Determining the Band Alignment at the BiVO4|NiOOH Interface Using the Hybrid DFT Technique

It is important to understand the band offsets between semiconductors, which are crucial to determine the direction of electron transfer at the interfaces. Two methods are normally used to determine the direction from the first principles: alternating slabs put in contact (without empty spaces between them) and separate calculations for each material surface in the presence of vacuum spaces. The first method may introduce distortions due to insufficient epitaxial match, which may lead to bandgap changes, and the second may neglect electron transfer at the interface, which may be important in systems exhibiting very different average electronegativities. This can also imply a spill of electronic density into the vacuum spaces, which will not be present at real interfaces. Herein, both approaches were used to study the BiVO4/NiOOH interface, and the results were compared; the results are here relevant for photoelectrochemistry. The method is based on hybrid Density Functional Theory methods which give for the bulk phases Bandgap values that agree with the experimental ones (in one case, a value reflecting the theoretical value). The distances between the (hybrid DFT-derived) band positions and the corresponding profiles of the Hartree electrostatic potential were transferred to the interfaces. This helps determining the appropriate positions of the valence and conduction bands (as has been suggested by C. G. Van de Walle & R. M. Martin, Phys. Rev. B 1987, 35, 8154). It is ensured that the interfaces are nonpolar (Tasker’s criterion: P.W. Tasker, J. Phys. C: Solid State Phys. 1979, 12, 4977).