Hole trap formation in polymer light-emitting diodes under current stress

Abstract

Polymer light-emitting diodes (PLEDs) are attractive for use in large-area displays and lighting panels, but their limited stability under current stress impedes commercialization. In spite of large efforts over the last two decades a fundamental understanding of the degradation mechanisms has not been accomplished. Here we demonstrate that the voltage drift of a PLED driven at constant current is caused by the formation of hole traps, which leads to additional non-radiative recombination between free electrons and trapped holes. The observed trap formation rate is consistent with exciton-free hole interactions as the main mechanism behind PLED degradation, enabling us to unify the degradation behaviour of various poly(p-phenylene) derivatives. The knowledge that hole trap formation is the cause of PLED degradation means that we can suppress the negative effect of hole traps on voltage and efficiency by blending the light-emitting polymer with a large-bandgap semiconductor. Owing to trap-dilution these blended PLEDs show unprecedented stability.

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Fig. 1: PLED degradation under current stress.
Fig. 2: Hole trap formation in a PLED under current stress.
Fig. 3: PLED luminance decay under current stress.
Fig. 4: Hole trap formation as function of ageing time.
Fig. 5: Effect of blending on PLED degradation.

References

  1. 1.

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

    Article  Google Scholar 

  2. 2.

    Parker, I. D., Cao, Y. & Yang, C. Y. Lifetime and degradation effects in polymer light-emitting diodes. J. Appl. Phys. 85, 2441–2447 (1999).

    Article  Google Scholar 

  3. 3.

    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).

    Article  Google Scholar 

  4. 4.

    Stegmaier, K. et al. Influence of electrical fatique on hole transport in poly(p-phenylenevinylene)-based organic light-emitting diodes. J. Appl. Phys. 110, 034507 (2011).

    Article  Google Scholar 

  5. 5.

    Gassmann, A. et al. Study of electrical fatigue by defect engineering in organic light-emitting diodes. Mater. Sci. Eng. B 192, 26–51 (2015).

    Article  Google Scholar 

  6. 6.

    Scholz, S., Kondakov, D., Lüssem, B. & Leo, K. Degradation mechanisms and reactions in organic light-emitting diodes. Chem. Rev. 115, 8449–8503 (2015).

    Article  Google Scholar 

  7. 7.

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

    Article  Google Scholar 

  8. 8.

    Niu, Q., Wetzelaer, G. A. H., Blom, P. W. M. & Crăciun, N. I. Modeling of electrical characteristics of degraded polymer light-emitting diodes. Adv. Electr. Mater. 1600103 (2016).

  9. 9.

    Spreitzer, H. et al. Soluble phenyl-substituted PPVs-new materials for highly efficient polymer LEDs. Adv. Mater. 10, 1340–1343 (1998).

    Article  Google Scholar 

  10. 10.

    Yoshioka, T. et al. An improved method for lifetime prediction based on decoupling of the Joule self-heating effect from Coulombic degradation in accelerated aging tests of OLEDs. SID Symp. Dig. Tech. Pap. 45, 642–645 (2014).

    Article  Google Scholar 

  11. 11.

    Yang, L., Wei, B. & Zhang, J. Transient thermal characterization of organic light-emitting diodes. Semicond. Sci. Technol. 27, 105011 (2012).

    Article  Google Scholar 

  12. 12.

    Lampert, M. A. & Mark, P. Current Injection in Solids (Academic, New York, 1970).

    Google Scholar 

  13. 13.

    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).

    Article  Google Scholar 

  14. 14.

    Schmidt, T. D., Jäger, L., Noguchi, L., Ishii, H. & Brütting, W. Analyzing degradation effects of organic light-emitting diodes via transient optical and electrical measurements. J. Appl. Phys. 117, 215502 (2015).

    Article  Google Scholar 

  15. 15.

    Wild, W., Seilmeier, A., Gottfried, N. H. & Kaiser, W. Ultrafast investigations of vibrationally hot molecules after internal conversion in solution. Chem. Phys. Lett. 119, 259–263 (1985).

    Article  Google Scholar 

  16. 16.

    Nakashima, N. & Yoshihara, K. Role of hot molecules formed by internal conversion in UV single-photon and multiphoton chemistry. J. Phys. Chem. 93, 7763–7771 (1989).

    Article  Google Scholar 

  17. 17.

    Langevin, P. Sur la loi de recombination des ions. Ann. Chim. Phys. 28, 443–530 (1903).

    Google Scholar 

  18. 18.

    Rörich, I., Mikhnenko, O. V., Gehrig, D., Blom, P. W. M. & Crăciun, N. I. Influence of energetic disorder on exciton lifetime and photoluminescence efficiency in conjugated polymers. J. Phys. Chem. B 121, 1405–1412 (2017).

    Article  Google Scholar 

  19. 19.

    Abbaszadeh, D. et al. Elimination of charge carrier trapping in diluted semiconductors. Nat. Mater. 15, 628–633 (2016).

    Article  Google Scholar 

Download references

Acknowledgements

Parts of the text and results reported in this work have been reproduced from the thesis of Q.N., at the Johannes Gutenberg University Mainz, and accessible at https://publications.ub.uni-mainz.de/theses/frontdoor.php?source_opus=100001527&la=en. We thank C. Bauer, F. Keller and H. Raich for technical support. We acknowledge financial support from BASF SE.

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P.W.M.B. proposed the project, N.I.C. supervised the project. Q.N. and R.R. carried out experiments, G.-J.A.H.W. analysed the transport data, Q.N., N.I.C. and P.W.M.B. wrote the manuscript.

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Correspondence to N. Irina Crăciun.

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The authors declare no competing interests.

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Supplementary Sections 1–13, Supplementary Figures 1–10, Supplementary references

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Niu, Q., Rohloff, R., Wetzelaer, G.A.H. et al. Hole trap formation in polymer light-emitting diodes under current stress. Nature Mater 17, 557–562 (2018). https://doi.org/10.1038/s41563-018-0057-x

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