First‐Principles Investigation of Indium‐Based Halide Perovskites InMP 3 (M = Ge, Sn; P = F, Cl, Br, I) for Advanced Optoelectronic and Thermoelectric Devices

ABSTRACT This study investigates the electronic, optical, and thermal properties of cubic lead‐free InMP3 perovskites (M = Ge, Sn; P = F, Cl, Br, and I) using first‐principles HF and DFT (B3LYP/LanL08) calculations. The HOMO‐LUMO gaps for InGeP3 and InSnP3 range from 0.89 to 1.70 eV (HF) and 0.98–2.20 eV (DFT), and 0.79–1.49 eV (HF) and 0.81–1.52 eV (DFT), respectively. A systematic reduction in bandgap occurs with cation (Ge to Sn) and anion (F to Cl to Br to I) substitution, optimizing these materials for photovoltaics. InMI3 exhibits the highest refractive index and dielectric constant, thereby enhancing its potential for solar cell applications. Thermally, InMI3 exhibits superior thermodynamic stability (lower enthalpy and more negative Gibbs free energy), making it suitable for thermoelectric applications. These findings highlight InMP3 perovskites as environmentally friendly alternatives with tunable optoelectronic and thermal properties for energy conversion devices.