This article reports degradation experiments on organic thin film transistors using the small organic molecule pentacene as the semiconducting material. Starting with degradation inert p-type silicon wafers as the substrate and SiO 2 as the gate dielectric, we show the influence of temperature and exposure to ambient air on the charge carrier field-effect mobility, on-off-ratio, and threshold-voltage. The devices were found to have unambiguously degraded over 3 orders of magnitude in maximum on-current and charge carrier field-effect mobility, but they still operated after a period of 9 months in ambient air conditions. A thermal treatment was carried out in vacuum conditions and revealed a degradation of the charge carrier field-effect mobility, maximum on-current, and threshold voltage.

The metallization of organic thin films is a crucial point in the development of molecular electronics. However, there is no method established yet to detect trace amounts of metal atoms in those thin films. Radiotracer measurements can quantify even very small amounts of material penetrating into the bulk, in our case less than 0.01% of a monolayer. Here, the application of this technique on two different well-characterized organic thin film systems (diindenoperylene and pentacene) is demonstrated. The results show that Ag is mainly adsorbed on the surface, but indicate that already at moderate deposition temperatures Ag can penetrate into the organic thin films and agglomerate at the film/substrate interface.

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Organic field effect transistors with the organic semiconductor pentacene, using silicon substrates, were successfully built on conventional inorganic dielectrics like silicon dioxide or silicon nitride. They can drive drain currents up to 15 mA. Beyond that, polymer films were investigated as gate dielectrics in order to achieve transistors on plastic films. On polyester substrates with an inorganic–organic gate dielectric, devices reach drain currents comparable to transistors on silicon dioxide and charge carrier mobilities of up to 0.35 cm2/V s. Analysis of the pentacene surface by atomic force microscopy showed pentacene crystallites achieving dimensions of more than 1.5 µm. The unprotected organic devices suffer from degradation due to water and oxygen incorporation. Therefore, the application of a hydrophobic polytetrafluoroethylene layer as capping layer is studied. Because of the reduced influence of water, a shift to positive threshold voltages is caused. (© 2008 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)

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