Smartphone touch screens and flat panel televisions currently use transparent electrodes to detect touch and to quickly switch the colour of each pixel. As silver is less brittle and more chemically resistant than materials currently used to make these electrodes, the researchers believe these new films could offer a high-performance and long-lasting option for use with flexible screens and electronics.
"The approach we used for fabrication is highly reproducible and creates a chemically stable configuration with a tuneable trade-off between transparency and conductive properties," said the paper's first author, Jes Linnet from the University of Southern Denmark. "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."
The anti-corrosive nature of noble metals such as gold, silver and platinum makes them promising indium tin oxide alternatives (the material most currently used to make transparent electrodes), which must be processed carefully to achieve reproducible performance and are too brittle to use with flexible electronics.
According to the researchers, these noble metal transparent conductive films could be used to create long-lasting, chemically resistant electrodes for flexible substrates. The problem is these types of conductive film suffer from high surface roughness, which can degrade performance because the interface between the film and other layers isn't flat.
Transparent conductive films can also be made using carbon nanotubes, but these films don't currently exhibit high enough conductance for all applications and also tend to suffer from surface roughness due to the nanotubes stacking on top of each other.
To overcome this, the researchers created a masking layer by coating a 10cm wafer with a single layer of evenly sized, close-packed plastic nanoparticles and placed them into a plasma oven to shrink the size of all the particles evenly. When they deposited a thin film of silver onto the masking layer, the silver entered the spaces between the particles. They then dissolved the particles, leaving a precise pattern of honeycomb-like holes that allow light to pass through, producing an electrically conductive and optically transparent film.
The researchers demonstrated that their large-scale fabrication method can be used to create silver transparent electrodes with as much as 80% transmittance, while keeping electrical sheet resistance below 10ohms per square. This is around a tenth of what has been reported for carbon-nanotube-based films with the equivalent transparency. The lower the electrical resistance, the better the electrodes are at conducting an electrical charge.
