Graphene (Gr)/Si-based optoelectronic devices have attracted a lot of academic attention due to the simpler fabrication processes,low costs,and higher performance of their two-dimensional (2D)/three-dimensional (3D) hybrid interfaces in Schottky junction that promotes electron--hole separation.However,due to the built-in potential of Gr/Si as a photodetector,the Iph//dark ratio is often hindered near zero-bias at relatively low illumination intensity.This is a major drawback in self-powered photodetectors.In this study,we have demonstrated a self-powered van der Waals heterostructure photodetector in the visible range using a Gr/hexagonal boron nitride (h-BN)/Si structure and clarified that the thin h-BN insertion can engineer asymmetric carrier transport and avoid interlayer coupling at the interface.The dark current was able to be suppressed by inserting an h-BN insulator layer,while maintaining the photocurrent with minimal decrease at near zero-bias.As a result,the normalized photocurrent-to-dark ratio(NPDR) is improved more than 104 times.Also,both Ipd//dark ratio and detectivity,increase by more than 104 times at-0.03 V drain voltage.The proposed Gr/h-BN/Si heterostructure is able to contribute to the introduction of next-generation photodetectors and photovoltaic devices based on graphene or silicon.