Sub-1 V Electrolyte-Gated Polymer Transistors with Ionic Liquid Electrolyte and High-Surface Area Carbon Gate Electrode

Electrolyte-gated (EG) transistors permit to achieve current modulations of several orders of magnitude at relatively modest gate voltages, by exploiting the exceptionally high capacitance of electrical double layer forming at the electrolyte/transistor channel interface. Different doping mechanisms have been proposed to explain the gating process in EG transistors. For organic polymers, the common doping mechanism is faradic, depends on the channel electrical potential and the doping charge is about two orders of magnitude larger than for electrostatically doped non-porous materials. Moreover, organic channel and electrolyte have to be selected taking into account that channel modulation has to be performed by applying gate-source voltages (V_gs) which are compatible with the electrochemical stability window of the electrolyte. Ionic liquid electrolytes, for their exceptionally high chemical and electrochemical stability and good conductivity at room temperature are of interest as electrolyte gating media in EG transistor. The faradic nature of the polymer channel doping also requires the use of gate electrode materials that are non-limiting in terms of their capability to supply the charge required for channel modulation within the electrochemical stability window of the electrolyte.

We targeted the use of high surface area carbons as gate electrode materials because of their capability to electrostatically supply the charge required to dope organic polymer transistor channels, within narrow electrode potential excursion.

Here, we report on a new generation of low voltage EG transistors making use of a low-cost, high surface area gate electrode, an organic electronic polymer, like MEH-PPV (poly[2-methoxy-5-(2'-ethylhexyloxy)-p-phenylene vinylene), as the channel material and ionic liquid, like [EMIM][TFSI] (1-ethyl-3-methylimidazolium bis(trifluoromethylsulfonyl)imide), as the electrolyte gating medium. Using such configuration, is it possible to apply V_gs biases lower than 1.0 V to achieve effective channel modulations  (ON/OFF ratio larger than 10³) and  hole mobility of about 10^-3 cm²V^-1s^-1.

Acknowledgement

This work was financially supported by NSERC (Discovery grants, CS and FC) and FQRNT (Nouveau Chercheur, CS). JS acknowledges financial support by CONACYT.

References

[1] J. Sayago, F. Soavi, F. Cicoira, C. Santato, Adv. Mater., submitted.