Disentangling Redox Properties and Capacitance in Solution-Processed Conjugated Polymers

The unique ability of combined ionic and electronic transport in conjugated, semiconducting polymers has resulted in the emergence of a variety of redox-based technologies ranging from energy storage and conversion, to bioelectronics, to on-demand color control. Although conjugated polymers have been extensively studied for decades, the recent revival of organic bioelectronics, in particular, has demonstrated that there needs to be a better understanding of the interplay between mixed ion and electron transport and the underlying film morphology. Many of the conjugated polymers that are effectively doped electrochemically and that exhibit a combination of high capacitance, fast and reversible redox switching, and exceptional stability lack long-range order making it more challenging to evaluate how the morphology evolves as a function of oxidation state. Here, we demonstrate how readily accessible electrochemical and spectroscopic techniques can offer a great deal of insight into ion and electron transport in redox-active conjugated polymers regardless of their degree of order. Furthermore, we show how numerous redox properties, including onset of oxidation, capacitance, and conductance profile, of five dioxythiophene-based copolymers can be manipulated by the size and polarity of the functional groups that are incorporated to provide solution processability.