Revealing elastic, thermophysical, optoelectronic, and transport characteristics of halide double perovskites Na₂TlSbZ₆ (Z = Cl/Br/I) for eco-friendly technologies: DFT analysis

Halide double perovskites (HDPs) exhibit advantageous functional characteristics, making them extremely suitable for utilization in photovoltaics and thermoelectrics. The current investigation utilized the WIEN2k simulation code, which is based on the principle of density functional theory (DFT), to analyze the structural, elastic, thermophysical, electro-optic, and transport properties of Na₂TlSbZ₆ (Z = Cl/Br/I). The cubic phase and chemical stability have been verified by calculating the tolerance factor and formation energy. The elastic features that exhibit flexibility, ductility, and mechanical stability for studied HDPs have been demonstrated. Three-dimensional Young's modulus plots confirm the anisotropy in all examined HDPs. The electronic characteristics have been estimated to determine the band gap and details regarding the distribution of electronic states across bands. The band gap values of examined HDPs ranging between 1.40 and 0.78 eV confirm their semiconductor nature. The optical attributes, including dielectric function, absorption, reflectivity, and loss function, have been studied in detail. The reported optical absorption spectrum indicates that Na₂TlSbZ₆ (Z = Cl/Br/I) perovskites can be utilized in optoelectronic and solar energy technologies. Transport parameters have been comprehensively elucidated to predict the thermal energy conversion capability. The anticipated merit values of 0.84, 0.88, and 0.92 at room temperature validate their higher thermoelectric response for technological applications. These theoretical findings indicate the significant potential of these HDPs for solar cells and thermoelectric devices.