Exploring the structural, electronic, optical, mechanical and thermoelectric properties of copper based double perovskites Rb2YCuX6 (X=Br, I)

Recently advances in perovskites materials have highlighted their exceptional photoelectric properties, sparked substantial scientific interest and felled effort to identify new perovskite variants with improved stability and environment friendliness. These materials are emerging as promising candidates for efficient solar light harvesting. In our study, we utilize first principle calculations grounded in Density Functional Theory (DFT) to explore the structural, electronic, mechanical, optical and thermoelectric characteristics of Rb₂YCuX₆ (X = Br, I) for advance solar cell and thermoelectric applications and support the advancement of environmentally sustainable perovskites materials. Materials with stable cubic perovskite structures are found to exhibit structural stability as determined by the tolerance factor. The thermodynamic stability is verified by computing the formation energy. Phonon dispersion curve is calculated to confirm the dynamic stability. The examination of electronic properties shows that for Rb₂YCuBr₆ and Rb₂YCuI₆ have semiconducting nature. Band gaps for Rb₂YCuBr₆ and Rb₂YCuI₆ have been determined to be 2.28 eV and 2.21 eV, respectively. Elastic constants measurement confirms the mechanical stability and reveals that they are anisotropic and ductile. In the visible and near-visible wavelength range, both materials exhibit strong optical absorption. Furthermore, we calculated the thermoelectric properties of both materials. The maximum Seebeck coefficient of 1.55 × 10⁻³ V/K is found for both materials at room temperature. Based on the research, these materials may make the finest choices for thermoelectric and optoelectronic applications.