First-principles density functional theory calculations were employed to investigate the structural, electronic, and vibrational properties of the lead-free double perovskite Rb2YCuCl6 for photovoltaic applications. Structural optimization and equation-of-state analysis yield an equilibrium volume of approximately 798.2 ？3 and a bulk modulus of 30.89 GPa, confirming mechanical stability and moderate compressibility typical of halide-based frameworks. Electronic band-structure calculations reveal an indirect semiconducting band gap of ~1.30 eV, with the valence band primarily composed of Cu-d and Cl-p hybridized states and the conduction band dominated by Y-d states. This orbital arrangement supports efficient optical absorption and favorable charge-transport pathways. Phonon dispersion analysis shows no imaginary frequencies across the Brillouin zone, indicating dynamical stability and robust lattice behavior. The combined mechanical integrity, suitable band gap, and vibrational stability highlight Rb2YCuCl6 as a promising environmentally benign candidate for next-generation lead-free solar absorber materials.
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