A Simple Approach for Preparing Transparent Conductive Graphene Films Using the Controlled Chemical Reduction of Exfoliated Graphene Oxide in an Aqueous Suspension

We report a simple method for preparing transparent conductive graphene films using a chemically converted graphene (CCG) suspension that was obtained via controlled chemical reduction of exfoliated graphene oxide (GO) in the absence of dispersants. Upon thermal annealing of the CCG films, the films displayed a sheet resistance on the order of 10(3) Omega.square(-1) at 80% transparency (550 nm), with a bulk conductivity on the order of 10(2) S.cm(-1). FT-IR, UV-visible, and X-ray photoelectron spectroscopy results showed that the combination of the controlled reduction of GO in suspension and thermal annealing of the CCG films efficiently restored the sp(2) carbon networks of the graphene sheets, facilitating charge carrier transport in the individual CCG sheets. Furthermore, grazing-incidence X-ray diffraction results showed that the thermal annealing of the CCG films reduced the interlayer distance between the CCG sheets to a distance comparable to that in bulk graphite, facilitating charge carrier transport across the CCG sheets. Polymer solar cell devices composed of the CCG films as transparent electrodes showed power conversion efficiencies, eta, of 1.01 +/- 0.05%, which corresponded to half the value (2.04 +/- 0.1%) of the reference devices, in which indium tin oxide-covered glass was used for the transparent electrode.