First-principles investigation of K2InSbZ6 (Z= I, Br, Cl, F) eco-friendly halide double perovskites: Structural, thermodynamic, optoelectronic, and thermoelectric properties for efficient energy harvesting applications

This study investigates K2InSbZ6 (Z = I, Br, Cl, F) HDPs for energy conversion applications using first-principles analysis. We confirm their structural and thermodynamic stability through Goldsmith's tolerance factor and the enthalpy of formation. The analysis of pressure-temperature dependencies show that the phonon heat capacity reaches the Dulong-Petit limit at around 700 K. A small thermal expansion coefficient indicates their volumetric stability. The electronic band structure reveals that these materials behave as direct semiconductors. The band gap decreases from 2.732 to 1.047, 0.407, and 0.048 eV for K2InSbZ6 (Z = F, Cl, Br, I), respectively. All HDPs exhibit optical activity in ultraviolet and visible regions. K2InSbCl6 shows significant absorption in the visible spectrum, achieving a SLME of 31.90 %, making it suitable as an efficient solar cell absorber. We also assess the thermoelectric performances of these materials. The high figure of merit and thermoelectric efficiency highlight their potential importance for thermoelectric generators.