Improved opto-electro-mechanical properties of Cs2TeBr6 double perovskite by Ge doping

Toxicity and instability of lead-based perovskite materials are two key issues for emerging inorganic perovskite solar cells. Therefore, the development of stable, lead-free inorganic perovskite materials has attracted great attention in the photovoltaic field. In this study, we report the effects of Ge-doped on the structural stability, mechanical, and optoelectronic properties of Cs2TeBr6 double perovskite by first-principles calculations. The results show that the Cs2Te1−xGexBr6 (x = 0, 0.25, 0.5, 0.75, and 1) doped system is structurally and mechanically stable, and the lattice constants decrease gradually with the increase of Ge4+ doping concentration. The Cs2TeBr6 undergoes a transition from brittleness to ductility after doping with Ge element, which is beneficial to the fabrication of flexible photovoltaic and optoelectronic devices. Especially, the perovskite derivative Cs2Te0.25Ge0.75Br6 has the highest ductility. Electronic structure calculations indicated that a transition from indirect to direct bandgap occurred when the Ge4+ doping concentration was increased from 0.25 to 0.5, which is beneficial to light absorption. According to the Shockley–Queisser limit, Cs2Te0.25Ge0.75Br6 is the best candidate for the solar cell absorber material due to the suitable bandgap (1.31 eV). Cs2Te0.75Ge0.25Br6 (1.46 eV) and Cs2Te0.5Ge0.5Br6 (1.23 eV) also show great potential as a solar cell absorber. Furthermore, an optical analysis revealed that the optical properties of the Cs2Te1−xGexBr6 doped system were improved with the doping of Ge4+ concentration.