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

Paper EM+SS-WeM6
The Influence of Alkyl Side-chains and Charge-Transfer Complex Formation on Sexithiophene/Metal Interface Energetics

Wednesday, November 2, 2005, 10:00 am, Room 309

Session: Contacts to Organic and Molecular Devices
Presenter: S. Duhm, HU-Berlin, Germany
Authors: S. Duhm, HU-Berlin, Germany
H. Glowatzki, HU-Berlin, Germany
R.L. Johnson, Hamburg University, Germany
J.P. Rabe, HU-Berlin, Germany
N. Koch, HU-Berlin, Germany
Correspondent: Click to Email
The energy level alignment at metal/organic interfaces is a key issue for improved performance of novel organic (opto-) electronic devices. In certain cases, solution-based processing of organic materials (i.e., spin-coating, ink-jet printing) is preferred over vacuum sublimation. Frequently, alkyl side-chains are attached to the conjugated moieties for improved solubility. In order to investigate the influence of alkyl side-chain addition on interface energetics, we studied interfaces formed between the organic molecules sexithiophene (6T) and @alpha@,@omega@-dihexylsexithiophene (DH6T) and the metal surfaces Ag(111) and polycrystalline Au with ultraviolet photoelectron spectroscopy (UPS). Samples were prepared by sublimation of the organic substances on clean metal surfaces in ultrahigh vacuum. Interestingly, we observed significantly lower hole injection barriers (0.2 - 0.4 eV) for DH6T on the metal surfaces than for 6T. We propose that the mechanism responsible for our observations is closely related to the "electron push-back effect" at metal/organic interfaces. Furthermore, the influence of molecular orientation will be discussed. Additionally, we demonstrate that the hole injection barrier at interfaces between 6T (DH6T) and metals can be further reduced by the formation of charge transfer complexes comprising tetrafluoro-tetracyanoquinodimethane (F4-TCNQ).