•An alternative of organic-inorganic and Pb based perovskites.•Absorption in visible region increase their potential for solar cells.•Minimum optical loss and reflectivity.•High value of thermodymic and structural stability.•Low thermal conductivity and high figure of merit. The double perovskites are emerging materials for renewable energy and potential alternatives to the organic and lead-based solar cells. In the present work, we have elaborated on the optoelectronic, thermoelectric, and thermodynamic properties of new double perovskites Rb2TeX6 (X = Cl, Br, and I). The tolerance factor and enthalpy of formation have been reported for structural and thermodynamic stability. The Passion and Pugh's ratio has been calculated from elastic constants to distinguish the brittle and ductile character. Furthermore, the highly precise Tran-Blaha modified Becke-Johnson potential exchange-correlation potential is executed to elaborate the band gaps. The band gaps exhibit from ultraviolet to visible region (3.2 eV–1.80), which increases the performance of these double perovskites for optoelectronic devices and solar cell applications. The optical behavior has been elucidated by the absorption of photon energy, polarization, and optical losses. The absorption is shifted to lower energy due to tuning of the band gap by the replacement Cl with Br and I ions. Thermoelectric behavior has been described by electrical and thermal conductivities, Seebeck coefficient, and figure of merit, while thermodynamic performance is attributed by Debye temperature and Navier sound velocities.