Engineering the Band Gap of Chalcogenide Perovskite CaZrS3 via Ti Alloying for Enhanced Photovoltaic Performance

Abstract Band gap modulation of chalcogenide perovskites has proven an effective strategy for optimizing their photovoltaic performance. In this work, we investigate the effect of Ti alloying on the structural, electronic, optical, and photovoltaic properties of CaZrS3 using density functional theory (GGA+U) and spectroscopic-limited maximum efficiency (SLME). The results show a significant reduction in the band gap after alloying, decreasing from 1.859 eV for CaZrS3 to 1.382 and 1.298 eV for CaZr0.75Ti0.25S3 and CaZr0.5Ti0.5S3, respectively, improving visible light absorption. All compounds exhibit high absorption coefficients, greater than 105 cm–1, near the band edge, attributed to strong p–d interband transitions involving the 3p orbitals of sulfur and the d orbitals of Zr and Ti. Electron localization function analysis reveals more covalent Ti–S interactions than Zr–S bonds, suggesting increased orbital hybridization after Ti alloying. Finally, the SLME results reveal an improvement in the theoretical power conversion efficiency, increasing from 18% for CaZrS3 to 24 and 27% for CaZr0.75Ti0.25S3 and CaZr0.5Ti0.5S3 at L = 800 nm, confirming that the Ti alloy is an effective strategy for optimizing the optoelectronic and photovoltaic properties of CaZrS3.