DFT and SCAPS-1D investigation of Ae₂LiSbI₆ (Ae = Rb, Cs) perovskites for solar energy applications

Lead-free halide double perovskites have emerged as promising alternatives to Pb-based materials for solar energy applications. In this work, structural, optoelectronic, and thermodynamic properties of Ae₂LiSbI₆ (Ae = Rb, Cs) double perovskites are studied using first-principles calculations and device-level simulations. Both compounds crystallize in a stable cubic phase, supported by favorable tolerance factors and negative formation energies, ab initio molecular dynamics (AIMD) and phonon dispersion analysis. Their indirect band gaps, 1.694 eV for Rb2LiSbI6 and 1.733 eV for Cs2LiSbI6 (GGA-PBE), and 1.721 eV and 1.763 eV for Rb and Cs, respectively (HSE06), fall within the optimal range for visible-light absorption, while their strong optical responses, characterized by high absorption coefficients and low reflectivity, underscore their excellent potential for efficient solar photon harvesting. SCAPS-1D simulations further predict power conversion efficiencies (PCEs) approaching 28%, positioning these double perovskites as promising and competitive candidates for next-generation photovoltaic technologies, based on theoretical screening and idealized device simulations. These findings not only expand the family of environmentally benign perovskites but also provide insights into the design of stable, high-performance absorbers for sustainable solar cells.