Abstract
Solution-processed graphene quantum dots (GQDs) possess a moderate bandgap, which make them a promising candidate for optoelectronics devices. However, negative photoconductivity (NPC) and hysteresis that happen in the photoelectric conversion process could be harmful to performance of the GQDs-based devices. So far, their origins and relations have remained elusive. Here, we investigate experimentally the origins of the NPC and hysteresis in GQDs. By comparing the hysteresis and photoconductance of GQDs under different relative humidity conditions, we are able to demonstrate that NPC and hysteresis coexist in GQDs and both are attributed to the carrier trapping effect of surface adsorbed moisture. We also demonstrate that GQDs could exhibit positive photoconductivity with three-order-of-magnitude reduction of hysteresis after a drying process and a subsequent encapsulation. Considering the pervasive moisture adsorption, our results may pave the way for a commercialization of semiconducting graphene-based and diverse solution-based optoelectronic devices.
Highlights
Graphene is a monolayer of carbon atoms densely packed in a honeycomb crystal lattice
By comparing the hysteresis and photoconductance of graphene quantum dots (GQDs) under different relative humidity conditions, we are able to demonstrate that negative photoconductivity (NPC) and hysteresis coexist in GQDs and both are attributed to the carrier trapping effect of surface adsorbed moisture
We demonstrate that GQDs could exhibit positive photoconductivity with three-order-of-magnitude reduction of hysteresis after a drying process and a subsequent encapsulation
Summary
Graphene is a monolayer of carbon atoms densely packed in a honeycomb crystal lattice. Thereby, endowing graphene semiconducting properties with a moderate bandgap is highly desired. The electronic properties are extremely sensitive to the geometrical parameters of the graphene ribbons, which require an extreme precision in cutting the graphene.[17,20,21] In addition, electronic properties of GO are strongly affected by the attached oxygen-containing functional groups, which undermines its reliability.[17] Recently, zero-dimensional graphene quantum dots (GQDs) have been shown to exhibit a moderate bandgap due to the quantum size effect.[24,25,26] solution-processed GQDs are highly uniform and controllable in size and morphology, 2158-3226/2016/6(4)/045214/7
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