Dresden 2009 – scientific programme
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DS: Fachverband Dünne Schichten
DS 16: Poster I
DS 16.23: Poster
Tuesday, March 24, 2009, 09:30–12:30, P5
Investigation of the highly crystalline morphology of a low molecular weight oligoquaterthiophene fraction with low polydispersity — •Patrick Pingel1, Dieter Neher1, Markus Breusing2, Thomas Elsaesser2, Thomas Fischer3, Joachim Stumpe3, Jian Zhang4, Norbert Koch4, Sybille Allard5, and Ullrich Scherf5 — 1Institut für Physik und Astronomie, Universität Potsdam — 2Max-Born-Institut für Nichtlineare Optik und Kurzzeitspektroskopie, Berlin — 3Fraunhofer-Institut für Angewandte Polymerforschung, Potsdam — 4Institut für Physik, Humboldt-Universität zu Berlin — 5Institut für Chemie, Universität Wuppertal
We have recently shown that spin-cast layers of an oligomeric polyquaterthiophene fraction (PQT-12, Mw= 1,700 g/mol, PDI=1.03) exhibit a field-effect mobility of 10−3 cm2/Vs, which is unusually high for low-Mw polyalkylthiophenes. Here we show that these layers exhibit a hierarchical architecture with structural order on different length scales. AFM studies reveal that they consist of needle-like crystallites that form oriented domains at the µm-scale. We even observe optical anisotropy in conventional polarization microscopy, meaning that adjoining domains exhibit a common orientation over tens of micrometers. Using broadband confocal spectroscopy with high lateral resolution, we identified regions rich in chains with lower conjugation, which we ascribe to partially ordered domains in between highly crystalline areas. Combined with a flat-on molecular orientation on the substrate, we conceive that the presence of disordered domains determines the field-effect mobility in these polycrystalline layers.