Organic Charge Modulated Transistors (OECTs) are planar devices consisting of three electrodes: the source and drain electrodes are connected by a conductive polymer, which acts as channel; the channel and the gate electrode are separated by an electrolyte which acts as gate dielectric. Distinctive features of OECTs realized at DEALAB are realized by using a printer for organic inks and are all made of poly(3,4-ethylenedioxy-thiophene):poly(styrene sulfonate) (PEDOT:PSS), a polythiophene derivative which becomes a p-type semiconductor when doped with PSS. In its pristine state PEDOT:PSS is partially doped: by applying a negative potential to drain with respect to source, a current flows in the channel. When the gate is positively biased, ions form the electrolyte penetrate the polymer bulk neutralizing the PSS charge and thus causing the semiconductor de-doping according to the chemical reaction:
As a matter of fact, the gate potential modulates the electrochemical de-doping of the semiconductor.
OECTs are particularly suitable for chemosensing and biosensing in liquid because they can be operated at low voltage and PEDOT:PSS is biocompatible.