Understanding the Static and Transient Behavior of Organic Electrochemical Transistors

Abstract

An organic electrochemical transistor (OECT) is a type of transistor with both ionic and electronic carriers involved in device operation. Recently, OECTs have emerged as promising candidates for both neuromorphic computing and biosensing applications as they exhibit direct response to biologically relevant ions, neurotransmitters, and metabolites. Moreover, the typically soft and flexible nature of organic semiconductors opens the possibility of the implementation of OECTs in both brain-machine interfaces and implantable biosensors. Nevertheless, deeper understanding of static and transient behavior of OECTs is necessary to unleash the full potential of OECTs for all the promising real-world applications aforementioned. Here, we first study the impact of the polymer side chain on the transconductance and the speed of OECT devices. Specifically, we show higher transconductance and faster kinetics if more polar function groups are on the side chain, or if the polar functional group is farther away from the polymer backbone. Next, we elucidate why accumulation mode organic electrochemical transistors turn off much faster than they turn on, which is a phenomenon prevalent in published studies yet cannot be explained by existing models. We further identify that ion transport is limiting the device’s operation speed and provide guides for engineering faster OECTs from both device and materials perspectives. Last, we synthesize new polymers and characterize their OECT performance. We verify that higher polymer crystallinity indeed reduces the OECT electronic carrier mobility. Together, these studies help to expand our understanding of the static and transient behavior of OECTs.