Next-Generation Polymeric Organic Semiconductors for Electrochemical Application in Aqueous Electrolytes

Over the last decade, significant progress has been made in developing redox-active polymeric organic semiconductors for electrochemical applications in aqueous electrolytes. Next to performance improvements, the investigation of chemical structures with improved electrochemical stability paved the way for exciting electrochemical applications, including electrochemical transistors [1,2], neuromorphic computing [4], electrochemical sensors [5], and energy storage devices [6]. While tuning energy levels (via backbone engineering) and the local environment (via side-chain engineering) are successful strategies for improving the electronic and ionic charge transport properties of polymeric OSCs in electrochemical devices, little is known about the reason why some polymeric OSCs achieve a higher performance than others.<br/>In my talk, I will discuss our recent findings on in-situ electrochemical characterization techniques where we investigated the origin of high-performance of state-of-the-art polymers based on polythiophene with hydrophilic side chains in electrochemical transistors [1,2]. Our findings show that aggregate formation in polymeric OSCs is beneficial for achieving high electronic charge carrier mobilities (leading to high transconductances (<i>g</i>_m)), but only if these aggregates are electrochemically accessible on fast time scales. Our finding suggests that the role of the side-chain expands beyond controlling the morphology and enabling interactions with solvent molecules from the electrolyte. When chosen accordingly, side chains can provide a framework for reversibly accessing ordered aggregates with electrochemical doping, yielding highly mobile electronic charge carriers and high transconductances Finally, I will discuss strategies for utilizing this concept to improve the performance of hole-transporting conjugated polymers for electrochemical devices.<br/>[1] A. Giovannitti, D.-T. Sbircea, S. Inal, <i>et. al.,</i> <i>Proc. Natl. Acad. Sci.</i> <b>2016</b>, <i>113</i>, 12017. [2] M. Moser, T. C. Hidalgo, J. Surgailis, <i>et. al.</i> Adv. Mater. 2020, 32, 2002748. [3] A. Giovannitti, K. J. Thorley, C. B. Nielsen, <i>et. al.,</i> <i>Adv. Funct. Mater.</i> <b>2018</b>, <i>28</i>, 1706325. [4] A. Melianas, T. J. Quill, G. LeCroy, <i>et. al.,</i> <i>Sci. Adv.</i> <b>2020</b>, <i>6</i>. [5] S. T. M. Tan, A. Giovannitti, A. Melianas, <i>et. al.,</i> <i>Adv. Funct. Mater.</i> <b>2021</b>, <i>31</i>, 2010868. [6] A. A. Szumska, I. P. Maria, L. Q. Flagg, <i>et. al.</i> <i>J. Am. Chem. Soc.</i> <b>2021</b>, <i>143</i>, 14795.