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Improving the performance of doped π-conjugated polymers for use in organic light-emitting diodes

Nature volume 405, pages 661–665 (2000)Cite this article

Abstract

Organic light-emitting diodes (OLEDs) represent a promising technology for large, flexible, lightweight, flat-panel displays1,2,3. Such devices consist of one or several semiconducting organic layer(s) sandwiched between two electrodes. When an electric field is applied, electrons are injected by the cathode into the lowest unoccupied molecular orbital of the adjacent molecules (simultaneously, holes are injected by the anode into the highest occupied molecular orbital). The two types of carriers migrate towards each other and a fraction of them recombine to form excitons, some of which decay radiatively to the ground state by spontaneous emission. Doped π-conjugated polymer layers improve the injection of holes in OLED devices4,5,6,7,8,9; this is thought to result from the more favourable work function of these injection layers compared with the more commonly used layer material (indium tin oxide). Here we demonstrate that by increasing the doping level of such polymers, the barrier to hole injection can be continuously reduced. The use of combinatorial devices allows us to quickly screen for the optimum doping level. We apply this concept in OLED devices with hole-limited electroluminescence (such as polyfluorene-based systems10,11,12), finding that it is possible to significantly reduce the operating voltage while improving the light output and efficiency.

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Figure 1: Electrochemical and electro-optical properties of PDBT and its performance as the hole injection contact of hole-only OLED devices.
Figure 2: I–V characteristics of hole-only devices with differently doped PDBT injection–contacts.
Figure 3: Performance of various OLED devices with the general structure anode/PFO/Ca.
Figure 4: Two-dimensional combinatorial OLED array.

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References

  1. Friend, R. H. et al. Electroluminescence in conjugated polymers. Nature 397, 121–128 (1999).

    Article  ADS  CAS  Google Scholar 

  2. Heeger, A. J. Light emission from semiconducting polymers: light-emitting diodes, light-emitting electrochemical cells, lasers and white light for the future. Solid State Commun. 107, 673–679 (1998).

    Article  ADS  CAS  Google Scholar 

  3. Salbeck, J. Electroluminescence with organic compounds. Ber. Bunsenges. Phys. Chem. 100, 1667–1677 (1996).

    Article  CAS  Google Scholar 

  4. Gustafsson, G. et al. Flexible light-emitting diodes made from soluble conducting polymers. Nature 357, 477–479 (1992).

    Article  ADS  CAS  Google Scholar 

  5. Yang, Y. & Heeger, A. J. Polyaniline as a transparent electrode for light-emitting diodes: Lower operating voltage and higher efficiency. Appl. Phys. Lett. 64, 1245–1247 (1994).

    Article  ADS  CAS  Google Scholar 

  6. Gao, J., Heeger, A. J., Lee, Y. J. & Kim, C. Y. Soluble polypyrrole as the transparent anode in polymer light-emitting diodes. Synth. Met. 82, 211–223 (1996).

    Article  Google Scholar 

  7. Carter, S. A., Angelopoulos, M., Karg, S., Brock, P. J. & Scott, J. C. Polymeric anodes for improved polymer light-emitting diode performance. Appl. Phys. Lett. 70, 2067–2069 (1997).

    Article  ADS  CAS  Google Scholar 

  8. Scott, J. C., Carter, S. A., Karg, S. et al. Angelopoulos, M. Polymeric anodes for light-emitting diodes. Synth. Met. 85, 1197–1200 (1997).

    Article  CAS  Google Scholar 

  9. Cao, Y., Yu, G., Zhang, C., Menon, R. & Heeger, A. J. Polymer light-emitting diodes with polyethylene dioxythiophene-polystyrene sulfonate as the transparent anode. Synth. Met. 87, 171–174 (1997).

    Article  CAS  Google Scholar 

  10. Grice, A. W. et al. High brightness and efficient blue light-emitting polymer diodes. Appl. Phys. Lett. 73, 629–631 (1998).

