Electronic transport properties of Rb2AsAuX6 (X = Cl, Br) halide double perovskites for energy harvesting applications

Herein, we investigated the physical characteristics of two narrow band gap halide double perovskites (HDPs) Rb₂AsAuX₆ (X = Cl, Br) by using density functional theory (DFT) calculations. Both compounds exhibit thermodynamical stability with non-magnetic ground states and stable cubic symmetry supported by geometry optimization, tolerance factor criteria, and negative formation enthalpies. The electronic structure analysis reveals semiconducting behavior, with bandgaps of 0.66 for Rb₂AsAuCl₆ and 0.07 eV for Rb₂AsAuBr₆, attributed primarily to the interaction between As and Au states near the Fermi level. Optical investigations highlight significant absorption in the visible spectrum with onset edges in the infrared (IR) region in addition to low reflectivity (less than 10 %) and high conductivity makes both HDPs potential contender for optoelectronic device applications across a broad spectrum. The thermoelectric analysis reveals promising efficiency, with figure of merit (ZT) values approaching ∼0.8 for Rb₂AsAuCl₆ and ∼0.5 for Rb₂AsAuBr₆ at room temperature. The results indicate that Rb₂AsAuCl₆ and Rb₂AsAuBr₆ have the potential to be used in future optoelectronic and thermoelectric applications due to their unique combination of structural stability, tunable bandgaps, and efficient thermoelectric performance.