Synergistic optoelectronic and thermoelectric performance in Rb2AsAuBr6 and Rb2AsAuCl6 double perovskites for multifunctional energy conversion

In this work, we use density functional theory (DFT) to thoroughly analyze the structural, electrical, optical, and thermoelectric characteristics of halide double perovskites Rb₂AsAuX₄ (X = Br, Cl). Both compounds' structural stability is confirmed by the optimized lattice characteristics, with Rb₂AsAuBr₄ showing somewhat larger cell dimensions than Rb₂AsAuCl₄. Indirect band gaps of 0.338 eV (Br) and 0.885 eV (Cl), which are within the optimal range for solar applications, are shown by electronic band structure simulations. Strong absorption coefficients in the visible region above 1.2 × 10¹ cm^-1 are shown in optical spectra, suggesting great potential for solar energy harvesting. High Seebeck coefficients of up to 310 μV/K (Br) and 285 μV/K (Cl) at ambient temperature are shown by thermoelectric analysis, together with electrical conductivities that facilitate effective charge transfer. Thermoelectric performance is further improved by the comparatively low thermal conductivity (0.9-1.1 W/m·K). Together, our findings demonstrate Rb₂AsAuX₄'s versatility and establish Rb₂AsAuBr₆ and Rb₂AsAuCl₄ as viable options for next optoelectronic and energy-harvesting applications.