First principles insight on mechanical stability, optical and thermoelectric response of novel lead-free Rb2ScCuBr6 and Cs2ScCuBr6 double perovskites

In this article, the structural properties, mechanical stability as well as electronic, optical, and thermoelectric response of novel lead-free Rb2ScCuBr6 and Cs2ScCuBr6 double perovskites were investigated through the first principles study. The optimization of the structure and tolerance factors validated the stability of these double perovskites. Born stability criteria based on computed elastic constants C11, C12, and C44 ensured elastic stability. The resulting negative values of Gibbs free energy and formation energy confirmed thermodynamic stability. Both perovskite materials reflected anisotropic behavior as well as ductility. The electronic properties corre-sponding to their band structures and density of states were determined. These findings revealed semiconducting behavior with indirect bandgaps. To evaluate the suitability for optical applications, the real and imaginary dielectric functions, absorption coefficients, optical conductivities, refractive index, reflectivity, and energy loss utilizing OPTIC code within the framework of WEIN2k were examined. Both materials exhibit optical bandgaps of 1.68 and 1.28 eV, calculated by Tauc's plot. Thermoelectric properties, including the Seebeck coefficient, electrical conductivity, thermal conductivity, power factor, and figure of merit, were evaluated by the BoltzTraP code. Results reveal that, Rb2ScCuBr6 and Cs2ScCuBr6 exhibit higher figure of merit (ZT) up to 0.81 and 0.78, respectively. Hence, these perovskites are potential materials for photovoltaic and thermoelectric applications.