Ionic liquid–water mixtures and ion gels as electrolytes for organic electrochemical transistors

Abstract

Organic Electrochemical Transistors (OECTs) are widely investigated for applications in bioelectronics. Ionic liquids (ILs) are, in principle, interesting candidates as gating media in OECTs. Nevertheless, ILs can exhibit excessively high viscosity that prevents their straightforward application in OECTs. Here we report two processing approaches to apply the highly viscous ionic liquid triisobutyl(methyl)phosphonium tosylate (Cyphos® IL 106) in OECTs based on poly(3,4-ethylenedioxythiophene) polystyrenesulfonate (PEDOT:PSS), namely IL–H₂O binary mixtures and ion gels. The use of Cyphos® IL 106–H₂O binary mixtures and ion gels as gating media determines an increase of the OECT modulation, with respect to the pure ionic liquid. This increase cannot be explained simply by the change of the viscosity and ionic conductivity of the ionic liquid–H₂O mixtures with the increase of the H₂O content. Using high surface area activated carbon gates, ON/OFF ratios as high as 5000 are achieved with Cyphos® IL 106–H₂O mixtures at 5 and 10% H₂O v/v.