Jiuk Jang1 Sangyoon Ji1 Byeong Wan An1 Jang-Ung Park1

1, Ulsan National Institute of Science and Technology, Ulsan, , Korea (the Republic of)

Recently emerging electronic devices, including displays, light-emitting diodes (LEDs), touch screens, smart windows, and heaters requires transparent electrodes with high optical transmittance (T) and low sheet resistance (Rs). Although the indium tin oxide (ITO) shows the excellent electrical and optical properties, its brittleness limits many potential applications in stretchable and wearable electronics. There are numerous studies for high-performance, stretchable and transparent electrode to substitute the ITO-based transparent electrode, however, most of them are virtually unavailable to the industry because of their low production rates, high process temperature and lack of reliability.
Here, we report the rapid electrospinning process that can directly form one-dimensional (1D), ultra-long Ag nanofibers (AgNFs) as a large-area, and continuous network for stretchable, transparent electrodes. The electrospinning process is simple and cost-effective because AgNFs can be formed directly on a substrate while minimizing the waste of functional inks. Since this process is based on a roll collector, it enables the roll-based rapid production of a large-area and transparent electrode film that is composed of AgNF network. In this work, the electrode film exhibits superb electrical characteristics (Rs of ~1.3 ohm/sq) with high optical transmittance of ~90% in a visible regime and outstanding mechanical properties (90% stretchability and minimum bending radius of curvature of 70 um). In addition, the annealing temperature of AgNF network relatively low (< 150 oC), suggesting that the polymer substrate such as polyethylene terephthalate (PET) can be used directly without any transfer process. For a continuous roll-to-roll process, a photonic annealing of functional inks has been utilized and the production speed was 4.5 to 12 m/min. As an application of this high-performance transparent electrode, we fabricated a stretchable and transparent heater in a large area (300 mm x 300 mm) using the roll-to-roll process. The heater presents high temperature (250 oC) at a low operating voltage and excellent temperature reliability under large strain. Furthermore, we integrated the heater with wireless operation system by connecting Bluetooth module so that the temperature is controlled directly using smart devices. According to the target purpose, temperature also can be automatically controlled by applying logic circuit to the micro-controller unit. We believe that this approach presents a promising strategy for future wearable electronic devices.