This study shows the results attained during the electrodeposition of Cu 2 O films on fluorine-doped tin oxide (FTO) substrate from a dimethyl sulfoxide (DMSO) solution in the presence of chloride ions. Before the film electrodeposition and in order to establish the best conditions for the Cu 2 O electrodeposition, a detailed electrochemical study of the precursors in the presence of chloride ions was performed. The voltammetric profiles obtained show significant differences compared to those previously obtained during the study of the Cu 2 O electrodeposition from a free-chloride DMSO solution. These differences are the result of the coordination complexes formation between chloride ions and the different copper species in solution. The films were potentiostatically electrodeposited between -1.4 V and -1.6 V vs Ag/AgCl (sat) reference electrode. Then, these films were characterized through different techniques: X-ray diffraction, scanning electron microscopy, optical characterization, and capacitance measurements through electrochemical impedance spectroscopy.Keywords: Cu 2 O, Electrodeposition, DMSO solution, Chloride effect.
INTRODUCTIONPhotovoltaic devices based on metal oxide semiconductors have being a matter of great interest, because to their chemical stability. This way, due to its properties (p-type semiconductor, direct band gap of 2.0 -2.2 eV) Cu 2 O has been considered an excellent material that can be employed in photovoltaic cells based on p-n junction thin films. Furthermore, Cu 2 O is made up of abundant non-toxic elements, which allows it to become a low-cost material 1 .Cu 2 O thin films have been prepared through the use of different techniques such as magnetron sputtering 2-3 , chemical vapor deposition 4-5 , thermal oxidation 6 , and chemical reduction 7 . Electrochemical techniques are easy and inexpensive methods for Cu 2 O thin films formation. Copper sulfate in the presence of lactic acid / lactate aqueous solution is usually the most used electrolyte for the electrodeposition of Cu 2 O thin film on different substrates [8][9][10] . However, this research group has recently verified that the electrodeposition of Cu 2 O thin films can be carried out from a dimethyl sulfoxide (DMSO) solution, using CuClO 4 and molecular oxygen as precursors 11 . These films were p-type semiconductors with an optical band gap that varied between 2.18 eV -2.25 eV with a doping level between 8.2 x 10 18 cm -3 -2.0 x 10 19 cm -3 , depending on the electrodeposition temperature. On the other hand, it is a well known fact that during the electrodeposition process, the addition of complexing agents produces drastic changes in the morphology and properties of semiconductor materials 12-13 and metals [14][15] . This way, the influence of chloride ions as a complexing agent during the Cu 2 O electrodeposition process from a DMSO solution is analyzed in this article. The results were then compared with those obtained in the absence of chloride ions. The films were smoother than those obtained in the absence ...