Plenary Talk: Advanced Organic Optoelectronic Devices and Materials Enabled by Precise Charge-Transfer Control

The first current-injection organic electroluminescence (EL) was demonstrated in the 1960s using anthracene single crystals. However, these early devices required millimeter-thick crystals and operated at extremely high voltages, ranging from several hundred to several thousand volts, leaving a substantial gap toward practical applications. Even at that stage, the formation ratio of singlet to triplet excitons (1:3) under electrical excitation had already been recognized, highlighting the critical importance of utilizing triplet excitons for achieving high efficiency.

When we began working on OLEDs in the late 1980s, one of the central challenges was the lack of suitable electron-transport materials. While weak donor molecules such as triphenylamine derivatives exhibited excellent hole-transport properties, strong acceptor materials often induced excessive charge-transfer (CT) interactions at interfaces, leading to inefficient exciton formation despite enabling charge transport. To address this issue, we proposed a molecular design concept based on “weak acceptor character with a wide energy gap,” which led to the discovery of electron-transport materials such as oxadiazole derivatives.¹ This development enabled the realization of double heterostructures consisting of hole-transport, emissive, and electron-transport layers, thereby establishing the fundamental architecture of modern OLEDs with efficient carrier and exciton confinement.²

Interestingly, exciplex formation—initially regarded as a loss pathway—became the key to the next breakthrough. At donor–acceptor interfaces, CT complexes and exciplexes are formed and were once considered detrimental to emission. However, we later recognized that precise control of intermolecular CT interactions can minimize the singlet–triplet energy gap to a few hundred meV or less, thereby enabling efficient utilization of triplet excitons. Based on this concept, thermally activated delayed fluorescence (TADF) was realized in 2012 using donor–acceptor molecules.³ In TADF systems, triplet excitons are converted into singlet excitons via reverse intersystem crossing, enabling 100% internal quantum efficiency.

From this historical perspective, the essence of OLED technology lies in the precise control of CT interactions between weak donors and weak acceptors. These interactions govern not only charge transport and exciton formation but also molecular orientation, electronic polarization, charge separation, and even device degradation processes. The advancement of OLEDs has therefore been achieved through the integration of molecular design and process technologies such as thin-film formation and impurity control.

Today, the control of CT interactions extends far beyond OLEDs. It underpins the operation of organic photovoltaics, persistent luminescent systems,⁴ thermoelectric devices,⁵ and charge-generation layers in tandem OLEDs. Furthermore, fundamental photophysical properties—including large radiative decay rates and orientation-dependent optical phenomena—are deeply rooted in intra- and intermolecular CT interactions. Looking ahead, organic electronics is expected to evolve into a broader platform encompassing quantum, molecular, and bioelectronics, serving as a fundamental principle for next-generation devices. In this talk, I will revisit the past and present of organic electronics and discuss future directions driven by the precise control of charge-transfer interactions.

References: [1] C. Adachi et al., Appl. Phys. Lett., 55, 1489 (1989). [2] C. Adachi et al., Appl. Phys. Lett., 57, 531 (1990). [3] T. Uoyama et al., Nature, 492, 234 (2012). [4] R. Kabe and C. Adachi, Nature, 550, 384 (2017), [5] S. Kondo et al., Nat. Commun.,15, 8115 (2024).

Professor Chihaya Adachi is the director of Kyushu University’s Advanced Organic Photonics and Electronics Research Center (OPERA) and a world-class chemist specializing in organic photoelectronic, organic photonic and electronic properties, and functional molecular design.

In 1991, he received a doctorate in engineering and materials engineering from Kyushu University, and then began his career as a researcher and physicist at Ricoh Chemical Research Institute, Ltd., and served as an assistant in the Department of Functional Polymers, Faculty of Textile Science and Technology, Shinshu University. After serving as a researcher at Princeton University’s Center for Photonics and Optoelectronic Materials (POEM), he also worked as a professor at Chitose University of Science and Technology. From 2010 he became a professor at Kyushu University’s Graduate School of Engineering and director of the Advanced Organic Photonics and Electronics Research Center (OPERA), where he has been engaged in OLED research.

In 2009, Professor Adachi succeeded in developing the third-generation of OLED technology called “Thermal Activated Delayed Fluorescence” (TADF), which can achieve 100% internal quantum efficiency without using rare metals, making this a groundbreaking development. Adachi’s original TADF technology research has been published in Nature Magazine in 2012, and subsequently, in 2013, the same laboratory succeeded in developing Hyperfluorescence™ light-emitting technology that overcomes the weaknesses of TADF.

