Effects of annealing temperature and hard coating layer on mechanical flexibility of indium tin oxide electrode

For flexible electronics, the application of the indium tin oxide (ITO) electrode was limited due to the brittleness of the ITO. Several alternative flexible electrodes have been developed, but it is still difficult to successfully achieve high quality as good as ITO. In this study, we investigated the effects of the annealing temperature and the hard coating (HC) layer on flexibility of the ITO films. The flexibility of ITO films on the polyethylene terephthalate (PET) were investigated by the bending and fragmentation tests. As the annealing temperature increased, the bendability of the film generally increased due to the internal compressive stress of the film induced during annealing process. The ITO with the HC layer exhibited a lower bendability than ITO without the HC layer due to the brittle HC layer. On the other hand, the fragmentation tests indicated the existence of white spots or defects, which are the filler materials on PET, decreased the stretchability and adhesion strength of the ITO film. Addition of the HC layer on PET substrate is indispensable. However, development of a softer and more durable HC layer is required for the flexible ITO electrode.