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Highly Efficient Thermally Activated Delayed Fluorescence Materials with Reduced Efficiency Roll-Off and Low On-Set Voltage

Abstract

Two carbazoles or diphenylamines were combined with carbazole to obtain two branch-shaped donor units and then connected with a benzophenone unit, acquiring two donor-acceptor (D-A) typed thermally activated delayed fluorescence (TADF) materials named CCDC and CCDD. CCDC and CCDD demonstrate converse phenomena in THF/H2O mixed solvent despite their structural similarity. Photoluminescence (PL) of CCDC drops drastically as water proportion goes up, while PL of CCDD increases with rising water ratio. The dampened PL emission of CCDD in good solvents may be attributed to the vibration and rotation of phenyl rings on the diphenylamine donors, and PL emission rises when the intramolecular movement is restricted. However, PL quantum yield (PLQY) tests and device performance indicate that both materials experience aggregation-caused quenching (ACQ) to some extent in solid state film. This is because when intramolecular vibration and rotation is restrained in solid state, intermolecular stacking still hampers fluorescence emission of CCDD. Also, the materials perform well in doped devices. A maximal external quantum efficiency (EQE) of 15.9% is achieved in blue-emitting devices with CCDC as the emitter. Green-emitting devices where CCDD is utilized as the emitter are well-performed concerning their overall properties. Not only do their maximal EQE exceed 22%, but also an on-set voltage as low as 2.6 V is achieved with a 30% doping concentration. Moreover, efficiency roll-off of the CCDD-based devices is well controlled. An EQE of nearly 20% is maintained at the luminance of 1000 cd m-2.

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Publication details

The article was received on 04 May 2017, accepted on 07 Jun 2017 and first published on 13 Jun 2017


Article type: Research Article
DOI: 10.1039/C7QM00195A
Citation: Mater. Chem. Front., 2017, Accepted Manuscript
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    Highly Efficient Thermally Activated Delayed Fluorescence Materials with Reduced Efficiency Roll-Off and Low On-Set Voltage

    H. Zhao, Z. Wang, X. Cai, K. Liu, Z. He, L. xin, Y. Cao and S. Su, Mater. Chem. Front., 2017, Accepted Manuscript , DOI: 10.1039/C7QM00195A

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