TY - JOUR
T1 - Phosphonic acid modification of indium-tin oxide electrodes
T2 - Combined XPS/UPS/ contact angle studies
AU - Paniagua, Sergio A.
AU - Hotchkiss, Peter J.
AU - Jones, Simon C.
AU - Marder, Seth R.
AU - Mudalige, Anoma
AU - Marrikar, F. Saneeha
AU - Pemberton, Jeanne E.
AU - Armstrong, Neal R.
PY - 2008/5/29
Y1 - 2008/5/29
N2 - Indium-tin oxide (ITO) electrodes have been modified with both fluorinated alkyl and aryl phosphonic acids [n-hexylphosphonic acid (HPA) and n-octadecylphosphonic acid (ODPA); 3,3,4,4,5,5,6,6,7,7,8,8,8-tridecaf-luorooctyl phosphonic acid (FHOPA), pentafluorobenzyl phosphonic acid (PFBPA), and tetrafluorobenzyl-1,4-diphosphonic acid (TFBdiPA)]. These are modifiers designed to control both wetting properties toward nonpolar molecular solids and to provide a wide range of tunability in effective surface work function. The molecular nature of surface attachment and changes in electronic and wetting properties were characterized by X-ray photoelectron spectroscopy (XPS), UV-photoelectron spectroscopy (UPS), photoelastic modulation infrared reflection-absorption spectroscopy (PM-IRRAS), and contact angle measurements using both water and hexadecane. Interface dipoles from the PA modifiers contribute to shifts in the low kinetic energy regions of UPS spectra (local vacuum level shifts, which translate into changes in effective surface work function). We show that for ITO surfaces modified with FHOPA, and to a lesser extent with PFBPA, the high work function obtained by oxygen plasma cleaning can be maintained after modification, while decreasing the polar component of surface energy. This approach to oxide surface modification is a strategy that may be beneficial for the modification of transparent conducting oxide surfaces in both organic light emitting diodes and in organic solar cells, where oxide/organic compatibility can affect device performance.
AB - Indium-tin oxide (ITO) electrodes have been modified with both fluorinated alkyl and aryl phosphonic acids [n-hexylphosphonic acid (HPA) and n-octadecylphosphonic acid (ODPA); 3,3,4,4,5,5,6,6,7,7,8,8,8-tridecaf-luorooctyl phosphonic acid (FHOPA), pentafluorobenzyl phosphonic acid (PFBPA), and tetrafluorobenzyl-1,4-diphosphonic acid (TFBdiPA)]. These are modifiers designed to control both wetting properties toward nonpolar molecular solids and to provide a wide range of tunability in effective surface work function. The molecular nature of surface attachment and changes in electronic and wetting properties were characterized by X-ray photoelectron spectroscopy (XPS), UV-photoelectron spectroscopy (UPS), photoelastic modulation infrared reflection-absorption spectroscopy (PM-IRRAS), and contact angle measurements using both water and hexadecane. Interface dipoles from the PA modifiers contribute to shifts in the low kinetic energy regions of UPS spectra (local vacuum level shifts, which translate into changes in effective surface work function). We show that for ITO surfaces modified with FHOPA, and to a lesser extent with PFBPA, the high work function obtained by oxygen plasma cleaning can be maintained after modification, while decreasing the polar component of surface energy. This approach to oxide surface modification is a strategy that may be beneficial for the modification of transparent conducting oxide surfaces in both organic light emitting diodes and in organic solar cells, where oxide/organic compatibility can affect device performance.
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U2 - 10.1021/jp710893k
DO - 10.1021/jp710893k
M3 - Article
AN - SCOPUS:45149085353
SN - 1932-7447
VL - 112
SP - 7809
EP - 7817
JO - Journal of Physical Chemistry C
JF - Journal of Physical Chemistry C
IS - 21
ER -