Researchers at the University of Sussex have developed a new way to make smartphone touch screens that are cheaper, less brittle, and more environmentally friendly, using graphene. In addition, the new approach is also said to yield devices that use less energy and are more responsive.
The problem that the team set out to solve was that indium tin oxide, which is currently used to make smartphone screens, is brittle and expensive. The primary constituent, indium, is also a rare metal and is ecologically damaging to extract. Silver, which has been shown to be the best alternative to indium tin oxide, is also expensive. The potential solution by the University of Sussex is to combine silver nanowires with graphene, to create a new hybrid material that matches the performance of the existing technologies at a reduced cost.
In particular, the way in which these materials are assembled is new. By creating a stamp of sorts, the scientists can pick up the graphene and lay it on top of the silver nanowire film in a pattern. The stamp itself is made from poly(dimethyl siloxane) - the same kind of silicone rubber used in kitchen utensils and medical implants. While silver nanowires have been used in touch screens before, no one has tried to combine them with graphene. What’s exciting about what we’re doing is the way we put the graphene layer down. We float the graphene particles on the surface of water, then pick them up with a rubber stamp, a bit like a potato stamp, and lay it on top of the silver nanowire film in whatever pattern we like", the team explained.
The addition of graphene to the silver nanowire network also increases its ability to conduct electricity by around a factor of ten thousand. This means we can use a fraction of the amount of silver to get the same, or better, performance. As a result screens will be more responsive and use less power.
Although silver is also a rare metal, like indium, the amount we need to coat a given area is very small when combined with graphene. Since graphene is produced from natural graphite which is relatively abundant - the cost for making a touch sensor drops dramatically.
It was also stated that one of the issues with using silver is that it tarnishes in air. What we’ve found is that the graphene layer prevents this from happening by stopping contaminants in the air from attacking the silver.... What we’ve also seen is that when we bend the hybrid films repeatedly the electrical properties don’t change, whereas you see a drift in the films without graphene that people have developed previously. This paves the way towards one day developing completely flexible devices.