Mechanical, Optoelectronic, and Thermoelectric Performance of Li-based Double Perovskites Li₂CuSbZ₆ (Z = Cl, Br, I): First-Principles Calculations

Lead-free double perovskites with tunable bandgap are emerging as a potential candidate for solar cell applications due to their high absorption coefficient, large structural stability, and environmentally friendly nature. In this work, Li₂CuSbZ₆ (Z = Cl, Br, I) double perovskites have been examined utilizing the FP-LAPW approach in WIEN2k software. Modified Becke-Johnson exchange-correlation potential and BoltzTrap code are adopted to calculate the optoelectronic and thermoelectric characteristics. The results showed that the DPs had negative formation energies and stable structures. Born stability criteria exhibited their mechanical stability. All compounds are semiconductors having direct band-gaps of 1.7, 1.3, and 0.9 eV for Li₂CuSbCl₆, Li₂CuSbBr₆, and Li₂CuSbI₆, respectively. Orbital contributions are later investigated through partial (PDOS) and total (TDOS) density of states calculations. Optical response analysis revealed that these perovskites are characterized by low energy loss and higher absorption in the visible region making them good candidates for solar cell devices. Additionally, their thermoelectric response such as the high figure of merit, Seebeck coefficients, and low thermal conductivity exposed their potential for conversion devices.