摘要：Two-dimensional （2D） materials have attracted growing attention since the discovery of graphene [1]. Transition metal dichalcogenide （TMD） semiconductors, such as MoS2 and WS2, became popular materials in recent years, because they usually have intrinsic bandgaps and an in- direct-to-direct bandgap transition from bulk to mono- layer limit [2-6]. Although graphene and TMDs are promising materials in field-effect devices [7-9], their heterostructures are more advanced in charge-splitting functions for the applications in optoelectronic devices [10-15].