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Efficient and stable single-layer organic light-emitting diodes based on thermally activated delayed fluorescence

Abstract

From a design, optimization and fabrication perspective, an organic light-emitting diode consisting of only one single layer of a neat semiconductor would be highly attractive. Here, we demonstrate an efficient and stable organic light-emitting diode based on a single layer of a neat thermally activated delayed fluorescence emitter. By employing ohmic electron and hole contacts, charge injection is efficient and the absence of heterojunctions results in an exceptionally low operating voltage of 2.9 V at a luminance of 10,000 cd m−2. Balanced electron and hole transport results in a maximum external quantum efficiency of 19% at 500 cd m−2 and a broadened emission zone, which greatly improves the operational stability, allowing a lifetime to 50% of the initial luminance of 1,880 h for an initial luminance of 1,000 cd m−2. As a result, this single-layer concept combines high power efficiency with long lifetime in a simplified architecture, rivalling and even exceeding the performance of complex multilayer devices.

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The data that support the plots within this paper and other findings of this study are available from the corresponding author upon reasonable request.

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References

  1. 1.

    Tang, C. W. & Van Slyke, S. A. Organic electroluminescent diodes. Appl. Phys. Lett. 51, 913–915 (1987).

  2. 2.

    Burroughes, J. H. et al. Light-emitting diodes based on conjugated polymers. Nature 347, 539–541 (1990).

  3. 3.

    Blom, P. W. M., De Jong, M. J. M. & Vleggaar, J. J. M. Electron and hole transport in poly(p-phenylene vinylene) devices. Appl. Phys. Lett. 68, 3308–3310 (1996).

  4. 4.

    Nicolai, H. T. et al. Unification of trap-limited electron transport in semiconducting polymers. Nat. Mater. 11, 882–887 (2012).

  5. 5.

    Kuik, M., Koster, L. J. A., Dijkstra, A. G., Wetzelaer, G. A. H. & Blom, P. W. M. Non-radiative recombination losses in polymer light-emitting diodes. Org. Electron. 13, 969–974 (2012).

  6. 6.

    Kido, J., Kimura, M. & Nagai, K. Multilayer white light-emitting organic electroluminescent device. Science 267, 1332–1334 (1995).

  7. 7.

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

  8. 8.

    Adachi, C. et al. Nearly 100% internal phosphorescence efficiency in an organic light-emitting device. J. Appl. Phys. 90, 5048–5051 (2001).

  9. 9.

    Pfeiffer, M., Forrest, S. R., Leo, K. & Thompson, M. E. Electrophosphorescent p–i–n organic light emitting devices for very high efficiency flat panel displays. Adv. Mater. 14, 1633–1636 (2002).

  10. 10.

    He, G. et al. High-efficiency and low-voltage p–i–n electrophosphorescent organic light-emitting diodes with double-emission layers. Appl. Phys. Lett. 85, 3911–3913 (2004).

  11. 11.

    Walzer, K., Maennig, B., Pfeiffer, M. & Leo, K. Highly efficient organic devices based on electrically doped transport layers. Chem. Rev. 107, 1233–1271 (2007).

  12. 12.

    Uoyama, H., Goushi, K., Shizu, K., Nomura, H. & Adachi, C. Highly efficient organic light-emitting diodes from delayed fluorescence. Nature 492, 234–238 (2012).

  13. 13.

    Liu, Y., Li, C., Ren, Z., Yan, S. & Bryce, M. R. All-organic thermally activated delayed fluorescence materials for organic light-emitting diodes. Nat. Rev. Mater. 3, 18020 (2018).

  14. 14.

    Cui, L.-S. et al. Long-lived efficient delayed fluorescence organic light-emitting diodes using n-type hosts. Nat. Commun. 8, 2250 (2017).

  15. 15.

    Zhang, Q. et al. Nearly 100% internal quantum efficiency in undoped electroluminescent devices employing pure organic emitters. Adv. Mater. 27, 2096–2100 (2015).

  16. 16.

    Kotadiya, N. B. et al. Universal strategy for ohmic hole injection into organic semiconductors with high ionization energies. Nat. Mater. 17, 329–334 (2018).

  17. 17.

    Wu, T.-L. et al. Diboron compound-based organic light-emitting diodes with high efficiency and reduced efficiency roll-off. Nat. Photon. 12, 235–240 (2018).

  18. 18.

    Zhou, M. et al. Effective work functions for the evaporated metal/organic semiconductor contacts from in-situ diode flatband potential measurements. Appl. Phys. Lett. 101, 013501 (2012).

  19. 19.

    Kao, K.-C. & Hwang, W. Electrical Transport in Solids (Pergamon Press, 1981).

  20. 20.

    Koster, L. J. A., Smits, E. C. P., Mihailetchi, V. D. & Blom, P. W. M. Device model for the operation of polymer/fullerene bulk heterojunction solar cells. Phys. Rev. B 72, 085205 (2005).

  21. 21.

    Shirota, Y. & Kageya, H. Chem. Rev. 107, 953–1010 (2007).

  22. 22.

    Kuik, M. et al. Charge transport and recombination in polymer light-emitting diodes. Adv. Mater. 26, 512–531 (2014).

