This paper presents three self-powered photodetectors namely, p+-bilayer graphene (BLG)/n+-ZnO nanowires (NWs), p+-BLG/n+-Si NWs/p--Si and p+-BLG/n+-ZnO NWs/p--Si. The Silvaco Atlas TCAD software is utilized to characterize the optoelectronic properties of all the devices and is validated by analytical modeling. The proposed dual-junction photodetectors cover broadband spectral response varying from ultraviolet to near-infrared wavelengths. The dual-heterojunction broadband photodetector exhibits photocurrent switching with the rise and fall time of 1.48 and 1.27 ns, respectively. At -0.5 V bias, the highest external quantum efficiency, photocurrent responsivity, specific detectivity, and the lowest noise equivalent power of 71%, 0.28 A W-1, 4.2 × 1012 cmHz1/2 W-1, and 2.59 × 10-17 W, respectively, are found for the dual-heterojunction device with a wavelength of 480 nm at 300 K. The proposed nanowires based photodetectors offer great potential to be utilized as next-generation optoelectronic devices.