AI3 (A = As, Sb) Single Layers and Their vdW Heterostructure for Photocatalysis and Solar Cell Applications

Abstract

Two-dimensional (2D) layered materials and their van der Waals (vdW) heterostructures are promising candidates for highly efficient renewable energy application. On the basis of density functional theory, we investigated systematically the structure, stability, and electronic and optical properties of the group-VA trihalides AI3 (A = As, Sb) single layers and their vdW heterostructure. Our results suggest that the AI3 (A = As, Sb) single layers can be exfoliated from their bulk crystal easily and are also dynamically stable. Standard PBE predicts that the band gap of AI3 increases with element number of A, which is in conflict with the experimental results of the bulk. This unreasonable trend can be corrected when the spin–orbit coupling (SOC) effect is considered. The inconsistence between PBE and PBE+SOC calculations can be understood by the competition of two contrary effects for gap variation induced by lattice expansion and relativistic effect. Our PBE+SOC calculations indicate the AsI3 and SbI3 monolayers are potential photocatalysts for water splitting with indirect band gaps of 2.00 and 1.89 eV and moderate electron mobility (∼102 cm2 V–1 s–1). By stacking AsI3 and SbI3 vertically, a strongly binding vdW heterostructure with a type-II band alignment can be formed. Excitingly, the indirect band gap is reduced to 1.63 eV, and the absolute band edges still straddle the water redox potentials, implying that it can be used as a potential photocatalyst with strong adsorption for visible light. Moreover, such a vdW heterostructure can also be an effective excitonic solar cell material with theoretical power conversion efficiency up to 18%. These results show that the AI3 (A = As, Sb) single layers and their vdW heterostructure are potential candidates for future solar energy conversion applications.