Professor Adachi has received numerous awards both domestically and internationally for his groundbreaking research and inventions. In addition, he was selected as a Highly Cited Researcher for five consecutive years since 2018, and in 2023, he made a significant contribution to the invention of TADF, deepening the principles of materials chemistry, photochemistry, and condensed matter physics, and promoting the display industry in the real world. He was highly praised for his work, received the prestigious Medal with Purple Ribbon, and continued to play an active role as a leading expert in OLED research.

Dr L. Jay Guo, Professor of Electrical Engineering and Computer Science, Professor of Mechanical Engineering, Macromolecular Science and Engineering, Applied Physics, University of Michigan.

L. Jay Guo started his academic career at the University of Michigan in 1999, and has been a full professor of Electrical Engineering and Computer Science since 2011, with dry appointment in Applied Physics, Mechanical Engineering, Macomolecular Science and Engineering. He has > 230 refereed journal publications with over 25,000 citations.

Prof. Guo’s researches include hybrid photovoltaics and photodetectors, polymer-based photonic devices and sensor applications, flexible transparent conductors, plasmonic and nanophotonics, nanoimprint-based and roll to roll nanomanufacturing technologies.

We are interested in developing photovoltaics that are suitable for building-integration or vehicle integration, especially with proper color appearance while maintaining high efficiency. We are also developing novel optical coatings that can control the transmission, reflection and absorption of electromagnetic waves in the desired frequency range for a number of applications.

Plenary Talk: Organic Molecular Sieve Membranes for Energy-relevant Applications

A number of emerging microporous organic polymers have exhibited the great potential as building blocks of molecular or ionic separation membranes. In this presentation, the concept of organic molecular sieve membranes (OMSMs) will be first introduced with the focus on the precise construction of membrane hierarchical structures and efficient intensification of membrane separation processes. The platform chemistries, designing principles, assembly methods for the precise construction of OMSMs are elaborated. Confined mass transport mechanisms for the membrane separation process intensification are elucidated based on the multiple interactions between OMSMs and permeants. ‘STEM’ (Synergistic rigidity and flexibility, Tunable pore/channel size, Even philicity and phobicity, Moderate reaction activity) guidelines on the rational design of OMSMs are highlighted. The major research activities and advances in covalent organic framework membranes for fuel cells and chemical separations in our research group will be reviewed as examples of OMSMs.

Zhongyi Jiang is a professor at School of Chemical Engineering and Technology of Tianjin University. He obtained Ph.D. degree in Chemical Engineering from Tianjin University in 1994. He was a visiting scholar of University of Minnesota with Prof. Edward Cussler in 1997 and a visiting scholar in California Institute of Technology with Prof. David Tirrell in 2009.

He is the winner of NSFC Outstanding Young Investigator Award, Cheung Kong Chair Professorship, fellow of the Royal Society of Chemistry (FRSC), fellow of The Chemical Industry and Engineering Society of China (CIESC), fellow of Chinese Chemical Society (CCS). He serves the chair of ACS Jingjinji International Chapter (2021-).

He is the leader of a scientific innovation team supported by Ministry of Science and Technology of China. He is the Chief Scientist of National Key Research and Development Program (twice). He is the Associate Editor of Advanced Membranes, Research journals, Materials Horizons and the Editorial Board Member of several journals, including Journal of Membrane Science, Macromolecules, Separation and Purification Technology, Green Chemical Engineering, etc.

His research interest primarily focuses on membranes and membrane processes, and enzyme-photo-coupled catalysis. He pioneered the Biomimetic & Bioinspired Membranes and Membrane Processes research direction in membrane field. He proposed the “Organic Molecular Sieve Membrane” concept and “ New Three Transfers (electron-proton-molecule) concept. Until now, he has published over 800 SCI papers with total citations over 52000 and h-index 118 (data from Web of Science). He has been consecutively selected on the list of highly cited scholars in the world.

Hyungjun Kim (Member, IEEE) received the B.S. and M.S. degrees from the Department of Inorganic Materials, Seoul National University, Seoul, South Korea, in 1990 and 1992, respectively, and the Ph.D. degree in materials science and engineering from the University of Illinois at Urbana-Champaign, Champaign, IL, USA, in 1998.,He is a Professor with the School of Electrical and Electronic Engineering, Yonsei University, Seoul. He is also the Director of the Air Liquide-Yonsei Joint Research Center (ALYC), Yonsei University.

