Small molecule chemisorption on indium - Tin oxide surfaces: Enhancing probe molecule electron-transfer rates and the performance of organic light-emitting diodes

Chet Carter, Michael Brumbach, Carrie Donley, Richard D. Hreha, Seth R. Marder, Benoit Domercq, Seunghyup Yoo, Bernard Kippelen, Neal R. Armstrong

Research output: Contribution to journalArticle

42 Scopus citations

Abstract

Indium - tin oxide (ITO) surfaces have been modified by chemisorption of carboxylic acid functionalized small molecules: ferrocene dicarboxylic acid (1), 3-thiophene acetic acid (2), and 6-{4-[{4′-[[4-(5-carboxy-pentyloxy)- phenyl]-(4-methoxy-phenyl)-amino]-biphenyl-4-yl}-(4-methoxy-phenyl)-amino] -phenoxy}-hexanoic acid (p-OMe)2-TPD-(C5-COOH) 2) (3). Voltammetrically determined surface coverages of 1-3 increased in two stages, the first stage completing in minutes, the latter stage taking several hours. Electron-transfer rate coefficients, kS, for the probe molecule ferrocene in acetonitrile likewise increased in two stages with increasing surface coverages of 1, 2, and 3. Fourier transform infrared spectroscopy of In2O3 powders, exposed for long periods to ethanol solutions of each modifier, confirmed the formation of indium oxalate-like surface species. X-ray photoelectron spectroscopy of carboxy-terminated alkanethiol-modified gold surfaces, exposed to these same In2O3(powder)/small molecule modifier solutions, showed the capture of trace levels of indium as a result of the chemisorption of these small molecules, suggesting that slow etching of the ITO surface also occurs during the chemisorption event. Conventional aluminum quinolate/bis-triarylamine organic light-emitting diodes (OLEDs) created on ITO surfaces modified with 1, 2, and 3, with and without an overlayer of PEDOT:PSS (a poly(thiophene)/ poly(stryenesulfonate) ITO modifier), showed leakage currents lowered by several orders of magnitude and an increase in OLED device efficiency.

Original languageEnglish (US)
Pages (from-to)25191-25202
Number of pages12
JournalJournal of Physical Chemistry B
Volume110
Issue number50
DOIs
StatePublished - Dec 21 2006

ASJC Scopus subject areas

  • Physical and Theoretical Chemistry
  • Surfaces, Coatings and Films
  • Materials Chemistry

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