Experimental and numerical investigation of flexibility of ITO electrode for application in flexible electronic devices

For flexible electronic devices, the transparent conductive electrode (TCE) is the most important material for determining the flexibility of devices. Due to the brittleness of the indium tin oxide (ITO) electrode, several alternative TCEs have been developed. However, it is still difficult to successfully achieve quality as good as ITO. In this study, the flexibility of the ITO electrode was investigated with strain and fracture analysis. Effects of thickness of the ITO and the substrate on the flexibility of ITO were investigated by bending tests, numerical simulation and theoretical analysis. Flexibility of ITO electrode can be increased by reducing the thickness of ITO and substrate material. An ITO electrode with a substrate less than 50 μm could be bent to less than 4 mm without failure, and used in flexible electronics. Effects of different substrate materials on the flexibility of ITO were also investigated based on fracture analysis. We investigated the effects of PEDOT [poly(3,4-ethylenedioxythiophene)] as a buffer layer to improve flexibility. Higher flexibility of the ITO/PEDOT hybrid electrode compared to ITO was attributed to the PEDOT layer, which smoothened ITO surface and decreased the density of pinholes or voids of ITO, resulting in higher crack resistance.