Water Molecules Adsorption, Stability, and Optoelectronic Characteristics of Pb-Free Hybrid Double Perovskites Cs2AgInX6 (X = Br, Cl) for Solar Cells Application: A DFT Analysis

Abstract

The development of halide double perovskites has received a lot of interest from many researchers due to solving the problem of poor stability and toxicity of lead-based perovskites, which hinders the commercialization of perovskite solar cells. Therefore, in this work, the adsorption of water molecules, stability, optical, and electronic properties of double perovskites Cs₂AgInX₆ (X = Br, Cl) are investigated using Density Functional Theory (DFT) calculations. Theoretical analysis shows that these double perovskites are thermodynamically stable. The diffusion coefficient of water in layers of Cs₂AgInBr₆ and Cs₂AgInCl₆ is much lower than that of MAPbI₃ according to means square displacement analysis, and also based on values of adsorption energy, the hydrophilicity of the proposed structure is lower than that of PbI₂-terminated and MAI-terminated surfaces. These materials demonstrate better ductility and mechanical stability than their corresponding 3D perovskites. For Cs₂AgInBr₆ and Cs₂AgInCl₆, direct bandgap values are 1.49 and 3.14 eV, respectively, using hybrid Perdew-Berke-Ernzerhof + spin-orbit-coupling(PBE0+SOC) functional. Calculations of key solar cell parameters predict that Cs₂AgInBr₆ may achieve efficiencies competitive with MAPbI₃ due to its high short-circuit current, making it a promising stable, non-toxic perovskite absorber material. This work provides fundamental insights that can guide further research on double perovskites for lead-free, moisture-resistant perovskite solar technologies.