Photoinduced Small Hole Polarons Formation and Recombination in All-Inorganic Perovskite from Quantum Dynamics Simulation.

We conducted ab initio molecular dynamics (AIMD) and nonadiabatic MD to simulate polaron formation and recombination in all-inorganic CsBiBr perovskite. The meticulously designed AIMD simulations show that two types of small hole polaron, including localized and semidelocalized small hole polaron on either an intralayer or an interlayer Br dimer, are adiabatically formed within 1.71 ps. The localized small hole polaron reduces nonadiabatic coupling and decoherence time and, thus, delays charge recombination to 213 ns. In contrast, the dominant semidelocalized polaron increases nonadiabatic coupling by enhancing electron-hole overlap and restores the energy gap and decoherence time to the pristine system, accelerating recombination to 4.7 ns compared to a 10 ns charge carrier lifetime in the pristine system. All the obtained time scales agree well with experiments. The study offers a fundamental understanding of the excited-state dynamics of small hole polaron in CsBiBr and helps to design high-performance perovskite optoelectronics and photovoltaics.