Abstract
The combination of both very high brightness and deep blue emission from phosphorescent organic light-emitting diodes (PHOLED) is required for both display and lighting applications, yet so far has not been reported. A source of this difficulty is the absence of electron/exciton blocking layers (EBL) that are compatible with the high triplet energy of the deep blue dopant and the high frontier orbital energies of hosts needed to transport charge. Here, we show that N-heterocyclic carbene (NHC) Ir(III) complexes can serve as both deep blue emitters and efficient hole-conducting EBLs. The NHC EBLs enable very high brightness (>7,800 cd m−2) operation, while achieving deep blue emission with colour coordinates of [0.16, 0.09], suitable for most demanding display applications. We find that both the facial and the meridional isomers of the dopant have high efficiencies that arise from the unusual properties of the NHC ligand—that is, the complexes possess a strong metal–ligand bond that destabilizes the non-radiative metal-centred ligand-field states. Our results represent an advance in blue-emitting PHOLED architectures and materials combinations that meet the requirements of many critical illumination applications.
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Acknowledgements
This work was supported by the Air Force Office of Scientific Research (AFOSR) and Universal Display Corporation.
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J.L. designed, fabricated and optimized the PHOLEDs, and analysed the optical and electrical properties of materials with S.R.F., M.E.T. and P.I.D. H.-F.C., T.B. and M.E.T. synthesized and measured the photophysical and electrochemical properties of materials. C.C. provided EQE roll-off theory and modelling. S.R.F. supervised the project, analysed data, and wrote the manuscript with J.L.
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M.E.T. and S.R.F. have an equity interest in one of the sponsors of this work (Universal Display Corp.).
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Lee, J., Chen, HF., Batagoda, T. et al. Deep blue phosphorescent organic light-emitting diodes with very high brightness and efficiency. Nature Mater 15, 92–98 (2016). https://doi.org/10.1038/nmat4446
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DOI: https://doi.org/10.1038/nmat4446
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