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

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.

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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.

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.

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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).

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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.

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Correspondence to Gert-Jan A. H. Wetzelaer.

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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.

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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

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