Eco‐Friendly Halide Perovskites Cs3Ag2X5 (X═Cl, Br, I): DFT Study on Electronic Structure, Optical and Thermodynamic Properties, Elastic Constants, and Toxicity

Abstract To explore lead‐free halide perovskites for optoelectronic applications, we studied the structural, electrical, optical, elastic, and thermodynamic properties of Cs 3 Ag 2 Cl 5 , Cs 3 Ag 2 Br 5 , and Cs 3 Ag 2 I 5 , using Cs 3 Cu 2 I 5 as a reference crystal. Hybrid HSE06 and five GGA functionals (PBE, RPBE, PW91, WC, and PBE SOL ) were examined to optimize geometry and band structure, with RPBE yielding the closest band gap (3.53 eV) to the experimental value (3.55 eV). Using RPBE, the band gaps of Cs 3 Ag 2 Cl 5 , Cs 3 Ag 2 Br 5 , and Cs 3 Ag 2 I 5 were determined to be 2.71, 2.90, and 3.26 eV, respectively. Among the four pseudopotential types, norm‐conserving pseudopotentials yielded the most accurate results. UV‐visible spectra showed high absorption in the 200–370 nm region, indicating potential for UV photodetectors. Elastic constants proved mechanical stability, whereas bonding investigations revealed both ionic and covalent properties. Additional optical properties such as dielectric function, absorption coefficient, refractive index, and Urbach energy were also investigated. In silico toxicity evaluations indicated that the materials are non‐toxic, non‐carcinogenic, and ecologically safe. These results indicate that Cs 3 Ag 2 X 5 (X═Cl, Br, I) compounds are suitable Pb‐free options for reliable and eco‐friendly UV optoelectronic devices.