Cs 2 CuLuY 6 (Y = Br, I) Double Halide Perovskites: Structural, Optoelectronic, Thermoelectric and Thermo-mechanical Insights for Sustainable Technologies

Abstract

This research provides an in-depth thorough assessment of the physical characteristics of Cs 2 CuLuY 6 (Y = Br, I) materials with DFT. Structural stability was investigated by tolerance factor, modified tolerance factor, octahedral factor, and formation energy evaluation, while thermodynamic stability was studied via free energy(G), entropy (S), and heat capacity (Cᵥ). The elastic constants extracted adhere to the Born stability requirements, ensuring that these DP materials are both mechanically and thermally durable. The evaluated Pugh's and Poisson's ratios show ductile nature, and the elastic anisotropy index (A) highlights anisotropic mechanical behaviour. The electronic band structure (EBS) indicates semiconducting energy gaps of 2.76 eV (YS-PBE0) for Cs 2 CuLuBr 6 , and 2.09 eV (YS-PBE0) for Cs 2 CuLuI 6 . Optical investigation reveals high absorption in the visible to ultraviolet zone, with first absorption coefficients (FAC) of our investigated compounds proposing their ability in optoelectronic and photovoltaic devices applications. Thermoelectric evaluation shows maximum ZT values of 0.99 (100 K) and 0.92 (1200 K) for Cs₂CuLuI₆, 0.78 and 0.74 for Cs₂AuLuI₆, 0.68 and 0.69 for Cs₂CuLuBr₆, and a nearly constant ZT of ~0.75 over 300-1200 K for Cs₂AuLuBr₆, indicating their suitability for lowtemperature cooling and high-temperature waste heat recovery applications. These findings point to Cs 2 XLuY 6 alloy as a versatile potential material for renewable energy applications, predominantly in solar cell and thermoelectric applications.