A study of the conjugated Ooct-OPV5 oligomer/gold interface using photoelectron spectroscopy

The electronic structure of the interface between polycrystalline Au and a five-ring n-octyloxy substituted phenylenevinylene oligomer was studied by XPS and UPS, as a model system for the respective polymeric film. High purity oligomer films of up to 25 nm thickness were prepared on the sputter-cleaned metal surface by stepwise evaporation in UHV. The C 1s XPS peak after the first deposition step consisted of three components with binding energies (BE) 288.4, 286.7 and 284.4 eV, the first related to the interface and the latter two to oligomer functional groups. During growth, both C 1s and O 1s in the film exhibited an upward BE shift up to 0.52±0.05 eV, from which the band bending at the interface was evaluated. The UP spectra of the film exhibited characteristic peaks at 2.4 and 3.8 eV (delocalized electrons from π-bands) and at 6.5 and 8.5 eV (electrons in the benzene rings). The work function was ∼4.0±0.1 eV. The HOMO position in the spectrum was used in conjunction with the band bending, in order to yield the band line-up at the interface.