title: Coumarin-Based Thermally Activated Delayed Fluorescence Emitters with High External Quantum Efficiency and Low Efficiency Roll-off in the Devices.
abstract: Thermally activated delayed fluorescence (TADF) emitters have attracted much interest for their great applications in organic light-emitting diodes (OLEDs), but the TADF OLEDs are limited by large efficiency roll-offs. In this study, we report two coumarin-based TADF emitters, 3-methyl-6-(10H-phenoxazin-10-yl)-1H-isochromen-1-one (PHzMCO) and 9-(10H-phenoxazin-10-yl)-6H-benzo[c]chromen-6-one (PHzBCO), with relatively high photoluminescence quantum yields (PLQYs) and extremely small singlet-triplet splittings. OLEDs using these two TADF compounds as the emitters respectively demonstrate high external quantum efficiencies of 17.8% for PHzMCO and 19.6% for PHzBCO, which are the highest among the reported coumarin-derivative-based OLEDs. More importantly, these devices based on PHzMCO and PHzBCO remained 10.3% and 12.9% at 10000 cd m-2, respectively, showing relatively low efficiency roll-offs at high brightness. These results reveal that the TADF emitters with high PLQYs can effectively reduce the efficiency roll-off in the devices.
authors.affiliation: Jiangsu Key Laboratory for Carbon-Based Functional Materials & Devices, Institute of Functional Nano & Soft Materials, Soochow University , Suzhou, Jiangsu 215123, P. R. China.
authors.forename: Jia-Xiong
authors.initials: JX
authors.lastname: Chen
authors.affiliation: Nano-organic Photoelectronic Laboratory and Key Laboratory of Photochemical Conversion and Optoelectronic Materials, Technical Institute of Physics and Chemistry, Chinese Academy of Sciences , Beijing 100190, P. R. China.|College of Materials Science and Engineering, Beijing Institute of Technology , Beijing 100081, P. R. China.
authors.forename: Wei
authors.initials: W
authors.lastname: Liu
authors.affiliation: School of Optoelectronic Information, University of Electronic Science and Technology of China , Chengdu 610054, P. R. China.|Nano-organic Photoelectronic Laboratory and Key Laboratory of Photochemical Conversion and Optoelectronic Materials, Technical Institute of Physics and Chemistry, Chinese Academy of Sciences , Beijing 100190, P. R. China.
authors.forename: Cai-Jun
authors.initials: CJ
authors.lastname: Zheng
authors.affiliation: Jiangsu Key Laboratory for Carbon-Based Functional Materials & Devices, Institute of Functional Nano & Soft Materials, Soochow University , Suzhou, Jiangsu 215123, P. R. China.|Nano-organic Photoelectronic Laboratory and Key Laboratory of Photochemical Conversion and Optoelectronic Materials, Technical Institute of Physics and Chemistry, Chinese Academy of Sciences , Beijing 100190, P. R. China.
authors.forename: Kai
authors.initials: K
authors.lastname: Wang
authors.affiliation: Jiangsu Key Laboratory for Carbon-Based Functional Materials & Devices, Institute of Functional Nano & Soft Materials, Soochow University , Suzhou, Jiangsu 215123, P. R. China.
authors.forename: Ke
authors.initials: K
authors.lastname: Liang
authors.affiliation: Jiangsu Key Laboratory for Carbon-Based Functional Materials & Devices, Institute of Functional Nano & Soft Materials, Soochow University , Suzhou, Jiangsu 215123, P. R. China.
authors.forename: Yi-Zhong
authors.initials: YZ
authors.lastname: Shi
authors.affiliation: Jiangsu Key Laboratory for Carbon-Based Functional Materials & Devices, Institute of Functional Nano & Soft Materials, Soochow University , Suzhou, Jiangsu 215123, P. R. China.
authors.forename: Xue-Mei
authors.initials: XM
authors.lastname: Ou
authors.affiliation: Jiangsu Key Laboratory for Carbon-Based Functional Materials & Devices, Institute of Functional Nano & Soft Materials, Soochow University , Suzhou, Jiangsu 215123, P. R. China.
authors.forename: Xiao-Hong
authors.identifier: http://orcid.org/0000-0002-6732-2499
authors.initials: XH
authors.lastname: Zhang
keywords: coumarin derivatives; high external quantum efficiency; low efficiency roll-off; organic light-emitting diodes; thermally activated delayed fluorescence