Study of excitonic effects, 3D-elastic, optoelectronic and thermoelectric properties of new inorganic double perovskites CsKAgSbX₆ (X = Cl, Br) for solar cell applications

Novel halide double perovskites CsKAgSbX₆ (X = Cl, Br) have been theoretically investigated in the current study to determine their optoelectronic, elastic, and thermoelectric properties. The Density Functional Theory based on the GGA-PBE and HSE functionals using the Quantum Espresso code was applied. The optimization of the cubic structure of the perovskites resulted in the optimized lattice constants of about 10.78 Å and 11.31 Å for CsKAgSbCl₆ and CsKAgSbBr₆, respectively. The results also revealed that both materials are stable in the cubic structure and are mechanically stable as well as ductile in nature. The anisotropy of CsKAgSbX₆ (X = Cl, Br) has been investigated by evaluating the highest and lowest values of the shear modulus, Bulk modulus, and the Young’s modulus. Moreover, the investigation of their electronic properties indicated that they are semiconductors with energy gap values found to be 1.36 eV for CsKAgSbCl₆ and 0.87 eV for CsKAgSbBr₆ using the GGA approximation and 2.49 eV and 1.81 eV for the respective perovskites using the HSE functional. Regarding their optical properties, these materials show an excellent UV light absorption, low reflectivity and high-power conversion efficiency, making them promising for solar cell applications. Finally, with a reasonably high figure of merit, CsKAgSbX₆ (X = Cl, Br) double perovskites also have potential for thermoelectric devices.