Optoelectronic response and interfacial properties of BiOI/BiOX (X=F, Cl, Br) heterostructures based on DFT investigation

The bismuth oxyhalide heterostructures BiOI/BiOX (X ​= ​F, Cl, Br) are systematically investigated under the framework of first principles by using the Heyd-Scuseria-Enrzerhof (HSE06) hybrid functional with the van der Waals (vdW) corrections. The calculated formation energies of BiOI/BiOX ensure the stable adsorption state of BiOX nanosheet on BiOI surface. The indirect band gaps of BiOCl, BiOBr and BiOI are 3.83 ​eV, 3.41 ​eV and 2.31 ​eV, while the direct band gaps of BiOF, BiOI/BiOF, BiOI/BiOCl and BiOI/BiOBr are 4.85 ​eV, 2.66 ​eV, 2.40 ​eV and 2.14 ​eV, respectively. Compared with the original host materials, the reduced band gaps of BiOI/BiOX heterostructures lead to a large transition of electrons from valence band (VB) to conduction band (CB) due to the incorporation of I-5p orbital in VB. The absorption edge of BiOI/BiOX has a red shift with respect to BiOX nanosheet, leading to effectively enhanced absorption in ultraviolet (UV) and visible (Vis) light range. The total and planar-averaged (along z direction) charge density difference, as well as band edge potentials demonstrate that the built-in electric field can effectively separate the photogenerated carriers and benefit the photocatalytic performances under Vis light irradiation.