POSTECH News

[POSTECH University Professor Series ②] Tireless Efforts Establish a Renowned Organic Semiconductor Lab Kilwon Cho, Professor of Chemical Engineering, Carves His Name into the Legacy of Organic Semiconductors

2024-09-27 246

The boy was fascinated by his ancestry, eager to learn about his great-grandparents, great-great-grandparents, and even distant ancestors from centuries or millennia ago, whose names had long faded from memory. He wondered what they looked like and what events had shaped their lives. Like a young archaeologist, he blended the facts he gathered from books with his imagination, crafting his own vision of the past.

As a young man, his curiosity turned to the future. The rapid advances in science and technology captivated him, and he marveled at the new creations shaping the modern world. This passion led him to choose chemical engineering as his major. After earning his bachelor’s and master’s degrees in industrial and engineering chemistry from Seoul National University, he embarked on a PhD in polymer science at the University of Akron in the U.S. As a chemical engineer, he transformed the fantastical inventions of science fiction into reality, using his ideas to push the boundaries of what was possible.

By middle age, reality posed new challenges. He felt his research ideas dwindling and yearned to explore new fields, but the unfamiliar terrain seemed daunting. Then, like many scientists before him, a moment of serendipity struck. A presentation session on “Organic Semiconductors” at a conference captured his attention and ignited a fresh research idea. What once seemed intimidating now fueled his enthusiasm, and the challenges transformed into new ideas. It became an exhilarating period of discovery.

Through the years that followed, his curiosity and passion for research never waned. Today, he stands as one of the world’s leading experts in organic semiconductors and flexible electronic materials and devices. With over 100 master’s and doctoral students emerging from his lab, including 25 who have secured professorships, his lab is renowned within POSTECH. His name, POSTECH University Professor Kilwon Cho, will be remembered for generations to come.

인터뷰3
– The bookshelves in your lab are impressive. It feels like I’m walking into a historic archive room. What was your first day as a researcher like?

Hearing you speak of historic archives reminds me that, as a kid, I was equally fascinated by archaeology, history, science, and engineering. I often found myself imagining how people lived in the past or what my distant ancestors were like. What I’m trying to emphasize is that “curiosity” lies at the root of all academic research, especially in fields like natural sciences and engineering. My own curiosity is what drove me to become a researcher. I chose the chemistry-based field of polymers because I was intrigued by the idea of creating something new from them.

– How did you transition to working on organic semiconductors and flexible electronic materials and devices, which have become your signature research area?

My initial focus was on polymers, specifically their surfaces, interfaces, and the physico-chemical properties of polymer thin films. This was the core of my research when I earned my PhD in 1986 and joined POSTECH in 1988. After about 15 years in that area, I felt like I was running out of fresh ideas and wanted to explore a new research direction. I sought a field where I could merge my expertise, and bio-interfaces and electronic device interfaces emerged as promising options. In the early 2000s, as Korea’s IT industry was on the rise, I decided to venture into electronic devices after careful consideration. The transition was challenging, and I was uncertain about my potential for success, but I dedicated myself to studying this new field intensively alongside my students in the lab.

In 2003, I attended the Materials Research Society (MRS) conference in the U.S. During a session on organic semiconductors—a field I had been studying with great interest—there was a presentation on flexible organic electronic materials and devices. As I listened, an idea began to form, one that could merge my expertise in polymeric surfaces, interfaces, and thin films. After returning from the conference, I applied this idea to organic transistors, and it proved highly successful. The findings were published in “Advanced Functional Materials” in 2005. While it has since become a highly cited paper, its real significance lies in being a foundational study that spurred continued research in this area by other researchers.

– So this marked the beginning of your full-scale research into organic semiconductors?

Yes, we initially focused on organic semiconductor materials and thin films as well as organic transistors before expanding into organic solar cells. Transitioning into the field was relatively straightforward because we were already working on polymer surfaces, interfaces, thin films, and polymer blends, and we applied the same research techniques we had been using. Organic electronic devices are composed of multilayer structures with very thin films, and organic solar cells consist of a blend of electron donor and electron acceptor semiconductors. This made it a perfect match for our expertise. Leveraging our knowledge allowed us to evolve into a world-class research group in organic semiconductors, with significant achievements in the study of their structure and physical properties, organic transistors, solar cells, and photodetectors. We successfully shifted our research focus by building on our specialized areas of expertise.

– Your research has an impressive citation count and H-Index, and you’ve also been honored as a Highly Cited Researcher (HCR). What’s the most memorable study you’ve conducted?

