Influence of Channel Thickness and Counterion Composition on the Performance and Stability of Interdigitated Organic Electrochemical Transistors (OECTs) Using Electrochemically Deposited PEDOT

Organic electrochemical transistors (OECTs) prepared from poly(3,4-ethylenedioxythiophene) (PEDOT) doped with poly(styrenesulfonate) (PSS) have been widely investigated, typically with films prepared by spin-casting and drying from aqueous commercially available suspensions. Electrochemical deposition of PEDOT makes it possible to more precisely control film thickness and counterion composition. Here, we examined the influence of channel thickness and counterion composition on the properties of OECTs fabricated using electrochemically polymerized PEDOT with p-toluene sulfonate (pTS) and PSS on interdigitated gold electrodes. While PEDOT:PSS films deposited with a particular charge density were somewhat thicker (with more PSS in the film), PEDOT:pTS films showed higher volumetric capacitances consistent with their more rough, irregular surface morphologies. The maximum transconductance (g_m,max) (∼70 mS) and on-current levels barely changed over the examined range of channel thicknesses (100–800 nm) with both counterions. The device stability (current retention in ON/OFF cycling) and transient response times (∼10 ms) were enhanced with larger counterions, thinner channel films (∼100 nm), and lower applied drain voltages (under −0.1 V). These design insights were used to create channel-functionalized OECT-based label-free glucose sensors with high stability. These results demonstrate the ability to optimize and enhance the performance and stability of electrochemically deposited PEDOT-based interdigitated OECT devices.