Indirect-to-direct band gap transition and optical properties of metal alloys of CsTe Ti I: a theoretical study.

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 CsTe Ti I solid solutions using first-principles calculations based on density functional theory. These compounds exhibit good structural stability compared to CHNHPbI. The results suggest that CsTeI 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 Ti is 0.50. Moreover, an ideal direct band gap of 1.31 eV is obtained for CsTeTiI. The calculated results indicate that all the structures are ductile materials except for CsTeTiI. 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.