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Deep blue phosphorescent organic light-emitting diodes with very high brightness and efficiency

Nature Materials volume 15, pages 92–98 (2016)Cite this article

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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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Figure 1: Molecular structure and photophysical characteristics.
Figure 2: Temperature and solution dependence of the phosphors.
Figure 3: Device structure and its frontier orbital energies.
Figure 4: Characterization of exciton profiles in the device emission layer.
Figure 5: Electrophosphorescent device characteristics.

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References

  1. Baldo, M. A. et al. Highly efficient phosphorescent emission from organic electroluminescent devices. Nature 395, 151–154 (1998).

    Article  CAS  Google Scholar 

  2. Baldo, M. A., Lamansky, S., Burrows, P. E., Thompson, M. E. & Forrest, S. R. Very high-efficiency green organic light-emitting devices based on electrophosphorescence. Appl. Phys. Lett. 75, 4–6 (1999).

    Article  CAS  Google Scholar 

  3. Giebink, N. C. et al. Intrinsic luminance loss in phosphorescent small-molecule organic light emitting devices due to bimolecular annihilation reactions. J. Appl. Phys. 103, 044509 (2008).

    Article  Google Scholar 

  4. Sajoto, T. et al. Blue and near-UV phosphorescence from iridium complexes with cyclometalated pyrazolyl or N-heterocyclic carbene ligands. Inorg. Chem. 44, 7992–8003 (2005).

    Article  CAS  Google Scholar 

  5. Schildknecht, C. et al. Novel deep-blue emitting phosphorescent emitter. Proc. SPIE Int. Soc. Opt. Eng. 5937, 59370E (2005).

    Google Scholar 

  6. Hopkinson, M. N., Richter, C., Schedler, M. & Glorius, F. An overview of N-heterocyclic carbenes. Nature 510, 485–496 (2014).

    Article  CAS  Google Scholar 

  7. Chang, C.-F. et al. Highly efficient blue-emitting iridium(III) carbene complexes and phosphorescent OLEDs. Angew. Chem. Int. Ed. 47, 4542–4545 (2008).

    Article  CAS  Google Scholar 

  8. Chiu, Y.-C. et al. En route to high external quantum efficiency (∼12%), organic true-blue-light-emitting diodes employing novel design of iridium(III) phosphors. Adv. Mater. 21, 2221–2225 (2009).

    Article  CAS  Google Scholar 

  9. Sasabe, H. et al. High-efficiency blue and white organic light-emitting devices incorporating a blue iridium carbene complex. Adv. Mater. 22, 5003–5007 (2010).

    Article  CAS  Google Scholar 

  10. Hsieh, C.-H. et al. Design and synthesis of iridium bis(carbene) complexes for efficient blue electrophosphorescence. Chem. Eur. J. 17, 9180–9187 (2011).

    Article  CAS  Google Scholar 

  11. Lu, K.-Y. et al. Wide-Range color tuning of iridium biscarbene complexes from blue to red by different N∧N ligands: An alternative route for adjusting the emission colors. Adv. Mater. 23, 4933–4937 (2011).

    Article  CAS  Google Scholar 

  12. Fleetham, T., Wang, Z. & Li, J. Efficient deep blue electrophosphorescent devices based on platinum(II) bis(n-methyl-imidazolyl)benzene chloride. Org. Electron. 13, 1430–1435 (2012).

    Article  CAS  Google Scholar 

  13. Lee, S. et al. Deep-blue phosphorescence from perfluoro carbonyl-substituted iridium complexes. J. Am. Chem. Soc. 135, 14321–14328 (2013).

    Article  CAS  Google Scholar 

  14. Hang, X.-C., Fleetham, T., Turner, E., Brooks, J. & Li, J. Highly efficient blue-emitting cyclometalated platinum(II) complexes by judicious molecular design. Angew. Chem. Int. Ed. 52, 6753–6756 (2013).

    Article  CAS  Google Scholar 

  15. Fleetham, T., Li, G., Wen, L. & Li, J. Efficient ‘Pure’ blue OLEDs employing tetradentate Pt complexes with a narrow spectral bandwidth. Adv. Mater. 26, 7116–7121 (2014).

