Probing Operando Mixed Ionic/Electronic Transport in Conjugated Polymers: From Molecular Level to Device Performance

Abstract

Mixed ionic-electronic transport in conjugated polymers significantly impacts the performance of organic electronics, ranging from organic electrochemical transistors (OECTs) to next-generation neuromorphic computing architectures. The exceptional performance of conjugated polymers in these applications stems from their remarkable ability to efficiently accommodate counterions throughout the entire device volume during electrochemical redox processes. The dynamic changes in the electrical and chemical environment that occur during this process necessitate the utilization of operando characterization. In this dissertation, we present a series of comprehensive studies employing operando measurements to probe the intricacies of mixed ionic-electronic transport in OMIECs and their direct impact on device performance. First, we delve into the molecular-level structural changes of a n-type ladder OMIEC material upon the electrochemical process and found a unique mechanism which might provide crucial insights into next generation material design. Next, we focus on comprehending the switching dynamics of OECTs and identifying the speed limitations. Through this investigation, we explain the asymmetric accumulation mode OECTs switching behavior, which cannot fit in existing models. Also, we gain valuable knowledge on the interplay between electronic and ionic transport, shedding light on potential strategies for optimizing OECT switching characteristics. Finally, we target the root sources of OECT degradation over repeated cycling. With the operando tools, we decouple the contribution from ionic and electronic transport to the degradation. Together, our research highlights the power of operando characterization in unveiling the fundamental processes of mixed ionic-electronic transport and providing valuable insights for application-oriented molecular design and device optimization.