Search

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 situwith spectral reflectance (SR) and time-of-flight neutron reflectometry (ToF-NR). Additional in situelectrochemical 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.

The humidity influence on the electronic and ionic resistance properties of thin post-treated poly(3,4-ethylene dioxythiophene):poly(styrenesulfonate) (PEDOT:PSS) films is investigated. In particular, the resistance of these PEDOT:PSS films post-treated with three different concentrations (0, 0.05, and 0.35 M) of ethyl-3-methylimidazolium dicyanamide (EMIM DCA) is measured while being exposed to a defined humidity protocol. A resistance increase upon elevated humidity is observed for the 0 M reference sample, while the EMIM DCA post-treated samples demonstrate a reverse behavior. Simultaneously performed in situgrazing-incidence small-angle X-ray scattering (GISAXS) measurements evidence changes in the film morphology upon varying the humidity, namely, an increase in the PEDOT domain distances. This leads to a detriment in the interdomain hole transport, which causes a rise in the resistance, as observed for the 0 M reference sample. Finally, electrochemical impedance spectroscopy (EIS) measurements at different humidities reveal additional contributions of ionic charge carriers in the EMIM DCA post-treated PEDOT:PSS films. Therefrom, a model is proposed, which describes the hole and cation transport in different post-treated PEDOT:PSS films dependent on the ambient humidity.