The electronic structures at the interface region between fullerene and dielectric layers were investigated by in situ ultraviolet photoelectron spectroscopy (UPS) and X-ray photoelectron spectroscopy (XPS). The highest occupied molecular orbital (HOMO) onset of the fullerene layer saturates at 1.3 eV below the Fermi level of the SiO2 layer, which was based on the measurement of the sample with a 12.8 nm thick fullerene layer. On the other hand, the HOMO onset was measured at 2.0 eV below the SiON layer Fermi level. The magnitude of the interface dipole and band bending at the interface was determined, and the complete energy level diagrams for fullerene on SiO2 and SiON were evaluated. (C) 2010 Elsevier B.V. All rights reserved.