Programmable Interfacial Band Configuration in WS 2 /Bi 2 O 2 Se Heterojunctions.

van der Waals heterojunctions based on transition-metal dichalcogenides (TMDs) offer advanced strategies for manipulating light-emitting and light-harvesting behaviors. A crucial factor determining the light-material interaction is in the band alignment at the heterojunction interface, particularly the distinctions between type-I and type-II alignments. However, altering the band alignment from one type to another without changing the constituent materials is exceptionally difficult. Here, utilizing Bi 2 O 2 Se with a thickness-dependent band gap as a bottom layer, we present an innovative strategy for engineering interfacial band configurations in WS 2 /Bi 2 O 2 Se heterojunctions. In particular, we achieve tuning of the band alignment from type-I (Bi 2 O 2 Se straddling WS 2 ) to type-II and finally to type-I (WS 2 straddling Bi 2 O 2 Se) by increasing the thickness of the Bi 2 O 2 Se bottom layer from monolayer to multilayer. We verified this band architecture conversion using steady-state and transient spectroscopy as well as density functional theory calculations. Using this material combination, we further design a sophisticated band architecture incorporating both type-I (WS 2 straddles Bi 2 O 2 Se, fluorescence-quenched) and type-I (Bi 2 SeO 5 straddles WS 2 , fluorescence-recovered) alignments in one sample through focused laser beam (FLB). By programming the FLB trajectory, we achieve a predesigned localized fluorescence micropattern on WS 2 without changing its intrinsic atomic structure. This effective band architecture design strategy represents a significant leap forward in harnessing the potential of TMD heterojunctions for multifunctional photonic applications.