Electronic structure and anion engineering for perovskite oxysulfide BaTi(O,S)3

Barium titanate (BaTiO3), as a classical ferroelectric material, has been widely applied in photovoltaic cells due to its unique ferroelectric photovoltaic effect for charge separation. However, its large bandgap (3.40 eV) limits sunlight absorption efficiency. Anion substitution by elements with smaller electronegativity has been demonstrated as an emergent strategy for reducing bandgaps for traditional oxides. This work reports the electronic structure and anion engineering to replace the oxygen atoms in BaTiO3 with sulfur atoms, leading to a new material system of perovskite oxysulfide BaTi(O,S)3. First-principles calculations show that the bandgap of BaTiOS2 and BaTiS3 are 1.25 and 0.13 eV, respectively, which are significantly smaller than that of BaTiO3. Meanwhile, the optical absorption of BaTiOS2 and BaTiS3 is shown to be in the range of visible light and is improved remarkably as compared with BaTiO3. The presented results suggest that BaTiOS2 and BaTiS3 are promising candidates for photovoltaic materials.