Enhanced performance of self-powered ZnO-based PEC type UV photodetectors by loading GQDs to construct heterojunctions

The construction of semiconductor heterojunctions is an effective approach to enhance the performance of optoelectronic devices. In this study, graphene-quantum-dots (GQDs) were grown on ZnO nanorods arrays in-situ to form intimate heterojunctions. The fabricated photoelectrochemical (PEC) photodetector based on ZnO/GQDs heterojunctions displayed good self-powering characteristics, with an on/off current ratio of approximately 21 at zero bias, which was almost seven-fold higher than that of the bare ZnO device. The responsivity and detectivity of the ZnO/GQDs-based photodetector were also enhanced compared with those of bare ZnO devices. A unique type-II band alignment was established at the ZnO/GQDs heterojunction interface, which facilitated the carrier transfer. Moreover, the ZnO/GQDs heterojunction reduced the passivation of the surface states, resulting in large energy-band bending and an internal electric field at the semiconductor/electrolyte interface, which provided a powerful driving force for the separation and transport of photogenerated carriers. These combined effects enhance the performance of the photodetector, indicating that this approach can be used to fabricate high-performance PEC optoelectronic devices.