Comprehensive Analysis of the Physical Properties and Stability of Cs ₂ AgMoX ₆ (X = Cl, Br) Halide Double Perovskites for Advanced Applications

This work investigates the halide double perovskites (HDPs), Cs 2 AgMoCl 6 and Cs 2 AgMoBr 6 , as potential candidates for photovoltaic applications using first-principles calculations. Structural stability is confirmed by crystal geometries, while phonon dispersion curves validate their dynamical stability. Thermodynamic stability is confirmed by negative values of free energy and formation energy. The formation energy values are -1.87 eV and -3.37 eV for Cs 2 AgMoCl 6 and Cs 2 AgMoBr 6 . Heyd–Scuseria–Ernzerh of 2006 hybrid functional (HES06) and modified Becke–Johnson (mBJ) assumptions were used to determine electronic as well as optical characteristics, revealing that Cs 2 AgMoX 6 (X=Cl, Br) compounds are semiconductors with bandgaps ranging from 0.77 to 3.05 eV, making them highly suitable for solar applications. Cs 2 AgMoCl 6 and Cs 2 AgMoBr 6 exhibit strong UV light absorption with high absorption coefficients. Specifically, Cs 2 AgMoCl 6 reaches a peak absorption coefficient of 1.19 × 105 cm -1 , and Cs 2 AgMoBr 6 achieves a peak of 1.20 × 105 cm -1 at 10 eV. Combined with their low reflectance, these characteristics further support their photovoltaic potential. The thermoelectric characteristics demonstrate very strong figure of merit (ZT) values, with a ZT of 1.0 for Cs 2 AgMoBr 6 and 0.98 for Cs 2 AgMoCl 6 These values are benchmark for thermoelectric materials and suggest they have the ability to effectively convert heat to electric power. This is extremely important for Cs 2 AgMoCl 6 and Cs 2 AgMoBr 6 as promising lead-free and eco-friendly materials for next-generation cooling and solar cells.