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Proceedings Paper

Energy level alignment at polymer/electrode interfaces in light-emitting devices studied by photoelectron spectroscopy
Author(s): Grzegorz Greczynski; Thomas Kugler; William R. Salaneck
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Paper Abstract

The band alignment at the interface between electroluminescent polymers and the electrodes in polymer- LEDs was studied using photoelectron spectroscopy. Chemical factors like the formation of InCl3 during conversion of precursor-PPV on ITO could be directly monitored with XPS. Films of electroluminescent polymers were studied on a range of ITO and metal electrodes with different work functions, as well as with an intermediate, electrically conducting polymer layer, using UPS. For the polymers spin-coated directly onto the substrates, the vacuum levels are aligned. In the case of conducting polymer films on ITO or metal substrates, the F1ermi levels are aligned. With a conducting polymer layer sandwiched between the electroluminescent polymer and the ITO electrode, the polymer bands align to the vacuum level of the conducting polymer. Thus, the barrier to hole injection into the electroluminescent polymer is determined by the work function of the conducting polymer instead of the work function of the ITO electrode. Furthermore, the study of the band alignment at polymer electrode interfaces was extended to three-layer structures: The results are in agreement with the common assumption that the potential drop over the polymer layer in a polymer LED is equal to the difference between the electrode work functions.

Paper Details

Date Published: 2 February 2001
PDF: 14 pages
Proc. SPIE 4105, Organic Light-Emitting Materials and Devices IV, (2 February 2001); doi: 10.1117/12.416882
Show Author Affiliations
Grzegorz Greczynski, Linkoeping Univ. (Sweden)
Thomas Kugler, ACREO AB (Sweden)
William R. Salaneck, Linkoeping Univ. (Sweden)

Published in SPIE Proceedings Vol. 4105:
Organic Light-Emitting Materials and Devices IV
Zakya H. Kafafi, Editor(s)

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