Graphene (GR) photodetector devices have broad-range absorption, whereas WO3 devices are known to be sensitive to the ultraviolet (UV) radiation. In this work, we mainly focus on developing a hybrid bilayer of a WO3/GR photodetector device, which is sensitive to detect both UV and visible radiations. Introduction of GR onto WO3 would tune the device to sense visible light and also enhances the photocurrent under UV illumination. The final device can be expected to show good photocurrent, responsivity, and detectivity with minimized shot noise under the illumination of both UV and visible lights. This study provides a detailed mechanism of how the photoelectrons are drawn into GR without being trapped into WO3 due to the presence of the built-in electric field at the GR and WO3 interface and also explains in what manner this in-built field, applied bias voltage, and defect states assist for achieving the superior and tunable UV-visible photodetectors. © 2021 American Chemical Society.