Exfoliating and Dispersing Few-Layered Graphene in Low-Boiling-Point Organic Solvents towards Solution-Processed Optoelectronic Device Applications

摘要

With normal organic surfactants, graphene can only be dispersed in water and cannot be dispersed in low-boiling-point organic solvents, which hampers its application in solution-processed organic optoelectronic devices. Herein, we report the exfoliation of graphite into graphene in low-boiling-point organic solvents, for example, methanol and acetone, by using edge-carboxylated graphene quantum dots (ECGQD) as the surfactant. The great capability of ECGQD for graphene dispersion is due to its ultralarge pi-conjugated unit that allows tight adhesion on the graphene surface through strong pi-pi interactions, its edge-carboxylated structure that diminishes the steric effects of the oxygen-containing functional groups on the basal plane of ECGQD, and its abundance of carboxylic acid groups for solubility. The graphene dispersion in methanol enables the application of graphene: ECGQD as a cathode interlayer in polymer solar cells (PSCs). Moreover, the PSC device performance of graphene: ECGQD is better than that of Ca, the state-of-the-art cathode interlayer material.