Berlin 2005 – scientific programme

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SYOO: Organic Optoelectronics and Photonics

SYOO 1: Organic Field-Effect Transistors

SYOO 1.4: Talk

Monday, March 7, 2005, 10:30–10:45, TU C130

Investigation of interface and bulk properties in polymer field effect devices — •Silviu Grecu, Martin Roggenbuck, Andreas Opitz, and Wolfgang Brütting — Experimentalphysik IV, Universität Augsburg, 86135 Augsburg, Germany

The influence of substrate treatment with self-assembled monolayers and polymer film annealing was analysed by electrical and structural measurements on field effect transistors and metal-insulator semiconductor (MIS) diodes using poly(3-hexylthiophene) (P3HT) as a semiconducting polymer and Si/SiO₂ wafers as a substrate.

It is found that surface treatment using silanizing agents like hexamethyldisilazane (HMDS) and octadecyltrichlorosilane (OTS) can increase the field effect mobility by up to a factor of 20, reaching values of about 3×10⁻² cm²/Vs. While there is a clear correlation between the obtained field effect mobility and the contact angle of water on the treated substrates, X-ray diffraction and capacitance measurements on MIS diodes show that structural and electrical properties in the bulk of the P3HT films are not influenced by the surface treatment. Contrarily thermal annealing is found to cause an increase of grain size, bulk relaxation frequency and thereby of the mobility perpendicular to the SiO₂/P3HT interface, but has very little influence on the field effect mobility. In conclusion, our investigations reveal significant differences between interface and bulk properties in polymer field effect devices.