Efficient passivation of DY center in CH3NH3PbBr3 by chlorine: Quantum molecular dynamics

MAPbBr(3) (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 MAPbBr(3). 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 MAPbBr(3), 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.