As mentioned above, the chemical shifts caused by Vo 2+ , Vo 0 and surface without H adsorption are actually invisible in practical conditions. Investigation of bulk defects show that the widely adopted assignment in defect analysis, which links the commonly observed defect peak by XPS to the most stable defect (Vo) in ZnO, is very likely a misinterpretation. Vo was found to have little effect on the electronic structures of its adjacent O atoms, the origin of the VO signal. As a result, the max. CLS of Vo 2+ and Vo 0 are only 0.59eV and 0.1eV, respectively, which will not show any distinguishable features in the XPS spectrum.