Nano-sized Ag inserted into ITO films prepared by continuous roll-to-roll sputtering for high-performance, flexible, transparent film heaters

We demonstrate high-performance, flexible, transparent film heaters fabricated on a conductive Ag layer inserted into ITO films prepared by pilot-scale roll-to-roll (RTR) sputtering. The RTR sputtered ITO/Ag/ITO (IAI) multilayer on a 700 mm wide PET substrate at room temperature exhibits a high optical transmittance of 88.2% and a very low sheet resistance of 3.0 ohm per square, which are ideal for a low-voltage transparent film heater. The time–temperature profiles and heat distribution analysis demonstrate that the performance of the transparent film heater with the IAI multilayer is superior to that of a film heater with graphene, carbon nanotubes, amorphous ITO, Ag nanowires, or Ag networks, due to its very low sheet resistance (3–17 ohm per square). In particular, the thickness of the Ag interlayer in the IAI multilayer critically impedes the voltage for attaining 100 °C in the transparent film heater because the Ag interlayer provides a main conduction path in the IAI multilayer. In addition, the bending and cycling fatigue tests demonstrate comparable flexibility of the IAI multilayer to other transparent electrodes, indicating the potential of the IAI multilayer as an electrode for a highly flexible film heater. Therefore, the RTR sputtered IAI multilayer is the best substitute for conventional metallic Ag nanowire or ITO film heaters in order to realize a large-area, transparent, flexible film heater that is applicable to flexible and transparent defogging/deicing and heating systems.