Exploring structural, thermodynamic, elastic, electro-optic, and thermoelectric characteristics of double perovskites Rb2XInBr6 (X = Na, K) for photovoltaic applications: A DFT approach

•The materials are stable in their cubic structure as well as thermodynamically.•The elastic properties suggest mechanical stability of both compounds. The elastic parameters provide the results that the materials exhibit brittle nature.•Both materials exhibit direct band gaps.•The optical properties depict that the materials are suitable for photovoltaic applications.•The thermoelectric properties give valuable insight into thermoelectric efficiency of the examined materials. The structural, thermodynamic, elastic, electro-optic, and thermoelectric properties of the emerging double perovskites Rb2XInBr6 (X = Na, K) were investigated. The cubic phase of Rb2KInBr6 and Rb2NaInBr6 wasverified by tolerance factor (τ) values of 0.89 and 0.83, respectively. The negative formation energies and Gibbs free energies of both perovskites demonstrated their thermodynamic stability. The elastic parameters suggested the mechanical stability, brittle character, and anisotropic behavior of both materials. The electronic band gap and density of states calculations confirmed the presence of a direct band gap (Eg) for Rb2KInBr6 and Rb2NaInBr6, having an Eg of 3.2 eV and2.6 eV, respectively. The present research focuses on the investigation of light energy absorption, polarization, refractive index, and optical loss throughout the energyspectrum ranging from zero to 10 eV. The optical parameters were appropriate for photovoltaic systems since the absorption occurs in the ultraviolet range. The thermoelectric characteristics, as measured by the use of the BoltzTraP code, revealed that the maximum ZT values were determined to be 0.73and 0.72, respectively, for both materials. Despite the presence of moderate optical absorption and a ZT value in these materials, it is necessary to investigate efficient techniques for adjusting the electronic band gapto enhance the material's optical and thermoelectric response, therefore making it more suitable for practical applications in energy generation.