New bipolar host materials for high power efficiency green thermally activated delayed fluorescence $$\mathrm{OLEDs}$$

Journal Article · 08 April 2022 · Chemical Engineering Journal

DOI: https://doi.org/10.1016/j.cej.2022.136292 · OSTI ID:1976930

Chen, Chia-Hsun ^[1]; Lin, Shih-Chun ^[2]; Lin, Bo-Yen ^[3]; Li, Che-Yu ^[4]; Kong, Yu-Cheng ^[5]; Chen, Yi-Sheng ^[2]; Fang, Shao-Cheng ^[2]; Chiu, Ching-Huang ^[2]; Lee, Jiun-Haw ^[2]; Wong, Ken-Tsung ^[6]; Lin, Chi-Feng ^[4]; Hung, Wen-Yi ^[5]; Chiu, Tien-Lung ^[3]

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1. National Taiwan University, Taipei (Taiwan); OSTI
2. National Taiwan University, Taipei (Taiwan)
3. Yuan Ze University (Taiwan)
4. National United University, No.2, Miaoli City (Taiwan)
5. National Taiwan Ocean University (Taiwan)
6. National Taiwan University, Taipei (Taiwan); Institute of Atomic and Molecular Science, Academia Sinica, Taipei (Taiwan)

We report four bipolar molecules, namely m-CzPym, p-CzPym, m-CzTrz, and p-CzTrz, with carbazole (Cz) donor and a benzonitrile-substituted pyrimidine (Pym) or triazine (Trz) acceptor core were synthesized and characterized. The electron deficiency of heteroaryl cores together with the substitution pattern of benzonitrile were employed to tune the energy levels as well as the thermally activated delayed fluorescence (TADF) characteristics. The four molecules exhibited TADF behavior with inferior photoluminescent quantum yields (PLQYs) that limit their applications as emitters. These bipolar molecules were employed as TADF host materials for the benchmark TADF emitter 4CzIPN to achieve high-performing green TADF organic light-emitting diodes (OLEDs). Among the molecules, m-CzPym-hosted TADF-OLEDs achieved a maximum external quantum efficiency (EQE_max) of 31.5%, maximum power efficiency (PE_max) of 95.6 lm/W, and maximum current efficiency (CE_max) of 100.2 cd/A. Notably, p-CzPym-hosted TADF-OLEDs also achieved a PE_max of 116.5 lm/W, turn-on voltage of 2.5 V, and impressive low efficiency roll-off performance (>89% of EQE_max at 5000 cd/m²), representing one of the highest efficiencies ever reported in 4CzIPN-doped devices. The high device efficiency can be ascribed to the balanced ambipolar carrier-transporting character of the host materials and high PLQY as well as the outstanding light outcoupling efficiency of the emitting layer.

• Research Organization: National Taiwan University, Taipei (Taiwan); University of Michigan, Ann Arbor, MI (United States)
• Sponsoring Organization: Ministry of Science and Technology of Taiwan (MOST); Office of Naval Research (ONR); USDOE Office of Energy Efficiency and Renewable Energy (EERE)
• Grant/Contract Number: EE0006708
• OSTI ID: 1976930
• Journal Information: Chemical Engineering Journal, Journal Name: Chemical Engineering Journal Journal Issue: P1 Vol. 442; ISSN 1385-8947
• Publisher: ElsevierCopyright Statement
• Country of Publication: United States
• Language: English