Probing the Optoelectronic and Thermoelectric Properties of Methylammonium Germanium Halide Perovskites CH ₃ NH ₃ Ge(Br,Cl) ₃ within First Principles Calculations

Lead halide perovskites, particularly hybrid compounds based on germanium and methylammonium, offer a compelling combination of nontoxicity, environmental stability, and high efficiency, making them promising absorber materials for photovoltaic and thermoelectric applications. In this work, the optoelectronic and thermoelectric properties of methylammonium germanium halide perovskites CH 3 NH 3 Ge(Br,Cl) 3 are investigated through comprehensive first‐principles calculations. The electronic band structure results reveal that both CH 3 NH 3 GeCl 3 and CH 3 NH 3 GeBr 3 are direct bandgap semiconductors, with bandgaps of 2.95 and 2.10 eV, respectively. These compounds also exhibit remarkable optical properties, with absorption coefficients reaching 3.06 × 10 5 cm −1 for CH 3 NH 3 GeCl 3 and 3.24 × 10 5 cm −1 for CH 3 NH 3 GeBr 3 in the visible regions. Such strong absorption highlights their potential as efficient candidates for optoelectronic and photovoltaic applications. Furthermore, the figure of merit attains values of 0.99 for CH 3 NH 3 GeCl 3 and 0.98 for CH 3 NH 3 GeBr 3 near room temperature, underscoring their strong promise for thermoelectric applications.