Investigating the Physical Characteristics of Halide Double Perovskites X2LiSbI6 (X = K, Cs): A First-Principles Approach

This research presents the structural, dynamic, mechanical, optoelectronic, and thermoelectric (TE) features and energy storage potential of new halide double perovskite (HDPs) X2LiSbI6 (X = K, Cs) utilizing the modified Becke-Johnson potential (mBJ) within DFT. The materials' thermal stability was assessed through thermodynamical factors and formation enthalpy calculations and dynamical stability was confirmed by phonon dispersion curves. The brittle nature of Cs2LiSbI6 and ductile nature of K2LiSbI6 were validated by analyzing their mechanical properties. The indirect band gaps (Eg) for K2LiSbI6 and Cs2LiSbI6 calculated using mBJ potential are 2.2 eV and 2.1 eV, correspondingly. Optical features were analyzed to determine the suitability of these halides for photovoltaic devices. The optical absorption alpha(omega) graph shows largest values at 9.24 and 9.81 eV for Cs2LiSbI6 and K2LiSbI6, respectively. The BoltzTraP code was utilized to calculate TE properties, which revealed thermal energy conversion mechanisms and efficiency by evaluating thermoelectric characteristics. The TE efficiency parameter (zT) shows maximum values to be 0.73 at 750 K for Cs2LiSbI6 and 0.71 at 600 K for K2LiSbI6. It indicates their suitability for energy harvesting technologies. Findings show that these HDPs demonstrate significant potential for applications in energy-efficient devices, optoelectronic technologies, and TE systems.