Highly flexible and transparent film heater with electrospun copper conductive network via junction-free structure

Abstract

Flexible transparent film heaters (FTHs) are used in a variety of applications, including smart windows and wearable devices, because they are transparent to visible light while generating Joule heat. FTHs are designed for high transparency and conductivity, with thermal stability and mechanical durability as secondary requirements. In general, there is a trade-off between transparency and conductivity, such that both factors must be optimized simultaneously to maximize performance. In this study, a conductive nanofiber network was fabricated on a flexible substrate via electrospinning. Copper (Cu) heaters were materialized on the nanofiber network via electroless deposition. Overlap between nanofibers was removed by heat treatment, resulting in a junction-free Cu nanofiber network without contact resistance. The properties of these FTHs could be actively controlled by optimizing the electrospinning and electroless deposition times, yielding a transparency of more than 90% and sheet resistance (R-s) of several Omega/sq. As heaters, the optimized FTHs exhibited a uniform temperature distribution over their entire area, even when an external force was applied. The FTH fabrication method developed herein was based on direct electrospinning patterning and did not require any lift-off or transfer processes, which can result in defects. In addition, since electroless deposition has a low process complexity, it can be used in large-area processes and easily extended to fundamental technologies in various fields. (C) 2021 Elsevier B.V. All rights reserved.