Skip to main content

Thank you for visiting nature.com. You are using a browser version with limited support for CSS. To obtain the best experience, we recommend you use a more up to date browser (or turn off compatibility mode in Internet Explorer). In the meantime, to ensure continued support, we are displaying the site without styles and JavaScript.

  • Article
  • Published:

Universal strategy for Ohmic hole injection into organic semiconductors with high ionization energies

Nature Materials volume 17, pages 329–334 (2018)Cite this article

Subjects

A Publisher Correction to this article was published on 06 March 2018

This article has been updated

Abstract

Barrier-free (Ohmic) contacts are a key requirement for efficient organic optoelectronic devices, such as organic light-emitting diodes, solar cells, and field-effect transistors. Here, we propose a simple and robust way of forming an Ohmic hole contact on organic semiconductors with a high ionization energy (IE). The injected hole current from high-work-function metal-oxide electrodes is improved by more than an order of magnitude by using an interlayer for which the sole requirement is that it has a higher IE than the organic semiconductor. Insertion of the interlayer results in electrostatic decoupling of the electrode from the semiconductor and realignment of the Fermi level with the IE of the organic semiconductor. The Ohmic-contact formation is illustrated for a number of material combinations and solves the problem of hole injection into organic semiconductors with a high IE of up to 6 eV.

This is a preview of subscription content, access via your institution

Access options

Buy this article

  • Purchase on Springer Link
  • Instant access to full article PDF
Buy now

Prices may be subject to local taxes which are calculated during checkout

Fig. 1: Hole-injection enhancement in Spiro-TAD.
Fig. 2: Hole-injection enhancement with different interlayers.
Fig. 3: Space-charge-limited hole currents in four different materials.
Fig. 4: Experimental and calculated IE profiles across interlayer/hole-transport layer structures.
Fig. 5: UV-emitting TPBi OLEDs.

Similar content being viewed by others

Change history

  • 06 March 2018

    In the html version of this Article originally published, Paul W. M. Blom and Gert-Jan A. H. Wetzelaer were incorrectly listed as Paul M. W. Blom and Gert-Jan H. A. Wetzelaer, respectively, due to a technical error. This has now been amended in all online versions of the Article.

References

  1. Tao, Y., Yang, C. & Qin, J. Organic host materials for phosphorescent organic light-emitting diodes. Chem. Soc. Rev. 40, 2943–2970 (2011).

    Article  Google Scholar 

  2. Wong, M. Y. & Zysman-Colman, E. Purely organic thermally activated delayed fluorescence materials for organic light-emitting diodes. Adv. Mater. 29, 1605444 (2017).

    Article  Google Scholar 

  3. Koch, N. & Vollmer, A. Electrode-molecular semiconductor contacts: Work-function-dependent hole injection barriers versus Fermi-level pinning. Appl. Phys. Lett. 89, 162107 (2006).

    Article  Google Scholar 

  4. Helander, M. G. et al. Chlorinated indium tin oxide electrodes with high work function for organic device compatibility. Science 332, 944–947 (2011).

    Article  Google Scholar 

  5. Simmons, J. G. Richardson–Schottky effect in solids. Phys. Rev. Lett. 15, 967–968 (1965).

    Article  Google Scholar 

  6. Méndez, H. et al. Charge-transfer crystallites as molecular electrical dopants. Nat. Commun. 6, 8560 (2015).

    Article  Google Scholar 

  7. Tang, C. G. et al. Doped polymer semiconductors with ultrahigh and ultralow work functions for ohmic contacts. Nature 539, 536–540 (2016).

    Article  Google Scholar 

  8. Kröger, M. et al. Role of the deep-lying electronic states of MoO3 in the enhancement of hole-injection in organic thin films. Appl. Phys. Lett. 95, 123301 (2009).

    Article  Google Scholar 

  9. Kröger, M. et al. P-type doping of organic wide band gap materials by transition metal oxides: A case-study on molybdenum trioxide. Org. Electron. 10, 932–938 (2009).

