Breakdown of the static picture of defect energetics in halide perovskites: the case of the Br vacancy in CsPbBr3

TL;DR

This study reveals that defect energy levels in halide perovskites are highly dynamic due to structural fluctuations, challenging the traditional static defect model and impacting material properties.

Contribution

It demonstrates, through first-principles molecular dynamics, that defect energetics in halide perovskites are intrinsically dynamic and strongly coupled with structural motions.

Findings

Defect energy levels fluctuate by up to 1 eV at room temperature.

Structural dynamics are correlated with defect energetics and electrostatic potential.

Implications for defect analysis and carrier transport in halide perovskites.

Abstract

We consider the Br vacancy in CsPbBr3 as a prototype for the impact of structural dynamics on defect energetics in halide perovskites (HaPs). Using first-principles molecular dynamics based on density functional theory, we find that the static picture of defect energetics breaks down; the energy of the Br vacancy level is found to be intrinsically dynamic, oscillating by as much as 1 eV on the ps time scale at room temperature. These significant energy fluctuations are correlated with the distance between the neighboring Pb atoms across the vacancy and with the electrostatic potential at these Pb atomic sites. We expect this unusually strong coupling of structural dynamics and defect energetics to bear important implications for both experimental and theoretical analysis of defect characteristics in HaPs. It may also hold significant ramifications for carrier transport and defect tolerance in this class of photovoltaic materials.