Molecular engineering by σ-Bond spacer enables solution-processable host materials for TADF emitter towards high-performance OLEDs

• Published in: Chemical engineering journal (Lausanne, Switzerland : 1996) Vol. 396; p. 125276
• Main Authors: Li, Nengquan, Chai, Danyang, Chen, Zhanxiang, Zhou, Changjiang, Ni, Fan, Huang, Zhongyan, Cao, Xiaosong, Xie, Guohua, Li, Kai, Yang, Chuluo
• Format: Journal Article
• Language: English
• Published: Elsevier B.V 15.09.2020
• Subjects: Host materials; Molecular engineering; Organic light-emitting diodes; Solution process; Thermally activated delayed fluorescence; Thermally activated delayed fluorescence; Host materials; Molecular engineering; Organic light-emitting diodes; Solution process
• ISSN: 1385-8947; 1873-3212
• DOI: 10.1016/j.cej.2020.125276

[Display omitted] •Molecular engineering by σ-bond spacer is adopted for designing new host materials for the TADF emitter.•The newly developed host materials exhibit excellent solution processability and high triplet energy levels over 2.8 eV.•Host material with the lowest polarity achieves the highest reverse intersystem crossing rate.•Solution-processed TADF devices with a maximum external quantum efficiency up to 21.6% are demonstrated. High-performance solution-processable host materials for thermally activated delayed fluorescence (TADF) emitters are of great significance to the development of organic light-emitting diodes (OLEDs). In this study, three solution-processable hosts, namely mCP-Ph, mCP-Py, and mCP-BmPy featuring a basic structure paradigm of donor-σ-acceptor (D-σ-A) are reported for green TADF OLEDs. Attributing to the well-designed structure, the three host materials exhibited high triplet energy levels and excellent solution processability. It was found that the host materials had a significant impact on the excited state characteristics of the TADF emitter, and the mCP-Ph host with the lowest dipole moment showed the highest intersystem crossing rate constants (kISC and kRISC). In consequence, solution-processed TADF OLEDs based on the emitter 4-(4-(9,9-dimethylacridin-10(9H)-yl)phenyl)-2,6-diphenylpyridine-3,5-dicarbonitrile (DMAC-PCN) and the host 9-(3-(9H-carbazol-9-yl)phenyl)-3-(2,7-di-tert-butyl-9-phenyl-9H-fluoren-9-yl)-9H-carbazole (mCP-Ph) secured a maximum external quantum efficiency of 21.6%, demonstrating the effectiveness of the host engineering by σ-spacer. This work reveals the important principle for designing bespoke host for TADF emitters.