Toward Efficient and Sustainable Perovskite Solar Cells: A Combined First-Principles and Device Simulation Study of K₂LiGa(Cl/Br)₆ for Photovoltaic Performance Optimization

Abstract

This work employs an integrated computational framework combining density functional theory (DFT) and SCAPS-1D device simulations to investigate the lead-free double halide perovskites K2LiGaCl6 and K2LiGaBr6 as potential photovoltaic absorbers. First-principles calculations confirm that both compounds are thermodynamically and mechanically stable in the cubic elpasolite structure, and exhibit direct band-gap semiconducting behavior with tunable optoelectronic properties through halide substitution. The calculated band gaps of 2.53 eV for K2LiGaCl6 and 1.19 eV for K2LiGaBr6 indicate suitability for UV/tandem and visible-light photovoltaic applications, respectively, supported by strong optical absorption coefficients on the order of 10 4 cm⁻¹ in the visible region. Mechanical analysis reveals ductile characteristics and moderate elastic anisotropy, suggesting compatibility with thin-film device architectures. Furthermore, device-level simulations demonstrate that optimized solar-cell configurations based on K2LiGaBr6 can achieve simulated power conversion efficiencies approaching 27.13%, with high open-circuit voltage and fill factor. These results identify K2LiGaBr6 as a promising environmentally benign alternative to lead-based perovskites, and provide a rational multiscale design strategy for the development of sustainable, high-performance photovoltaic materials.