    Article  Google Scholar 

  10. Meyer, J. et al. Transition metal oxides for organic electronics: Energetics, device physics and applications. Adv. Mater. 24, 5408–5427 (2012).

    Article  Google Scholar 

  11. 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).

    Article  Google Scholar 

  12. Davids, P. S., Campbell, I. H. & Smith, D. L. Device model for single carrier organic diodes. J. Appl. Phys. 82, 6319–6325 (1997).

    Article  Google Scholar 

  13. Belisle, R. A., Jain, P., Prasanna, R., Leijtens, T. & McGehee, M. D. Minimal effect of the hole-transport material ionization potential on the open-circuit voltage of perovskite solar cells. ACS Energy Lett. 1, 556–560 (2016).

    Article  Google Scholar 

  14. White, R. T., Thibau, E. S. & Lu, Z.-H. Interface structure of MoO3 on organic semiconductors. Sci. Rep. 6, 21109 (2016).

    Article  Google Scholar 

  15. Mott, N. F. & Gurney, R. W. Electronic Processes in Ionic Crystals (Oxford University Press: Oxford, 1940).

  16. Li, C., Duan, L., Li, H. & Qiu, Y. Universal trap effect in carrier transport of disordered organic semiconductors: Transition from shallow trapping to deep trapping. J. Phys. Chem. C 118, 10651–10660 (2014).

    Article  Google Scholar 

  17. Greiner, M. T. et al. Universal energy-level alignment of molecules on metal oxides. Nat. Mater. 11, 76–81 (2012).

    Article  Google Scholar 

  18. Blakesley, J. C. & Greenham, N. C. Charge transfer at polymer-electrode interfaces: The effect of energetic disorder and thermal injection on band bending and open-circuit voltage. J. Appl. Phys. 106, 034507 (2009).

    Article  Google Scholar 

  19. Oehzelt, M., Koch, N. & Heimel, G. Organic semiconductor density of states controls the energy level alignment at electrode interfaces. Nat. Comm. 5, 4174 (2014).

    Article  Google Scholar 

  20. Oehzelt, M., Akaike, K., Koch, N. & Heimel, G. Energy-level alignment at organic heterointerfaces. Sci. Adv. 1, e1501127 (2015).

    Article  Google Scholar 

  21. Baldo, M. A. & Forrest, S. R. Interface-limited injection in amorphous organic semiconductors. Phys. Rev. B 64, 085201 (2001).

    Article  Google Scholar 

  22. Limketkai, B. N. & Baldo, M. A. Charge injection into cathode-doped amorphous organic semiconductors. Phys. Rev. B 71, 085207 (2005).

    Article  Google Scholar 

  23. 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).

    Article  Google Scholar 

  24. Hung, W.-Y. et al. Employing ambipolar oligofluorene as the charge-generation layer in time-of-flight mobility measurements of organic thin films. Appl. Phys. Lett. 88, 064102 (2006).

    Article  Google Scholar 

  25. Tse, S. C., Kwok, K. C. & So, S. K. Electron transport in naphthylamine-based organic compounds. Appl. Phys. Lett. 89, 262102 (2006).

    Article  Google Scholar 

  26. Bach, U., De Cloedt, K., Spreitzer, H. & Grätzel, M. Characterization of hole transport in a new class of spiro-linked oligotriphenylamine compounds. Adv. Mater. 12, 1060–1063 (2000).

    Article  Google Scholar 

  27. Noh, S., Suman, C. K., Hong, Y. & Lee, C. Carrier conduction mechanism for phosphorescent material doped organic semiconductor. J. Appl. Phys. 105, 033709 (2009).

    Article  Google Scholar 

  28. Matsusue, N., Suzuki, Y. & Naito, H. Charge carrier transport in neat thin films of phosphorescent iridium complexes. Jpn. J. Appl. Phys. 44, 3691–3694 (2005).

