The study optical, thermoelectric, and thermodynamic properties of double perovskites K2CuBiX6 (X = Cl, Br, I) for energy harvesting

•Double perovskites are more stable, cheap, and suitable materials for solar cells.•The large value of efficiency of conversion light energy into electrical energy.•The absorption bands of light energy exist visible to infrared region.•The large figure of merit at room temperature and ultralow lattice thermal conductivity. The double perovskites are promising aspirants for renewable energy applications. In present article, optoelectronic, thermoelectric, and thermodynamic characteristics are elaborated comprehensively for K2CuBiX6 (X = Cl, Br, I). The elastic constants show the mechanical stability and ductile nature. The tolerance factor (0.92 to 0.89) ensure structural stability and formation energy (−1.59 to −0.72 eV) show thermodynamic existance. The mechanical analysis confirms the ductile nature, large melting and Debye temperatures enhance their importance for device fabrication. The band gaps 1.21 eV, 0.94 eV, and 0.70 eV computed from band structures illustrate the importance of studied DPs for optoelectronic applications. The broad absorption band, and least dispersion are calculated from optical parameters. Moreover, the transport characteristics are analyzed by electrical conductivity, thermal conductivity, Seebeck coefficient, and Figure of merit. Thermodynamic parameters conclude the large Debye temperature, and ultralow lattice thermal conductivity.