Hybrid Heterostructures to Generate Long-Lived and Mobile Photocarriers in Graphene

We report the generation of long-lived and highly mobile photocarriers in hybrid van der Waals heterostructures that are formed by monolayer graphene, few-layer transition metal dichalcogenides, and the organic semiconductor F8ZnPc. Samples are fabricated by dry transfer of mechanically exfoliated MoS2 or WS2 few-layer flakes on a graphene film, followed by deposition of F8ZnPc. Transient absorption microscopy measurements are performed to study the photocarrier dynamics. In heterostructures of F8ZnPc/few-layer-MoS2/graphene, electrons excited in F8ZnPc can transfer to graphene and thus be separated from the holes that reside in F8ZnPc. By increasing the thickness of MoS2, these electrons acquire long recombination lifetimes of over 100 ps and a high mobility of 2800 cm2 V-1 s-1. Graphene doping with mobile holes is also demonstrated with WS2 as the middle layers. These artificial heterostructures can improve the performance of graphene-based optoelectronic devices.