A DFT investigation of Ti-substituted CaZrS3 for tailored photovoltaic properties

Transition Metal Chalcogenide Perovskites (TMCP) have been in the spotlight due to their exceptional optoelectronic properties. ${\mathrm{CaZrS}}_3$ is one among them with an experimental bandgap of 1.90 eV. If its bandgap is tuned to lower values, it can be employed in additional photovoltaic applications, such as solar cell absorbers. In this work, the transition metal element Zr in ${\mathrm{CaZrS}}_3$ is substituted with Ti atoms in different proportions and the optoelectronic properties are investigated using Density Functional Theory (DFT). The optoelectronic calculations are all done using the DFT+U method including the spin–orbit coupling. With substitutional alloying, we successfully tuned the energy gap from 1.91 eV to 1.18 eV and the photovoltaic properties were also observed to be modified. For the substituted ${\mathrm{CaZr}}_{1-x}{\mathrm{Ti}}_x{S}_3$ samples, large birefringence is observed. This indicates enhancement in optical anisotropy via substitutional alloying which is significant in both linear and nonlinear optoelectronic applications like polarizers, wave plates etc.