Si:WO₃heterostructure for Z-scheme water splitting: an ab initio study

Abstract

The Si:WO 3 heterostructure is expected to have suitable band alignment for the Z-scheme water splitting, but the heterostructure interfaces have been scarcely studied. In this work, a series of interfaces between the WO 3 (100) and Si (001) surfaces, which have a small lattice-mismatch, are studied using ab initio calculations. When there is no atom diffusion across the interface, a Si-O bonded interface with Si dimers is the most stable. Analysis of the electronic structure shows that the interfacial Si and O atoms are fully saturated, leading to a clean interface without localized gap states. O diffusion from WO 3 into Si is found to be thermodynamically possible, but it does not affect the full bond saturation of the interfacial atoms. A type-II band alignment exists between Si and WO 3 , with the WO 3 conduction band about 0.5 eV higher than the Si valence band, which is not influenced by O diffusion. A band diagram is plotted for the Si:WO 3 heterostructure to evaluate its photocatalytic capability, and the influence of the small Schottky barrier and the interface amorphous layer is discussed.

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