    Article  ADS  CAS  Google Scholar 

  11. Janiez, S. et al. Electrochemical determination of the ionization potential of poly(9,9-dioctylfluorene). Appl. Phys. Lett. 73, 2453–2455 (1998).

    Article  ADS  Google Scholar 

  12. Grell, M. et al. Polarized electroluminescence from a liquid crystalline polyfluorene. Adv. Mater. 11, 671–674 (1999).

    Article  CAS  Google Scholar 

  13. Nuesch, F., Rothberg, L. J., Forsythe, E. W., Quoc Toan, L. & Gao, Y. A. Photoelectron spectroscopy study on the indium tin oxide treatment by acids and bases. Appl. Phys. Lett. 74, 880–882 (1999).

    Article  ADS  CAS  Google Scholar 

  14. Kim, J. S. et al. Indium tin oxide treatments for single and double layer polymeric light emitting diodes. The relation between the anode physical, chemical, and morphological properties and the device performance. J. Appl. Phys. 84, 6859–6870 (1998).

    Article  ADS  CAS  Google Scholar 

  15. Skotheim, T. A. Handbook of Conducting Polymers (Dekker, New York, 1986).

    Google Scholar 

  16. Bard, A. J. & Faulkner, L. A. Electrochemical Methods—Fundamentals and Applications (Wiley, New York, 1984).

    Google Scholar 

  17. Xing, K. Z., Fahlman, M., Chen, X. W., Inganäs, O. & Salaneck, W. R. The electronic structure of poly(3,4-ethylene-dioxyghiophene): studied by XPS and UPS. Synth. Met. 89, 161–165 (1997).

    Article  CAS  Google Scholar 

  18. Brown, T. M. et al. Built-in field electroabsorption spectroscopy of polymer light-emitting diodes incorporating a doped poly(3,4-ethylene dioxythiophene) hole injection layer. Appl. Phys. Lett. 75, 1679–1681 (1999).

    Article  ADS  CAS  Google Scholar 

  19. Dietrich, M. & Heinze, J. Poly(4,4′-Dimethoxybithiophene)—A new conducting polymer with extraordinary redox and optical properties. Synth. Met. 41–43, 503–506 (1991).

    Article  Google Scholar 

  20. Malliaras, G. G. & Scott, J. C. Numerical simulations of the electrical characteristics and the efficiencies of single-layer organic light emitting diodes. J. Appl. Phys. 85, 7426–7432 (1999).

    Article  ADS  CAS  Google Scholar 

  21. Malliaras, G. G., Salem, J. R., Brock, P. J. & Scott, C. Electrical characteristics and efficiency of single-layer organic light-emitting diodes. Phys. Rev. B 58, R13411–R13414 (1998).

    Article  ADS  CAS  Google Scholar 

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Acknowledgements

We thank J. Heinze for making some bithiophene available, W. Brütting for discussions, and Bayer AG (Leverkusen, Germany) for the donation of Baytron P.

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Authors and Affiliations

  1. Institut für Physikalische Chemie, Ludwig-Maximilian-Universität München, Butenandtstrasse 11, München, 81377, Germany

    Markus Gross, David C. Müller, Christoph Bräuchle & Klaus Meerholz

  2. Max-Planck Institute für Polymerforschung, Institut Ackermannweg 10, Mainz, 55037, Germany

    Heinz-Georg Nothofer & Ulrich Scherf

  3. Institut für Experimentalphysik, Universität Potsdam, Am Neuen Palais 10, Potsdam, 14469, Germany

    Dieter Neher

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  1. Markus Gross
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Correspondence to Klaus Meerholz.

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Gross, M., Müller, D., Nothofer, HG. et al. Improving the performance of doped π-conjugated polymers for use in organic light-emitting diodes. Nature 405, 661–665 (2000). https://doi.org/10.1038/35015037

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