A Computational Study of the Structural, Optoelectronic, and Thermoelectric Properties of Rb₂BiAuX₆ (X = Cl, Br) Halide Double Perovskites

Here, first‐principles exploration of the geometrical, optoelectronic, phonon, elastic tensors, and thermoelectric attributes of halide double perovskites Rb 2 BiAuX 6 ( X = Cl, Br) is presented, using density functional theory via the WIEN2k code. The stability of Rb 2 BiAuCl 6 and Rb 2 BiAuBr 6 is confirmed by their tolerance ( τ ) values of 0.94 and 0.93, and octahedral mismatch (Δ μ ) values of 0.049 and 0.045, respectively. The electronic band structures, calculated using the modified Becke–Johnson potential, reveal indirect semiconducting behavior with bandgaps of 0.48 eV for Rb 2 BiAuCl 6 and 0.69 eV for Rb 2 BiAuBr 6 . Both compounds demonstrate strong optical absorbance in visible and ultraviolet regions, suggesting their potential for next‐generation optoelectronic devices. Notably, Rb 2 BiAuCl 6 and Rb 2 BiAuBr 6 exhibit absorption peaks of 104 cm −1 at 8.7 eV and 115 cm −1 at 9.40 eV, respectively. Thermoelectric analysis across 50–800 K indicates a peak power factor of 1.69 W/K 2 ms for Rb 2 BiAuCl 6 at 300 K and 7.68 W/K 2 ·ms for Rb 2 BiAuBr 6 at 800 K, highlighting their excellent energy conversion potential. These findings position Rb 2 BiAuX 6 materials as promising candidates for experimental exploration in advanced optoelectronic and thermoelectric applications.