<p>The quest for efficient and sustainable materials for energy applications is essential for managing global energy challenges. This work investigates the electronic structure, optical, mechanical, and thermoelectric nature of Ba₂CaXO₆ (X = Se and Te) double perovskite to identify their potential for photovoltaic applications. We calculate electronic band structures, density of state, and optical characteristics employing density functional theory (DFT) and using advanced exchange-correlation functionals. These materials possess direct wide band gaps, which make them ideal for photovoltaic and optoelectronic applications. Optical absorption investigations suggest substantial absorption in the ultraviolet-visible (UV-Vis) band, which improves their utility in solar energy harvesting. Both materials have mechanical stability, ductility, and near-isotropic elastic behavior, which makes them ideal for structural and device applications. Ba₂CaTeO₆ exhibits greater stiffness and shear resistance; while Ba₂CaSeO₆ appears more ductile and compliant. In addition, thermoelectric performance is examined employing Boltzmann transport theory, which reveals an appealing combination of high Seebeck coefficients and low thermal conductivity, indicating thermoelectric device functionality. The relationship between structural stability, electronic configuration, and thermal transport mechanisms is thoroughly examined, with an emphasis on the effect of X-site substitution on functional characteristics. Our results show that Ba₂CaSeO₆ and Ba₂CaTeO₆ have incredible potential as multifunctional materials for clean energy technologies, providing a route to enhance next-generation solar energy and thermoelectric systems.</p>