High‐Performance Nondoped Blue Delayed Fluorescence Organic Light‐Emitting Diodes Featuring Low Driving Voltage and High Brightness

• Published in: Advanced science 2020-02, Vol.7 (3), p.1902508-n/a
• Main Authors: Zou, Shi‐Jie, Xie, Feng‐Ming, Xie, Miao, Li, Yan‐Qing, Cheng, Tao, Zhang, Xiao‐Hong, Lee, Chun‐Sing, Tang, Jian‐Xin
• Format: Article
• Language: English
• Subjects: blue emission; Diodes; Efficiency; NMR; nondoped TADF emitters; Nuclear magnetic resonance; organic light‐emitting diodes; thermally activated delayed fluorescence; Thin films
• ISSN: 2198-3844; 2198-3844
• DOI: 10.1002/advs.201902508

Thermally activated delayed fluorescence (TADF) provides great potential for the realization of efficient and stable organic light‐emitting diodes (OLEDs). However, it is still challenging for blue TADF emitters to simultaneously achieve high efficiency, high brightness, and low Commission Internationale de l'Eclairage (CIE) y coordinate (CIEy) value. Here, the design and synthesis of two new benzonitrile‐based TADF emitters (namely 2,6‐di(9H‐carbazol‐9‐yl)‐3,5‐bis(3,6‐diphenyl‐9H‐carbazol‐9‐yl)benzonitrile (2PhCz2CzBn) and 2,6‐di(9H‐carbazol‐9‐yl)‐3,5‐bis(3,6‐di‐tert‐butyl‐9H‐carbazol‐9‐yl)benzonitrile (2tCz2CzBn)) with a symmetrical and rigid heterodonor configuration are reported. The TADF OLEDs doped with both the emitters can achieve a high external quantum efficiency (EQE) over 20% and narrowband blue emission of 464 nm with a CIEy < 0.2. Moreover, the incorporation of a terminal tert‐butyl group can weaken the intermolecular π–π stacking in the nondoped TADF emitter, and thus significantly suppress self‐aggregation‐caused emission quenching for enhanced delayed fluorescence. A peak EQE of 21.6% is realized in the 2tCz2CzBn‐based nondoped device with an extremely low turn‐on voltage of 2.7 V, high color stability, a high brightness over 20 000 cd m−2, a narrow full‐width at half‐maximum of 70 nm, and CIE color coordinates of (0.167, 0.248). A new blue thermally activated delayed fluorescence emitter of 2tCz2CzBn is synthesized with a symmetrical and rigid heterodonor configuration, enabling significant suppression of self‐aggregation‐caused emission quenching. High‐performance nondoped organic light‐emitting diodes are achieved with a high external quantum efficiency of 21.6%, an extremely low turn‐on voltage of 2.7 V, and narrowband blue emission.