Dynamic Shortening of Disorder Potentials in Anharmonic Halide Perovskites

TL;DR

This paper investigates how nuclear dynamics in halide perovskites dynamically shorten disorder potentials, explaining their sharp optical edges and low Urbach energies despite inherent anharmonic effects.

Contribution

It reveals a dynamic mechanism that shortens disorder potentials in halide perovskites, clarifying their efficient optoelectronic properties despite large anharmonic effects.

Findings

Disorder potential is dynamically shortened by nuclear motions.

Short-range correlated disorder potential leads to sharp absorption edges.

Mechanism explains low Urbach energies in anharmonic halide perovskites.

Abstract

Halide perovskites are semiconductors that exhibit sharp optical absorption edges and small Urbach energies allowing for efficient collection of sunlight in thin-film photovoltaic devices. However, halide perovskites also exhibit large nuclear anharmonic effects and disorder, which is unusual for efficient optoelectronic materials and difficult to rationalize in view of the small Urbach energies that indicate a low amount of disorder. To address this important issue, the disorder potential induced for electronic states by the nuclear dynamics in various paradigmatic halide perovskites is studied with molecular dynamics and density functional theory. We find that the disorder potential is dynamically shortened due to the nuclear motions in the perovskite, such that it is short-range correlated, which is shown to lead to favorable distributions of band edge energies. This dynamic mechanism allows for sharp optical absorption edges and small Urbach energies, which are highly desired properties of any solar absorber material.