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Proceedings Paper

Temperature dependence of the ordering of semiconducting fluorene-thiophene copolymers on rubbed polyimide alignment layers
Author(s): Lisa R. Pattison; Alexander Hexemer; Edward J. Kramer; Pierre M. Petroff; Daniel A. Fischer
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Paper Abstract

There has been great interest in recent years in using solution processible conjugated organic polymers as the active layers in semiconducting devices including field-effect transistors (FETs), light emitting diodes (LEDs), and photovoltaics (PVs). The structure of the polymer film is very important to device performance at the interfaces where charge separation and collection occur, as well as in the bulk of the film, where it has been shown that alignment of the polymer backbone can increase the pi-orbital overlap, thus enhancing charge carrier mobility. In this work, we report on the temperature-dependent alignment of liquid crystalline fluorene-thiophene copolymer thin film surfaces using the near-edge X-ray fine absorption structure (NEXAFS) technique. Partial electron yield spectra were recorded over a range of temperatures to observe directly the bond orientation in various polymer phases. In addition, samples were annealed under varying processing conditions and spectra were taken at room temperature on these heat-treated samples. The NEXAFS data shows: a) in thin polyfluorene films, the polymer backbone lies flat in the plane of the substrate, b) that along the main chain axis, biphenyl and thiophene rings have a preference to lie flat in the plane of the surface, c) the orientation of the polymer backbone can be controlled using a rubbed polyimide alignment layer as a template for liquid crystal orientation, and d) under proper annealing conditions, there is strong temperature-dependent alignment of the copolymer main-chain axis to the rubbing direction with dichroic ratio (R) reaching R=0.7.

Paper Details

Date Published: 3 October 2005
PDF: 8 pages
Proc. SPIE 5938, Organic Photovoltaics VI, 59380O (3 October 2005); doi: 10.1117/12.617868
Show Author Affiliations
Lisa R. Pattison, Univ. of California, Santa Barbara (United States)
Alexander Hexemer, Univ. of California, Santa Barbara (United States)
Edward J. Kramer, Univ. of California, Santa Barbara (United States)
Pierre M. Petroff, Univ. of California, Santa Barbara (United States)
Daniel A. Fischer, National Institute of Standards and Technology (United States)


Published in SPIE Proceedings Vol. 5938:
Organic Photovoltaics VI
Zakya H. Kafafi; Paul A. Lane, Editor(s)

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