Indirect-to-direct band gap transition and optical properties of metal alloys of Cs(2)Te(1−x)Ti(x)I(6): 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 Cs(2)Te(1−x)Ti(x)I(6) solid solutions using first-principles calculations based on density functional theory. These compounds exhibit good structural stability compared to CH(3)NH(3)PbI(3). The results suggest that Cs(2)TeI(6) 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(4+) is 0.50. Moreover, an ideal direct band gap of 1.31 eV is obtained for Cs(2)Te(0.75)Ti(0.25)I(6). The calculated results indicate that all the structures are ductile materials except for Cs(2)Te(0.50)Ti(0.50)I(6). 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.