Transparent Conductive Three-Layered Composite Films Based on Carbon Nanotubes with Improved Mechanical Stability
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Transparent Conductive Three-Layered Composite Films Based on Carbon Nanotubes with Improved Mechanical Stability Hans-Christoph Schwarz1, Andreas M. Schneider1, Stephen Klimke1, Bibin T. Anto2, Stefanie Eiden2, Peter Behrens1 1 Institut für Anorganische Chemie, Leibniz Universität Hannover, Callinstr. 9 30167 Hannover, Germany 2 Bayer Technology Services GmbH, 51368 Leverkusen, Germany ABSTRACT A layered composite coating material with favorable properties for application as a transparent conductor is presented. It is composed of layers of three nanoscopic materials, namely zinc oxide nanoparticles, single wall nanotubes, and graphene oxide nanosheets. The electrically conducting layer consists of single wall nanotubes (SWNTs). The layer of zinc oxide nanoparticles acts as a primer. It increases the adhesion and the stability of the films against mechanical stresses. The top layer of graphene oxide enhances the conductivity of such coatings. Such three-layer composite coatings show better conductivity (without compromising transparency) and improved mechanical stability compared to pure SWNT films. The processes used in the preparation of such coatings are easily scalable. INTRODUCTION The development of highly transparent films containing single wall carbon nanotubes (SWNTs) is of large interest as these materials may potentially replace indium tin oxide (ITO) in the field of optoelectronic materials [1]. An additional benefit is the possibility to prepare such films by solution-based processes. Previously, it was shown that the application of a thin layer of highly oxidized graphene oxide nanosheets on such SWNT films results in a distinct increase of conductivity since graphene oxide acts as a p-doping agent [2]. In addition, the transparency of films modified in this way remains nearly constant as compared to pure SWNT films. A serious disadvantage of carbon nanotube films is their poor adhesion on different substrates. We found that films applied on not-pretreated substrates (as glass or foils) may be easily washed off with water or be removed by wiping. This limits the possible application of these materials in technical processes as post-preparation or cleaning steps are restricted. To improve the adhesion and overall mechanical stability of the films, we have introduced a layer of zinc oxide nanoparticles on the substrate which acts as an adhesion promoter for the SWNT layer and does not influence the transparency of the films. Hence, transparent conductive films with increased adhesion and resistance towards water and mechanical stress can be obtained. For such transparent conductive films, we thus propose a three-layered composite material consisting of a primer layer of zinc oxide nanoparticles, a layer of SWNTs and a final layer of graphene oxide nanosheets. Here, we describe the preparation of such constructs using easily scalable spray-coating techniques in all steps. The prepared coatings are characterized by electron microscopy as well as transparency and conductivity measurements. In addition, we a
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