PEDOT:PSS films-Effect of organic solvent additives and annealing on the film conductivity

We report results on conductivity of PEDOT:PSS films, which contain different amounts of organic solvents, i.e., dimethyl sulphoxide (DMSO) or ethylene glycol (EG), and annealed at different temperatures. The maximum of conductivity of the resulting films was reached at about 5wt.% of DMSO or EG in the. solution. At the same time, the presence of the solvent residue in the film also resulted in the poor control of the film morphology and conductivity. It was found that conductivity of a film prepared with the same DMSO content is sensitive to the surface quality of the substrate used. It was also found that annealing substantially reduces conductivity of the films prepared with and without the additives. The higher the temperature of annealing, the smaller film conductivity was observed. Correlation in changes of the electronic absorption of the PEDOT:PSS film in the near-IR and the film conductivity induced by the solvent additive was also found. Exposure of PEDOT:PSS films to the solvent vapors has been employed as an alternative controlled method to increase film conductivity. This method, in combination with quartz microbalance measurements, showed a great capability of the film to absorb DMSO vapors and that a saturation limit for conductivity is reachable after more than 20 h of exposure. Swelling and interconnection of the polymer chains is suggested to be the main factor responsible for the conductivity increase. (C) 2009 Elsevier B.V. All rights reserved.