Dynamic shortening of disorder potentials in anharmonic halide perovskites

Christian Gehrmann,David A Egger

doi:10.1038/s41467-019-11087-y

Christian Gehrmann, David A Egger

Open Access

https://doi.org/10.1038/s41467-019-11087-y

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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.

Highlights

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
Our theoretical approach employs molecular dynamics (MD) calculations based on density functional theory (DFT), which treat the nuclear anharmonicity to all orders in the Taylor expansion of the crystal potential and thereby allow for monitoring and quantifying its consequences for physical observables in a straightforward manner
The disorder potential in MAPbI3 is confined to very short ranges spectrum[16] and quantified the correlation length of the disorder potential in MAPbI3 using classical MD37

Summary

Introduction

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. 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. Ample experimental and theoretical evidence point to highly anharmonic nuclear motion and disorder being active in HaPs at room temperature, which involves the ions in the crystal contributing to the frontier electronic band structure[13,14,15,16,17,18,19,20,21,22,23,24,25] Such anharmonic effects are uncommon for efficient optoelectronic materials[26] and difficult to rationalize in view of the low Urbach energy. CsPbBr3, CsPbI3, and MAPbI3 to exhibit narrow band-gap distributions, sharp optical absorption edges and small Urbach energies at elevated temperatures, which are highly desired properties of any solar absorber material used in thin-film devices

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