Dispersion degree and sheet spacing control of graphene products via oxygen functionalities and its effect on electrical conductivities of P3HT-graphene composite coatings

Graphene products have been used as conductor filler in polymers matrix, resulting in a conductive composite for optoelectronic applications. In this work, the effect of oxygen content of reduced graphene oxide (rGO) products on its dispersion in poly(3-hexylthiophene) (P3HT) and the electrical properties of the P3HT-rGO composites is studied. Graphene oxides (GOs) with different concentrations of oxygen species were first prepared by a modified Tour method. Each GO product was reduced with the same amount of L-ascorbic acid to obtain the corresponding rGO. By using X-Ray Photoelectron Spectroscopy (XPS) and Raman spectroscopy, oxygen-related species and their concentration in GO and rGO products have been identified. The sizes of graphene sheets in those two carbon products are estimated by Dynamic Light Scattering (DLS) method. We find that the dispersion degree of the rGO product in a hydrophobic P3HT matrix depends on content of carboxyl (–COOH) and epoxy (C–O–C) groups on GO as well as on the graphene sheet size. At the same time, the most reduced and conductive rGO product (rGO-4) comes from a GO with the lowest oxygen content and lowest concentration of –COOH species, giving the largest graphene sheet sizes and spacing between the sheets. The homogeneous P3HT-rGO-4 composite material shows a micrometer sized laminated structure and a percolation threshold point around 20 wt%. The electrical conductivity of the composite is close to 10^–1 S m⁻¹, two orders of magnitude larger than the pristine P3HT. It is concluded that the electrical properties of rGO products can be improved by tailoring the type and concentration of oxygen species in GO.