Before he joined the Faculty of Yonsei University in 2009, he was a Faculty with the Department of Materials Science and Engineering, Pohang University of Science and Technology (Postech), Pohang, South Korea, from 2004 to 2009; and a Research Staff Member with the Department of Silicon Technology, IBM Research Division, Yorktown Heights, NY, USA, from 2000 to 2004. He pioneered plasma-enhanced ALD (PE-ALD) of metals and nitrides for Cu interconnect technologies and explored various thin-film processes for CMOS and novel nanodevices fabrication. Prior to joining IBM Research in 2000, he was a Visiting Research Professor with the University of Illinois at Urbana-Champaign, where he carried out research in the surface chemistry and growth of thin layers of silicon–germanium alloys and metal and nitride thin films. He also served as the Director for the Applied-Materials Yonsei Emerging Research Center (AYET) from 2009 to 2014.

He is the author of more than 200 technical publications in international journals and filed or awarded more than 50 patents. His main research interests include advanced thin-film technology focusing on atomic layer deposition (ALD) and nanoscale device fabrication.,Dr. Kim is a member of the American Vacuum Society. He is also a member of the Organizing Committee for several international conferences, including the American Vacuum Society, the Materials Research Society, and the Topical Conference on Atomic Layer Deposition. He is also an Editorial Board Member of Thin Solid Films and Metals and Materials International. He has also given invited lectures/presentations at numerous technical conferences and is active in conference organizing. He served as the Organizing Chair for the 2006 ALD Topical Conference on ALD, Seoul.(Based on document published on 8 March 2023).

Plenary Talk: Research and development of high entropy alloy coatings and their potential applications

Since the pioneering work of Prof. Yeh and Prof. Cantor in 2004, high entropy alloys (HEAs) have revolutionized materials design by enabling unprecedented compositional flexibility and synergistic property optimization. Extending this concept to thin films, HEA coatings synthesized via advanced plasma-based deposition techniques offer a powerful platform for engineering multifunctional surfaces for extreme environments and next-generation energy systems. In this work, we present a comprehensive research framework for the design, synthesis, and application of refractory HEA coatings, including oxides, carbides, borides, and nitrides, fabricated primarily using the high power impulse magnetron sputtering (HiPIMS) technique. By tailoring elemental composition and plasma conditions, we demonstrate how phase stability, defect structure, and surface chemistry can be precisely controlled to achieve superior functional performance. Representative examples include oxygen-rich VNbMoTaWOₓ oxide coatings that significantly enhance electrochemical activity in vanadium redox flow batteries under strongly acidic conditions, and CrMoNbTiWCₓ carbide coatings that exhibit outstanding corrosion resistance for proton exchange membrane fuel cell bipolar plates. Additionally, (HfVTiZrW)B₂ boride coatings show remarkable resistance to both sulfuric acid chemical corrosion and HF plasma-induced degradation, while nitrogen-engineered AlCoCrFeNiNₓ coatings enable efficient electrocatalysis in alkaline saline environments, highlighting their promise for seawater electrolysis. These results underscore a central paradigm: through compositional complexity and plasma-enabled synthesis, HEA coatings can be rationally designed to meet the demands of harsh and multifunctional applications. This work not only advances the fundamental understanding of HEA thin films but also opens new pathways for their deployment in sustainable energy, advanced manufacturing, and harsh environment technologies.

Dr. Jyh-Wei (Jeff) Lee is a Chair Professor at the Department of Materials Engineering at the Ming Chi University of Technology (MCUT), Taiwan, and a Joint Appointment Distinguished Professor at the College of Engineering, Chang Gung University, Taiwan，China. He served as the Director of the Center for Plasma and Thin Film Technologies (CPTFT) from August 2021 to January 2025 and as the Director of the International Ph.D. Program in Plasma and Thin Film Technology, MCUT, from August 2023 to January 2025.

Prof. Lee has been a Fellow of the American Vacuum Society (AVS) since 2024. He is the Chair of the AVS-Taiwan Chapter from 2023 to 2024 and a member of the Editorial Board of Surface & Coatings Technology, Applied Surface Science Advances, China Surface Engineering, and International Journal of Advanced Manufacturing and Material Processing (IJAMMP). He is a member of the Executive Committee of Advanced Surface Engineering Division (ASED) of AVS, the Program Committee of ASED, the Program Chair of ICMCTF 2023, and the General Chair of ICMCTF 2024. He is also an International Program Committee Member, Symposium Chair, and Session Chair of several world-famous international thin film and plasma-related conferences, such as PSE, AEPSE, TACT, and ICMCTF.

