Electrode Work Function Engineering with Phosphonic Acid Monolayers and Molecular Acceptors: Charge Redistribution Mechanisms

Melanie Timpel, Hong Li, Marco V. Nardi, Berthold Wegner, Johannes Frisch, Peter J. Hotchkiss, Seth R. Marder, Stephen Barlow, Jean Luc Brédas, Norbert Koch

Research output: Contribution to journalArticlepeer-review

17 Scopus citations

Abstract

The uses of self-assembled monolayers (SAMs) of dipolar molecules or of adsorbed molecular acceptors on electrode materials are common strategies to increase their work function, thereby facilitating hole injection into an organic semiconductor deposited on top. Here it is shown that a combination of both approaches can surpass the performance of the individual ones. By combined experimental and theoretical methods it is revealed that in a three-component system, consisting of an indium-tin-oxide (ITO) electrode, a carbazole-based phosphonic acid SAM, and a molecular acceptor layer on top of the SAM, charge transfer occurs from the ITO through the SAM to the acceptor layer, resulting in an electrostatic field drop over the charge-neutral SAM. This result is in contrast to common expectations of either p-doping the carbazole of the SAM or charge transfer complex formation between the carbazole and the acceptor molecules. A high work function of 5.7 eV is achieved with this combined system; even higher values may be accessible by exploiting the fundamental charge redistribution mechanisms identified here with other material combinations.

Original languageEnglish (US)
Article number1704438
JournalAdvanced Functional Materials
Volume28
Issue number8
DOIs
StatePublished - Feb 21 2018
Externally publishedYes

Keywords

  • density functional theory
  • indium-tin-oxide
  • phosphonic acid
  • photoelectron spectroscopy
  • self-assembled monolayer

ASJC Scopus subject areas

  • Chemistry(all)
  • Materials Science(all)
  • Condensed Matter Physics

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