AVS 51st International Symposium
    Organic Films and Devices Wednesday Sessions
       Session OF+EM-WeM

Paper OF+EM-WeM9
Electronic Polarization at the Pentacene - Gold Interface

Wednesday, November 17, 2004, 11:00 am, Room 304C

Session: Molecular and Organic Films and Devices - Electronics
Presenter: F. Amy, Princeton University
Authors: F. Amy, Princeton University
A. Kahn, Princeton University
Correspondent: Click to Email
Pentacene has been successfully used as a high-mobility hole transport material. One of the reasons is that the energy of relaxation of the molecular ion is smaller by at least a factor of two than in other commonly used hole transport materials@footnote 1@. However, the full benefit of this relatively high mobility can be realized only if charge carrier injection is not a significant bottleneck in the device. The pentacene/metal interface energetics are therefore of prime importance. We focus here on the specific issue of polarization and narrowing of the transport gap at the pentacene/Au interface. Tsiper et al.@footnote 2@ have shown both experimentally and theoretically for PTCDA/Au that the polarization induced by an electron (P@sub -@) or a hole (P@sub +@) resident on a molecule at the interface increases by ~0.2 eV with respect to the polarization in the bulk of the film. This increase is due to the large polarizability of the metal substrate and results in a narrowing of the transport gap at the interface. This, in turns, affects the modeling of charge injection at interfaces. In this work, we use ultra-violet and inverse photoemission spectroscopy (UPS, IPES) to measure highest occupied and lowest unoccupied molecular orbitals (HOMO, LUMO) of pentacene as a function of film thickness, from one to ten molecular layers. HOMO and LUMO levels represent the hole and electron transport levels, respectively. We find the increase in polarization at the interface to be in line with that measured on PTCDA. @FootnoteText@ @footnote 1@ N.E. Gruhn, et al. J. Am. Chem. Soc., 124, 7918 (2002)@footnote 2@ E.V. Tsiper, Z. Soos, W. Gao and A. Kahn, Chem. Phys. Lett. 360, 47 (2002) .