This paper reports on the use of electrochemical impedance spectroscopy to investigate the electrochemical behavior of spinel CuIn5S8/electrolyte interface. The CuIn5S8 spinel films have been potentiostatically deposited onto indium tin oxide (ITO)-coated glass substrate. CuCl2 and InCl3 mixed solutions with different [Cu]/[In] ratios were used as cation precursor and Na2S2O3 as the anion precursor in acidic solution and at room temperature. The effect of the [Cu]/[In] ratio in the precursor solution on the structural, chemical stoichiometry, and morphological properties of prepared samples, as well as the electrochemical behavior of the CuIn5S8/electrolyte interface was investigated. The electrochemical impedance spectroscopy data have been modeled using an equivalent circuit approach. Several parameters such as, flat-band potential and free carrier concentration were determined by the change in the Mott-Schottky plots. (C) 2014 Elsevier Ltd. All rights reserved.