Atomically thin layered materials such as graphene and transition-metal dichalcogenides exhibit great potential as active materials in optoelectronic devices because of their high carrier-transporting properties and strong light-matter interactions. Here, we demonstrated that the photovoltaic performances of graphene/Si Schottky junction solar cells were significantly improved by inserting a chemical vapor deposition (CVD)-grown, large MoS2 thin-film layer. This layer functions as an effective passivation and electron-blocking/hole-transporting layer. We also demonstrated that the photovoltaic properties are enhanced with increasing number of graphene layers and decreasing thickness of the MoS2 layer. A high photovoltaic conversion efficiency of 11.1% was achieved with the optimized trilayer-graphene/MoS2/n-Si solar cell. ; Comment: Main text: 24 pages, 5 figures; Supporting Information: 8 pages, 5 figures, 1 table