Ferroelectric oxide material BiFeO 3 , which is promising for potential photovoltaic applications, has attracted the attention of researchers due to its large polarization. However, its development is limited by the small photocurrent, which is caused by the larger band gap and serious charge recombination. The sulfur, which has lower electronegativity than oxygen, is chosen to substitute for oxygen in BiFeO 3 to tune its band gap in present work. Based on the first-principles calculations, the effects of the substitution of S for O in BiFeO 3 on its electronic structure and photovoltaic properties are investigated. It is found that the BiFeO 3- x S x has lower electronic and optical band gap than that of pure BiFeO 3 . The band gap reduction mainly originates from the decreased charge of Fe due to the introduction of sulfur in BiFeO 3 , which causes the Fe 3d unoccupied states to shift toward the low energy level. Especially, the BiFeO 2 S 1 exhibits enhanced optical absorption and increased ferroelectric polarization (up to 160.2 µC/cm²) simultaneously comparing with pure BiFeO 3 . Meanwhile, the BiFeS 3 has relatively good ferroelectricity and improved electrical transport properties, which are favorable to promote charge separation and inhibit charge recombination. These results demonstrate that sulfur substitution constitutes a viable strategy for engineering the bandgap and polarization of ferroelectric materials.
Zhang et al. (Sun,) studied this question.