Flexible Broadband Graphene Photodetectors Enhanced by Plasmonic Cu_3-x P Colloidal Nanocrystals

The integration of graphene with colloidal quantum dots (QDs) that have tunable light absorption affords new opportunities for optoelectronic applications as such a hybrid system solves the problem of both quantity and mobility of photocarriers. In this work, a hybrid system comprising of monolayer graphene and self-doped colloidal copper phosphide (Cu_3-x P) QDs is developed for efficient broadband photodetection. Unlike conventional PbS QDs that are toxic, Cu_3-x P QDs are environmental friendly and have plasmonic resonant absorption in near-infrared (NIR) wavelength. The half-covered graphene with Cu_3-x P nanocrystals (NCs) behaves as a self-driven p-n junction and shows durable photoresponse in NIR range. A comparison experiment reveals that the surface ligand attached to Cu_3-x P NCs plays a key role in determining the charge transfer efficiency from Cu_3-x P to graphene. The most efficient three-terminal photodetectors based on graphene-Cu_3-x P exhibit broadband photoresponse from 400 to 1550 nm with an ultrahigh responsivity (1.59 × 10⁵ A W^-1 ) and high photoconductive gain (6.66 × 10⁵ ) at visible wavelength (405 nm), and a good responsivity of 9.34 A W^-1 at 1550 nm. The demonstration of flexible graphene-Cu_3-x P photodetectors operated at NIR wavelengths may find potential applications in optical sensing, biological imaging, and wearable devices.