Orientation of phenylphosphonic acid self-assembled monolayers on a transparent conductive oxide: A combined NEXAFS, PM-IRRAS, and DFT study

Matthew Gliboff, Lingzi Sang, Kristina M. Knesting, Matthew C. Schalnat, Anoma Mudalige, Erin L. Ratcliff, Hong Li, Ajaya K. Sigdel, Anthony J. Giordano, Joseph J. Berry, Dennis Nordlund, Gerald T. Seidler, Jean Luc Brédas, Seth R. Marder, Jeanne E. Pemberton, David S. Ginger

Research output: Contribution to journalArticle

42 Scopus citations

Abstract

Self-assembled monolayers (SAMs) of dipolar phosphonic acids can tailor the interface between organic semiconductors and transparent conductive oxides. When used in optoelectronic devices such as organic light emitting diodes and solar cells, these SAMs can increase current density and photovoltaic performance. The molecular ordering and conformation adopted by the SAMs determine properties such as work function and wettability at these critical interfaces. We combine angle-dependent near-edge X-ray absorption fine structure (NEXAFS) spectroscopy and polarization modulation infrared reflection absorption spectroscopy (PM-IRRAS) to determine the molecular orientations of a model phenylphosphonic acid on indium zinc oxide, and correlate the resulting values with density functional theory (DFT). We find that the SAMs are surprisingly well-oriented, with the phenyl ring adopting a well-defined tilt angle of 12-16 from the surface normal. We find quantitative agreement between the two experimental techniques and density functional theory calculations. These results not only provide a detailed picture of the molecular structure of a technologically important class of SAMs, but also resolve a long-standing ambiguity regarding the vibrational-mode assignments for phosphonic acids on oxide surfaces, thus improving the utility of PM-IRRAS for future studies.

Original languageEnglish (US)
Pages (from-to)2166-2174
Number of pages9
JournalLangmuir
Volume29
Issue number7
DOIs
StatePublished - Feb 19 2013

ASJC Scopus subject areas

  • Materials Science(all)
  • Condensed Matter Physics
  • Surfaces and Interfaces
  • Spectroscopy
  • Electrochemistry

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    Gliboff, M., Sang, L., Knesting, K. M., Schalnat, M. C., Mudalige, A., Ratcliff, E. L., Li, H., Sigdel, A. K., Giordano, A. J., Berry, J. J., Nordlund, D., Seidler, G. T., Brédas, J. L., Marder, S. R., Pemberton, J. E., & Ginger, D. S. (2013). Orientation of phenylphosphonic acid self-assembled monolayers on a transparent conductive oxide: A combined NEXAFS, PM-IRRAS, and DFT study. Langmuir, 29(7), 2166-2174. https://doi.org/10.1021/la304594t