Graphene photodetectors capable of operating in the sub-bandgap region relative to the bandgap of semiconductor nanoparticles, as well as methods of manufacturing the same, are provided. A photodetector can include a layer of graphene, a layer of semiconductor nanoparticles, a dielectric layer, a supporting medium, and a packaging layer. The semiconductor nanoparticles can be semiconductors with bandgaps larger than the energy of photons meant to be detected.