Thermal, optoelectronic and thermoelectric properties of inorganic double perovskites semiconductors Cs2(Sn, Pt, Te)I6 for application as intermediate-band solar cells

First-principle calculations using the Wien2k code and the GGA-mBJ exchange potential were used in the study of the thermodynamic, dynamic, chemical and elastic stability, as well as the electronic, optical and thermoelectric properties of Cs2(Sn, Pt, Te)I6. The presence of an intermediate band in Cs2(Sn, Pt, Te)I6 semiconductors confirmed by absorption peaks appeared at photon energy corresponding to the band gap enhances the efficiency of solar cells. The ideal band gap, high dielectric constants and optimal absorption make the double perovskites under study perform well in solar cells. The calculated minimum formation energy, Helmholtz free energy and phonon modes through the first Brillouin zone for the investigated Cs2(Sn, Pt, Te)I6 family confirm their thermal, thermodynamic and dynamic stability. The acoustic phonon contribution modes come from the Cs-6s and I-5p electrons, while the Pt-6s, Sn-5p, Te-5p and I-5p electrons participate in the optical phonon modes. The narrowness of the upper valence band and the band gap in the visible region for Cs2PtI6 advantage this double perovskite in energy harvesting. The geometric Goldschmidt tolerance factor value between 0.8 and 1.0 and octahedral factor 0.41 indicate that Cs2SnI6 double perovskite is more stable. •We explore Cs2(Sn, Pt, Te)I6 as potential thermoelectric materials because of their intrinsic p-type conductivity.•Efficient and high-performance thermoelectric materials such as Cs2(Sn, Pt, Te)I6 exhibit low electronic thermal conductivity due to phonon-phonon scattering and optical emission.•The weaker elastic constants explain the large inter reticular distances and lower hardness and binding ionic forces.•The analysis of electronic structures proves that the band gap and optical gap in these materials are dictated by the energies of the empty (Sn-5s, Te-5p and Pt-6s) states at the lowest unoccupied band.•The efficiency of Cs2SnI6, Cs2TeI6 and Cs2PtI6 in the conversion of heat into electrical energy is due to the p-type charge carriers, which give almost a factor of merite estimated at 83 %, 80.5 % and 78 %.•The considerable charge in the (Sn, Pt, Te)-I bonds due to a small difference in electronegativity and the hybridization between these levels reflects their covalent bonds.