Radical Polymer-Based Organic Electrochemical Transistors

Abstract

Organic electrochemical transistors\n(OECTs) are an emerging platform\nfor bioelectronic applications. Significant effort has been placed\nin designing advanced polymers that simultaneously transport both\ncharge and ions (i.e., macromolecules that are mixed conductors).\nHowever, the considerations for mixed organic conductors are often\ndifferent from the established principles that are well-known in the\nsolid-state organic electronics field; thus, the discovery of new\nOECT macromolecular systems is highly desired. Here, we demonstrate\na new materials system by blending a radical polymer (i.e., a macromolecule\nwith a nonconjugated backbone and with stable open-shell sites at\nits pendant group) with a frequently used conjugated polymer. Specifically,\npoly­(4-glycidyloxy-2,2,6,6-tetramethylpiperidine-1-oxyl) (PTEO) was\nblended with poly­(3-hexylthiophene) (P3HT) to create thin films with\ndistinct closed-shell and open-shell domains. Importantly, the sharp\nand unique oxidation–reduction (redox) potential associated\nwith the radical moieties of the PTEO chain provided a distinct actuation\nfeature to the blended films that modulated the ionic transport of\nthe OECT devices. In turn, this led to controlled regulation of the\ndoping of the P3HT phase in the composite film. By decoupling the\nionic and electronic transport into two distinct phases and by using\nan ion transport phase with well-controlled redox activity, never-before-seen\nperformance for a P3HT-based OECT was observed. That is, at loadings\nas low as 5% PTEO (by weight) OECTs achieved figure-of-merit (i.e.,\nμC*) values >150 F V^–1 cm^–1 s^–1, which place the performance on the same order\nas state-of-the-art conjugated polymers despite the relatively common\nconjugated macromolecular moiety implemented. As such, this effort\npresents a design platform by which to readily create a tailored OECT\nresponse through strategic macromolecular selection and polymer processing.