Fully Solution-Based AgNW/AlOx Nanocomposites for Stable Transparent Heaters

Abstract

Transparent heaters (TH) have a lot of potential in flexible and wearable applications. Consequently, interest in using nanomaterials, such as metallic networks, grids, and meshes, has expanded as an alternative to conventional transparent conductive oxides like indium tin oxide. In particular, silver nanowire (AgNW) networks are very promising transparent and flexible electrodes thanks to their optimum physical properties and the possibility to obtain them by low-cost fabrication techniques. However, AgNW networks suffer from instabilities that affect their electrical performance at high operating voltages or over time and thus require a protective layer, often deposited by vacuum-based techniques. In this work, we implemented a low-cost solution-based aluminum oxide (AlOx) coating produced by combustion synthesis to encapsulate spray-coated AgNW networks. The TH with an AlOx coating obtained from a 0.4 M precursor solution concentration presents the best compromise between optical transmittance and electrical resistance. Besides this, such a coating provides a robust protection against corrosion under accelerated environmental stress (relative humidity = 80%; temperature = 70 °C) up to 7 days. As a proof-of-concept, a 50 × 50 mm2 TH was fabricated and tested as a defroster (down to −21 °C) showing a highly reproducible heating performance (up to 90 °C at 6 V) and stability for 12 h. In addition, different morphologies of the AlOx thin film, namely smooth or porous, can be obtained when either conventional thermal annealing or Joule heating of AgNWs is used, respectively, to carry out the combustion reaction. This offers a promising tunability for different final applications.