Regensburg 2004 – wissenschaftliches Programm
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SYOH: Organic and Hybrid Systems for Future Electronics
SYOH 5: Poster
SYOH 5.30: Poster
Donnerstag, 11. März 2004, 18:00–21:00, B
Direct and inverse photoemission spectroscopy on organic semiconductors in the pristine and reduced state — •Torsten Schwieger1, Martin Knupfer1, Weiying Gao2, and Antoine Kahn2 — 1Leibniz Institute for Solid State and Materials Research Dresden, D-01069 Dresden, Germany — 2Department of Electrical Engineering, Princeton University, Princeton, NJ 08544, USA
Phthalocyanines and α-NPD are organic semiconductors which are
commonly used in organic electronic devices like transistors and diodes.
We intercalated the organic semiconducting film with potassium in order to
investigate the impact of negative charge to the electronic structure of
the organic system. A combined direct and inverse photoemission
spectroscopy study of the occupied and unoccupied states of the organic
semiconductors ZnPc and α-NPD in the pristine and K-intercalated
state is presented. A combination of PES and IPES allows the determination
of the transport gap in organic materials both in the undoped and doped
state. The observed splitting of the lowest unoccupied molecular orbitals
upon potassium intercalation leads to an evaluation of the size of
correlation effects in both molecular systems. These effects are discussed
in detail.
As expected, the Fermi level is found to shift towards the vacuum level
upon intercalation. However, the results clearly demonstrate that the
Fermi level in potassium intercalated organic semiconductors cannot a
priori be assumed to be pinned at the onset of the lowest unoccupied
molecular orbital in all cases.