X-ray photoelectron spectroscopy was used to investigate the valence-band offsets (VBOs) of the Cu2O-ZnO heterojunctions fabricated by magnetron sputtering. A significant forward-backward asymmetry was observed in the band alignments of Cu2O/ZnO-ZnO/Cu2O heterojunctions. The valence band offsets of 2.91 eV and 2.52 eV were achieved in Cu 2O/ZnO and ZnO/Cu2O heterojunctions respectively. The asymmetry was attributed to the lattice distortion of the Cu2O at the interface of Cu2O/ZnO heterojunction. The compressed Cu2O lattices lead to the upward shift of the top of the valence-band of Cu 2O;
and thus the measured VBO of Cu2O/ZnO is larger than that of ZnO/Cu2O. Considering the band alignments;
the ZnO/Cu 2O structure is expected to have more advantage in photovoltaic application than Cu2O/ZnO structure. © 2013 Elsevier B.V. All rights reserved;