Unraveling the Protective Role of Twin Boundaries on Carrier Lifetimes in Metal Halide Perovskites via Machine Learning-Accelerated Quantum Dynamics

Twin boundaries (TBs) in metal halide perovskites are known to mitigate nonradiative recombination, yet their microscopic role in the presence of intrinsic defects remains elusive. Here, we combine machine-learning-accelerated deep potential molecular dynamics with time-dependent density functional theory and nonadiabatic molecular dynamics to probe carrier dynamics in formamidinium lead iodide at nanosecond time scales. We show that TBs suppress nonadiabatic electron-hole coupling and stabilize carrier lifetimes exceeding 10 ns. Iodine vacancies, although reducing the bandgap and inducing local lattice distortions, do not generate midgap states and only slightly shorten lifetimes. Pb_I antisite defects introduce shallow trap states and rapid electron capture, yet structural reorganization diminishes recombination efficiency, maintaining nanosecond-scale lifetimes. These results identify TBs as electronically benign and defect-tolerant structures, clarify the interplay between extended and point defects, and establish a mechanistic basis for the long carrier lifetimes observed experimentally in TB-containing perovskites.