Controlling the electrical, optical, and morphological properties of sol–gel spin-coated indium tin oxide films

In this research, transparent conductive films of indium tin oxide (ITO) were deposited by solution processing sol–gel ink through spin coating on soda-lime glass and sheet glass substrates. The processing parameters evaluated include the deposition humidity, spin coating speed, and ink concentration. The optical transmittance of the ITO thin films was collected by UV–vis spectrophotometry, while the electrical properties were studied by sheet resistance measurements and impedance spectroscopy (IS) using an in-plane configuration. The lowest sheet resistance achieved for a single layer film is 104 Ω/□, with a corresponding low frequency impedance magnitude of 2 × 105. These values were obtained at medium humidity values while maintaining high optical transparency (>90%) in the visible light region. High humidity values were found to affect the substrate wetting property of the ITO ink and increased the possibility of hydrolysis during deposition, resulting in the formation of non-uniform surface patterns. A spin coating speed of 4000 rpm or more is required to obtain a uniform ITO film with desirable electrical and optical properties. Once the optimum combination of parameters is obtained, the sheet resistance and impedance magnitude can be reduced to ∼102 Ω/□ through multilayer deposition and annealing in a reducing atmosphere with minimal effect on the optical transmittance (>90%) and surface morphology, making these materials useful as electrodes for electro-optic applications. When the optimal values of the main deposition parameters are used, the ink concentration was found to have minimal effect on the quality and properties of the ITO films.