Next-Generation Polymeric Organic Semiconductors for Electrochemical Transistors with Applications in Bioelectronics

Abstract

Over the last decade, significant progress has been made in developing efficient mixed-organic-ionic-electronic conductors (OMIECs) for electrochemical transistors. Improvements in device performance for both transconductance and operational stability paved the way for applications of electrochemical transistors for health monitoring, neuromorphic computing, or electrochemical sensors. While the tuning of the energy levels (via backbone engineering) and the local environment of the polymers (via side-chain engineering) is reported to be a successful strategy for improving the electronic and ionic charge transport properties, little is known about how the short- and long-range order of polymers impacts the device performance.In my talk, I will discuss the importance of microstructure and dynamic microstructural rearrangements of OMIECs which greatly influence the electronic charge transport properties in electrochemical transistors [1]. By combining electrochemical and spectroelectrochemical measurements alongside electrochemical X-ray diffraction measurements, we observe that holes and anions are placed in ordered aggregates and crystallites at relatively low charge carrier densities (< 2x1020 cm-3) for selected OMIECs, explaining the large increase in transconductance at low operational voltages. Moreover, we find that the electrochemical charging of p-type polymeric OMIECs induces structural order along the polymer backbones. We interpret this structural ordering as the key factor for achieving high transconductance since percolating networks can form more easily when polymer chains are planarizing. Surprisingly, these dynamic microstructural rearrangements are highly reversible, however only when high charge carrier densities are avoided where bipolarons are forming. Based on these findings, I will discuss chemical design strategies for next-generation OMIECs with improved transconductance and operation stability in electrochemical transistors.[1] Garrett LeCroy, Camila Cendra, Tyler J. Quill, et.al., Role of aggregates and microstructure of mixed-ionicelectronic-conductors on charge transport in electrochemical transistors, Mater. Horiz., 2023, accepted.