Berlin 2005 – scientific programme

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SYOO: Organic Optoelectronics and Photonics

SYOO 6: Poster

SYOO 6.34: Poster

Monday, March 7, 2005, 18:00–20:00, Poster TU A

Charge carrier mobility measurements in organic single crystals — •J. Niemax, A.K. Tripathi, and J. Pflaum — 3. Phys. Inst., Universität Stuttgart, Germany

Charge carrier mobilities in ultra-pure organic single crystals define benchmarks for the transport in the corresponding thin films. But depending on the handling of the samples and the respective experimental setup, a broad variation of the transport parameters of single crystals is reported in literature. We therefore, present transport measurements on single crystals of polyacenes in combination with their chemical analysis. As previously shown, time-of-flight spectroscopy can be used to measure hole and electron transients along the c’-direction, in case the material can be purified by zone-refinement. For tetracene, which can be purified by sublimation only, the electron transport is strongly dispersive. In agreement with measurements of the field-effect mobility, the hole transport is thermally activated showing a behavior described by the Hoestery-Letson model. In this context, we obtained the highest FET hole mobility of 0.8 cm²/Vs at room temperature reported so far. Comparing trap density and energy deduced from this model with gas chromatography data, the conclusion can be drawn that the trapping is mainly caused by chemical impurities rather than by structural defects.