Berlin 2008 – scientific programme

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DS: Fachverband Dünne Schichten

DS 3: Organic Thin Films

DS 3.1: Talk

Monday, February 25, 2008, 14:30–14:45, H 2013

Grain-boundary evolution in a pentacene monolayer — •Jian Zhang, Jürgen P. Rabe, and Norbert Koch — Institut für Physik, Humboldt-Universität zu Berlin, Newtonstrasse 15, D-12489 Berlin

Significant charge carrier trapping defects were shown to exist at grain boundaries (GBs) in polycrystalline pentacene films, and these GBs are the principal bottleneck for charge transport in organic thin-film transistors (OTFTs) and they also affect the overall lifetime of OTFTs. In order to better comprehend the growth of organic polycrystalline films and controlling the number of grain boundaries in these films, the formation and evolution of GBs in pentacene films has to be understood. In this work, the evolution of GBs in the first pentacene layer on SiO2 substrates was studied. Using transverse shear microscopy, we directly observed GBs within single pentacene topographical islands. These intra-island GBs form at very early stages of pentacene film growth (in the present case at a coverage of 0.05 ML). Consequently, the existence of GBs within single pentacene islands (not visible in height images) will complicate "single-grain" transport measurements. During island growth the intra-island GB density increases linearly, suggesting a continued formation of new grain boundaries also before islands coalesce. Additionally, post-fabrication thermal annealing can reduce the GB density significantly in the pentacene layer in direct contact with SiO2, which should lead to a considerable decrease of charge carrier trapping sites in OTFTs.