University of Cambridge > Talks.cam > Chemical Engineering and Biotechnology Departmental Seminars > Bigger Picture Talks with Professor Chihaya Adachi: The past, present and future prospects of OLEDs

Bigger Picture Talks with Professor Chihaya Adachi: The past, present and future prospects of OLEDs

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Our departmental seminar series, Bigger Picture Talks, runs throughout the academic year, inviting thought-leaders from across the world driving significant advances in our impact areas of energy, health and sustainability to share and discuss their work with us.

Abstract

Through the extensive R&D of organic light-emitting diodes (OLEDs) for more than 30 years, plenty of well-elaborated novel organic optoelectronic materials and device architectures have been extensively developed, resulting in the unique commercial utilization of OLE Ds for cutting-edge smartphones, large-area TVs, and further new future display applications by taking advantage of light-weight and flexibility. From the aspect of materials science, the creation of novel light-emitting materials in OLE Ds has been the central issue aimed at high electroluminescence quantum efficiency. Starting from the development of conventional fluorescence materials during 1990-2000th, the room-temperature phosphorescence and thermally activated delayed fluorescence continuously pioneered the novel possibilities of organic emitters, resulted in not only high-performance OLE Ds but also enriched organic photochemistry. In recent days, there have been a wide variety of studies on TADF -OLEDs because of the unlimited possibilities of TADF molecular design. Further, hyperfluorescence-OLEDs have been developed since they can realize the compatibility of high efficiency and narrow spectral width, which is ideal for practical display applications. Here we report our recent cutting-edge HP-OLEDs demonstrating high OLED performance by optimizing host, TADF , and terminal emitter molecules1-3. In particular, we focus on the blue-emission, which is capable of showing narrow FWHM and high EL quantum yield. Blue HP-OLEDs based on two new TEs are fabricated, resulting in high external quantum efficiency of over 20%, high color purity, and high brightness. By analyzing the transient PL characteristics of the HP-OLEDs, we found the presence of efficient FRET between TADF -assistant dopant and TE molecules. Further, transient EL analysis confirmed that a smaller EHOMO difference between TADF -AD and TE efficiently helps to decrease hole trapping inside the emitting layer, hence resulting in a lower efficiency rolloff and a longer operational device lifetime. This report provides a designing principle for a TADF and TE in HP-OLEDs with well-matched energy levels, leading to efficient FRET and no significant carrier trapping.

In this presentation, we mention the importance of the charge transfer phenomenon in designing high-performance organic light-emitting molecules in OLE Ds. Also, CT issues play a crucial role in maximizing the device’s operation. Further, we outlook the prospect of advanced CT technologies.

Bio

Chihaya Adachi is a distinguished professor at Kyushu University and director of Kyushu University’s Center for Organic Photonics and Electronics Research (OPERA). He is also the director of the Fukuoka i3 center for Organic Photonics and Electronics Research. Chihaya Adachi obtained his doctorate in Materials Science and Technology in 1991 from Kyushu University and held positions at the Chemical Products R&D Center at Ricoh Co., the Department of Functional Polymer Science at Shinshu University, the Department of Electrical Engineering at Princeton University, and Chitose Institute of Science and Technology before returning to Kyushu University as a professor.

Adachi’s research combines the areas of chemistry, physics, and electronics to advance the field of organic light-emitting materials and devices from both the materials and device perspectives through the design of new molecules with novel properties, the study of processes occurring in individual materials and complete devices, and the exploration of new device structures, and he has co-authored over 600 research papers.

This talk is part of the Chemical Engineering and Biotechnology Departmental Seminars series.

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