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This perspective offers insights from discussions conducted during the Telluride Science meeting on organic mixed ionic and electronic conductors, outlining the challenges associated with understanding the behavior of this intriguing materials class.

 

Abstract Organic electrochemical transistors are a promising technology for bioelectronic devices, with applications in neuromorphic computing and healthcare. The active component enabling an organic electrochemical transistor is the organic mixed ionic-electronic conductor whose optimization is critical for realizing high-performing devices. In this study, the influence of purity and molecular weight is examined for a p-type polythiophene and an n-type naphthalene diimide-based polymer in improving the performance and safety of organic electrochemical transistors. Our preparative GPC purification reduced the Pd content in the polymers and improved their organic electrochemical transistor mobility by ~60% and 80% for the p- and n-type materials, respectively. These findings demonstrate the paramount importance of removing residual Pd, which was concluded to be more critical than optimization of a polymer’s molecular weight, to improve organic electrochemical transistor performance and that there is readily available improvement in performance and stability of many of the reported organic mixed ionic-electronic conductors. 

Polymeric mixed ionic-electronic conductors (MIECs) combine aspects of conjugated polymers, polymer electrolytes, and polyelectrolytes to simultaneously transport and couple ionic and electronic charges, opening exciting new applications in energy storage and conversion, bioelectronics, and display technologies. The many applications of polymeric MIECs lead to a wide range of transport conditions. Ionic and electronic transport are directly coupled through electrochemical doping, while the mechanisms of ionic and electronic transport depend on distinctly different chemical functionality, (macro)molecular structure, and morphology. Despite this, ionic and electronic transport are surprisingly tunable, independent of one another. We review the various types of polymeric MIECs, the mechanisms of ionic and electronic charge transport across conditions, and the interrelations between the two, with special emphasis on the unique aspects of polymeric MIEC transport phenomena. Expected final online publication date for the Annual Review of Materials Science, Volume 51 is August 2021. Please see http://www.annualreviews.org/page/journal/pubdates for revised estimates.