The narrow band bap double perovskites X₂CuInCl₆ (X = K, Rb, Cs) for optoelectronics, and thermoelectric applications

The lead free, non-toxic, dynamically stable behavior of double perovskites make them promising materials for thermoelectric and optoelectronic applications. Therefore, the mechanical, optoelectronic, and transport characteristics of X₂CuInCl₆ (X = K, Rb, Cs) are addressed comprehensively by density functional theory. The phonon dispersion band structures are computed for dynamic stability, and tolerance factor for structural stability. The band structures show narrow band gaps (0.25, 0.42, 0.56) eV which are significantly important for infrared detectors and other optoelectronic devices operating with visible and IR light. The absorption peaks of maximum intensity are noted at 1.5 eV (827 nm), 2.0 eV (620 nm), and 2.5 eV (496 nm) for K, Rb, and Cs based DPs. Furthermore, thermoelectric behavior has been analyzed by the figure of merit, power factor, Seebeck coefficient, electrical to thermal conductivity ratio against chemical potential (−0.1 eV to 0.1 eV) and temperature (100–500 K). The ultralow values of lattice vibration, and large ZT increase their importance for thermoelectric generators.