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Excitation transfer across the interfaces between graphene, perylenetetracarboxylic diimide (PTCDI), and titanyl phthalocyanine (TiOPc) was studied by using transient absorption and photoluminescence spectroscopy. Both photoluminescence quenching and transient absorption measurements confirm the presence of a type-II interface between PTCDI and TiOPc. While the graphene/PTCDI interface is expected to exhibit type-I behavior, transient absorption measurements indicate that only electrons transfer from PTCDI to graphene, with no evidence of hole transfer. Density functional theory calculations reveal significant ground-state electron transfer from graphene to PTCDI, resulting in band bending that prevents excited holes from transferring from PTCDI to graphene. This feature is exploited in a trilayer heterostructure of graphene/PTCDI/TiOPc, where the spatial separation of photoexcited electrons and holes in graphene and TiOPc, respectively, leads to the formation of long-lived photoexcitations with a lifetime of approximately 500 ps. Furthermore, spatially resolved transient absorption measurements reveal the immobile nature of these excitations, confirming that they are charge-transfer excitons rather than free electrons and holes. These results provide valuable insights into the complex interlayer photoexcitation transfer properties and demonstrate precise control over the layer population and the recombination lifetime of photocarriers in such hybrid heterostructures. 

We report experimental evidence that MoSe2 and WS2 allow the formation of type-I and type-II interfaces, according to the thickness of the former. Heterostructure samples are obtained by stacking a monolayer WS2 flake on top of a MoSe2 flake that contains regions of thickness from one to four layers. Photoluminescence spectroscopy and transient absorption measurements reveal a type-II interface in the regions of monolayer MoSe2 in contact with monolayer WS2. In other regions of the heterostructure formed by multilayer MoSe2 and monolayer WS2, features of type-I interface are observed, including the absence of charge transfer and dominance of intralayer excitons in MoSe2. The coexistence of type-I and type-II interfaces in a single heterostructure offers opportunities to design sophisticated two-dimensional materials with finely controlled photocarrier behaviors.