In recent years, large progress has been made in the realization of electronic circuits based on organic field-effect transistors (OFETs). However, these circuits as being built-up of unipolar (mostly p-type) OFETs only, have a number of drawbacks. To overcome them, recently, ambipolar OFETs have been suggested as a first step towards complementary organic circuits.
This contribution will analyse the ambipolar charge carrier transport and the interface properties of OFETs using blends of small organic molecules. These mixed layers are prepared by co-evaporation of n-conducting fullerene (C60) and p-conducting copper-phthalocyanine (CuPc) on pre-structured TFT-substrates. The film structure and the morphology were investigated by X-ray diffraction and scanning force microscopy. It was found that the electrical characteristics (e.g. mobilities of holes and electrons and threshold voltages) depend strongly on the composition of the blend and on the preparation conditions like substrate treatment and substrate temperature during evaporation. The results will be discussed with respect to the organic/organic and the organic/insulator interface.
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