Optoelectronic and photocatalytic applications of hBP-XMY (M = Mo, W; (X ≠ Y) = S, Se, Te) van der Waals heterostructures.

Stacking of layers via weak van der Waals interactions is an important technique for tuning the physical properties and designing viable electronic products. Using first-principles calculations, the geometry, electronic structure, and optical and photocatalytic performance of novel vdW heterostructures based on hexagonal boron phosphide (hBP) and Janus (XMY (M = Mo, W; (X ≠ Y) = S, Se, Te)) monolayers are investigated. Favorable (dynamically and energetically) stacking patterns of two different models of hBP-XMY heterostructures are presented with an alternative order of chalcogen atoms at opposite surfaces in SMSe. A direct type-II band alignment is obtained in both models of hBP-SMoSe, hBP-SWSe and hBP-SeWTe, while the rest are type-II indirect bandgap semiconductors. The Bader charge, and planer-averaged and plane-averaged charge density differences are investigated, which show that hBP donates electrons to the SMoSe and SWSe layer in the hBP-SMoSe and hBP-SWSe vdW heterostructure, while in the case of the hBP-SMoTe (hBP-SWTe) and hBP-SeMoTe (hBP-SeWTe) vdW heterostructures, the transfer of electrons is observed from SMoTe (SWTe) and SeMoTe (SeWTe) to hBP. The imaginary part of the dielectric function shows that the lowest energy transitions are dominated by excitons with a systematic red shift for heavier chalcogen atoms. Furthermore, the photocatalytic performance indicates that the hBP-XMY (M = Mo, W; (X ≠ Y) = S, Se, Te) vdW heterostructures in model-I are suitable for water splitting at pH = 0.