Design of thermally activated delayed fluorescent sensitizers for high efficiency over 20% and long lifetime in yellow fluorescent organic light-emitting diodes

• Published in: Journal of materials chemistry. C, Materials for optical and electronic devices Materials for optical and electronic devices, 2020-04, Vol.8 (15), p.5265-5272
• Main Authors: Kim, Ji Han, Lee, Kyung Hyung, Lee, Jun Yeob
• Format: Article
• Language: English
• Subjects: Activated carbon; Carbazoles; Dihedral angle; Emitters; Emitters (electron); Energy gap; Energy transfer; Fluorescence; Light emitting diodes; Organic light emitting diodes; Quantum efficiency; Service life assessment
• ISSN: 2050-7526; 2050-7534
• DOI: 10.1039/d0tc00178c

Yellow thermally activated delayed fluorescence (TADF) materials were synthesized using 2,4,6-triphenylpyrimidine-5-carbonitrile and 4-(3-cyanophenyl)-2,6-diphenylpyrimidine-5-carbonitrile acceptors combined with a very strong donor moiety of 5,10-diphenyl-10,15-dihydro-5 H -diindolo[3,2- a :3′,2′-c]carbazole. The strong electron acceptors and the strong donor twisted from the acceptor plane with a large dihedral angle decreased the singlet and triplet energy gaps and managed the Dexter energy transfer. The 4-(4-(10,15-diphenyl-10,15-dihydro-5 H -diindolo[3,2- a :3′,2′- c ]carbazol-5-yl)phenyl)-2,6-diphenylpyrimidine-5-carbonitrile yellow TADF emitter showed short delayed fluorescence lifetime, high rate constant of reverse intersystem crossing and a high external quantum efficiency (EQE) of 21.6%. The TADF emitter was used as the sensitizer of the yellow emitting 2,8-di- tert -butyl-5,11-bis(4- tert -butylphenyl)-6,12-diphenyltetracene and the TADF assisted fluorescent organic light-emitting diodes achieved a high EQE of 20.2% and a device lifetime of 1400 h up to 90% of the initial luminance of 1000 cd m −2 . This study provides a strategy for developing yellow TADF emitters to assist the fluorescence emission to achieve high EQE and long lifetime simultaneously. Yellow thermally activated delayed fluorescence materials were synthesized using two types of acceptors of 2,4,6-triphenylpyrimidine-5-carbonitrile and 4-(3-cyanophenyl)-2,6-diphenylpyrimidine-5-carbonitrile combined with a strong donor.