Natural mixed ionic–electronic conductors (NMIECs) are a highly desired category of materials for unconventional uses, such as bioelectronics, neuromorphic computing, and bio-fuel cells, due to their dual electronic and ionic conduction characteristics. In order to ensure a much broader acceptance of these intriguing materials, there is a necessity to diversify their properties and develop methods that enable customization of the features of NMIEC-based devices for specific applications. An essential part of this process is to create techniques for assessing the various properties of these materials. However, despite the increasing popularity of NMIECs, there is a severe shortage of research on the molecular orientation-dependent transient behaviors of such conductors.
Now, nonetheless, an international team of researchers from Korea and the UK, headed by Professor Myung-Han Yoon from the School of Materials Science and Engineering at Gwangju Institute of Science and Technology, aimed to fill this void in our understanding of natural mixed ionic–electronic conductors. In their recent groundbreaking study published in Nature Communications on 28 November 2023, the team investigated peculiar transient behaviors of NMIECs controlled by variations in molecular orientation using an organic electrochemical transistor (OECT). Previously, several studies have explored NMIECs using the OECT platform, indicating that various factors, such as direction, length, side chain symmetry, polymer backbone structure, and film crystallinity, adjust the properties of OECTs.
“OECTs are recognized for replicating the computing mechanisms of neurons and synapses in spiking neural networks (SNNs) and are thus considered promising,” explains Prof. Yoon while discussing this study. “To support the growing interest in exploring the dynamic behaviors of OECTs in the frequency domain, we focused on an aspect that is frequently overlooked. We chose to investigate the connection between backbone planarity-dependent molecular orientation and transient OECT features.”
For this purpose, the researchers initially synthesized two new 1,4-dithienylphenylene (DTP)-based OMEICs, DTP-2T and DTP-P, with co-monomer units, 2,2′-bithiophene and phenylene, respectively. Although the polymers possessed the same ionic and electronic properties, by manipulating the polymer backbone planarity, the researchers managed to govern the dominant molecular orientation of the mixed conductor system.
The DTP polymer was then utilized to create OECT devices, which were subjected to electrochemical analysis. Initially, the team observed that both polymers exhibited similar electrochemical properties despite having different molecular orientations. They then altered the ion injection direction when there was a certain current/voltage during the analysis. They noted that the ion injection direction relative to the molecular orientation influenced the length of the ion drift pathway, which, due to an indirect correlation with ion mobility within the polymers, resulted in peculiar transient responses in OECT devices.
The conclusions of this study offer a distinctive viewpoint into the realm of molecular orientation-dependent traits of OECT devices. “OECT-based SNN architectures are projected to supplant current computing systems in the future by enhancing computation speed and reducing energy consumption. Our findings are anticipated to facilitate the realization of SNN-based computing systems soon,” concludes Prof. Yoon. Additionally, the team also believes that the insights from this study could aid in the design and development of advanced organic mixed conductor materials for biomolecular and biosignal sensors.
With any luck, this work will pave the way for numerous exciting futuristic technologies!
About the institute
The Gwangju Institute of Science and Technology (GIST) was established in 1993 by the Korean government as a research-oriented graduate school to ensure Korea’s continued economic growth and prosperity by developing advanced science and technology with an emphasis on collaboration with the international community. Since then, GIST has pioneered a highly regarded undergraduate science curriculum in 2010 that has become a model for other science universities in Korea. To learn more about GIST and its exciting opportunities for researchers and students alike, please visit: http://www.gist.ac.kr/.
About the author
Prof. Myung-Han Yoon is a full Professor at the Department of Materials Science and Engineering, GIST (Gwangju Institute of Science and Technology). Yoon received his Ph.D. in Materials Chemistry from Northwestern University in 2006 and later completed his postdoctoral training at Prof. Hongkun Park’s lab at Harvard University. His current areas of interest include the development of bio-interface integrated devices using organic and inorganic electronic materials for bioelectronic technology. His group is working on the fabrication of biodegradable composite materials for sustainable electronic devices.