The conductivity of PEDOT:PSS films was significantly enhanced from 0.3 S cm(-1) to 3065 S cm(-1) through a treatment with dilute sulfuric acids. PEDOT:PSS films with a sheet resistance of 39 Ω sq(-1) and transparency of around 80% at 550 nm are obtained. These PEDOT:PSS films with conductivity and transparency comparable to ITO can replace ITO as the transparent electrode of optoelectronic devices.

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This article reports a novel method to significantly enhance the conductivity of conducting poly(3,4-ethylenedioxythiophene):poly(styrenesulfonate) (PEDOT:PSS) films through a treatment with aqueous solutions of various salts, such as copper(II) chloride. Conductivity enhancement by a factor of about 700 was observed. Many salts were investigated, and the conductivity enhancement depended on the softness parameter of cations and the concentration of the salts in solution. A salt like copper(II) chloride or indium chloride, whose cation has positive softness parameter, could enhance the conductivity of the PEDOT:PSS film by 2 orders in magnitude, while other salt like sodium chloride or magnesium chloride, whose cation has negative softness parameter, gave rise to negligible effect on the conductivity. The mechanism for the conductivity enhancement was studied by various characterizations. It is attributed to PSS loss from the PEDOT:PSS film, and conformational change of PEDOT chains resulted from the salt-induced charge screening between PEDOT and PSS.

Significant conductivity enhancement was observed on transparent and conductive poly(3,4-ethylene dioxythiophene):poly(styrene sulfonate) (PEDOT:PSS) films after a treatment with organic and inorganic acids, including acetic acid, propionic acid, butyric acid, oxalic acid, sulfurous acid, and hydrochloric acid. The conductivity could be enhanced from 0.2 to over 200 S cm(-1), that is, by a factor of more than 1000. The conductivity enhancement was dependent on the structure of the acids and the experimental conditions during the treatment, such as the acid concentration and the temperature. The optimal temperature was in the range of 120 to 160 degrees C. The resistance dropped rapidly when a PEDOT:PSS film was treated with acid solution of high concentration, whereas it gradually increased and then decreased when it was treated with an acid solution of low concentration. The mechanism for this conductivity enhancement was studied by various chemical and physical characterizations. The temperature dependence of conductivity indicates that the energy barrier for charge hopping among the PEDOT chains become lower in the highly conductive PEDOT:PSS film after the acid treatment. The ultraviolet-visible-near-infrared (UV-vis-NIR) absorption spectroscopy, the X-ray photoelectron spectroscopy (XPS) and scanning electron microscopy (SEM) indicate the loss of polystyrene sulfonic acid (PSSH) chains from the PEDOT:PSS film after the acid treatment, and the atomic force microscopy (AFM) suggest conformational change of the polymer chains. Therefore, the conductivity enhancement is attributed to the loss of PSSH chains from the PEDOT:PSS film and the conformational change of the PEDOT chains, which are induced by the acids.

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Poly(3,4-ethylenedioxythiophene):poly(styrenesulfonate) (PEDOT:PSS) is promising to be the next-generation transparent electrode of optoelectronic devices. This paper reports the differences between two commercially available grades of PEDOT:PSS: Clevios P and Clevios PH1000. The as-prepared PEDOT:PSS films from Clevios P and Clevios PH1000 solutions have close conductivities of 0.2-0.35 S cm(-1). Their conductivities can be enhanced to 171 and 1164 S cm(-1), respectively, through a treatment with hydrofluoroacetone trihydrate (HFA). The differences between Clevios P and Clevios PH1000 were studied by various characterizations on PEDOT:PSS aqueous solutions and PEDOT:PSS films. The gel particles are larger in Clevios PH1000 solution than in Clevios P solution as revealed by dynamic light scattering and fluorescence spectroscopy of pyrene in these solutions. These results suggest that PEDOT of Clevios PH1000 has a higher average molecular weight than that of Clevios P. The difference in the molecular weight of PEDOT for the two grades of PEDOT:PSS is confirmed by the characterizations on their polymer films, including atomic force microscopy and temperature dependences of the resistances of as-prepared and HFA-treated PEDOT:PSS films. The different molecular weights of PEDOT also gives rise to significant differences in the electrochemical behaviors of the two grades of PEDOT:PSS, as revealed by the cyclic voltammetry, in situ UV-vis-NIR absorption spectroscopy and potentiostatic transient measurements.