Optimization and numerical design of lead-free double halide perovskites K 2 AgSbX 6 for photovoltaic applications through WIEN2K and SCAPS-1D

In this study, we analyze the structural, electronic, optical, and thermoelectric properties of lead-free double halide perovskite K 2 AgSbX 6 ( X = Cl , F , I ) materials for potential solar energy and thermal conversion applications. First principles calculations were performed using the full-potential linearized augmented plane wave (FP-LAPW) method through WIEN2k and BoltzTrap, employing both GGA and mBJ exchange–correlation functionals. Substituting iodine with chlorine or fluorine increased the energy band gap from 1.07 eV to 2.23 eV and 4.29 eV, well-matched to the visible spectrum and enhancing solar absorption. Optical analyses revealed strong ε₂(ω) peaks and high absorption coefficients. Due to their promising optoelectronic potentials, K 2 AgSbCl 6 and K 2 AgSbI 6 were analyzed via SCAPS-1D simulations, with K 2 AgSbF 6 was excluded for weak electronic properties The simulated devices show promising results for photovoltaic applications. The optimized device based on K 2 AgSbCl 6 achieves a PCE of 12.31%, V OC of 1.784 V, J SC of 8.15 mA / cm 2 , and FF of 85.06%, while the K 2 AgSbI 6 achieves a PCE of 28.44%, V OC of 0.83 V, J SC of 42.92 mA / cm 2 , and FF of 77.49%, with minimal recombination losses, highlighting K 2 AgSbCl 6 and K 2 AgSbI 6 as promising lead-free and eco-friendly next-generation perovskite solar cell absorbers. • First combined study of three double halide perovskites K 2 AgSbX 6 ( X = Cl , F , I ) for photovoltaic applications. • The K 2 AgSbF 6 fully characterized for the first time in literature. • DFT (GGA+ mBJ) predicts structural, electronic, optical, and thermoelectric properties. • Band gaps corrected using mBJ functional. • SCAPS-1D simulation confirms photovoltaic potential.