Computational insight on K2AuBiX6 (X = F, Cl, Br, I) double perovskites to comprehensively investigate mechanical, optoelectronic, and thermoelectric features for green energy applications

•K2AuBiX6(X = F, Cl, Br, I)are stable in cubic phase.•The structural stability is confirmed by the negative formation energy, tolerance factor and molecular dynamic simulation.•The optical propertiesshows that the materials are suitable for solar cellapplications.•These materials show substantial characteristics to serve as sustainable green energy alternatives as they demonstrate significant ZT values. In this article, we investigated the structural, elastic, electronic, optical, and thermoelectriccharacteristics of K2AuBiX6 (X = F, Cl, Br, and I) using density functional theory (DFT). To verify the stability of the cubic structure tolerance, octahedral factors, and formation energy have been determined. The mechanical stability has been governed by Born stability criteria. These parameters ensure its strength, ductility, brittleness, and anisotropy. The bandgaps of K2AuBiF6, K2AuBiCl6, K2AuBiBr6, and K2AuBiI6 have been determined using the TB-mBJ potential. The calculated values of energy band gaps are 2.88, 2.02, 1.38, and 0.95 eV, respectively. These materials exhibit a broad absorption in visible regions, a refractive index range of around 1–3, and low light scattering, which makes them ideal for optoelectronic applications. In addition, the figure of merit (ZT) values for these compounds at room temperature are 0.76, 0.78, 0.77, and 0.80, ensuring their suitability for use in thermal devices.