Polarization and built-in electric field improve the photocatalytic overall water splitting efficiency of C2N/ZnSe heterostructures

Abstract

The type-II van der Waals heterostructure photocatalytic system is an ideal band alignment structure for photocatalysis, which the high separation efficiency of photo-induced carriers. By using density functional theory, we predicted two van der Waals (vdW) heterostructures, namely, C2N/ZnSe-ML (monolayer) and C2N/ZnSe-BL (bilayer), respectively. For the C2N/ZnSe-BL heterostructure, it has an intrinsic type-II band alignment, in which the built-in electric field formed at the interface accelerates the separation of photogenerated electrons-holes in heterostructure. The photogenerated electrons-holes have been accumulated near the conduction band minimum of C2N and the valence band maximum of ZnSe-BL, respectively, which the C2N/ZnSe-BL heterostructure is a type-II photocatalytic heterostructure. However, the C2N/ZnSe-ML heterostructure has a strong built-in electric field from C2N to ZnSe-ML because the ZnSe-ML is a polarized material with a polarized electric field inside, which form a type-Ⅱ heterostructure and realizes the effective separation of photogenerated electron-holes under the action of built-in electric field. The C2N/ZnSe-X (ML, BL) heterostructures are both direct band-gap semiconductors and they can harvest sunlight efficiently almost in the range of the solar spectrum. These distinguishing features confirm that the C2N/ZnSe-X (ML, BL) heterostructures have promising prospects in the sphere of photocatalysis for the separation of photogenerated electron-holes.