Solution-Processed PEDOT:PSS Films with Conductivities as Indium Tin Oxide through a Treatment with Mild and Weak Organic Acids

New transparent conductive materials are urgently needed for optoelectronic devices. Poly(3,4-ethylenedioxythiophene):poly(styrenesulfonate) (PEDOT:PSS) will be a promising next-generation transparent electrode material if its conductivity is comparable to that of indium tin oxide (ITO). To enhance significantly the conductivity of PEDOT:PSS with mild compounds has practical significance. In this work, significant conductivity enhancements are achieved on PEDOT:PSS films after treatment with mild and weak organic acids. The treated PEDOT:PSS films exibit metallic behavior at room temperature. Their conductivity increases to about 3300 S cm(-1) after they are treated with 8 M methanesulfonic acid. The conductivity enhancement depends on the acidity and physical properties of the organic acids. The mechanism for the conductivity enhancement is ascribed to proton transfer from the mild or weak organic acids to PSS(-) of PEDOT:PSS. There are two factors for the proton transfer from mild or weak organic acids to PSS. One factor is the high acid concentration during the treatment, particularly after the vaporization of the water solvent. Another factor is the phase segregation of PSSH from PEDOT:PSS, because PSSH is hydrophilic, whereas PEDOT is hydrophobic. This method is better than that using very strong and corrosive acids like sulfuric acid. These highly conductive and highly transparent PEDOT:PSS films are promising for use as next-generation transparent electrodes.