Unraveling the Humidity Influence on the Electrical Properties of Ionic Liquid Posttreated Poly(3,4-ethylene dioxythiophene):Poly(styrenesulfonate) Films

The conductive polymer blend poly­(3,4-ethylene dioxythiophene):poly­(styrenesulfonate) (PEDOT:PSS), popular for numerous organic applications, is investigated in terms of the influences that ionic liquid (IL) treatment and ambient humidity have on its conductivity properties. PEDOT:PSS thin films posttreated with different concentrations of the IL 1-ethyl-3-methylimidazolium dicyanamide (EMIM DCA) are exposed to different relative humidity (RH) steps from 0% RH up to 90% RH. Simultaneously, the film swelling and increase in the scattering length density (SLD), indicating a water uptake of the films, are monitored in situ with spectral reflectance (SR) and time-of-flight neutron reflectometry (ToF-NR). Additional in situ electrochemical impedance spectroscopy (EIS) shows that the pristine PEDOT:PSS has only an electronic conductivity, while for the IL-treated samples, an additional ionic conductivity contribution is observed. Upon humidity increase, the electronic conductivity of all PEDOT:PSS thin films decreases, while the ionic conductivity for IL posttreated thin films is enhanced by the intake of water molecules.