With the advent of devices based on single crystals, the performance of organic field‐effect transistors has experienced a significant leap, with mobility now in excess of 10 cm2 V−1 s−1. The purpose of this review is to give an overview of the state‐of‐the‐art of these high‐performance organic transistors. The paper focuses on the problem of parameter extraction, limitations of the performance by the interfaces, which include the dielectric–semiconductor interface, and the injection and retrieval of charge carriers at the source and drain electrodes. High‐performance devices also constitute tools of choice for investigating charge transport phenomena in organic materials. It is shown how the combination of field‐effect measurements with other electrical characterizations helps in elucidating this still unresolved issue.

We realized ambipolar Field-Effect Transistors by coupling exfoliated thin flakes of tungsten disulphide (WS 2 ) with an ionic liquid-dielectric. The devices show ideal electrical characteristics, including very steep sub-threshold slopes for both electrons and holes and extremely low OFFstate currents. Thanks to these ideal characteristics, we determine with high precision the size of the band-gap of WS 2 directly from the gate-voltage dependence of the source-drain current. Our results demonstrate how a careful use of ionic liquid dielectrics offers a powerful strategy to study quantitatively the electronic properties of nano-scale materials.

Organic field-effect transistors (OFETs) promise for printed intelligence embedded into, and coated onto many different items that previously have been considered impossible to make electronically active. It is crucial that this technology is driven at low voltage and power. Also, we need to obtain solid understanding of the charge transport in organic semiconductors. Different materials [1] and architectures have been utilized as the probe to reveal the nature of charge transport along the transistor channel and to achieve low-voltage switching. In transistors operating according to field-effect or electrochemical principles, respectively, vacuum, air, [2] oxides, [3] high-permittivity dielectrics, [4] organic mono-layers, [5] and electrolytes [6] have successfully served as the medium to electronically separate the gate from the transistor channel, of which the latter three allow low-voltage operation. In particular electrolytes have attracted much attention lately since they generate very high electric fields at the organic transistor channel/electrolyte interface already at very low voltages, i.e., below 1 V. One issue with those devices is that electrochemical switching and field-effect modulation of the organic channel often coexist, [7] which result in transistors that are typically slow and that exhibit a great degree of hysteresis. Here, we report OFETs gated via pure water that operates entirely in the field-effect mode of operation. Our findings shed new light on low-voltage operating OFETs, their charge transport characteristics under exposure to water [8] and opens for sensor applications using water-gated OFETs as transducers in aqueous media.[9] Because of the simplicity and readiness of its production, it could also reveal a very helpful tool for rapid testing of new organic semiconductor compounds.Electrolyte (insulator)/semiconductor interfaces have attracted much attention during the last decades, in part driven by an interest to achieve high-performing sensors operating in water, to reach low-voltage operation for OFETs and to study the fundamentals of charge transport in semiconducting solids. In ion-sensitive field-effect transistors (ISFETs), the electrical potential at the electrolyte/insulator interface is translated into a modulation of the transistor output characteristics.[10] Actually, the modulation originates from that the threshold voltage (V T ) is sensitive to the ion concentration. The high electric field that is possible to establish at electrolyte/solid interfaces becomes a powerful tool for probing various features of the transport and accumulation of charges inside solids. Electrostatic field-operated transistors and switches, including for instance silicon, carbon nanotubes, [11] rubrene, [12] or manganites [13] as the active material, have been extensively studied in the past. In all those cases pure field-effect operation, without any parasitic electrochemical reactions of the bulk of the solid, is achieved simply because the materials included in the devices are known ...