Ionic-Liquid Component Dependence of Carrier Injection and Mobility for Electric-Double-Layer Organic Thin-Film Transistors

Electrostatic carrier injection and electrochemical doping of octathio[8]circulene thin films is examined for six kinds of ionic liquids using in situ cyclic voltammetry (CV) and conductivity measurements. The frequency dependence of the capacitance measurements indicates that the ionic liquids form electric-double-layers (EDLs) below 10(2) Hz. The performance of the EDL-organic thin film transistors (OTFTs) of octathio[8]circulene demonstrates that the transistor carrier mobility shows a linear decrease with an increase in the capacitance of the ionic liquids. In contrast, the electrochemical oxidation potentials and the threshold voltage of the EDL-OTFT are governed only by one component of the ionic liquid; namely, the electrostatic and electrochemical hole injections are significantly affected by the anions.