Synthesis of Nitrogen-Doped Graphene Quantum Dots for High Efficiency Self-Powered UV Photodetector

We report a straightforward bottom-up approach for the synthesis of high-quality nitrogen-doped graphene quantum dots (NGQDs). This approach is cost-effective, environmentally friendly, and suitable for production of high quality NGQDs on large-scale. The as-synthesized NGQDs have high crystalline quality with an average size of 3.26 nm, are water soluble, and show strong fluorescence. The UV-vis spectra indicate that N-doping introduces new energy levels into the electronic structure of graphene, which tune the optical properties resulting in photoluminescence quantum yield (PLQY) of 73%. The NGQDs show excitation wavelength-dependent fluorescence with a maximum excitation and emission at 340 and 431 nm, respectively. Using the as-synthesized NGQDs, we fabricated a high-efficiency fast-response self-powered UV photodetector. Under the illumination of 365 nm UV light with power density of 25 mW/cm, the NGQD photodetector shows a high photoresponsivity of 37 A/W, detectivity of 1 * 10 Jones, and external quantum efficiency (EQE) of 12.6 * 10 %. This UV photoresponse is fast, with rise time of 0.29 s and fall time of 0.33 s. This work paves the way for the development of graphene-based high-performance optoelectronic devices.