Unveiling the Valence State of Interstitial Bromine on Charge Carrier Lifetime in CH₃NH₃PbBr₃ by Quantum Dynamics Simulation

Abstract

Interstitial halogens are detrimental to the optoelectronic properties of metal halide perovskites. Using nonadiabatic (NA) molecular dynamics, we demonstrate that the valence state of interstitial bromine strongly changes the carrier lifetimes of MAPbBr 3 (MA = CH 3 NH 3 + ). Both neutral and negatively charged interstitial bromine create no midgap states, and they decrease the bandgap, weaken the NA coupling, and accelerate decoherence in a different extent with respect to pristine MAPbBr 3 , making free charge recombination either slow down about a 3-fold or remain largely unchanged. In contrast, a positively charged interstitial bromine forms a Br trimer and introduces a deep electron trap state, causing a 1.4-fold increase of charge recombination followed by a rapid electron trapping or across the bandgap because of an enhanced NA coupling. The simulations uncover the influence of different charged interstitial bromine defects on MAPbBr 3 carrier lifetimes and provide rational guidelines for optimizing perovskite solar cells.

Anisotropic Carrier Dynamics and Laser-Fabricated Luminescent Patterns on Oriented Single-Crystal Perovskite Wafers

“…For the MAPbBr3 bulk crystal, due to its long carrier diffusion length and low trap-state density, most of the free carriers generated in the surface layer diffuse inward to the bulk region rather than recombine into radiative excitons in the surface layer. In addition, the non-radiative deep traps caused by bromine interstitials or lead vacancies 32,33 and the reabsorption from the interior crystal would further deteriorate its radiation capacity. For the laserprocessed microstructures, the micron-scale (much smaller than the free carrier diffusion length in single crystal 34 ) and tentacle-like profiles on the one hand prominently limit the carrier diffusion within the microstructure to increase the recombination popularity, and on the other hand eliminate the reabsorption loss owing to their nano-scale thickness.…”

Tuning the Nonradiative Electron–Hole Recombination with Defects in Monolayer Black Phosphorus

“…Defects unavoidably exist in BP samples and show diverse behavior in electronic properties, including deep trap states or trap-free . The effects of defects on charge carrier dynamics are more complicated because charge dynamics are controlled by the interplay between the bandgap, nonadiabatic (NA) coupling, and decoherence. − The former is a static property, while the latter two factors are dynamic correlation, which cannot be obtained from a single-shot electronic structure calculation. Therefore, a detailed time-domain simulation at the atomistic level is urgently needed to explore the BP charge dynamics affected by defects.…”

Charge Recombination Dynamics in a Metal Halide Perovskite Simulated by Nonadiabatic Molecular Dynamics Combined with Machine Learning

“…The classical path approximation was further used to accelerate the NA-MD simulations by treating lighter and faster electrons quantum mechanically and heavier and slower nuclei semiclassically. The approach has been applied to investigate photoexcitation dynamics in a broad range of systems. − …”