First-Principles Study of the Chalcogenide Double Perovskites A2YTaSe6 (A = Ca, Sr, and Ba) for Solar Cell and Electronic Applications

This study focuses on the structural, electronic, optical, elastic, thermoelectric, and thermodynamic properties of chalcogenide double perovskites A 2 YTaSe 6 (A = Ca, Sr, and Ba) using density functional theory (DFT) calculations with the generalized gradient approximation Perdew–Burke–Ernzerhof (GGA-PBE) and modified Beck–Johnson potential (mBJ-GGA) approach. The study reveals that these compounds exhibit stability in the cubic perovskite structure with calculated optimized lattice constants of 10. 4717 Å (Ca 2 YTaSe 6), 10. 586 Å (Ba 2 YTaSe 6), and 10. 5245 (Sr 2 YTaSe 6), particularly in the nonmagnetic phase (NM), while their energies of formation are found to be −2. 94 eV, −2. 81 eV, and −2. 91 eV for Ca 2 YTaSe 6, Sr 2 YTaSe 6, and Ba 2 YTaSe 6, respectively. All three compounds display semiconducting nature with direct bandgaps at high-symmetry points \ ( (-) \) ranging from 1. 19 eV (Ca 2 YTaSe 6) to 1. 24 eV (Ba 2 YTaSe 6) and 1. 26 eV (Sr 2 YTaSe 6). Also, the positive elastic constants confirm that the three selected compounds are mechanically stable, with high bulk modulus and shear resistance. Similarly, the three-dimensional (3D) graphical representations demonstrate the anisotropic nature of the materials. Optical analysis, including the absorption coefficient, reflectivity, refractive index, and dielectric function, reveals strong absorption in the visible and near-ultraviolet (UV) regions, supporting their suitability for photovoltaic and electronic applications.