Researchers from Zhejiang University in China and the KTH Royal Institute of Technology in Sweden report that they have fabricated meter-scale transparent conductive circuits based on silver nanowire networks, demonstrated in both rigid and flexible transparent LED screens. The approach, described in The Optical Society journal Optical Materials Express, could help lower the costs of transparent LED screens and allow the technology to be used on substrates that are flexible or curved. Researchers demonstrate rigid and flexible transparent LED screens based on their new silver nanowire transparent conductive circuits. Courtesy of Liu Yang, Zhejiang University. “Transparent LED screens act much like traditional LCDs or LED televisions, but the fact that they don’t block light enables creative applications not possible with conventional display technology,” said Liu Yang, who led the Zhejiang University research team. “The circuits we fabricated are highly transparent, conductive, and flexible, thus are very promising as a replacement for transparent circuits used today.” Traditional methods of creating transparent LED screens, such as using fluorine-doped oxide or indium tin oxide (ITO), tend to be costly and complex, and the results don’t offer the durability for flexible applications. Instead, the researchers developed a method using silver nanowires, which are easily synthesized and distributed over a large area. The material has a high level of clarity and flexibility, and it is highly conductive. The material has been used to create transparent conductive films, but creating long circuits has proved challenging. The researchers’ fabrication process used a spray coating method and sacrificial masks to create a 1.2-m silver nanowire transparent conductive circuit, consisting of randomly distributed silver nanowires that are applied in a pattern to a substrate such as plastic or glass. The network has to be dense enough for the electrical current to travel well, but not so dense as to compromise transparency. Analysis of the silver nanowire circuits showed that they were highly transparent while exhibiting higher conductivity than ITO. The researchers also performed stress tests in which they bent silver nanowire conductive strips and ITO transparent strips deposited on a plastic film to a radius as small as 2 mm. The silver nanowire strip showed mechanical flexibility and stable performance during the bending tests while the ITO strips were unable to maintain performance. The researchers then incorporated the silver nanowire transparent conductive circuits into prototype LED displays with glass or plastic substrates. These included a plastic display that performed well even when wrapped around a small bottle or dynamically bent to a radius as small as about 15 mm. “Because of our very simple and low-cost fabrication method and the inherent flexibility of silver nanowires, these new transparent conductive circuits could lower the cost and expand the applications of the transparent LED screens to flexible and large-angle curved areas,” Yang said. The researchers pointed out that just a few simple steps could turn their prototype screens into practical transparent screens. For example, the transparent conductive circuits could easily be designed to allow programming of connected LEDs for displaying videos. Also, the circuits would need to be protected with a coating to avoid chemical reactions with the environment and to enhance their adhesion to the substrates. The screens could also be integrated with sandwiched glass or transparent plastic films for further protection and easy maintenance. The research was published in Optical Materials Express (www.doi.org/10.1364/OME.9.004483).