Multi-functional nitrogen self-doped graphene quantum dots for boosting the photovoltaic performance of BHJ solar cells

The tunable heteroatom doping density in graphene quantum dots (GQDs) can provide unique opportunities for advanced electrochemical and opto-electronic applications with control of intrinsic properties that allow exploiting new phenomena. Herein, we report a facile one-step synthesis of the nitrogen-doped high-crystallinity GQDs (nGQDs) from poly-acrylonitrile (PAN)-based CFs using the solvo-thermal cutting method. Interestingly, the optical properties of nGQDs can be simply controlled by varying the heat treatment temperature of the CFs with different N contents. We also conduct an in-depth study on the optical properties of nGQDs according to the variation of N atom density that can be readily modulated by controlling the graphitization temperature of CFs, via both experimental and computational analyses. The synthesized nGQDs are blended with PEDOT:PSS as an anodic buffer layer to induce efficient hole extraction and energy-down-shift in organic photovoltaic (OPV) devices that provide an enhanced power conversion efficiency (PCE) from 7.5% to 8.5%. Because of the wide absorption band, high carrier extraction, and non-toxicity, these nGQDs are demonstrated to be excellent probes for high-performance opto-electronic applications.