Electronic structures and optical properties of BiOBr/BiOI heterojunction with an oxygen vacancy

BiOBr/BiOI heterojunction and oxygen vacancy promote the photocatalytic efficiency of BiOX-based catalysts. [Display omitted] •Experimentally observed photocatalytic promotion in BiOX catalysts is intepreted.•A built-in field is formed at the interface of BiOBr/BiOI heterostructure.•Oxygen vacancy promotes carrier separation and photocatalytic efficiency.•The combination of heterojunction and O vacancy improves light absorption efficiency. BiOX (X = Br, I) is one of the promising photocatalysts in solar energy conversion, but its photocatalytic efficiency needs further promotion. The BiOBr/BiOI heterostructures with and without an oxygen vacancy are designed and studied by means of first-principles calculations. Compared to monolayer BiOX, the heterostructure has a narrow band gap that favors optical absorption of low-energy light, and forms a built-in field at the interface that facilitates electron-hole separation. The addition of oxygen vacancy produces impurity levels that broaden the optical absorption into the infrared region and promote further the charge carrier separation. Our calculations reveal the origin of enhanced photocatalytic efficiency in the BiOX heterostructures, which is helpful for the design of novel structures with promoted photocatalytic performances.