The isolation of two-dimensional (2D) materials and the possibility to assemblage as a vertical heterostructure have significantly promoted the development of ultrathin and flexible devices. Here, we demonstrate the fabrication of high efficiency graphene/MoS2/Si Schottky barrier solar cells with Molybdenum disulfide (MoS2) interlayers. MoS2 monolayers were prepared by sulfurizing pre-annealed molybdenum foil, which allows not only to precisely control the layer number, but also the nondestructive transference onto arbitrary substrates. The inserted MoS2 layers function as hole transport layer to facilitate the separation of electron-hole pairs as well as electron blocking layer to suppress the recombination at graphene/silicon interfaces. By optimizing the thickness of MoS2 layers, a high photovoltaic conversion efficiency of 15.8% was achieved in graphene/MoS2/Si solar cells. This study provides a novel approach for the synthesis of large-area MoS2 monolayers and their potential application for ultrathin and low-cost photovoltaic devices.