The metal - organic semiconductor interface: Dipole and band bending

In recent years there has been growing interest in the field of thin organic films due to their successful application in optical and electronic devices, such as light emitting diodes, solar cells or field effect transistors. The family of the phthalocyanines (PC’s) represents one of the most promising candidates for ordered organic thin films, as these systems possess advantageous attributes such as chemical stability, excellent film growth and electronic properties. The knowledge of barrier heights at interfaces between the electrodes and the active layers is of enormous importance for understanding and improvement of semiconductor devices. Possible processes at inorganic semiconductor/metal interfaces were intensively studied since many years [1]. As schematically depicted in Fig. 1, for these systems the adjustment of equilibrium conditions is connected with a charge transfer across the interface, which leads to interfacial electric dipole layers ∆ and a band bending in the semiconductor. Also at organic semiconductor/metal interfaces the alignment of the Fermi levels (EF) and the possible formation of ∆ have been reported for many cases. However, the size and the nature of ∆ seem to depend on many factors and thus it is very difficult to predict the electronic interface properties from the well-known bulk values. In order to shed more light into the rules of Heiko Peisert, Martin Knupfer, Gernot Paasch, Jörg Fink