SINCE 2006, when Corning, an American glassmaker, developed Gorilla Glass to give Apple’s first iPhone a scratch-resistance screen, many other types of toughened glass have appeared for use in handsets. But as rugged as they are, people keep cracking and breaking them. Jingwei Hou thinks he has found a way to prevent that.
Dr Hou and his colleagues at the University of Queensland, in Australia, are among a number of researchers working on a group of materials called perovskites. The original perovskite, calcium titanium oxide, is a mineral (see picture) discovered in the Ural mountains in 1839 and named after Count Lev Perovski, a Russian mineralogist. Since then, the name has come to be used for a number of materials that share a similar crystal structure.
Much of the interest in perovskites comes because those which combine metal atoms with chlorine, bromine or iodine (members of a group of elements called halogens) are semiconductors. This makes them potentially useful in a variety of electronics. In particular, one promising feature of metal halides is that they can be used to make new types of solar cells which are more efficient at converting sunlight into electricity than the silicon-based cells currently employed. Oxford PV, a British company, is bringing some of the first perovskite solar cells to market.
However, what works in one direction will often work in the other, and so it is with perovskites. This means that instead of converting sunlight into electricity, metal-halide perovskites can operate in reverse, by emitting light in response to an electric charge. An array of tiny specks of perovskites could therefore work like a grid of LEDs in a display screen.
To produce such screens, Dr Hou and his team developed a way to bind tiny “nanocrystals” of lead-halide perovskites into a specially treated synthetic glass composite. As these nanocrystals are extremely sensitive, and decay rapidly if exposed to moisture in the air, being bound up in the glass protects them. It also prevents lead ions, which are toxic, leaching out of the material. At the end of their lives, the screens would be recyclable.
A study Dr Hou carried out in collaboration with teams from Britain and France, which was published recently in Science, showed that perovskite screens made in this way were efficient light emitters able to produce sharp, bright images. The light could also be tuned to different colours by altering the nanocrystals’ characteristics.
An added bonus was that the screens were extremely tough, because of the way the nanocrystals bonded with the glass. That was helped by the mechanical structure of the glass (known technically as a zeolitic imidazolate framework) having a spongelike atomic structure. This provides a degree of flexibility, thus avoiding breakage problems caused by brittleness.
In as much as anything can be considered unbreakable, perovskite screens just might be that, reckons Dr Hou—and they might be used not just for phones, but also for products ranging from televisions and computers to lighting. But he does think it could take five to ten years of development before this will happen. In the meantime, people should take a bit more care with the screens on their devices.