It’s like asking which of your children you love the most—it’s difficult to choose. There have been so many memorable studies, but if I had to pick one, it would be my first paper in organic semiconductor research. It was published in “Advanced Functional Materials”, as I mentioned earlier. In that study, we improved the charge transfer of organic transistors by controlling the interfacial structure of organic insulators. The idea was that by treating the surface of an organic insulator with self-assembled thin films of various functional groups, we could alter its surface properties, which in turn influenced the crystal orientation of the organic semiconductor polymer. This allowed us to control the charge transfer characteristics of organic transistors. It’s particularly special to me because it laid the groundwork for surface-induced self-assembly in organic semiconductors and was our lab’s first work in the field.

Another memorable study was the creation of polymeric organic semiconductor giant single crystals. We produced the largest polymeric organic semiconductor single crystal ever reported at the time. However, we were unable to publish it in the top journals we aimed for due to a lack of sophisticated analysis and electrical characterization to fully explain why the giant single crystal formed. That setback left a lasting impression on me.

– You’ve just completed your role in the highly publicized Global Frontier Research Center. How do you feel about its beginning and conclusion?

From 2011 to 2020, I led the “Global Frontier Research Center for Advanced Soft Electronics.” As the name suggests, the center focused on developing flexible electronic materials, devices, and fusion technologies essential for electronic devices that can bend, flex, and fold. Our goal went beyond basic research and publishing papers; we aimed to create original technologies with real-world applications. It was a large-scale project, with an annual budget of about 9 billion won and a total investment of over 80 billion won across 9 years.

Today, foldable smartphones and monitors with curved displays are available on the market, but back in 2011, these ideas were still in the conceptual stage—merely sketches and discussions. Developing these technologies required a highly innovative and challenging approach. While the substantial research funding came with significant psychological pressure, we successfully completed the project by transforming that pressure into a strong sense of responsibility.

– It must have been a lot of work for the researchers you collaborated with. How did their efforts pay off?

During its time, the Global Frontier Research Center, including our center, brought together the top researchers in their respective fields in Korea. Our success in pioneering soft electronics and achieving strong results was due to the exceptional talent within our team. Many of the researchers who worked with us are now mid-career professionals making significant contributions in their fields, with some becoming world-class researchers. Graduate students from our team have since become colleagues in the field, contributing as emerging researchers. The significance of the Global Frontier Research Center for Advanced Soft Electronics extends beyond just pioneering the field—it also nurtured the next generation of talented scientists.

In terms of quantitative achievements, we excelled as well. During the center’s operation, 10% of all SCI-level papers on soft electronics worldwide came from Korea, with 60% of those originating from our research center. Additionally, wearable electronics technologies, such as printing processes, led to the creation of startups. Although we regret that the soft electronics market didn’t fully take off during our time, we are proud to have made significant contributions to shaping the current era of soft electronics.

– It sounds like you’ve faced your share of challenges. How do you overcome them?

Challenges are an inevitable part of research. Often, we don’t achieve the goals or findings we initially hope for, and all the work we publish comes after a lot of trial and error. There are definitely times when the odds of success seem incredibly low, and sometimes we have to abandon certain directions. However, the key is not to give up out of frustration. Instead, we come together, analyze the results, and seek out new possibilities.

Another challenge we face is when a research paper is rejected after long and dedicated effort. It’s understandable when a paper is rejected for not meeting the necessary standards, but it’s particularly disheartening when we feel the rejection is due to an unfair evaluation—whether due to preconceptions, biases, or cultural differences among reviewers. Those moments are tough, especially for the students who can get discouraged. In those situations, I remind them that “Good research will ultimately be judged for its substance, not just the name of the journal.” This helps them regain focus and motivation for the next study.

– Could that be why your lab is regarded as one of the most prestigious at POSTECH with the highest number of graduates? What kind of mindset and attitude do you emphasize in your teaching?

There’s a question I always ask students during interviews for my lab: “What kind of person do you need to be to become a good researcher?” I receive various answers, such as “passion,” “curiosity,” and “competence.” This question is inspired by two researchers I consider my mentors. One is the late Dr. Alan Gent, my PhD advisor at the University of Akron, who always said, “Think different,” emphasizing the importance of thinking differently from others. The other is the late Professor Tae-Gyu Lee of KAIST, a significant role model in my journey. When I was a freshman at Seoul National University, I attended a lecture upon hearing that a world-renowned scholar would be speaking. During the lecture, Professor Lee posed a question to the audience: “What qualities define a good researcher?” He then wrote “Keen observation and Never-ceasing efforts” in large letters on the blackboard. That stuck with me, and I’ve carried those three principles—thinking differently, keen observation, and relentless effort—throughout my career.

