Exploring the structural, electronic, optical and thermodynamic properties of halide perovskites InXI3 (X=Ge, Sn, Pb) for optoelectronic applications

We report on the structural, electronic, optical and thermodynamic properties of halide perovskites InXI₃ (X = Pb,Ge,Sn). The structural optimization revealed that all compounds adopt a cubic symmetry, with a gradual increase in the lattice constant from Ge to Pb, consistent with the increasing ionic radii of the X-site cations. The electronic band structure calculations reveal that each material possesses a direct band gap located at the R point, with values of 0.972 eV for InGeI₃, 0.807 eV for InSnI₃, and 1.636 eV for InPbI₃. Density of states analysis shows that the conduction band edge is primarily composed of In-5p and X-site p orbitals, whereas the valence band maximum is largely influenced by the iodine 5p states, highlighting the critical role of halogen contributions in the electronic structure. The optical analysis shows that the static refractive index n(0) decreases from 3.15 to 2.97 2.57, when passing from Ge to Pb with a high absorption coefficient in the range of 10⁵ cm⁻¹ for all the studied perovskites. Thermodynamic analyses of heat capacity and entropy highlight how X site substitution influences lattice dynamics and thermal stability, confirming the materials resilience to temperature changes. These results properties position InXI₃ compounds as promising candidates for next-generation energy harvesting and optoelectronic applications.