    Article  CAS  Google Scholar 

  16. Baldo, M. A., Adachi, C. & Forrest, S. R. Transient analysis of organic electrophosphorescence. II. Transient analysis of triplet–triplet annihilation. Phys. Rev. B 62, 10967–10977 (2000).

    Article  CAS  Google Scholar 

  17. Zhang, Y., Lee, J. & Forrest, S. R. Tenfold increase in the lifetime of blue phosphorescent organic light-emitting diodes. Nature Commun. 5, 5008 (2014).

    Article  CAS  Google Scholar 

  18. Erickson, N. C. & Holmes, R. J. Engineering efficiency roll-off in organic light-emitting devices. Adv. Funct. Mater. 24, 6074–6080 (2014).

    Article  CAS  Google Scholar 

  19. Park, M. S. & Lee, J. Y. Indolo acridine-based hole-transport materials for phosphorescent OLEDs with over 20% external quantum efficiency in deep blue and green. Chem. Mater. 23, 4338–4343 (2011).

    Article  CAS  Google Scholar 

  20. Holmes, R. J. et al. Saturated deep blue organic electrophosphorescence using a fluorine-free emitter. Appl. Phys. Lett. 87, 243507 (2005).

    Article  Google Scholar 

  21. Deaton, J. C., Young, R. H., Lenhard, J. R., Rajeswaran, M. & Huo, S. Photophysical properties of the series fac- and mer-(1-Phenylisoquinolinato-N∧C2′)x(2-phenylpyridinato-N∧C2′)3−x iridium(III) (x = 1–3). Inorg. Chem. 49, 9151–9161 (2010).

    Article  CAS  Google Scholar 

  22. Tamayo, A. B. et al. Synthesis and characterization of facial and meridional tris-cyclometalated iridium(III) complexes. J. Am. Chem. Soc. 125, 7377–7387 (2003).

    Article  CAS  Google Scholar 

  23. Sajoto, T. et al. Temperature dependence of blue phosphorescent cyclometalated Ir(III) complexes. J. Am. Chem. Soc. 131, 9813–9822 (2009).

    Article  CAS  Google Scholar 

  24. Lauerhaas, J. M. et al. Reversible luminescence quenching of porous silicon by solvents. J. Am. Chem. Soc. 114, 1911–1912 (1992).

    Article  CAS  Google Scholar 

  25. Xiao, L. et al. Recent progresses on materials for electrophosphorescent organic light-emitting devices. Adv. Mater. 23, 926–952 (2011).

    Article  CAS  Google Scholar 

  26. Yook, K. S. & Lee, J. Y. Organic materials for deep blue phosphorescent organic light-emitting diodes. Adv. Mater. 24, 3169–3190 (2012).

    Article  CAS  Google Scholar 

  27. Djurovich, P. I., Mayo, E. I., Forrest, S. R. & Thompson, M. E. Measurement of the lowest unoccupied molecular orbital energies of molecular organic semiconductors. Org. Electron. 10, 515–520 (2009).

    Article  CAS  Google Scholar 

  28. Jeon, S. O., Jang, S. E., Son, H. S. & Lee, J. Y. External quantum efficiency above 20% in deep blue phosphorescent organic light-emitting diodes. Adv. Mater. 23, 1436–1441 (2011).

    Article  CAS  Google Scholar 

  29. Reineke, S., Walzer, K. & Leo, K. Triplet-exciton quenching in organic phosphorescent light-emitting diodes with Ir-based emitters. Phys. Rev. B 75, 125328 (2007).

    Article  Google Scholar 

  30. Su, S.-J., Gonmori, E., Sasabe, H. & Kido, J. Highly efficient organic blue-and white-light-emitting devices having a carrier- and exciton-confining structure for reduced efficiency roll-off. Adv. Mater. 20, 4189–4194 (2008).

    CAS  Google Scholar 

  31. Seino, Y., Sasabe, H., Pu, Y.-J. & Kido, J. High-performance blue phosphorescent OLEDs using energy transfer from exciplex. Adv. Mater. 26, 1612–1616 (2014).

