Chihaya Adachi

Chihaya Adachi.pngChihaya Adachi is a distinguished professor at KyushuUniversity and director of Kyushu University’s Center for Organic Photonics andElectronics Research (OPERA). He is also program coordinator of KyushuUniversity’s Advanced Graduate da Vinci Course on Molecular Systems for Devicesand director of the Fukuoka i3 center for Organic Photonics andElectronics Research. Chihaya Adachi obtained his doctorate in Materials Scienceand Technology in 1991 from Kyushu University and held positions as at theChemical Products R&D Center at Ricoh Co., the Department of FunctionalPolymer Science at Shinshu University, the Department of Electrical Engineeringat Princeton University, and Chitose Institute of Science and Technology beforereturning to Kyushu University as a professor.

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

Recent awards he has received include 24thNagoya of Organic Chemistry “The silver medal ” (2019), Nishina Memorial Prize (2017) and ThomsonReuters Research Front Award (2016), and he was named a 2018201920202021Highly Cited Researcher.


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Operation mechanism of TADF/hyperfluorescence OLEDs aimed for highstability

Chihaya Adachi

Center for OrganicPhotonics and Electronics Research (OPERA), Kyushu University

744 Motooka, Nishi,Fukuoka 819-0395, Japan

Through the extensiveR&D of organic light-emitting diodes (OLEDs) for more than 30 years, plentyof well-elaborated novel organic optoelectronic materials anddevice architectures have been extensively developed, resulted in the uniquecommercial utilization of OLEDs for cutting-edge smartphones, large-area TVs,and further new future display applications by taking advantage of light-weightand flexibility. From the aspect of materials science, the creation of novellight-emitting materials in OLEDs has been the central issue aimed for highelectroluminescence quantum efficiency (EQE). Starting from the development ofconventional fluorescence materials (1st generation) during1990-2000th, the room-temperature phosphorescence (2000-) (2ndgeneration) and thermally activated delayed fluorescence (TADF) (2012-) (3rdgeneration) continuously pioneered the novel possibilities of organicemitters, resulted in not only high-performance OLEDs but also enriched organicphotochemistry. In recent days, there have been a wide variety of studies onTADF-OLEDs because of the unlimited possibilities of TADF molecular design.Further, hyperfluorescence (HP)-OLEDs have been developed since they canrealize the compatibility of high efficiency and narrow spectral width, whichis ideal for practical display applications. Here we report our recentcutting-edge HP-OLEDs demonstrating high OLED performance by optimizing host,TADF, and terminal emitter (TE) molecules1-3). In particular, wefocus on the blue-emission, which is capable of showing narrow FWHM and high ELquantum yield. Blue HP-OLEDs based on two new TEs are fabricated, resulting inhigh external quantum efficiency (EQE) of over 20%, high color purity, and highbrightness. By analyzing the transient PL characteristics of the HP-OLEDs, wefound that the presence of efficient FRET between TADF-assistant dopant(TADF-AD) and TE molecules. Further, transient EL analysis confirmed that asmaller EHOMO difference between TADF-AD and TEefficiently helps to decrease hole trapping inside the emitting layer, henceresulting in a lower efficiency rolloff and a longer operational devicelifetime. This report provides a designing principle for a TADF and TE inHP-OLEDs with well-matched energy levels, leading to efficient FRET and nosignificant carrier trapping.

References:

[1] C-Y. Chan et al., NaturePhotonics, 15, 203 – 207 (2021).

[2] Y-T. Lee et al., AdvancedElectronic Materials, 7, 4,2001090 (2021).

[3] M. Tanaka etal., ACS Applied Materials &Interfaces, 12, 45, 50668 –50674 (2020).