We determined the shifts in the energy levels of thick poly[2-methoxy-5-(-ethyl-hexyloxy)-1,4-phenylene vinylene] films deposited on various substrates including self-assembled monolayer (SAM) modified Au surfaces using photoelectron spectroscopy. As the unmodified substrates included Au, indium tin oxide, Si (with native oxide), and Al (with native oxide), a systematic shift in the detected energy levels of the organic semiconductor was observed to follow the work function values of the substrates. Furthermore, we used polar SAMs to alter the work function of the Au substrates. This suggests the opportunity to control the energy level positions of the organic semiconductor with respect to the electrode Fermi level. Photoelectron spectroscopy results showed that, by introducing SAMs on the Au surface, we successfully increased and decreased the effective work function of Au surface. We found that in this case, the change in the effective work function of the metal surface was not reflected as a shift in the energy levels of the organic semiconductor, as opposed to the results achieved with different substrate materials. Our study showed that when a substrate is modified by SAMs (or similarly by any adsorbed molecules), a new effective work function value is achieved; however, it does not necessarily imply that the new modified surface will behave similar to a different metal where the work function is equal to the effective work function of the modified surface. Various models and their possible contribution to this result are discussed.
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21 February 2008
Research Article|
February 20 2008
Energy level alignment at organic semiconductor/metal interfaces: Effect of polar self-assembled monolayers at the interface
K. Demirkan;
K. Demirkan
1Department of Materials Science and Engineering,
University of Delaware
, Newark, Delaware 19716, USA
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A. Mathew;
A. Mathew
1Department of Materials Science and Engineering,
University of Delaware
, Newark, Delaware 19716, USA
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C. Weiland;
C. Weiland
1Department of Materials Science and Engineering,
University of Delaware
, Newark, Delaware 19716, USA
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Y. Yao;
Y. Yao
2Department of Chemistry, Department of Mechanical Engineering, Department of Materials Science, and the Smalley Institute for Nanoscale Science and Technology,
Rice University
, Houston, Texas 77005, USA
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A. M. Rawlett;
A. M. Rawlett
3Multifunctional Materials Division,
U.S. Army Research Laboratory
, Aberdeen Proving Ground, Maryland 21005-5069, USA
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J. M. Tour;
J. M. Tour
2Department of Chemistry, Department of Mechanical Engineering, Department of Materials Science, and the Smalley Institute for Nanoscale Science and Technology,
Rice University
, Houston, Texas 77005, USA
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R. L. Opila
R. L. Opila
a)
1Department of Materials Science and Engineering,
University of Delaware
, Newark, Delaware 19716, USA
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a)
Electronic mail: opila@udel.edu.
J. Chem. Phys. 128, 074705 (2008)
Article history
Received:
April 10 2007
Accepted:
December 11 2007
Citation
K. Demirkan, A. Mathew, C. Weiland, Y. Yao, A. M. Rawlett, J. M. Tour, R. L. Opila; Energy level alignment at organic semiconductor/metal interfaces: Effect of polar self-assembled monolayers at the interface. J. Chem. Phys. 21 February 2008; 128 (7): 074705. https://doi.org/10.1063/1.2832306
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