Berlin 2008 – wissenschaftliches Programm

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SYSA: Symposium Tayloring Organic Interfaces: Molecular Structures and Applications

SYSA 5: Poster Session SYSA

SYSA 5.26: Poster

Dienstag, 26. Februar 2008, 14:30–20:00, Poster A

Charge injection in light emitting organic field effect transistors — •Martin Schidleja, Christian Melzer, and Heinz von Seggern — Electronic Materials Division, Institute of Materials Science, Technische Universität Darmstadt, Petersenstr. 23, 64287 Darmstadt, Germany

Light emitting organic field effect transistors with different metals used as source and drain contacts are investigated. The transistors are built in a top-gate, bottom-contact configuration with poly(9,9-di-n-octyl-fluorene-alt-benzothidiazole) (F8BT) as organic semiconductor and poly(methyl methacrylate) (PMMA) as gate-dielectric. For the drain and source electrodes either gold or silver is used. While gold results in balanced injection barriers for hole and electron injection of about 1 eV, the use of silver disturbs this essential balance in the injection properties.

The drain current and the position of the recombination zone in the transistor channel at different voltages are measured for the respective transistors. It is found that the experimental data cannot be explained by the standard equations for ambipolar transistors, most probably due to large injection barriers and hence, high contact resistances. In order to evaluate the results, a numerical model is introduced, taking into account the influence of different injection-barriers on the ambipolar behaviour of organic field effect transistors by separate calculation of the injection currents at the source and drain contacts, respectively. Our results stress the importance of contact phenomena in light emitting organic field effect transistors.