For students, I particularly emphasize “relentless effort.” Failure is inevitable in research, and it’s through repeated failures that we uncover new possibilities and ultimately achieve success. Persistence and hard work are essential to navigating this process, so I tell my students they must be willing to give it their all. When I first meet with students, I also ask them to envision where they see themselves in 10 years—what they’ll be doing and how they’ll be living—and to actively work toward that goal. This helps them understand that they shouldn’t take their graduate school experience lightly.

– You’ve been recognized as a University Professor at POSTECH for your outstanding research and teaching. How does it feel to receive this honor?

What I appreciated most was the extension of the retirement age, as it allowed me to continue my research. In U.S. universities, and in most U.K. institutions except for a few, there’s no mandatory retirement age, so many professors continue to be actively engaged in research well into their later years. My PhD advisor, for example, continued his research until the age of 80, and that deeply inspired me to be a professor who not only has passion but also consistently produces excellent research over the long term. I was excited when POSTECH’s University Professor program extended my retirement age, allowing me to continue my work as I approach retirement.

– You were really pleased and smiled when you mentioned that you could continue your research, which is something I often hear from researchers nearing retirement who are upset about leaving their work.

The discussion around extending the retirement age shouldn’t merely focus on increasing it; it should be aligned with the unique characteristics of universities, research institutions, and companies, while also considering the current age demographics. This approach can help create a comprehensive plan to support sustainable research. Naturally, the passion and exceptional skills of researchers are fundamental to this.

Generational differences also play a significant role. Some conflicts arise purely from age differences, while others stem from the nature of the work itself. For instance, when evaluating research project selections based on achievements, senior scientists with more extensive careers tend to have an advantage, which can lead to complaints from younger researchers. Conversely, senior scientists may feel penalized for their age if they are overlooked. Given that the science and technology community is relatively small compared to other sectors and research funding needs to be allocated among projects, this creates a competitive atmosphere that heightens sensitivities. To address these issues, it’s crucial to build consensus across generations and foster an ecosystem that benefits everyone. Especially in Korea, where we are facing a demographic cliff, this issue needs to be carefully considered to effectively utilize our exceptional scientific and technological talent.

– In May, you won the Samyang Group’s Sudang Award. It seems like your research is thriving, reaching its peak. What are your next goals and plans?

One of our current research focuses is on doping organic semiconductors to enhance their electrical properties. While this topic has been explored since the inception of organic semiconductors, it has gained renewed interest recently due to advancements in synthesis and computational science. On a fundamental level, we aim to understand how the chain structure and thin-film architecture of doped organic semiconductors influence an increase in charge concentration and charge transfer. Additionally, we are concentrating on stretchable organic semiconductor polymers. Our goal is to conduct in-depth research into the structure, electrical, and mechanical properties of these materials, which can maintain excellent semiconductor characteristics even when stretched like rubber.

– Do you have a plan for after retirement?

I’m still contemplating how I will pursue my research after retiring in two years, but I intend to continue my work. I aspire to emulate professors in countries like the U.S., where there is no mandatory retirement age, who remain passionate about their work and continue to make significant contributions as they age. Through this, I hope to further advance the field of organic semiconductors that I’ve dedicated my career to and be remembered as a passionate researcher, all while helping to lay the foundation for the next generation of talent.

– What advice would you give to students and young researchers who are pursuing their dreams and striving to turn them into reality?

My message to young students contemplating their career paths is that science and technology is an exciting and boundless field capable of enriching our lives and transforming the world. The impact of science and technology throughout history is a testament to this. I truly believe that emerging talents in these areas can drive change and contribute to human progress by honing their strengths and embracing the challenges of in-depth research.

My message to young students contemplating their career paths is that science and technology is an exciting and boundless field capable of enriching our lives and transforming the world. The impact of science and technology throughout history is a testament to this. I genuinely believe that talented individuals in these fields can drive change and contribute to human progress by honing their strengths and embracing the challenges of deep, in-depth research.

– Do you have any final thoughts you’d like to share?

First and foremost, I want to say, “Thank you.” It’s been 36 years since I joined POSTECH in 1988, during the early days of the university. I attribute my research achievements to the exceptional research environment at POSTECH. I want to express my gratitude to the students and researchers who have collaborated with me. I feel incredibly blessed to have worked with such a remarkable group of students, and I believe that POSTECH will continue to nurture outstanding individuals who will uphold its founding principles and educational philosophy, ultimately making a difference in the world.