WS2 Quantum Dots on e-Textile as a Wearable UV Photodetector: How Well Reduced Graphene Oxide Can Serve as a Carrier Transport Medium?

We document the fabrication and investigations of a novel photodetector based on a WS2 quantum dots and reduced graphene oxide (RGO) (WS2-QDs/RGO) heterostructure. The proposed photodetector is simple, scalable, cost-effective, and flexible and works in an ambient environment. An enhanced photodetection efficiency is observed due to the superior electronic properties of WS2-QDs and excellent electrical as well as thermal properties of the carrier transportation medium, RGO. For device fabrication, GO and WS2-QDs were separately synthesized via different chemistry followed by decorating WS2-QDs on RGO coated cotton textile. Characterization studies confirm the transformation of exfoliated WS2-2D flakes into WS2-0D quantum dots and graphene oxide (GO) to RGO. The optimized photodetection performance of WS2-QDs/RGO demonstrates its photoresponsivity of 5.22 mA W-1 at 1.4 mW mm-2 power density of a 405 nm illumination source. Other sensor parameters such as photosensitivity (∼20.2%), resolution (∼0.031 mW mm-2 μA-1), response time (1.57 s), recovery time (1.83 s), and specific detectivity (∼1.6 × 106 jones) are found for WS2-QDs/RGO sensor, and a few of these parameters are comparable and even superior to some of the devices as reported. Photosensing mechanism is explained in terms of charge transfer caused by appropriate band alignment across the interface between WS2-QDs and RGO, where dimensionality and quantum confinement of nanostructures synergistically enhance the overall performance of the heterostructure. The device flexibility is examined through bending, stretching, and twisting experiments and successfully demonstrated its potentiality. Sensor performance even after being soaked in water and subsequent drying shows the possibility of reuse. The attributes of flexibility, high sensitivity and responsivity, superior resolution, and cost-effectiveness of our novel flexible photodetector indicate its promising potential for flexible and wearable optical detectors operating in UV band. Although negative photoconductance of the WS2-QDs/RGO sensor is a major cause for not allowing the sensor to show its best performance, a trade-off is made with improved device design to qualify the expectations of being a competitive device, and this has been demonstrated with experimental facts.