Promising Blue Phosphorene/C2N van der Waals Type-II Heterojunction as Solar Photocatalyst: First-principes Study

Appropriate band structure and effective carrier separation are very important for the performance of solar photocatalyst. In this paper, based on first-principles calculations, it is predicted that blue phosphorene (BlueP) and C2N monolayer can form a promising metal-free type-II heterojunction. The electronic structure of BlueP/C2N heterojunction facilitates the overall water splitting reactions well. The projected band structure shows that the conduction band edge is contributed by C2N and the valence band edge is dominated by BlueP. Under the combination of driving force of band offset and the built-in electric field between the two layers, the photo-generated electron and holes can transfer spontaneously to the conduction band of C2N and the valance band of BlueP, respectively. Effective carries separation in the heterostructure can thus be achieved. More notably, the obtained light absorption of the BlueP/C2N junction shows obvious red-shift, which can greatly extend the area of light adsorption to visible light. We further propose that strain can be also used to modulate the band gap and the band edge positions of the heterojunction. Our results not only provide a theoretical design but also reveal the fundamental separation mechanism of photo-generated carriers in BlueP/C2N heterojunction.