AVS 50th International Symposium
    Contacts to Organic Materials Topical Conference Monday Sessions
       Session OM-MoA

Paper OM-MoA7
Electronic Structures of Al/Liq/Alq@sub 3@ Interfaces Studied by Photoemission Spectroscopy

Monday, November 3, 2003, 4:00 pm, Room 318/319

Session: Contacts to Molecules and Molecular Films (II)
Presenter: Y. Park, Korea Research Institute of Standards and Science
Authors: Y. Park, Korea Research Institute of Standards and Science
J. Lee, Samsung Advanced Institute of Technology, Korea
J.W. Choi, KRISS, Korea
M. Han, University of Seoul, Korea
Correspondent: Click to Email
Lithium quinoate (Liq) has recently been attracting a good deal of attention for a cathode interlayer material in organic light-emitting devices (OLEDs)@footnote 1@ as it showed electron injection performance as good as most commonly used LiF. Using X-ray and UV photoemission spectroscopy (XPS & UPS) techniques, we studied the evolution of the electronic structures at Al/Liq/Alq@sub 3@ interface as it is formed in ultrahigh vacuum condition. The valence region spectra taken with UPS showed that the HOMO peaks move to higher binding energy (relative to Fremi level, E@sub F@) as Liq is deposited on Alq@sub 3@. This indicates that the deposition of Liq caused density of states inside the HOMO-LUMO gap although its intensity is too weak to be observed clearly with UPS. The total amount of the peak movement is ~ 1.8 eV comparable to the value for LiF (~1.9 eV). We believe this shift of Fermi level (relative to vacuum level) toward LUMO level is principal cause of the observed improvement in device performance. The evolution of XPS peaks during the interface formation is very similar to the case of LiF and there is no appreciable direct chemical reaction when Liq was initially deposited on Alq@sub 3@. We further discuss the possible origins of the observed HOMO peak movement.