Chemical passivation of methylammonium fragments eliminates traps, extends charge lifetimes, and restores structural stability of CH₃NH₃PbI₃ perovskite

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.