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 Cs 2 AgInX 6 (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 Cs 2 AgInBr 6 and Cs 2 AgInCl 6 is much lower than that of MAPbI 3 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 PbI 2 ‐terminated and MAI‐terminated surfaces. These materials demonstrate better ductility and mechanical stability than their corresponding 3D perovskites. For Cs 2 AgInBr 6 and Cs 2 AgInCl 6 , 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 Cs 2 AgInBr 6 may achieve efficiencies competitive with MAPbI 3 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.