Low-energy pathways lead to self-healing defects in CsPbBr$_3$

TL;DR

This study uncovers low-energy defect diffusion pathways in CsPbBr$_3$, revealing mechanisms that could enable defect self-healing and improve the material's performance in photovoltaic applications.

Contribution

It identifies a novel low-energy diffusion pathway involving a concerted interstitial mechanism in CsPbBr$_3$, advancing understanding of defect dynamics in all-inorganic perovskites.

Findings

Defect pathways with activation energy ≤ 0.53 eV match experimental observations.

Discovery of a 'domino effect' interstitial mechanism facilitating defect diffusion.

Potential for defect self-healing to enhance perovskite solar cell stability.

Abstract

Self-regulation of free charge carriers in perovskites via Schottky defect formation has been posited as the origin of the well-known defect tolerance of metal halide perovskite materials that are promising candidates for photovoltaic applications, like solar cells. Understanding the mechanisms of self-regulation, here for a representative of more commercially viable all-inorganic perovskites, promises to lead to the fabrication of better-performing solar cell materials with higher efficiencies. We investigated different mechanisms and pathways of the diffusion and recombination of interstitials and vacancies (Schottky pairs) in CsPbBr$_3$. We use Nudged Elastic Band calculations and ab initio-derived pseudopotentials within Quantum ESPRESSO to determine energies of formation, migration, and activation for these defects. Our calculations uncover defect pathways capable of producing an activation energy at or below the value of 0.53~eV observed for the slow, temperature-dependent recovery of light-induced conductivity in CsPbBr$_3$. Our work reveals the existence of a low-energy diffusion pathway involving a concerted "domino effect" interstitial mechanism, with the net result that interstitials can diffuse more readily over long distances than expected. Importantly, this observation suggests that defect self-healing can be promoted if the "domino effect" strategy can be engaged.