The mechanism of the underpotential electrodeposition of copper indium diselenide (CIS) in the presence of an excess of In3+ was studied. It was found that the value of indium and copper ratio (In/Cu) in the films electrodeposited in the potentials area from -0.2 to -0.6 V (vs. SCE) is independent of the concentration ratio of Cu2+/In3+. At the same time, the concentration of indium in the films obtained is determined both by the deposition potential and the ratio of Se(IV)/Cu2+ in the solution. The proposed model provides the list of the formed compounds as a function of the solution concentration and the applied potential. (c) 2005 Elsevier B.V All rights reserved.