Electrochemically assisted deposition as a new route to transparent conductive indium tin oxide films

Tin-doped indium oxide (ITO) films with Sn/In atomic ratios in the range 0-0.1 were synthesized by electrochemically assisted deposition (EAD). The process involves a fast one-step cathodic deposition of a highly crystalline In-Sn hydroxide (InSnOH) film followed by thermal conversion into ITO at 300 °C. The cathodic precipitation of InSnOH is preceded by formation of an In-Sn complex in solution. The films were characterized by field emission scanning electron microscopy, X-ray photoelectron spectroscopy, X-ray diffraction, UV-visible spectroscopy, and electrical measurements. In the Sn/In atomic ratio range 0-0.1, InSnOH and ITO films adopt the morphologies and cubic crystal structures of In(OH)₃ and In₂O₃, respectively. The atomic environment of Sn and O atoms in the ITO films was shown to resemble that of films deposited by other techniques and commercial ITO samples made by chemical vapor deposition. Separate tin oxide/hydroxide phases were not observed by any of the characterization methods. The morphology of the EAD ITO films consists of submicrometer-size bundles of parallel thin nanorods as the major structural blocks. The orientation of these bundles strongly affects the electronic conductivity of the film. The resistance of the EAD ITO films decreases by more than 2 orders of magnitude as the Sn/In atomic ratio increases from 0 to 0.1. After heating in air at 600 °C, 200-300 nm thick EAD ITO films show visible transmission of about 84% and resistivity on the order of 10^-1 Ω cm.