Synthesis and Modification of Carbon Nanomaterials for Potential Device Applications
Graphene and its derivatives have shown potential to replace indium tin oxide in electronic applications because of their high theoretical conductivity and high optical transmittance. While certain factors prevent the immediate incorporation of graphene as a general transparent electrode material, particularly in solution-processible organic electronics, advances have been made in bringing this material closer to commercial applications. This work explores graphene derived from two popular synthesis methods as an electrode material in organic electronic devices, namely solution processible reduced graphene oxide and chemical vapor deposition (CVD) on copper. Chemical modification with thionyl chloride greatly enhanced the conductivity of chemically reduced graphene. When examined in detail, it was found that thionyl chloride adsorbed on the surface induces charge transfer from the graphitic base to the adsorbed molecule. Although the conductivity of this material is now almost comparable with conventional transparent electrode materials, the process requires blending with carbon nanotubes to achieve consistency in production of continuous large area films.
Chemical vapor deposition is an effective method to deposit large areas of graphene, and after optimization of the growth and transfer conditions, continuous single layer graphene with minimal defects was synthesized on copper foils. When used as a transparent anode at the bottom of an organic bulk heterojunction device, the surface roughness and hydrophobicity hinder its performance. To improve adhesion and conductivity of the electrode, a layer of the conducting polymer poly(3,4-ethylenedioxythiophene) was electropolymerized directly and conformally on the graphene surface. The surface morphology and thickness of the polymer material was tracked with the growth time, and was also found to be heavily dependent on the quality of the graphene and contact with the potentiostat. With further optimization, this process could be an important advance toward creating multilayer polymer devices on graphene electrodes.