The electronic disorder landscape of mixed halide perovskites

TL;DR

This study uses localization landscape theory to analyze the impact of static disorder in mixed-halide perovskites, showing it contributes minimally to Urbach energy and highlighting the importance of dynamic effects.

Contribution

The paper introduces a modeling approach that accurately predicts the electronic disorder landscape in mixed-halide perovskites, emphasizing the small static disorder contribution.

Findings

Static disorder contributes at most 3 meV to Urbach energy.

Small effective masses lead to a natural length scale of ~20nm for potential fluctuations.

Modeling reproduces experimental absorption spectra and halide segregation effects.

Abstract

Bandgap tunability of lead mixed-halide perovskites makes them promising candidates for various applications in optoelectronics since they exhibit sharp optical absorption onsets despite the presence of disorder from halide alloying. Here we use localization landscape theory to reveal that the static disorder due to compositional alloying for iodide:bromide perovskite contributes at most 3 meV to the Urbach energy. Our modelling reveals that the reason for this small contribution is due to the small effective masses in perovskites, resulting in a natural length scale of around 20nm for the "effective confining potential" for electrons and holes, with short range potential fluctuations smoothed out. The increase in Urbach energy across the compositional range agrees well with our optical absorption measurements. We model systems of sizes up to 80 nm in three dimensions, allowing us to explore halide segregation, accurately reproducing the experimentally observed absorption spectra and demonstrating the scope of our method to model electronic structures on large length scales. Our results suggest that we should look beyond static contribution and focus on the dynamic temperature dependent contribution to the Urbach energy.