    Article  CAS  Google Scholar 

  32. Zhang, Q. et al. Efficient blue organic light-emitting diodes employing thermally activated delayed fluorescence. Nature Photon. 8, 326–332 (2014).

    Article  CAS  Google Scholar 

  33. Yang, C.-H. et al. Deep-blue-emitting heteroleptic iridium(III) complexes suited for highly efficient phosphorescent OLEDs. Chem. Mater. 24, 3684–3695 (2012).

    Article  CAS  Google Scholar 

  34. You, Y. & Nam, W. Photofunctional triplet excited states of cyclometalated Ir(III) complexes: Beyond electroluminescence. Chem. Soc. Rev. 41, 7061–7084 (2012).

    Article  CAS  Google Scholar 

  35. Tsuchiya, K., Ito, E., Yagai, S., Kitamura, A. & Karatsu, T. Chirality in the photochemical mer → fac geometrical isomerization of Tris(1-phenylpyrazolato,N,C2′)iridium(III). Eur. J. Inorg. Chem. 2009, 2104–2109 (2009).

    Article  Google Scholar 

  36. Kober, E. M., Sullivan, B. P. & Meyer, T. J. Solvent dependence of metal-to-ligand charge-transfer transitions. Evidence for initial electron localization in MLCT excited states of 2,2′-bipyridine complexes of ruthenium(II) and osmium(II). Inorg. Chem. 23, 2098–2104 (1984).

    Article  CAS  Google Scholar 

  37. Reineke, S., Rosenow, T. C., Lüssem, B. & Leo, K. Improved high-brightness efficiency of phosphorescent organic LEDs comprising emitter molecules with small permanent dipole moments. Adv. Mater. 22, 3189–3193 (2010).

    Article  CAS  Google Scholar 

  38. Padmaperuma, A. B., Sapochak, L. S. & Burrows, P. E. New charge transporting host material for short wavelength organic electrophosphorescence: 2,7-Bis(diphenylphosphine oxide)-9,9-dimethylfluorene. Chem. Mater. 18, 2389–2396 (2006).

    Article  CAS  Google Scholar 

  39. Calcagno, P. et al. Understanding the structural properties of a homologous series of bis-diphenylphosphine oxides. Chem. Eur. J. 6, 2338–2349 (2000).

    Article  CAS  Google Scholar 

  40. Kawamura, Y. et al. 100% phosphorescence quantum efficiency of Ir(III) complexes in organic semiconductor films. Appl. Phys. Lett. 86, 071104 (2005).

    Article  Google Scholar 

  41. Erk, P. et al. 11.2: Efficient deep blue triplet emitters for OLEDs. SID Symp. Dig. Tech. Pap. 37, 131–134 (2006).

    Article  CAS  Google Scholar 

  42. Shi, F., Xu, X., Zheng, L., Dang, Q. & Bai, X. Method development for a pyridobenzodiazepine library with multiple diversification points. J. Comb. Chem. 10, 158–161 (2008).

    Article  Google Scholar 

  43. Forrest, S. R., Bradley, D. D. C. & Thompson, M. E. Measuring the efficiency of organic light-emitting devices. Adv. Mater. 15, 1043–1048 (2003).

    Article  CAS  Google Scholar 

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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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Authors and Affiliations

  1. Department of Electrical Engineering and Computer Science, University of Michigan, Ann Arbor, Michigan 48109, USA

    Jaesang Lee & Stephen R. Forrest

  2. Department of Chemistry, University of Southern California, Los Angeles, California 90089, USA

    Hsiao-Fan Chen, Thilini Batagoda, Peter I. Djurovich & Mark E. Thompson

  3. Department of Physics, University of Michigan, Ann Arbor, Michigan 48109, USA

    Caleb Coburn & Stephen R. Forrest

  4. Department of Materials Science and Engineering, University of Michigan, Ann Arbor, Michigan 48109, USA

    Stephen R. Forrest

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Contributions

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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Correspondence to Stephen R. Forrest.

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Competing interests

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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