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CPP: Fachverband Chemische Physik und Polymerphysik

CPP 41: Organic Photovoltaics III

CPP 41.3: Talk

Friday, March 27, 2009, 11:00–11:15, ZEU 222

Tuning the ionization energy of organic-semiconductor films: The role of intramolecular polar bonds — •Ingo Salzmann¹, Steffen Duhm¹, Georg Heimel¹, Martin Oehzelt², Rolf Kniprath¹, Robert L. Johnson³, Jürgen P. Rabe¹, and Norbert Koch¹ — ¹Institut für Physik, Humboldt-Universität zu Berlin, Berlin, Germany — ²Institut für Experimentalphysik, Johannes Kepler Universität, Linz, Austria — ³Institut für Experimentalphysik, Universität Hamburg, Hamburg, Germany

For the prototypical conjugated organic molecules pentacene and perfluoropentacene, we demonstrate that the surface termination of ordered organic thin films with intramolecular polar bonds (e.g., -H versus -F) can be used to tune the ionization energy. The collective electrostatics of these oriented bonds also explains the pronounced orientation dependence of the ionization energy. Furthermore, mixing of differently terminated molecules on a molecular length scale allows continuously tuning the ionization energy of thin organic films between the limiting values of the two pure materials. Our study shows that surface engineering of organic semiconductors via adjusting the polarity of intramolecular bonds represents a generally viable alternative to the surface modification of substrates to control the energetics at organic/(in)organic interfaces.