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Study of the MDMO-PPV/metal interface and PCBM/metal interface by electroabsorption spectroscopy

Published online by Cambridge University Press:  15 February 2011

J. Reynaert
Affiliation:
also with Department of Electrical Engineering, Katholieke Universiteit Leuven, Belgium
Y.D. Jin
Affiliation:
IMEC vzw, Kapeldreef 75, B-3001 Leuven, Belgium
T. Aernouts
Affiliation:
IMEC vzw, Kapeldreef 75, B-3001 Leuven, Belgium
W. Geens
Affiliation:
IMEC vzw, Kapeldreef 75, B-3001 Leuven, Belgium
G. Borghs
Affiliation:
IMEC vzw, Kapeldreef 75, B-3001 Leuven, Belgium
R. Mertens
Affiliation:
also with Department of Electrical Engineering, Katholieke Universiteit Leuven, Belgium
P. Heremans
Affiliation:
also with Department of Electrical Engineering, Katholieke Universiteit Leuven, Belgium
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Abstract

In this work, we study the workfunction alignment of organic compounds and electrodes evaporated on top of these organic materials by means of electroabsorption (EA). The organic materials of this study are poly[2-methoxy-5-(3',7'-dimethyloctyloxyl)]-1,4-phenylene vinylene (MDMO-PPV) and methanofullerene [6,6]-phenyl C61-butyric acid methyl ester (PCBM). The electrodes are Al, Au, LiF/Au and LiF/Au, the latter two with a 1 nm thick layer of LiF, as well as with co-evaporation of LiF and the metal. In case of the MDMO-PPV, LiF enhances the built-in potential and thus reduces the electron injection barrier. Equal built-in potentials for a co-evaporated LiF:metal contact suggest doping is happening at the MDMO-PPV/metal interface. Unlike predicted by the Au and Al workfunction value, the built-in potentials for the PCBM/Al and PCBM/Au interface are equal. This suggests that Fermi level pinning occurs at these interfaces. The presence of a thin LiF layer screens the charge transfer from the metal to the PCBM.

Type
Research Article
Copyright
Copyright © Materials Research Society 2003

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