A fundamental component of flexible electronic displays is a highly conductive electrode, which supplies electrons to the light-emitting component while at the same time being transparent enough to allow the emitted light to shine through. The material most commonly used for transparent electrodes is indium tin oxide (ITO), but ITO has been around for some time and there is a need for materials that are more suitable for flexible electronics applications. Scientists from the Chinese Academy of Sciences in Fuzhou1 have now demonstrated that embedding a film of silver nanowires in a polymer matrix affords a flexible transparent electrode that rivals the performance of ITO in optoelectronic applications.

Silver nanowire films, together with similar materials like carbon nanotube films, graphene and other metallic nanowire meshes, have previously been considered as candidates to replace ITO. The step forward made by Can-Zhong Lu and his co-workers was the embedding of the film in a polyvinyl alcohol (PVA) matrix, which yields a transparent conductive film that is much smoother that the bare nanowire film and is more resistant to separation from the substrate.

Fig. 1: Photograph of a transparent and conductive film consisting of a silver nanowire film embedded in PVA.From Ref. 1. Reproduced with permission. © 2010 Wiley-VCH Verlag GmbH & Co. KGaA

The team prepared their transparent conductive films by immersing a silver nanowire film in a PVA solution, which filled the pores between the silver wires. Once dried, the surface of the film was many times smoother than that of the of the bare silver nanowire film, with a corresponding improvement in transparency. The polymer–nanowire film not only displayed excellent electrical conduction and optical transmission properties, it could also be folded over several times with very little degradation — an essential feature for flexible electrodes.

To demonstrate the potential of the film in practical applications, Lu and his colleagues tested an organic light-emitting diode (OLED) deposited on one of the films — the OLED had higher power efficiency compared with a similar OLED deposited on a commercial ITO electrode. “Compared with ITO, silver nanowire films can also be easily obtained under mild processing conditions,” says Lu. “Because of their good electrical properties, silver nanowire films could play an important role in organic optoelectronics and will certainly make up a share of the commercial market one day.”