Thickness Effects on the Thermal Expansion Coefficient of ITO/PET Film

Abstract

Indium Tin Oxide/Polyethylene Terephthalate(ITO/PET) thin film/flexible substrate have found many applications in dye sensitized solar cells, touch screens, energy efficient windows, etc. In this study, application of the digital image correlation method (DIC) for determining the coefficient of thermal expansion (CTE) of (ITO/PET) thin film was proposed and the effects of thickness variations of ITO and PET, respectively, on the CTE of the specimens were discussed. The observation range of experimental temperature was chosen from room temperature to the glass transition temperature of PET, 70°C. A novel DIC experimental process for reducing the errors caused from the variations of the refractive index of the surrounding heated air was proposed. As a result, the experimental error of CTE measurement was reduced from 15% ~ 23% to less than 4%. The experimental results showed that the CTE of ITO/PET specimen is anisotropic. Furthermore, the CTE of an ITO/PET specimen will be increased by decreasing the thickness of PET flexible substrate, and increased by increasing the thickness of ITO film – which means decreasing the surface resistance of ITO film.