First-Principles Scrutiny of Double Perovskite Halides A₂AlAuCl₆ (A = Cs, K, Rb): Potential Contenders for Renewable Energy

Double perovskite halides are potentially useful materials for producing renewable energy and are thought to meet the necessary criteria for addressing energy scarcity issues. The physical properties of A₂AlAuCl₆ (A = Cs, K, Rb) double perovskites were investigated using DFT calculations based on the all-electron FP-LAPW approach. Exchange–correlation effects are treated via mBJ. The analyzed halides are structurally and thermodynamically stable in the cubic phase as depicted from optimized curves and negative formation energies. Furthermore, by looking of the elastic properties, the Pugh and Poisson ratios’ examined values demonstrate a ductile nature. Direct bandgap of 2.10 eV, 2.08 eV and 1.98 eV is computed for Cs₂AlAuCl₆, Rb₂AlAuCl₆ and K₂AlAuCl₆, respectively. Furthermore, the optical properties of the studied halides are examined in the context of complex dielectric functions. These halides have the best light absorption in visible region and UV region, suggesting that they are suitable for use in photovoltaic devices. Semi-classical Boltzmann theory was employed to analyze the thermoelectric characteristics. ZT values 0.75, 0.72 and 0.62 for Cs₂AlAuCl₆, Rb₂AlAuCl₆ and K₂AlAuCl₆ are reported at room temperature, indicating their suitability for renewable energy devices.