Rapid production of large-area, transparent and stretchable electrodes using metal nanofibers as wirelessly operated wearable heaters

Abstract

A rapidly growing interest in wearable electronics has led to the development of stretchable and transparent heating films that can replace the conventional brittle and opaque heaters. Herein, we describe the rapid production of large-area, stretchable and transparent electrodes using electrospun ultra-long metal nanofibers (mNFs) and demonstrate their potential use as wirelessly operated wearable heaters. These mNF networks provide excellent optoelectronic properties (sheet resistance of ~1.3 Ω per sq with an optical transmittance of ~90%) and mechanical reliability (90% stretchability). The optoelectronic properties can be controlled by adjusting the area fraction of the mNF networks, which also enables the modulation of the power consumption of the heater. For example, the low sheet resistance of the heater presents an outstanding power efficiency of 0.65 W cm−2 (with the temperature reaching 250 °C at a low DC voltage of 4.5 V), which is ~10 times better than the properties of conventional indium tin oxide-based heaters. Furthermore, we demonstrate the wireless fine control of the temperature of the heating film using Bluetooth smart devices, which suggests substantial promise for the application of this heating film in next-generation wearable electronics. A quick method to make a large-area, stretchable and transparent electrode for wearable electronics has been developed by a team in Korea. Materials that are both transparent and conducting are useful for many optoelectronic applications. Indium tin oxide is a common choice, but it lacks the flexibility required for wearable technologies. Jang-Ung Park and co-workers from the Ulsan National Institute of Science and Technology spun long metal nanofibers to create a wearable heater that can operate wirelessly. They form a conductive random network of silver nanofibers as a random network on a flexible and stretchable substrate. The high thermal conductivity of silver means a current passing through the nanofiber can quickly attain a temperature of 250 degrees Celsius on a polyimide sheet. The stretchable and transparent, large-area electrode using electrospun, ultra-long metal nanofibers (mNFs) shows excellent optoelectronic and mechanical properties. It is mass-producible because of the roll-to-roll process and its fast production speed. The optoelectronic properties can be controlled by adjusting area fraction of mNF network. The large-area heater based on the mNF network exhibits outstanding power efficiency and mechanical reliability. The wireless operation of the wearable heater using Bluetooth is demonstrated.