The electrochemical behavior of polycrystalline molybdenum thin films in contact with acidic aqueous solutions containing Cu(II), In(III), and Se(IV) species was investigated. The substrate and solutions are used for the electrodeposition of CuInSe2 films in the field of photovoltaics. The chemical interaction between Mo electrode and the electrolyte at the initial steps of immersion is studied by in situ electrochemical measurements of the time evolution of the open-circuit potential. Ex situ field emission gun-scanning electron microscope observations for morphological investigations, X-ray photoelectron spectroscopy for surface composition, and chemical environment analysis was carried out. Raman spectroscopy, X-ray diffraction, and X-ray fluorescence were also performed. It is shown that molybdenum undergoes electrochemical cementation reactions associated with a characteristic potential increase with immersion time. Immediately after immersion, small nuclei of Cu-Se deposits appear on the surface, which then grow to form a quasi-continuous layer after 400 s. The chemical composition of the layer evolves with immersion time. No indium is incorporated. The global composition changes from a Se/Cu atomic ratio close to 0.3 to a ratio close to 0.7. The final layer contains at least two phases, i.e., umangite Cu3Se2 and CuSe. These complex evolutions are discussed in terms of competing electrochemical reactions and thermodynamic considerations. (c) 2007 The Electrochemical Society.