Surface Pb-Dimer Passivated by Molecule Oxygen Notably Suppresses Charge Recombination in CsPbBr3 Perovskites: Time-Domain Ab Initio Analysis

Experiments show that excess lead atoms accelerate charge recombination while oxygen passivation can heal the defects and enhance solar cell efficiency. Using ab initio nonadiabatic (NA) molecular dynamics, we demonstrate that an excess lead atom forms a Pb-dimer with a single surface lead atom of CsPbBr3(001) surface and creates a deep hole trap. The electron–hole recombination is accelerated to over 10 ps via fast hole trapping or bypassing the hole trap compared to the pristine CsPbBr3, occurring on tens of picoseconds. Pb-dimer passivated with oxygen molecules forms Pb–O bonds, breaks the Pb-dimer, and removes the trap state, leading to a decrease in the recombination and extending excited-state lifetime to over 100 ps. The deceleration arises mainly due to the reduced NA coupling and short decoherence time. The study advances our understanding of excited-state dynamics of all-inorganic perovskites in the presence of excess lead and oxygen atmosphere.