscopic mechanism underlying deterioration of perovskite performance due to molecular defects, and demonstrate an effective defect passivation strategy to obtain highly efficient and stable perovskite solar cells.

MAPbBr₃ (MA = CH₃NH₃⁺) doping with bismuth increases electric conductivity, charge carrier density and photostability, reduces toxicity, and expands light absorption. However, Bi doping shortens excited-state lifetimes due to formation of DY⁻ charge recombination centers. Using nonadiabatic molecular dynamics and time-domain density functional theory, we demonstrate that the DY⁻ center forms a deep, highly localized hole trap, which accelerates nonradiative relaxation ten-fold and is responsible for 90% of carrier losses. Hole trapping occurs by coupling between the valence band and the trap state, facilitated by the Br atoms surrounding the Bi dopant. Passivation of the DY⁻ center with chlorines heals the local geometry distortion, eliminates the trap state, and makes the carrier lifetimes longer than even in pristine MAPbBr₃. The decreased charge recombination arises from reduced nonadiabatic coupling and shortened coherence time, due to diminished electron–hole overlap around the passivated defect. Our study demonstrates accelerated nonradiative recombination in Bi-doped MAPbBr₃, suggests a strategy for defect passivation and reduction of nonradiative energy losses, and provides atomistic insights into unusual defect properties of metal halide perovskites needed for rational design of high-performance perovskite solar cells and optoelectronic devices.