Pinning of fullerene lowest unoccupied molecular orbital edge at the interface with standing up copper phthalocyanine

The electronic structure evolution of interfaces of fullerene (C60) with copper phthalocyanine (CuPc) on highly oriented pyrolitic graphite (HOPG) and on native silicon oxide has been investigated with ultra-violet photoemission spectroscopy and inverse photoemission spectroscopy. The lowest unoccupied molecular orbital edge of C60 was found to be pinned at the interface with CuPc on SiO2. A substantial difference in the electron affinity of CuPc on the two substrates was observed as the orientation of CuPc is lying flat on HOPG and standing up on SiO2. The ionization potential and electron affinity of C60 were not affected by the orientation of CuPc due to the spherical symmetry of C60 molecules. We observed band bending in C60 on the standing-up orientation of CuPc molecules, while the energy levels of C60 on the flat lying orientation of CuPc molecules were observed to be flat.

► Orientation of copper phthalocyanine (CuPc) on ordered graphite and silicon oxide.
► Pinning of lowest unoccupied molecular orbital edge of C60 to the Fermi level on CuPc.
► No C60 pinning or band bending was observed on flat laying CuPc.
► Results are useful for organic photovoltaic and organic light emitting diode research.