Probing the Disorder inside the Cubic Unit Cell of Halide Perovskites from First-Principles

TL;DR

This study uses first-principles molecular dynamics to reveal atomic-level structural fluctuations and dynamic coupling mechanisms in cubic CsPbBr3 halide perovskites, impacting their optoelectronic properties.

Contribution

It provides a detailed mechanistic understanding of atomic vibrations and disorder in halide perovskites through first-principles simulations, addressing experimental and theoretical challenges.

Findings

Neighboring Cs-Br atoms exhibit interlocking motions.

Most likely Cs-Br distances are shorter than in ideal cubic structure.

Shallow dynamic potential wells lead to local structural disorder.

Abstract

Strong deviations in the finite temperature atomic structure of halide perovskites from their average geometry can have profound impacts on optoelectronic and other device-relevant properties. Detailed mechanistic understandings of these structural fluctuations and their consequences remain, however, limited by the experimental and theoretical challenges involved in characterizing strongly anharmonic vibrational characteristics and their impact on other properties. We overcome some of these challenges by a theoretical characterization of the vibrational interactions that occur among the atoms in the prototypical cubic CsPbBr$_3$. Our investigation based on first-principles molecular dynamics calculations finds that the motions of neighboring Cs-Br atoms interlock, which appears as the most likely Cs-Br distance being significantly shorter than what is inferred from an ideal cubic structure. This form of dynamic Cs-Br coupling coincides with very shallow dynamic potential wells for Br motions that occur across a locally and dynamically disordered energy landscape. We reveal an interesting dynamic coupling mechanism among the atoms within the nominal unit cell of cubic CsPbBr$_3$ and quantify the important local structural fluctuations on an atomic scale.