DFT Insight on Future Prospects of Double Perovskites A₂YCuZ₆ (A = Rb, Cs and Z = Cl, Br) for Energy Conversion Technologies

This article comprehensively explores the structure, stability, mechanical, optoelectronic, and thermoelectric aspects of the emerging double perovskites A₂YCuZ₆ (A = Rb, Cs and Z = Cl, Br). The structural and mechanical characteristics are estimated using the PBE-GGA functional, whereas the optoelectronic and thermoelectric characteristics are computed using the modified Becke and Johnson potential. Tolerance factor, formation energies, and Gibbs free energies have validated the cubic phase and thermodynamic stability. The anticipated elastic values indicated that all the materials exhibited mechanical stability, ductility, and anisotropic behavior. The computed electronic features verified that Rb₂YCuCl₆, Rb₂YCuBr₆, Cs₂YCuCl₆, and Cs₂YCuBr₆ have indirect band gaps of 1.95, 1.30, 1.55, and 1.2 eV, respectively. This work also explores the optical response in the energy range 0 to 6 eV in terms of polarization, refractive index, absorption, and optical conduction. The visible and ultraviolet ranges of light are both significantly absorbed, making these materials optimal for use in solar systems. The BoltzTraP code has been used to calculate the transport parameters, demonstrating the p-type semiconductors nature of these materials. Further, the significant merit values of 0.77, 0.83, 0.82, and 0.81 at room temperature for analyzed materials suggest their potential applicability in thermoelectric devices. Hence, the investigated double perovskites, which are not empirically validated, have been recommended as extremely suitable alternatives for creating various energy conversion applications.