Transparent Film Heaters based on Silver Nanowire Random Networks
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Transparent Film Heaters based on Silver Nanowire Random Networks Jean-Pierre Simonato1, Caroline Celle1, Celine Mayousse1, Alexandre Carella1, Henda Basti1, Alexandre Carpentier1 1 CEA-LITEN / DTNM / LCRE, 17 rue des Martyrs, 38054 Grenoble, France Email: [email protected] ABSTRACT We present the fabrication and characterization of transparent thin film heaters (TTFHs) based on silver nanowires. The goal is to develop a simple process for the production of transparent heating elements by large area printing techniques. The TTFHs are based on recently developed random networks of silver nanowires. Thanks to the very low sheet resistance achievable with silver nanowires, we show that it is possible to obtain high heating rates and good steady state temperatures at low voltages, typically below 12 V. INTRODUCTION Transparent thin film heaters (TTFHs) represent a considerable market for various applications. Defrosting / defogging of car and plane windows is probably the most well known use of TTFHs. Interestingly, defrosting of windows in airplanes was the first application for TTFHs, permitting high-altitude bombing during World War II.[1] Another typical example is for maintaining LCD displays at optimum operating temperatures for screen response, notably for outdoor LCD displays. Up to now transparent conductive oxides (TCOs) have been widely used for this application, notably zinc oxide derivatives and indium tin oxide (ITO). The properties of TCOs are suitable for most application up to now. However many optoelectronic devices are now evolving to flexible substrates. Many functional systems based on bendable substrates have already been described, including thin film solar cells, OLED or LCD displays, touch screens… For all these devices TCOs can not be considered anymore since they are brittle and thus not resistant to mechanical constraints. Furthermore the manufacturing cost is relatively high, and processes based on indium tin oxide (ITO) are somehow risky because the price of indium is particularly fluctuating due to its scarcity, its increasing use and the still insufficient recycling process. Several innovative approaches to obtain flexible TTFHs have been developed these last years, in particular with carbon nanotubes [2-7] and grapheme [8, 9]. Nevertheless the sheet resistivity of the networks made with these materials at high transparency is still too high for low voltage applications. At the same time, new transparent conductors have been realized thanks to metallic nanowires. In particular silver nanowires (Ag NWs) are rather easy to make in large amount from batch solution reactions.[10-14] Performances of Ag NWs for conducting electrons at high transparency are excellent with very low sheet resistances, comparable to those of ITO (< 30 ohm.sq-1).[14-19] We present herein results on new electrothermal film heaters based on random
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Fabrication of random networks of silver nanowires Various techniques can be used to fabricate transparent electrodes including spin-coating, airbrush
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