His research focuses on the development of plasma-based thin film technologies to enhance the properties and performance of functional thin films and coatings. He investigates the nanocomposite and nanolaminated nitride, carbonitride, and boronitride hard coatings for tribological applications, corrosion, and oxidation protection in related industries. Recently, he has worked on the research and development of functional high entropy alloy thin films and thin film metallic glass materials, which can be applied in anti-radiation, anti-plasma etching, anti-oxidation, biomedical fields, and in the energy fields, such as the electrocatalytic materials for hydrogen production and vanadium redox flow batteries, and anti-corrosion coatings for bipolar plates in electrolyzers.

Prof. Lee is the PI and Co-PI of more than 30 projects from the Taiwan government and industries, with a total budget of around 7.0 million US$ in the past five years. He holds 13 patents and publishes more than 220 SCI journal papers and over 40 plenary/keynote/invited lectures in the field of PVD and related surface engineering technologies. The H-index of his published papers is 47. He is listed as the World’s Top 2% Scientists in “Annual Scientific Impact Ranking” from 2020 to 2025 and the “Lifetime Scientific Impact Ranking (1960- 2024)” published by Stanford University.

Plenary Talk: Advanced Thin Film Engineering Steering Health and Energy Transition

Advanced materials are driving innovation across a wide range of technological sectors, including energy conversion and storage, microelectronics, mobility, healthcare, and sustainable manufacturing. Among these, functional thin films and coatings play a particularly important role, as they enable the precise tailoring of surface and interfacial properties that govern the performance, efficiency, and durability of advanced devices. Their technological relevance extends from established industrial applications to emerging technologies, offering significant opportunities for value creation and sustainable innovation.

In the context of resource-efficient manufacturing, critical raw material substitution, and the transition toward climate-neutral technologies, the chemical design and processing of nanostructured ceramic thin films have become increasingly important. Through controlled synthesis and surface functionalization, key properties such as charge transport, catalytic activity, corrosion resistance, optical response, and interfacial stability can be optimized to meet demanding application requirements. This lecture will highlight recent advances in the chemical engineering of functional thin films and nanostructured ceramic interfaces for energy and healthcare applications. Examples will include functional oxide coatings for electrolysers and hydrogen production, interface engineering strategies for high-performance perovskite photovoltaics, and the role of tailored ceramic thin films in enhancing photon harvesting and charge-transfer processes. In addition, chemically functionalized SiO₂ nanomaterials will be presented as advanced drug-delivery platforms capable of transporting higher therapeutic payloads while minimizing off-target effects.

Sanjay Mathur is a Chair Professor and Director of the Institute of Inorganic Materials Chemistry at the University of Cologne in Germany. He is a Distinguished Professor at IIT Madras and IIT Hyderabad, India and an International Faculty at IIT Kharagpur, IIT Bhilai and IISER Tirupati. He is also the Director of the Institute of Renewable Energy Sources at the Xian Jiao Tong University, Xian, China and a World Class University Professor at the Chonbuk University in Korea. His research focuses on application of nanomaterials and advanced ceramics for energy technologies. He holds several patents and has authored/ co-authored over 600 research publications (h index, 86) and has edited several books. He serves as the Editor-in-Chief for Journal of Electroceramics, and Editor for Nano Energy and Progress in Materials Science. He is an Academician of the World Academy of Ceramics. He was awarded the Honorary Doctorate of Vilnius University in 2016. He is a Fellow of ACerS, ASM International and MRS. He was elected Fellow of the European Academy of Science in 2020 and as Foreign Fellow of National Academy of Science, India in 2021. He was awarded the Woody White Award of the Materials Research Society (MRS) in 2021 and had received the Medal of the Chemical Research Society of India (2022). He is also the recipient of the Materials Frontiers Award (2022) of the International Union of Materials Research Society (IUMRS, 2022). He has served as the President of the American Ceramic Society (ACerS, 2022-23), USA. He was recognized by the Orton Jr. Lecture (2022/23) of the ACerS. He is the Secretary of IUMRS, and he serves on the Boards of European Science Council, German Ceramic Society and German Materials Society. He was recognized with the M L Bhagat award of the Indian Ceramic Society (2024). He was elected Fellow of the European Ceramic Society (2025) and Academician of the African Academy of Science (2025).