Strain-driven tunability of the optical, electronic, and mechanical properties of lead-free inorganic CsGeCl3 perovskites

Abstract

Lead-free inorganic metal halide perovskites CsGeCl3 have recently gained prominent research interest in solar technology due to their outstanding optoelectronic properties and mechanical stability. Here, the density functional theory is considered to investigate the biaxial strain-driven (from −6% to +6%) structural configuration, mechanical stability, and optoelectronic properties of non-toxic CsGeCl3 metal halide. Optical properties such as absorption coefficient, dielectric functions, and electron loss function show that due to the biaxial strain (compressive and tensile), this material has a high absorption capacity of photons in the visible and ultraviolet regions, and that’s why it is very much suitable to apply in the solar cells and other optoelectronic energy devices. The electronic band structure shows that CsGeCl3 is a semiconductor material with a direct bandgap of 0.768 eV at the R-point. Moreover, we observed a semiconductor-to-metallic transition of the bandgap of CsGeCl3 in the presence of the compressive strain. The findings of the mechanical properties of the CsGeCl3 perovskites demonstrate that Ge could be a suitable replacement for Pb in the traditional Pb-based perovskite structures. Especially in the strain portion of −2% to +2%, the investigated metal halide perovskite structure, Pb being replaced by Ge, shows mechanical ductility, absorption of visible and UV radiation, prominent absorption peaks, tunable bandgap value of 0.123 to 0.896 eV and thus, is very much suitable to be considered for solar photovoltaic applications.