7. Top-Down Synthesized Graphene Quantum Dots in Photovoltaic Devices

Chapter 7 explores the significant potential of graphene quantum dots (GQDs) in the fabrication of high-performance optoelectronic devices, low toxicity, tunable photoluminescence, and cost-effectiveness. The chapter addresses the challenges in implementing GQDs in devices, particularly the issues of poor adhesion on substrates and interface contact resistance. To deeply understanding the physical mechanisms of GQDs in device contexts, the chapter explores surface functionalization and interface heterojunctions. It details various designs of GQD-based photodetectors utilizing top-down synthesized GQDs as the active layer. The GQDs are passivated by polyethylene glycol (PEG) to form the PEG-passivated GQDs to modify the surface to be hydrophilic. Furthermore, Poly(3,4-ethylenedioxythiophene)-poly(styrenesulfonate) (PEDOT: PSS) is functionalized as the hole transport layer, forming a heterojunction at the interface of PEG-GQDs/PEDOT: PSS in planar devices. The device is fabricated by physical vapor deposition (PVD) and solution processing method. The performance of the device is characterized by the behavior under the illumination of UV and LED light. Optical and electrical characterization methods are employed to study charge separation and carrier transport mechanisms. Conclusively, the GQD-based photodetectors as simple yet effective solutions, showcasing their promising performance in optoelectronic applications.