Organic Electrical Double Layer Transistors Based on Rubrene Single Crystals: Examining Transport at High Surface Charge Densities above 1013 cm–2

Abstract

We report comprehensive electrical characterization of electrolyte-gated field-effect transistors (FETs) incorporating organic single crystals of rubrene and several types of high capacitance ionic liquids (ILs). The specific capacitance associated with the liquid gate is exceptionally large, in the range of 1–10 μF/cm2, which facilitates the operation of devices at gate voltages below one volt. Gate-induced hole densities in rubrene single crystals are therefore on the order of 1013 cm–2, as determined from displacement current measurements (DCM) and confirmed by AC impedance measurements. Importantly, we observe a pronounced maximum in channel conductance with all ionic liquid gates which we attribute to a carrier localization effect at the semiconductor/liquid interface. Effective carrier mobility is a nonmonotonic function of gate voltage and depends on the choice of the IL. By gating with a tris(pentafluoroethyl)trifluorophosphate (FAP) containing IL, maximum carrier mobility in rubrene can be enhanc...