Electrochemical Fabrication and Characterization of Organic Electrochemical Transistors (OECTs) Using poly(3,4-ethylenedioxythiophene (PEDOT)

Organic electrochemical transistors (OECTs) with conductive polymers (CPs) as the active materials are one of the devices getting particular attention for bioelectronics due to their special properties such as low operating voltage and mixed ionic-electronic conductivity. Among various CPs, commercially available poly(3,4-ethylenedioxythiophene):poly(styrene sulfonate) (PEDOT:PSS) dispersions in the aqueous solutions have been widely used because they have high conductivity and biocompatibility. However, it has been difficult to modify the chemistry of PEDOT:PSS to control and functionalize device characteristics because of its high chemical stability. In this work, EDOT was electrochemically polymerized as the active material of OECTs with commonly used counterions of lithium perchlorate (LiClO₄), sodium <i>p</i>-toluene sulfonate (<i>p</i>TS), and poly(sodium 4-styrene sulfonate) (PSS). Commercially available gold interdigitated electrodes were used as the substrate and PEDOT served as the active channel material by filling the gaps between interdigitated electrodes during the electrochemical polymerization process. The electrochemically polymerized PEDOT films with large sized counterions (PSS), showed smooth and regular surfaces, while PEDOT films with relatively small sized counterions (LiClO₄ and <i>p</i>TS) showed much rougher and bumpy surfaces. PEDOT films with either <i>p</i>TS or PSS showed much better surface coverage ability for filling gaps between interdigitated electrodes rather than with LiClO₄. OECTs were successfully fabricated with PEDOT and various counterions by the electrochemical polymerization process. The maximum transconductance, g_m, of a PEDOT OECT was 46 mS with the highest on-current level (&gt; 10 mA) using <i>p</i>TS as the counterion. These results provide a relatively simple and efficient way to fabricate high performance OECTs with various monomers, counterions, and additives as active materials in order to modify and control the device characteristics for various applications.