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 similar to 0.8 for Rb2AsAuCl6 and similar to 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.