Transparent film heaters with highly enhanced thermal efficiency using silver nanowires and metal/metal-oxide blankets

Abstract

For the last few decades, flexible transparent conductive materials (f-TCM) have garnered great attention as electrodes, an essential component of flexible optoelectronic devices such as organic light-emitting diodes (OLED) and solar cells. In addition to the optoelectronic devices, a transparent film heater (TFH) is also an important application of f-TCMs. The latter uses Joule heating to increase the temperature of a system under a fixed voltage drop (ϕ), while the former uses or produces an electric current. In this study, we developed flexible TFHs (f-TFHs) based on hybrid films of Ag nanowire networks (AgNWs) with metals or metal oxides. AgNWs were formed on polyimide (PI) substrates by spin coating, and Ag nanoparticles (AgNPs) and indium tin oxide (ITO) were deposited atop and between the AgNWs by spin-coating and DC magnetron sputtering, respectively. According to our experimental results, the hybrid films have lower sheet resistance (Rs) and enhanced mechanical reliability compared to bare AgNWs on PI. The matrix AgNPs and ITO not only act as an insulating film that holds the heat generated from the AgNWs but also form the heater itself. At a fixed ϕ up to a certain limit, a higher temperature and more uniform heating were attained in the hybrid TFHs compared to the AgNWs. However, the operation of the TFHs of the AgNWs and the hybrid of AgNWs with AgNPs failed over the limit ϕ because local melting of the AgNWs occurred in and adjacent to the center of the TFHs.