ABSTRACT
Norbert Koch and Gunther Leising Institute of Nanostructured Materials and Photonics, Joanneum Research Forschungs GmbH, Weiz, Austria
Aparna Rajagopal Rutgers University, Piscataway, New Jersey
Jean-Jacques Pireaux Facultes Universitaires Notre-Dame de la Paix, Namur, Belgium
I. INTRODUCTION
The possible interactions between conjugated organic materials (COM) and metals cover the whole range from physisorption to covalent bonding and charge transfer in terms of ionic bonding. This makes it virtually impossible to predict a certain energy level alignment at a given interface, based on individually determined materials properties such as metal work function, ionization potential, and electron affinity. Without doubt, investigations on the electronic properties at metal-organic interfaces with photoemission spectroscopy (PES) techniques can provide the information required for a better understanding of the nature of the interaction and the energy level alignment, which determine to a large extent the stability and performance of organic light-emitting devices, photovoltaic cells, or field effect transistors. As will be outlined below, great care must be taken when employing PES on COMs. Often, concepts valid for inorganic semiconductors are not appropriate for these organic materials.
