SL 28


W. Brütting, A. Opitz, M. Bronner

Institute of Physics, University of Augsburg, 86135 Augsburg, Germany (,

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. We will discuss the influence of the preparation conditions and the composition of the blends on film morphology, electronic structure and electrical characteristics. Structural investigations give strong evidence for phase separation on the length scale of a few ten nanometres with percolation pathways for both electrons and holes. By variation of the mixing ratio it is possible to balance the transport of both carrier types. We demonstrate ambipolar and complementary inverters with these materials as a basic constituent of more complex organic electronic circuits [1]. Furthermore, the electronic properties of these blends were analysed by X-ray and ultraviolet photoelectron spectroscopy. The effects of the variation of the C60/CuPc mixing ratio on the electronic properties of the blend system will be discussed with respect to injection barriers and energy-level offsets in related organic devices [2].

[1] A. Opitz, M. Bronner, W. Brütting, J. Appl. Phys. 101, 063709 (2007)
[2] A. Opitz, M. Bronner, W. Brütting, M. Himmerlich, J.A. Schaefer, S. Krischok, Appl. Phys. Lett. 90 (2007), in press