Stretchable Transparent Wireless Charging Coil Fabricated by Negative Transfer Printing

Wearable electronics, such as smartwatches, VR (virtual reality)/AR (augmented reality) smartglasses, and E-textiles, are an emerging technology platform that is reshaping the way people interact with the surrounding world. However, the power source of these devices can be a critical issue, causing short operational/standby times and frequent charging. Here, a stretchable transparent wireless charging coil fabricated by negative adhesive transfer printing (NATP) is demonstrated. The stretchable transparent conductor is based on the silver nanowire (AgNW)-polyurethane acrylate (PUA) composite with high conductivity and robustness under harsh mechanical treatment. A 10.6 ohm/sq thin film has a transmittance of 84% and is still conductive under a mechanical deformation up to 60% tensile strain. A maximum power of 59 mW (power transfer efficiency ∼24%) is transferred wirelessly. A green-light-emitting diode (LED) was wirelessly powered to illustratively demonstrate the functionality of the system. This work provides an alternative power solution which is compatible with the soft and flexible components of wearable devices.