Regensburg 2007 – wissenschaftliches Programm
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SYOE: Symposium Organic Thin Film Electronics: From Molecular Contacts to Devices
SYOE 8: Poster Session SYOE
SYOE 8.16: Poster
Dienstag, 27. März 2007, 18:00–20:00, Poster B
The effect of fluorination on pentacene/Au interface energetics and charge reorganization energy — •Antje Vollmer1, Steffen Duhm2, Youichi Sakamoto3, Toshiyasu Suzuki3, and Norbert Koch2 — 1BESSY GmbH, Berlin, Germany — 2Humboldt-Universität zu Berlin, Inst. f. Physik, Berlin, Germany — 3Inst. f. Molecular Science, Okazaki, Japan
The energy level alignment between conjugated organic semiconductors and metals is a key factor determining the performance of organic-based electronic devices. Hole injection barriers (HIB) at organic/metal interfaces can be directly determined by ultraviolet photoelectron spectroscopy (UPS), while angle-resolved UPS allows to asses molecular orientations at surfaces. Using these methods we investigated interfaces between two prototypical organic semiconductors, pentacene (PEN) and perfluoropentacene (PFP), and Au(111). PEN and PFP are used in organic field-effect transistors with high hole (PEN) and electron (PFP) mobility. The present AR-UPS study highlights with unprecedented accuracy the effects of perfluoration (of PEN) on the interface energy levels, and of molecular layer thickness on interface energetics. The HIB for the monolayer of each organic material on Au was almost identical, despite the very different ionization energy of PEN and PFP. We also found distinctly different molecular level energies against layer thicknesses, attributed to different polarization energies. UPS for monolayers of the two organic materials corroborated that the charge reorganization energy of PEN/Au(111) is larger than for PEN in the gas phase, and even larger for PFP/Au(111).