Efficient Gating of Organic Electrochemical Transistors with In-Plane Gate Electrodes

Organic electrochemical transistors (OECTs) are electrolyte-gated transistors, employing an electrolyte between their gate and channel instead of an insulating layer. For efficient gating, non-polarizable electrodes, for example, Ag/AgCl, are typically used but unfortunately, this simple approach limits the options for multiple gate integration. Patterned polarizable Au gates on the other hand, show strongly reduced gating due to a large voltage drop at the gate/electrolyte interface. Here, an alternative, simple yet effective method for efficient OECT gating by scalable in-plane gate electrodes, is demonstrated. The fact that poly(3,4-ethylenedioxythiophene) polystyrene sulfonate (PEDOT:PSS) exhibits a volumetric capacitance in an electrolyte is made use of. As a result, the capacitance of PEDOT:PSS-based gates can be strongly enhanced by increasing their thickness, thereby reducing the voltage loss at the gate/electrolyte interface. By combining spin coating and electrodeposition, planar electrodes of various thicknesses are created on a multi-gated OECT chip and their effect on the gating efficiency, examined. It is shown that the gating performed by an in-plane PEDOT:PSS electrode can be tuned to be comparable to the one obtained by a Ag/AgCl electrode. Overall, the realization of efficient gating with in-plane electrodes paves the way toward integration of OECT-based biosensors and "organ-on-a-chip" platforms.