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Temperature Dependence of the Ordering of Semiconducting Fluorene Thiophene Copolymers on Rubbed Polyimide Alignment Layers



L R. Pattison, A Hexemer, E K. Kramer, P Petroff, Daniel A. Fischer


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 inthe 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 observe the temperature-dependent alignment of liquid crystalline fluorene-thiophene copolymer thin film surfaces using the near-edge X-ray absorption structure (NEXAFS) technique. Partial electron yield spectra were recorded at a range of temperatures to observe directly the orientation in various phases. In addition, samples were annealed under varying processing conditions and spectra were taken at room temperature on thsese heat-treated samples. The NEXAFS data for each case are compared. In thin polyfluorene films, the polymer backbone lies flat in the plane of the substrate. Using NEXAFS, we observe that along the main chain axis, biphenyl and thipohene rings have a preference to lie flat in the plane of the surface. Moreover, the orientation of the polymer backbone can be controlled using a rubbed polyimide alignment layer as a template for liquid crystal orientation. Under proper annealing conditions, we observe strong temperature-dependent alignment of the copolymer main-chain axis to the rubbing direction with dichroic ratio (R) reaching R=0.7.
Proceedings Title
Conference Dates
July 31-August 4, 2005
Conference Location
Conference Title
SPIE Optics and Photonics Conference


F8T2, fluorene, NEXAFS, semiconducting polymer, thiophene


Pattison, L. , Hexemer, A. , Kramer, E. , Petroff, P. and Fischer, D. (2005), Temperature Dependence of the Ordering of Semiconducting Fluorene Thiophene Copolymers on Rubbed Polyimide Alignment Layers, 2005, Undefined (Accessed April 17, 2024)
Created February 17, 2005, Updated October 12, 2021