Perovskites may sound like perogies or piroshkis, but no high-carb-cheese-and-potato-flavor-pocket can do what they do. They’re minerals that can do the same party trick as many of your favorite childhood toys and models (such as the classic AMT Interplanetary UFO Mystery Ship; oh, how I miss you) and teenage trinkets such as glowsticks and “neon” rave necklaces: that is, they absorb and emit light.
But perovskites emit more of the solar spectrum than does silicon. So much so that scientists at the University of Cambridge have reported that they can now make ultra-thin, stable layers of halide perovskites, thus allowing new ways to create low-cost, high-efficiency lasers, LEDs, solar cells, and even quantum technologies, all without using expensive silicon, the current go-to element for such purposes. Take that, perogies – all you can do is increase my risk of heart attacks.
"The hope was we could grow a perfect perovskite crystal where we change the chemical composition layer by layer, and that's what we did," said co-first author Dr. Yang Lu from Cambridge's Department of Chemical Engineering and Biotechnology and Cavendish Laboratory.
Perovskites are inorganic crystalline structures similar to the natural mineral perovskite (calcium titanium oxide, CaTiO3). Halides are binary compounds of halogens (such as fluoride from fluorine, or chloride from chlorine); they’re the inorganic salts of halogen acids (such as hydrochloric acid).
Previously, scientists faced limits in working with halide perovskites. Light, heat, and moisture make them unstable, and perovskite solar cells generally used lead, famous for causing developmental, neurological, and other damage (and without which, the cells were inefficient).
But now, using a vapor-based technique, co-first author Dr. Yang Lu and colleagues can grow individual 2D and 3D halide perovskite layers so thin they’re on the Angstrom level – that is, a tenth of a nanometer, or a billionth of a meter. Then, having been stacked in layers atop each other so their atoms align perfectly, the layers allow their electrons and holes (the electrons’ positively charged opposites) to move freely, like they’re riding escalators to different floors of a nanoscopic shopping mall, and absorbing or emitting light as they go.
The Cambridge method not only produces better results, but less hassle. "A lot of perovskite research uses solution processing, which is messy and hard to control," says Prof. Sam Stranks, who co-led the research. "By switching to vapor processing – the same method used for standard semiconductors – we can get that same degree of atomic control, but with materials that are much more forgiving."
The breakthrough may allow a production process similar to that used in creating semiconductors, but for manufacturing halide perovskite devices with greater efficiency, durability, and power than their silicon-based predecessors.
“We can now decide what kind of junction we want: one that holds charges together or one that pulls them apart, just by slightly changing the growth conditions,” said Prof. Sir Richard Friend from the Cavendish Laboratory, who co-led the research. “But more importantly, it shows how we can make working semiconductors from perovskites, which could one day revolutionize how we make cheap electronics and solar cells.”
The research was published in the journal Science.
Source: University of Cambridge
