Indirect-to-direct band gap transition and optical properties of metal alloys of Cs2Te1−xTixI6: a theoretical study

Abstract

In recent years, double perovskites have attracted considerable attention as potential candidates for photovoltaic applications. However, most double perovskites are not suitable for single-junction solar cells due to their large band gaps (over 2.0 eV). In the present study, we have investigated the structural, mechanical, electronic and optical properties of the Cs₂Te_1−xTi_xI₆ solid solutions using first-principles calculations based on density functional theory. These compounds exhibit good structural stability compared to CH₃NH₃PbI₃. The results suggest that Cs₂TeI₆ is an indirect band gap semiconductor, and it can become a direct band gap semiconductor with the value of 1.09 eV when the doping concentration of Ti⁴⁺ is 0.50. Moreover, an ideal direct band gap of 1.31 eV is obtained for Cs₂Te_0.75Ti_0.25I₆. The calculated results indicate that all the structures are ductile materials except for Cs₂Te_0.50Ti_0.50I₆. Our results also show that these materials possess large absorption coefficients in the visible light region. Our work can provide a route to explore stable, environmentally friendly and high-efficiency light absorbers for use in optoelectronic applications.