Ito Film In The Electrochemical Behavior Of The Solution Study

Indium Tin Oxides (ITO) are optoelectronic materials that are are both transparent to visible light and electrically conductive. Since the advent of more than fifty years, ITO films have been widely used in the fields of flat panel display, solar cells, anti-frost glass, gas sensing devices, energy saving window, aeronautics and astronautics etc. In addtion, ITO films have a broad application as transparent electrodes for electrochemical deposition, with which transmission spectrums of reactants could be obtained after deposition. In these applications, the electrochemical stabilities become a very significant scientific issue. In this paper, the electrochemical corrosion behaviors of ITO films during anodic and cathodic polarizations were investigated in sodium hydroxide solutions. The impacts of reaction parameters on the corrosion rate and extent, and the particular steps of corrosion were obtained. The results are as follows:1. ITO films remain stable after anodic polarization (1.5 V vs. saturated calomel electrode (SCE)). In contrast, serious corrosion occurs at cathodic polarization (-1.5 V (vs SCE)). Optical transmittance decreased greatly and sheet resistance increased by an order of magnitude. Some of In³⁺ ions in the ITO is reduced to metallic In attached to the surface. The chemical reaction equations are,Anode reaction: In₂O₃+3H₂O+6eâ†'2In + 6OH^-Cathode reaction: 4OH^-â†'O₂(g)+2H₂O+4e2.As increases of the polarization voltage, pH value of the solutions and the concentration of Cl-, both the rate and the extent of the corrosion are enhanced.3.Electrochemical impedance spectrums and their equivalent circuits of ITO film electrode are obtained. The parameters of equivalent circuit elements at different steps of the corrosion are calculated. With huge transfer resistance of solid-liquid interface between original ITO films and solutions, it decreases a lot during the corrosion process.That's because the surface area of ITO electrode increases and metallic In is generated and absorbed to the surface, which makes original semiconductor-solution interface become to be metal-solution one. It is also concluded that corrosion reactions occur and develop at the grain boundaries in the start, and the time when the electrode surface is all covered by both crystal and amorphous metallic In is the end of corrosion reaction.