<p>In this study, the thermoelectric, optical, and spin-polarized magnetic properties of double halide perovskites Cs₂SrTaCl₆, Cs₂SrTaBr₆, and Cs₂BaTaBr₆ are systematically investigated to assess their potential for photovoltaic and related optoelectronic applications. The calculated thermal conductivity values follow the trend: Cs₂SrTaCl₆ (2.68 × 10¹⁴ W/m·K·s) &gt; Cs₂BaTaBr₆ (2.32 × 10¹⁴ W/m·K·s) &gt; Cs₂SrTaBr₆ (2.19 × 10¹⁴ W/m·K·s). The corresponding power factor values are found to be: 2.69 × 10¹⁰ W/m·K²·s for Cs₂SrTaCl₆, 2.59 × 10¹⁰ W/m·K²·s for Cs₂BaTaBr₆, and 2.39 × 10¹⁰ W/m·K²·s for Cs₂SrTaBr₆. Optical analysis reveals peak real dielectric constants near 6.0&#xa0;eV as follows: Cs₂SrTaBr₆ (5.14) &gt; Cs₂BaTaCl₆ (4.77) &gt; Cs₂SrTaCl₆ (4.70). The static refractive indices are: Cs₂SrTaBr₆ (2.45) &gt; Cs₂BaTaCl₆ (2.26) &gt; Cs₂SrTaCl₆ (2.17). Spin-polarized magnetic calculations indicate paramagnetic behavior in all three compounds. The magnetic integrated spin density values are 3.36 ħ/2 for Cs₂BaTaCl₆, 3.35 ħ/2 for Cs₂SrTaCl₆, and 1.34 ħ/2 for Cs₂SrTaBr₆, respectively. These findings highlight the promising multifunctional nature of these perovskites for thermoelectric and photovoltaic device applications.</p>