Enhanced Thermoelectric and Optical Properties via In Substitution in Cs2XInBr6 (X═Na, In) Double Perovskites for Low-Cost Energy Applications

Double perovskite halides having emerged as sustainable green energy source for meeting the challenges globally. Notably, these halide perovskites exhibit considerable potential for energy storage devices and thermal applications. Our work inspected structural stability, optical and thermal aspects of Cs₂XInBr₆ (X═Na, In) halides via (DFT) implemented in Quantum ESPRESSO by utilizing generalized gradient approximation (GGA). These examinations of formation energy and tolerance factor indicted that these materials are thermodynamically stable with cubic arrangements. The band structure was examined to investigate structural behavior of these materials. Analysis shows the semiconductor behavior with indirect band gap in case of Cs₂InInBr₆ (E_g = 0.8 eV) and direct band gap in case of Cs₂NaInBr₆ (E_g = 1.7 eV). The optical characteristics revealed through dielectric function. The results of optical calculations showed that such substances are ideal for use in optics with maximum light absorption in UV region. All the optical parameters obtained including high absorption coefficient with minimal reflectivity and strong conductive properties. The thermoelectric calculations reveal significant seebeck value with a lower thermal conductivity with high-energy efficiency for Cs₂InInBr₆ than Cs₂NaInBr₆. All calculations implied that our tested combinations are suitable for energy storage usage such as thermoelectric and optoelectronic devices.