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

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 π‐conjugated unit that allows tight adhesion on the graphene surface through strong π–π 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. Graphene surfactant: We report the exfoliation of graphite into graphene in low‐boiling‐point organic solvents by using edge‐carboxylated graphene quantum dots (ECGQD) as the surfactant. 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.