    Article  Google Scholar 

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

    Article  Google Scholar 

  30. Ruehle, V. et al. Microscopic simulations of charge transport in disordered organic semiconductors. J. Chem. Theory Comput. 7, 3335–3345 (2011).

    Article  Google Scholar 

  31. Poelking, C. & Andrienko, D. Long-range embedding of molecular ions and excitations in a polarizable molecular environment. J. Chem. Theory Comput. 12, 4516–4523 (2016).

    Article  Google Scholar 

Download references

Acknowledgements

The authors thank C. Bauer, F. Keller, and H.-J. Guttmann for technical support. This project has received funding from the European Union Horizon 2020 research and innovation programme under Grant Agreement No. 646176 (EXTMOS). D.A. thanks the BMBF grant InterPhase (FKZ 13N13661) and the European Union Horizon 2020 research and innovation programme ‘Widening materials models’ under Grant Agreement No. 646259 (MOSTOPHOS).

Author information

Authors and Affiliations

  1. Max Planck Institute for Polymer Research, Mainz, Germany

    Naresh B. Kotadiya, Hao Lu, Anirban Mondal, Yutaka Ie, Denis Andrienko, Paul W. M. Blom & Gert-Jan A. H. Wetzelaer

  2. The Institute of Scientific and Industrial Research (ISIR), Osaka University, Ibaraki, Japan

    Yutaka Ie

Authors
  1. Naresh B. Kotadiya
    View author publications

    You can also search for this author in PubMed Google Scholar

  2. Hao Lu
    View author publications

    You can also search for this author in PubMed Google Scholar

  3. Anirban Mondal
    View author publications

    You can also search for this author in PubMed Google Scholar

  4. Yutaka Ie
    View author publications

    You can also search for this author in PubMed Google Scholar

  5. Denis Andrienko
    View author publications

    You can also search for this author in PubMed Google Scholar

  6. Paul W. M. Blom
    View author publications

    You can also search for this author in PubMed Google Scholar

  7. Gert-Jan A. H. Wetzelaer
    View author publications

    You can also search for this author in PubMed Google Scholar

Contributions

G.A.H.W. proposed and supervised the project. N.B.K. carried out sample preparation and electrical measurements. H.L. performed the UPS measurements. D.A. and A.M. performed molecular-dynamics and energy-alignment simulations. Y.I. synthesized and purified 4CzIPN. G.A.H.W., N.B.K. and P.W.M.B. analysed the experimental data. G.A.H.W. wrote the manuscript with input from D.A. and P.W.M.B.

Corresponding author

Correspondence to Gert-Jan A. H. Wetzelaer.

Ethics declarations

Competing interests

The authors declare no competing financial interests.

Additional information

Publisher’s note: Springer Nature remains neutral with regard to jurisdictional claims in published maps and institutional affiliations.

A correction to this article is available online at https://doi.org/10.1038/s41563-018-0043-3.

Supplementary information

Supplementary Information

Molecular structures of materials, Experimental techniques, Supporting experimental results, Molecular dynamics simulations, Density-of-states distributions, energy-level alignment calculations.

Rights and permissions

Reprints and permissions

About this article

Check for updates. Verify currency and authenticity via CrossMark

Cite this article

Kotadiya, N.B., Lu, H., Mondal, A. et al. Universal strategy for Ohmic hole injection into organic semiconductors with high ionization energies. Nature Mater 17, 329–334 (2018). https://doi.org/10.1038/s41563-018-0022-8

Download citation

  • Received:

  • Accepted:

  • Published:

  • Issue Date:

  • DOI: https://doi.org/10.1038/s41563-018-0022-8

This article is cited by

Search

Advanced search

Quick links

Nature Briefing

Sign up for the Nature Briefing newsletter — what matters in science, free to your inbox daily.

Get the most important science stories of the day, free in your inbox. Sign up for Nature Briefing