Improvement of conductivity and transmittance of PEDOT: PSS electrodes using graphene oxide and polar solvent

Poly(3,4-ethylenedioxythiophene):poly(styrenesulfonate), PEDOT:PSS, is a polymeric composite that can substitute indium tin oxide (ITO) as transparent electrode in electronic devices. However, PEDOT:PSS films have conductivities two orders of magnitude lower than ITO, which is still the main challenge in the achievement of ITO-free organic devices. Even PEDOT being a good conductor, PEDOT:PSS films have not the full electrical performance of PEDOT because of PSS, an insulator polymer added to provide water solubility. To enhance PEDOT electrical performance and overcome the insulator limitations, we prepared thin films based on graphene oxide (GO) aqueous dispersion and PEDOT:PSS solution by drop casting this mixture on substrates followed by a treatment on dried films with ethylene glycol (EG). An increment of two orders of magnitude in conductivity values was observed as well as increase in transmittance at visible region and in hydrophobicity of GO:PEDOT:PSS thin films due to partial removal of PSS. It was further investigated the films mechanical stability on PET substrates by torsion cycle and electrical measurements. Mass ratio equal to 0.058 of GO/PEDOT provides higher electrical conductivity due to higher chains orientation of PEDOT probed by NEXAFS and Resonant Auger Spectroscopy measurements, and EG treatment also decreased the roughness and thickness of thin films, which promoted increment in conductivity and light transmittance. Low temperature electrical measurements and application of Mott Variable Range Hopping (VRH) model showed that the conduction occurs in three dimensions (3D) and the solvent treatment increases the characteristic conductivity and decreases the activation hopping energy, remaining almost unchanged the characteristic temperature. It indicates that EG treatment promotes a decrease in charge transfer time and resistivity. (author)