Exploring physical characteristics of double perovskites Na₂CuAsX₆ (X = F, Cl, Br, and I) for solar energy harvesting and wasted heat recovery applications

The current research is intended to investigate the physical properties of the Na₂CuAsX₆ (X = F, Cl, Br, and I) double perovskites using the density functional theory (DFT) framework implemented in the WIEN2k code. Herein, the structural configuration, electronic, optical, thermoelectric, and thermodynamic features are thoroughly discussed. The structural investigation utilized the Murnaghan equation of state (EOS) and the generalized gradient approximation (GGA). The thermal and phase stability has been verified by the formation enthalpy and tolerance factor. The perovskites Na₂CuAsF₆, Na₂CuAsCl₆, Na₂CuAsBr₆, and Na₂CuAsI₆ exhibit semiconductor properties characterized by indirect band gaps of 1.28, 1.14, 0.85, and 0.52 eV, respectively. An extensive examination of the optical characteristics suggests the possible appropriateness of these materials for photovoltaic applications. Double perovskites exhibit a significant absorption in the visible spectrum. Thermodynamic properties have demonstrated the thermal stability of analyzed perovskites even at high temperatures. Additionally, the thermoelectric properties have been determined at specific temperatures and chemical potentials, indicating the p-type nature of studied perovskites. The figure of merit (ZT) values at 300 K are determined to be 0.79, 0.76, 0.77, and 0.80, suggesting Na₂CuAsX₆ may be sustainable thermoelectric materials with excellent performance. Consequently, the examined materials can serve as sustainable candidates for solar energy and wasted heat recovery applications.