Electronic properties of organic semiconductor blends: Ambipolar mixtures of phthalocyanine and fullerene

Mixtures of electron and hole transporting 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 and p-conducting copper-phthalocyanine. The electronic properties of these blends were analyzed by x-ray and ultraviolet photoelectron spectroscopy in dependence on the mixing ratio. The energies of the highest occupied molecular orbitals, the core levels, and the vacuum level are found to vary linearly with the mixing ratio. This energy shift is related to a common work function in the molecular blends.