Tuning the Work Function of Polar Zinc Oxide Surfaces by Modified Phosphonic Acid Self-Assembled Monolayers

  • chair:

    Lange, I. / Reiter, S. / Pätzel, M. / Zykov, A. / Nefedov, A. / Hildebrand, J. / Hecht, S. / Kowarik, S. / Wöll, C. / Heimel, G. / Neher, D. (2014)
  • place:

    Advanced Functional Materials (2014)
  • Date: 2014

  • Lange, I. / Reiter, S. / Pätzel, M. / Zykov, A. / Nefedov, A. / Hildebrand, J. / Hecht, S. / Kowarik, S. / Wöll, C. / Heimel, G. / Neher, D. (2014): „Tuning the Work Function of Polar Zinc Oxide Surfaces by Modified Phosphonic Acid Self-Assembled Monolayers“. In: Advanced Functional Materials (2014)

Abstract

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Zinc oxide (ZnO) is regarded as a promising alternative material for transparent conductive electrodes in optoelectronic devices. However, ZnO suffers from poor chemical stability. ZnO also has a moderate work function (WF), which results in substantial charge injection barriers into common (organic) semiconductors that constitute the active layer in a device. Controlling and tuning the ZnO WF is therefore necessary but challenging.

Here, a variety of phosphonic acid based self-assembled monolayers (SAMs) deposited on ZnO surfaces are investigated. It is demonstrated that they allow for tuning the WF over a wide range of more than 1.5 eV, thus enabling the use of ZnO as both the hole-injecting and electron-injecting contact.

The modified ZnO surfaces are characterized using a number of complementary techniques, demonstrating that the preparation protocol yields dense, well-defined molecular monolayers.