2018年3月修士卒業の 佐藤瞭さん (Mr. Ryo Sato) の電子輸送材料群の戦略的利用による超高電力効率緑色TADF有機ELに関する「Ultra-High Power Efficiency Thermally Activated Delayed Fluorescent OLEDs by the Strategic Use of Electron Transport Materials」と題する論文が Wiley の Advanced Optical Materials (IF: 6.87) に受理されました。本研究は、京都大学の梶弘典教授（Prof. Hironori Kaji）、鈴木克明助教（Prof. Katsuaki Suzuki）、九州大学の安達千波矢教授（Prof. Chihaya Adachi）との共同研究です。博士研究員の渡邊雄一郎君（Dr. Yuichiro Watanabe）も実験を強力にサポートしてくれました。
Title: Ultra-High Power Efficiency Thermally Activated Delayed Fluorescent OLEDs by the Strategic Use of Electron Transport Materials
By Hisahiro Sasabe*, Ryo Sato, Katsuaki Suzuki, Yuichiro Watanabe, Chihaya Adachi, Hironori Kaji*, Junji Kido*, Advanced Optical Materials, accepted.
Abstract: Thermally activated delayed fluorescent (TADF) emitters are one of the most promising candidates for developing low-cost organic light-emitting devices (OLEDs) that can achieve an internal quantum efficiency of 100%. However, the power efficiency values are still significantly lower than that of their phosphorescent counterparts. To achieve high power efficiency, both a high external quantum efficiency and low drive voltage are required. Here, we successfully developed TADF OLEDs with an ultra-high power efficiency of 133 lm W–1 and an unprecedented low turn-on voltage of 2.22 V via the strategic use of electron-transport materials (ETMs). We used 9-[4-(4,6-diphenyl-1,3,5-triazin-2-yl)phenyl]- N,N,N',N'-tetraphenyl-9H-carbazole-3,6-diamine (DACT-II) as a green TADF emitter. A series of green TADF OLEDs were fabricated using two different types of pyrimidine-based ETMs as an exciplex host partner and electron transport layer to minimize the drive voltages. The optimized device showed an external quantum efficiency of 29.2% and maximum power efficiency of 133.2 lm W–1 without any light-outcoupling enhancement. The device also showed 124.0 lm W–1 at 100 cd m–2, and 95.2 lm W–1 at a high brightness of 1000 cd m–2. The drive voltages were 2.48 V at 100 cd m–2 and 2.88 V at 1000 cd m–2. These performances are the best among TADF OLEDs to date, and comparable to state-of-the-art phosphorescent counterparts, even at high brightness of 1000 cd m–2. Our results demonstrate the potential of TADF OLEDs for future low power consumption eco-friendly display and lighting sources.