Nanopatterned silver can be fabricated into large-scale transparent conductive electrode films, according to researchers at the University of Southern Denmark. Transparent electrodes are essential components of smart phones, tablet computers and flat panel televisions. The user of silver, which is less brittle and more chemically resistant than current materials, could offer a tougher alternative for use with flexible screens and electronics.
The team reports transparent conducting thin-film electrodes fabricated on 100-millimeter diameter glass discs. [Linnet, J. et al. Opt. Mater. Express (2018) DOI: 10.1364/OME.8.001733] They explain that their theoretical calculations on performance closely match experiment and say that these electrodes might perform significantly better than those used for existing flexible displays and touch screens.
"The approach we used for fabrication is highly reproducible and creates a chemically stable configuration with a tunable tradeoff between transparency and conductive properties," explains Jes Linnet. "This means that if a device needs higher transparency but less conductivity, the film can be made to accommodate by changing the thickness of the film."
Most commercial transparent electrodes use indium tin oxide (ITO), which is up to 92 percent transparent when compared to a sheet of glass. ITO films require careful handling and are brittle and achieving reproducible performance is costly. The anti-corrosive nature of silver and other related metals could offer an alternative to ITO. However, until now high surface roughness in noble metal films has led to low performance because the interface between the film and other layers is not smooth. The team used colloidal lithography to create transparent conductive silver thin films that are sufficiently smooth to be viable. They first created a masking layer by coating a 100-mm wafer with a single layer of evenly sized, close-packed plastic nanoparticles. The particles were then shrunk evenly in a plasma oven. When a thin film of silver is deposited on to the masking layer, the silver enters the spaces between the particles. Finally, the researchers dissolve the particles, leaving a precise pattern of honeycomb-like holes that allow light to pass through, producing an electrically conductive and optically transparent film to 80 percent. Sheet resistance is low at less than 10 ohms "per square". This is about a tenth of what has been reported for carbon-nanotube-based films with similar transparency.
"The most novel aspect of our work is that we accounted for both the transmission properties and the conductance properties of this thin film using theoretical analysis that correlated well with measured results," explains Linnet. "Fabrication problems typically make it hard to get the best theoretical performance from a new material. We decided to report what we encountered experimentally and postulate remedies so that this information could be used in the future to avoid or minimize problems that may affect performance."
David Bradley blogs at Sciencebase Science Blog and tweets @sciencebase, he is author of the popular science book "Deceived Wisdom".