Ionization potential dependent air exposure effect on the MoO 3/organic interface energy level alignment

Abstract

We reported an ionization potential (IP) dependent air exposure effect on the MoO3/organic interface energy level alignment by carrying out in situ ultraviolet photoelectron spectroscopy and synchrotron light based X-ray photoelectron spectroscopy investigations. The electronic structures at MoO 3/organic interfaces comprising various π-conjugated small organic molecules with different IP on MoO3 substrate have been systematically investigated. For the molecules with low IP, MoO 3/organic interface electronic structures remained almost unchanged after air exposure. In contrast, for the molecules with high IP, the highest occupied molecular orbital (HOMO) leading edge (or hole injection barrier) increases gradually with the increasing molecule IP after air exposure. For the MoO3/copper-hexadecafluorophthalocyanine (F16CuPc, IP: ∼6.58 eV) interface, air exposure can induce a significant downward shift of the HOMO level as large as ∼0.80 eV. © 2012 Elsevier B.V. All rights reserved.