Electron-transfer processes in zinc phthalocyanine-phosphonic acid monolayers on ITO: Characterization of orientation and charge-transfer kinetics by waveguide spectroelectrochemistry

Hsiao Chu Lin, Nathan W. Polaske, Luis E. Oquendo, Matthew Gliboff, Kristina M. Knesting, Dennis Nordlund, David S. Ginger, Erin L. Ratcliff, Brooke M. Beam, Neal R. Armstrong, Dominic V. McGrath, S. Scott Saavedra

Research output: Contribution to journalArticle

25 Scopus citations

Abstract

Using a monolayer of zinc phthalocyanine (ZnPcPA) tethered to indium tin oxide (ITO) as a model for the donor/transparent conducting oxide (TCO) interface in organic photovoltaics (OPVs), we demonstrate the relationship between molecular orientation and charge-transfer rates using spectroscopic, electrochemical, and spectroelectrochemical methods. Both monomeric and aggregated forms of the phthalocyanine (Pc) are observed in ZnPcPA monolayers. Potential-modulated attenuated total reflectance (PM-ATR) measurements show that the monomeric subpopulation undergoes oxidation/reduction with k s,app = 2 × 10 2 s -1, independent of Pc orientation. For the aggregated ZnPcPA, faster orientation-dependent charge-transfer rates are observed. For in-plane-oriented Pc aggregates, k s,app = 2 × 10 3 s -1, whereas for upright Pc aggregates, k s,app = 7 × 10 2 s -1. The rates for the aggregates are comparable to those required for redox-active interlayer films at the hole-collection contact in organic solar cells.

Original languageEnglish (US)
Pages (from-to)1154-1158
Number of pages5
JournalJournal of Physical Chemistry Letters
Volume3
Issue number9
DOIs
StatePublished - May 3 2012

ASJC Scopus subject areas

  • Materials Science(all)
  • Physical and Theoretical Chemistry

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