Organic light-emitting diodes (OLEDs) employing thermally activated delayed fluorescence (TADF) have emerged as cheaper alternatives to high-performance phosphorescent OLEDs with noble-metal-based dopants. However, the efficiencies of blue TADF OLEDs are still low at high luminance, limiting full-colour display. Here, we report a blue OLED containing a 9,10-dihydroacridine/diphenylsulphone derivative that has a comparable performance to today's best phosphorescent OLEDs. The device offers an external quantum efficiency of 19.5% and reduced efficiency roll-off characteristics at high luminance. Through computational simulation, we identified six pretwisted intramolecular charge-transfer (CT) molecules with small singlet–triplet CT state splitting but different energy relationships between 3CT and locally excited triplet (3LE) states. Systematic comparison of their excited-state dynamics revealed that CT molecules with a large twist angle can emit efficient and short-lifetime (a few microseconds) TADF when the emission peak energy is high enough and the 3LE state is higher than the 3CT state.
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This work was supported by a Grant-in-Aid from the Funding Program for World-Leading Innovative R&D on Science and Technology (FIRST) and the International Institute for Carbon Neutral Energy Research (WPI-I2CNER) sponsored by MEXT. The authors thank J.-L. Brédas, M. Kotani and K. Tokumaru for stimulating discussions regarding this work. The authors also thank W. J. Potscavage Jr for assistance with preparation of this manuscript.
The authors declare no competing financial interests.
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Zhang, Q., Li, B., Huang, S. et al. Efficient blue organic light-emitting diodes employing thermally activated delayed fluorescence. Nature Photon 8, 326–332 (2014). https://doi.org/10.1038/nphoton.2014.12
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