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Proceedings Paper

Degradation of polyfluorene-type polymers: interface and bulk-related defects
Author(s): Stefan Gamerith; Christoph Gadermaier; Heinz G. Nothofer; Ullrich Scherf; Emil J.W. List
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Paper Abstract

The origin of a broad low-energy photo-luminescence (PL) and electro-luminescence (EL) band emerging upon oxidative degradation of hihgly emissive polyfluorenes (PFs) has recently been identified as the emission from on-chain keto defects acting as exciton and/or charge traps. In this work we compare several polyfluorenes with respect to their stability upon thermal degradation, and their stability upon fabrication and operation of PF-based polymer light emitting devices (PLEDs). We show that in addition to the keto emission a second type of defect emission, which is related to the deposition of the metal electrode, can also affect the color purity of PF-PLEDs. Investigated materials are a poly(9,9 dialkylfluorene) with hexahydrofarnesyl sidechains (PF111/12) a poly(9,9 dialkylfluorene) with ethyl-hexyl sidechains (PF 2/6) and two different slightly branched spiro-PFs with and without triphenylamine endcappers, respetively. We find significant differences in the spectral stability of the polymers which may on the one hand be explained by a difference of the chemical stability of the polymers but to some extent must be explained withiin the picture of excited energy migration. Regarding a comparison of the polymers, the end-capped spiro-type PF shows an overall improved performance compared to the other investigated polymers provided that the evaporation process of the metal cathode of an PLED is well controlled to avoid the formation of emissive defects at the interface.

Paper Details

Date Published: 8 September 2004
PDF: 10 pages
Proc. SPIE 5464, Organic Optoelectronics and Photonics, (8 September 2004); doi: 10.1117/12.545840
Show Author Affiliations
Stefan Gamerith, Technische Univ. Graz (Austria)
Institute of Nanostructured Materials and Photonics (Austria)
Christoph Gadermaier, Technische Univ. Graz (Austria)
Institute of Nanostructured Materials and Photonics (Austria)
Heinz G. Nothofer, Bergische Univ. Wuppertal (Germany)
Ullrich Scherf, Bergische Univ. Wuppertal (Germany)
Emil J.W. List, Technische Univ. Graz (Austria)

Published in SPIE Proceedings Vol. 5464:
Organic Optoelectronics and Photonics
Paul L. Heremans; Michele Muccini; Hans Hofstraat, Editor(s)

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