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

Journal article, 2025

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.