Electron-hole pair separation and photocurrent conversion at two-dimensional (2D) and three-dimensional (3D) hybrid interfaces are important for achieving high performance, self-powered optoelectronic devices such as photodetectors. In this regard, herein, we designed and demonstrated a graphene/silicon (Gr/Si) (2D/3D) van der Waals (vdW) heterostructure for high-performance photodetectors, where graphene acts as an efficient carrier collector and Si as a photon absorption layer. The Gr/Si heterojunction exhibits superior Schottky diode characteristics with a barrier height of 0.76 eV and shows good performance as a self-powered detector, responding to 532 nm at zero bias. The self-powered photodetector functions under the mechanism of photovoltaic effect and exhibits responsivity as high as 510 mA W with a photo switching ratio of 10 and a response time of 130 μs. The high-performance vdW heterostructure photodetector demonstrated herein is attributed to the Schottky barrier that effectively prolongs the lifetime of photo-excited carriers, resulting in fast separation and transport of photoexcited carriers. The self-powered photodetector with superior light harvesting and carrier transport behaviour is expected to open a window for the technological implementation of Si-based monolithic optoelectronic devices.