The modification of indium tin oxide with phosphonic acids

Mechanism of binding, tuning of surface properties, and potential for use in organic electronic applications

Peter J. Hotchkiss, Simon C. Jones, Sergio A. Paniagua, Asha Sharma, Bernard Kippelen, Neal R Armstrong, Seth R. Marder

Research output: Contribution to journalArticle

170 Citations (Scopus)

Abstract

Transparent metal oxides, in particular, indium tin oxide (ITO), are critical transparent contact materials for applications in next-generation organic electronics, including organic light emitting diodes (OLEDs) and organic photovoltaics (OPVs). Understanding and controlling the surface properties of ITO allows for the molecular engineering of the ITO-organic interface, resulting in fine control of the interfacial chemistries and electronics. In particular, both surface energy matching and work function compatibility at material interfaces can result in marked improvement in OLED and OPV performance. Although there are numerous ways to change the surface properties of ITO, one of the more successful surface modifications is the use of monolayers based on organic molecules with widely variable end functional groups. Phosphonic acids (PAs) are known to bind strongly to metal oxides and form robust monolayers on many different metal oxide materials. They also demonstrate several advantages over other functionalizing moieties such as silanes or carboxylic acids. Most notably, PAs can be stored in ambient conditions without degradation, and the surface modification procedures are typically robust and easy to employ.This Account focuses on our research studying PA binding to ITO, the tunable properties of the resulting surfaces, and subsequent effects on the performance of organic electronic devices. We have used surface characterization techniques such as X-ray photoelectron spectroscopy (XPS) and infrared reflection adsorption spectroscopy (IRRAS) to determine that PAs bind to ITO in a predominantly bidentate fashion (where two of three oxygen atoms from the PA are involved in surface binding). Modification of the functional R-groups on PAs allows us to control and tune the surface energy and work function of the ITO surface. In one study using fluorinated benzyl PAs, we can keep the surface energy of ITO relatively low and constant but tune the surface work function. PA modification of ITO has resulted in materials that are more stable and more compatible with subsequently deposited organic materials, an effective work function that can be tuned by over 1 eV, and energy barriers to hole injection (OLED) or hole-harvesting (OPV) that can be well matched to the frontier orbital energies of the organic active layers, leading to better overall device properties.

Original languageEnglish (US)
Pages (from-to)337-346
Number of pages10
JournalAccounts of Chemical Research
Volume45
Issue number3
DOIs
StatePublished - Mar 20 2012

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Phosphorous Acids
Surface properties
Tuning
Organic light emitting diodes (OLED)
Interfacial energy
Oxides
Metals
Surface treatment
Monolayers
Electronic equipment
indium tin oxide
Silanes
Energy barriers
Carboxylic Acids
Surface chemistry
Functional groups
X ray photoelectron spectroscopy

ASJC Scopus subject areas

  • Chemistry(all)

Cite this

The modification of indium tin oxide with phosphonic acids : Mechanism of binding, tuning of surface properties, and potential for use in organic electronic applications. / Hotchkiss, Peter J.; Jones, Simon C.; Paniagua, Sergio A.; Sharma, Asha; Kippelen, Bernard; Armstrong, Neal R; Marder, Seth R.

In: Accounts of Chemical Research, Vol. 45, No. 3, 20.03.2012, p. 337-346.

Research output: Contribution to journalArticle

Hotchkiss, Peter J. ; Jones, Simon C. ; Paniagua, Sergio A. ; Sharma, Asha ; Kippelen, Bernard ; Armstrong, Neal R ; Marder, Seth R. / The modification of indium tin oxide with phosphonic acids : Mechanism of binding, tuning of surface properties, and potential for use in organic electronic applications. In: Accounts of Chemical Research. 2012 ; Vol. 45, No. 3. pp. 337-346.
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