Very high-mobility organic transistors are fabricated with purified rubrene single crystals and high-density organosilane self-assembled monolayers. The interface with minimized surface levels allows carriers to distribute deep into the crystals by more than a few molecular layers under weak gate electric fields, so that the inner channel plays a significant part in the transfer performance. With the in-crystal carriers less affected by scattering mechanisms at the interface, the maximum transistor mobility reaches 18cm2∕Vs and the contact-free intrinsic mobility turned out to be 40cm2∕Vs as the result of four-terminal measurement. These are the highest values ever reported for organic transistors.

We report high-mobility rubrene single-crystal field-effect transistors with ionic-liquid (IL) electrolytes used for gate dielectric layers. As the result of fast ionic diffusion to form electric double layers, their capacitances remain more than 1μF∕cm2 even at 0.1MHz. With high carrier mobility of 1.2cm2∕Vs in the rubrene crystal, pronounced current amplification is achieved at the gate voltage of only 0.2V, which is two orders of magnitude smaller than that necessary for organic thin-film transistors with dielectric gate insulators. The results demonstrate that the IL/organic semiconductor interfaces are suited to realize low-power and fast-switching field-effect transistors without sacrificing carrier mobility in forming the solid/liquid interfaces.

Gate-voltage dependence of carrier mobility is measured in high-performance field-effect transistors of rubrene single crystals by simultaneous detection of the longitudinal conductivity sigma(square) and Hall coefficient R(H). The Hall mobility mu(H) (identical with sigma(square)R(H)) reaches nearly 10 cm(2)/V s when relatively low-density carriers (<10(11) cm(-2)) distribute into the crystal. mu(H) rapidly decreases with higher-density carriers as they are essentially confined to the surface and are subjected to randomness of the amorphous gate insulators. The mechanism to realize high carrier mobility in the organic transistor devices involves intrinsic-semiconductor character of the high-purity organic crystals and diffusive bandlike carrier transport in the bulk.

High-performance electronic function of current amplification is realized with the use of solid-to-liquid interfaces between organic semiconductors and ionic liquid. To hold in place the ionic liquid of 1-ethyl-3-methyl-imidazolium bis(trifluoromethanesulfonyl)imide known for low viscosity and high ionic conductivity, an elastomeric well structure is fabricated with polydimethylsiloxane on which organic single crystals of rubrene are electrostatically attached. As the result of rapid formation of electric double layers in the ionic liquid interfacing, the high-mobility organic semiconductor crystals’ fast-switching transistor function is demonstrated with the application of gate voltage, realizing the highest sheet transconductance, namely, amplifying performance, ever achieved.

We report high-mobility rubrene single-crystal field-effect transistors with ionic-liquid electrolytes used for gate dielectric layers. As the result of fast ionic diffusion to form electric double layers, their capacitances remain more than 10 μF/cm2 even at 0.1 MHz. With high carrier mobility of 1.2 cm2/Vs in the rubrene crystal, pronounced current amplification is achieved at the gate voltage of only 0.2 V, which is two orders of magnitude smaller than that necessary for organic thin-film transistors with dielectric gate insulators. The results demonstrate that the ionic-liquid/organic semiconductor interfaces are suited to realize low-power and fast-switching field-effect transistors without sacrificing carrier mobility in forming the solid/liquid interfaces.

Gating organic transistors with electric double layers (EDL) of electrolytes is advantageous in injecting high-density carriers with the application of minimum gate voltage. The drawback of such devices, however, has been that commonly used polymer electrolytes suffer relatively slow ionic diffusion before forming the EDLs. In this report, we disclose a new class of EDL devices incorporating low-viscosity room temperature ionic liquid as the electrolyte layer, so that the rapid ionic diffusion allows MHz operation for the transistor performance. We fabricate a well structure using an elastomeric rubber stamp of poly-dimethylsiloxane to hold the ionic liquid 1-ethyl 3-methyl-imidazolium bis(trifluoromethanesulfonyl)imide, known for high ionic conductivity. The transistor performs without hysteresis with the carrier mobility of 5 cm2V−1s−1, realizing the highest sheet transconductance ever achieved.