Effect of insertion of a thin bathocuproine layer at Au/Zn-phthalocyanine interface on energy level alignment and morphology

The effects of the insertion of a thin bathocuproine (BCP) layer at the Au/Zn-phthalocyanine (ZnPc) interface on the energy level alignment and morphology of each layer are investigated using photoelectron spectroscopy, atomic force microscopy and X-ray diffraction. The energy differences between the highest occupied molecular orbital (HOMO) of ZnPc and Fermi level of Au (EFAu) and between the HOMO of BCP and EFAu are about 0.7 eV and 2.4 eV, respectively. The HOMO level of ZnPc on Au is shifted to higher binding energies with increasing ZnPc thickness. The HOMO level of ZnPc on BCP, however, indicates an energy shift in the opposite direction to the lower binding energies as the thickness of ZnPc increases. Atomic force microscopy reveals that the roughness of the ZnPc surface is reduced by the insertion of the BCP layer. X-ray diffraction patterns show that the existence of the thin BCP layer promotes crystallization of ZnPc over the layer and the molecular planes of ZnPc are perpendicular to the BCP surface.