Zinc oxide nanoparticles (ZnO NPs) can be synthesized chemically, physically, and biologically. The biological method is deemed to be the cleanest and safest of all the available techniques because no hazardous chemicals are employed during the procedure. In this study, we aimed the green synthesis of ZnO NPs using different parts of the Lupinus pilosus L. plant due to their capping and reducing agents. Structural, optical, morphological, and electrical properties were investigated in detail. Scanning electron microscope results exhibited the micro/nanorods shape of ZnO NPs. Fourier transform infrared spectroscopy results confirmed peaks at 415.44 and 418.38 cm−1 which can be attributed to the Zn–O bond. Results from the UV–visible spectrophotometer showed peaks of ZnO clearly at 361 and 374 nm. Band gaps calculated from UV–VIS results were found to be 3.11 eV and 2.93 eV for ZnO nanoparticles, respectively. Typical planes of ZnO were obtained via X-ray diffraction (XRD) results. Moreover, ZnO nanoparticles showed crystallite size of 28.07 and 26.68 nm according to XRD results. Green synthesized ZnO NPs were used as interlayers between p-type Si and Al to obtain photodiode heterostructure and investigate the photosensing performances using current–voltage and current-transient measurements. Green synthesized ZnO nanorods recorded excellent photodetector properties reaching to 0.383 A/W responsivity and 7.03 × 1010 jones detectivity. Moreover, I–V measurements under 351 and 400 nm lights confirmed the applicability of the green synthesized of ZnO NPs in UV photodetection areas.