Facile synthesis of organo-soluble surface-grafted all-single-layer graphene oxide as hole-injecting buffer material in organic light-emitting diodes

Graphene oxide (GO) was modified by surface grafting and the product P-GO exhibited a surprisingly good solubility in common solvents (as high as 1.8 mg mL(-1) in DMF) without sonication and can be spin coated to form large single-layer sheets on a substrate. In contrast to GO, all-single-layer P-GO sheets are readily formed in solution, which are highly useful for separation from other multi-layer sheets and as precursors to all-single-layer graphene. The unique property of single-layer P-GO made it a promising functional material, such as hole-injecting buffer (HIB) material in organic light-emitting devices. The devices using P-GO as a hole-injecting buffer layer on the ITO electrode perform better than those with PEDOT:PSS.