Synthesis of ethanol-soluble few-layer graphene nanosheets for flexible and transparent conducting composite films

We report a facile method of preparing few-layer graphene nanosheets (FLGs), which can be soluble in ethanol. Atomic force microscopy and high-resolution transmission electron microscopy studies reveal that FLGs have average thicknesses in the range of 2.6-2.8 nm, corresponding to 8-9 layers. A graphene/nafion composite film has a sheet resistance of 9.70 kΩ/sq at the transmittance of 74.5% (at 550 nm) while the nafion film on polyethylene terephthalate has a sheet resistance of 128 kΩ/sq at transmittance of 90.0%. For the cycling/bending test, almost no change in resistance was exhibited when the film was bent at an angle up to 140°, and no obvious deviation in resistance could be found after 100 bending cycles was applied. In addition, an FLGs-poly(3,4-ethylenedioxythiophene):poly(styrenesulfonate) composite layer was demonstrated as the effective hole transporting layer to improve the hole transporting ability in an organic photovoltaic device, with which the power conversion efficiency was enhanced from 3.10% to 3.70%. The results demonstrated the promising applications of FLGs on graphene-based electronics, such as transparent electrode and flexible conducting film.