AVS 52nd International Symposium
    Electronic Materials and Processing Wednesday Sessions
       Session EM+SS-WeM

Paper EM+SS-WeM1
Energy Level Alignment at Interfaces in Organic Semiconductor Devices

Wednesday, November 2, 2005, 8:20 am, Room 309

Session: Contacts to Organic and Molecular Devices
Presenter: K. Demirkan, University of Delaware
Authors: K. Demirkan, University of Delaware
A. Mathew, University of Delaware
S. Vaidyanathan, University of Delaware
Z.I. Niazimbetova, University of Delaware
H. Christian-Pandya, University of Delaware
M.E. Galvin, University of Delaware
R.L. Opila, University of Delaware
Correspondent: Click to Email
Poly-phenylene vinylene based organic semiconductor polymers and oligomers were studied using X-ray Photoelectron Spectroscopy (XPS) and Ultraviolet Photoelectron spectroscopy (UPS). Valence bands and highest occupied molecular orbitals (HOMOs) (with respect to Fermi level) for these organic structures were determined. Due to the high electron withdrawing property of the oxadiazole moiety, polymers, which have a higher oxadiazole density, are found to have lower energy levels. Using optical absorbance spectra, the lowest unoccupied molecular orbitals (LUMO) for some of the organic semiconductor materials were estimated and the basic energy level diagrams were established with respect to the underlying electrode. The valence band spectra of the polymers spin coated on different substrates did not show any substantial variation except for shifts in the entire spectra. In the Mott-Schottky limit, the energy difference between the electrode Fermi level and the HOMO of the organic layer is expected to follow the work function of the electrode. The interface slope parameter, a measure of the change in HOMO-Fermi level difference as a function of electrode work function, was found to vary between 0.4 and 0.9. These values are intermediate to Mott-Schottky and Fermi level pinning. We will explain the interface slope parameter in light of the interfacial dipole and charge neutrality level at organic/metal interfaces.