# Exploring the Polaron Landscape in Germanium Halide Perovskites: CsGeCl3, CsGeBr3, and CsGeI3

## TL;DR

This paper studies the electronic properties of CsGeX3 perovskites and finds that polaron stability decreases from Cl to I, which could help optimize these materials for nonlinear optical applications.

## Contribution

The study provides new insights into polaron formation and self-trapped exciton binding in CsGeX3 perovskites using hybrid density functional theory.

## Key findings

- Polaron stability decreases from Cl to I in CsGeX3 perovskites.
- Single-electron polarons form favorably in CsGeCl3 and CsGeBr3, while single-hole polarons only form in CsGeCl3.
- Double electron polarons are energetically favorable across the CsGeX3 series.

## Abstract

The unique electronic
properties of CsGeX
3 perovskites (X = Cl, Br, I) make them
promising
candidates for nonlinear optical applications. Understanding charge
localization is needed to fully understand their physical and electronic
behavior. Here, we perform a theoretical investigation of electron
and hole polaron formation, and self-trapped exciton binding in CsGeX
3 using hybrid density functional theory. We
find that polaron stability decreases from Cl to I. In particular,
single-electron polarons form highly favorably in CsGeCl3 and CsGeBr3, whereas single-hole polarons can only be
formed in CsGeCl3. Double electron polarons are energetically
favorable across the series. In addition, CsGeCl3 and CsGeBr3 exhibit stable self-trapped exciton configurations. These
findings constitute a basis for understanding polaronic effects on
the electronic properties of CsGeX
3 perovskites
and open up access to their optimization in nonlinear optical applications.