Mixed organic materials are widely used for ambipolar organic field-effect transistors and photovoltaic cells. One particular material system used in both device types is a blend of n-conducting fullerene (C60) and p-conducting copper-phthalocyanine (CuPc) prepared by co-evaporation.
The electronic properties of these blends were analysed by X-ray and ultraviolet photoelectron spectroscopy in dependence on the mixing ratio. The HOMO levels, the core levels and the vacuum level of the C60/CuPc blends shift linearly with the mixing ratio. Thereby a common vacuum level exists in theses blends, which varies between the values of the neat materials. The HOMO and the core levels show the molecular features and there is no evidence for a charge transfer or a chemical reaction among the materials. 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 the performance of photovoltaic cells and organic field-effect transistors.