  23. 23.

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

  24. 24.

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

  25. 25.

    Kim, J.-M., Lee, C.-H. & Kim, J.-J. Mobility balance in the light-emitting layer governs the polaron accumulation and operational stability of organic light-emitting diodes. Appl. Phys. Lett. 111, 203301 (2017).

  26. 26.

    Niu, Q., Rohloff, R., Wetzelaer, G.-J. A. H., Blom, P. W. M. & Crăciun, N. I. Hole trap formation in polymer light-emitting diodes under current stress. Nat. Mater. 17, 557–562 (2018).

  27. 27.

    Meerheim, R., Furno, M., Hofmann, S., Lüssem, B. & Leo, K. Quantification of energy loss mechanisms in organic light-emitting diodes. Appl. Phys. Lett. 97, 253305 (2010).

  28. 28.

    De Bruyn, P., van Rest, A. H. P., Wetzelaer, G. A. H., de Leeuw, D. M. & Blom, P. W. M. Diffusion-limited current in organic metal–insulator–metal diodes. Phys. Rev. Lett. 111, 186801 (2013).

  29. 29.

    Meerheim, R., Walzer, K., He, G., Pfeiffer, M. & Leo, K. Highly efficient organic light emitting diodes (OLED) for diplays and lighting. Proc. SPIE 6192, 61920P (2006).

  30. 30.

    Sasabe, H. et al. Extremely low operating voltage green phosphorescent organic light-emitting devices. Adv. Funct. Mater. 23, 5550–5555 (2013).

  31. 31.

    Zhang, D. D., Qiao, J., Zhang, D. Q. & Duan, L. Ultrahigh‐efficiency green PHOLEDs with a voltage under 3 V and a power efficiency of nearly 110 lm W−1 at luminance of 10,000 cd m−2. Adv. Mater. 29, 1702847 (2017).

  32. 32.

    Sasabe, H. et al. Ultrahigh power efficiency thermally activated delayed fluorescent OLEDs by the strategic use of electron-transport materials. Adv. Opt. Mater. 6, 1800376 (2018).

  33. 33.

    Seino, Y., Inomata, S., Sasabe, H., Pu, Y.-J. & Kido, J. High-performance green OLEDs using thermally activated delayed fluorescence with a power efficiency of over 100 lm W−1. Adv. Mater. 28, 2638–2643 (2016).

  34. 34.

    Schaer, M., Nuesch, F., Berner, D., Leo, W. & Zuppiroli, L. Water vapor and oxygen degradation mechanisms in organic light emitting diodes. Adv. Funct. Mater. 11, 116–121 (2001).

  35. 35.

    Van de Weijer, P., Lu, K., de Winter, S. H. P. M., Janssen, R. R. & Akkerman, H. B. Mechanism of the operational effect of black spot growth in OLEDs. Org. Electron. 37, 155–162 (2016).

  36. 36.

    Phatak, R., Tsui, T. Y. & Aziz, H. Dependence of dark spot growth on cathode/organic interfacial adhesion in organic light emitting devices. J. Appl. Phys. 111, 054512 (2012).

  37. 37.

    De Bruyn, P., Moet, D. J. D. & Blom, P. W. M. All-solution processed polymer light-emitting diodes with air stable metal-oxide electrodes. Org. Electron. 13, 1023–1030 (2012).

  38. 38.

    Tang, S. et al. Design rules for light-emitting electrochemical cells delivering bright luminance at 27.5 percent external quantum efficiency. Nat. Commun. 8, 1190 (2017).

  39. 39.

    Godumala, M., Choi, S., Cho, M. J. & Choi, D. H. Recent breakthroughs in thermally activated delayed fluorescence organic light emitting diodes containing non-doped emitting layers. J. Mater. Chem. C 7, 2172–2198 (2019).

  40. 40.

    Silvestre, G. C. M., Johnson, M. T., Giraldo, A. & Shannon, J. M. Light degradation and voltage drift in polymer light-emitting diodes. Appl. Phys. Lett. 78, 1619–1621 (2001).

  41. 41.

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

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Acknowledgements

We thank C. Bauer, H.-J. Guttmann and F. Keller for technical support and Y. Ie for the synthesis of 4CzIPN. This project has received funding from the European Union Horizon 2020 research and innovation programme under grant agreement no. 646176 (EXTMOS).

Author information

G.-J.A.H.W. proposed the project. G.-J.A.H.W. and N.B.K. designed the experiments. N.B.K. carried out device fabrication and measurements. G.-J.A.H.W. performed simulations. G.-J.A.H.W. and P.W.M.B. supervised the project and wrote the manuscript.

Competing interests

The authors declare no competing interests.

Correspondence to Gert-Jan A. H. Wetzelaer.

Supplementary information

Supplementary Information

Molecular structures and optoelectronic characterization.

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Fig. 1: Device layout and molecular structure of the TADF emitter CzDBA.
Fig. 2: Charge transport in CzDBA and simulated recombination profile.
Fig. 3: Device performance of single-layer CzDBA OLEDs.
Fig. 4: Operational lifetime of single-layer CzDBA OLEDs.
Fig. 5: Ambient stability of a single-layer CzDBA OLED.