The dependence of aluminum-doped zinc oxide (AZO) work function on surface treatment, i.e. acetone solvent cleaning and ultraviolet (UV)-ozone cleaning, was studied by ultraviolet photoelectron spectroscopy and X-ray photoelectron spectroscopy. Comparing different cleaning methods, UV-ozone treated AZO achieved relative higher work function of 4.26 eV; whereas acetone solvent treated AZO had relative lower work function of 3.94 eV. Two factors, stoichiometry ratio of [O-ZnAl]/[Zn] + 1.5[Al] and carbon contamination on AZO surface, affected the work function and, moreover, the stoichiometry ratio was supposed to be the controlling factor. It was concluded that AZO with high stoichiometry ratio and reduced carbon concentration possessed high work function. (C) 2010 Elsevier B.V. All rights reserved.