Green synthesis of graphene quantum dots and the dual application of graphene quantum dots-decorated flexible MSM p-type ZnO device as UV photodetector and piezotronic generator

A novel method to synthesize graphene sheets and graphene quantum dots (GQDs) from agricultural waste is reported in this paper. The as-prepared GQDs were decorated on the antimony (Sb)-doped zinc oxide (ZnO) nanostructures to improve the opto-electrical properties of the photodetector. Morphological studies, elemental analysis, absorption and Raman spectroscopy studies were performed on the as-prepared graphene sheets and GQDs. A GQDs-decorated, p-type Sb-doped ZnO metal–semiconductor–metal (MSM) interdigitated UV photodetector was fabricated on a flexible ITO/PET substrate. Structural, morphological and elemental analyses were performed on the GQDs-decorated nanostructures. The Hall measurements show that the device exhibits p-type conductivity with hole concentration of 3 × 1019 cm−3 and Hall mobility of 2067 cm2 V−1 s−1. It is observed from the I–V studies that the Sb-doped ZnO MSM device with GQDs exhibits 103 times higher dark and photocurrents as compared to the device without GQDs decoration. The dynamic response is measured, and the turn-on (τon) and turn-off (τoff) times are found to be 3.67 and 12.26 s, respectively. The device also exhibited piezotronic dark potential on compression at a convex arc angle. Repeated compressions and relaxations were performed on the device and it behaved as a piezotronic generator.