(7cb) Structure–Property Relationships in Polymer-Based Transistors

Polymer electronic materials have been introduced as potential solutions in a wide range of electronic products including light-weight, flexible organic field-effect transistors (OFETs), organic photovoltaics (OPVs), and organic light-emitting diodes (OLEDs). The primary aim of my research is to address the fundamental structure-property relationships for improved performance and stability of flexible organic devices based on multi-component electronically-active materials (e.g., semiconducting polymer-polymer blends) when they are cast into thin films. For instance, OPV devices based on electron donor and electron acceptor (D-A) bulk heterojunctions show a critical relationship between the phase-separated structures and device efficiency. In addition, organic transistors based on blended films are one of the emerging device classes that exhibit excellent performance and stability relative to common transistors based on a single semiconducting film. The OFETs have attracted a significant amount of academic and industrial research attention over the past three decades due to their promise of delivering mechanically-robust (e.g., flexible and stretchable materials), low-cost, and easily processed electronic devices. Moreover, the study of multi-component polymer films has been another important arena of research as properly combining materials allows for the creation of attractive features of the constituent components that goes beyond the sum of the individual parts.

In the well-known realm of bulk heterojunction OPVs, the two components of blends are strongly involved in the charge exchange and transport in the active layers. In the less-studied realm of organic transistor composite active layers, the blends of a polymer and small molecule provide a synergistic effect that combines the high electrical performance from the small molecule and the easy film processing from the polymer, leading to high-performance organic transistors (i.e., high charge carrier mobility and high ON/OFF current ratio). Furthermore, the polymer blends based on an organic semiconductor and an insulator allow for superior performance and environmental stability of organic transistors, due to the enhanced doping effect by an insulating matrix. Critically, the performance and stability of these transistors based on blended films significantly depends on the active materials and their interfacial morphologies. However, elucidating the underlying mechanism and impact on the device performance of the interpenetrating structures is still an open opportunity in the literature. Also, the scope of application is currently limited. In order to meet these needs, we propose three specific research efforts. We will: (1) elucidate the fundamental mechanism of phase-separated structures by a range of analysis techniques and systematically investigating the structures by the control of the active structure through lithographic techniques; (2) fabricate optimized organic transistors based upon multi-component polymer blends in order to clarify the impact of the nanostructure on device performance; and (3) synthesize new linear, branched, star, and block polymers consisting of at least two components in order to develop the critical structure-property-performance relationships that are required for the success of multi-component organic transistors. I believe there are great challenges and opportunities in this multi-component system for the development of flexible organic transistors.

Research Experience:

My research at both Seoul National University (Mentor: Professor Kookheon Char) and Purdue University (Mentor: Professor Bryan W. Boudouris) has focused on the design of soft materials and their integration into next-generation flexible electronic devices. In brief, I have focused on: (1) determining the impact of nanostructure in phase-separated organic memory diodes in order to advance flexible logic circuits; (2) utilizing interfacial engineering with radical polymers in organic field-effect transistors for enhanced device performance; (3) and elucidating the charge transport mechanism of radical polymers in order to generate ambipolar, transparent thin film transistors. As a graduate student, I have a significant amount of experience with respect to the design, fabrication, and optimization of organic electronic devices. Moreover, I have been able to utilize these devices to probe the fundamental physics of charge transport in a unique and emerging conducting polymer system (i.e., open-shell macromolecules).

In addition, I have intentionally switched from more synthetic and device-focused work during my graduate career to a postdoctoral research position that is centered on polymer physics during my upcoming time at the University of Delaware (Mentor: Professor Thomas H. Epps III). This will allow my future research team to understand and improve the self-assembly and implementation of homopolymer and block polymer materials for energy storage devices. This work mainly involves the design, synthesis, and nanoscale characterization of macromolecules for energy applications (i.e., organic batteries). With well-established charge transport and synthetic optimization of energy materials, my future research will pursue materials development for advanced energy applications. Thus, my work to date has focused on linking nanoscale scientific phenomena to device engineering at the macroscale, and I anticipate utilizing this previous experience to launch my own research group in order to impact the realms of flexible and stretchable electronics, energy conversion devices, and energy storage devices in the near future.

Teaching Interests:

I was born and raised in South Korea, and I experienced military service for 2 years while I was an adult in South Korea. During this military service period, I learned the initiative and drive arising from positive attitudes play a crucial role in military operations. In a similar manner, a positive and supporting attitude from an instructor can allow students to overcome many difficulties in classroom as well as in the laboratory. Moreover, I have considerable formal teaching experience, and I have previously served as a teaching assistant for undergraduate courses on Engineering Mathematics, Transport Phenomena, and Design of Staged Separation Processes. In addition, this previous experience has allowed me to instruct many of the core, fundamental courses in chemical engineering at my previous institutions of Seoul National University and Purdue University. Thus, I was able to gain a deep insight into how to instruct undergraduate students in the fundamentals of chemical engineering from some of the most respected instructors in the field (e.g., Professor Phillip Wankat). Specifically, I delivered lectures for students, had regular office hours, and developed course materials. Thus, I can contribute to lead any course in the core chemical engineering curricula and more specific electives, such as polymer chemistry and organic electronics. In addition, I participated in the mentorship of undergraduate students as a part of their undergraduate thesis at Seoul National and Purdue. Based on my previous experiences, I can lead the next generation to the high level of learning and training.