Solar panels and LED lights are both potential applications of perovskites. Credit: mipan/ Stock / Getty Images Plus.
Scientists in Italy have found a way to fine-tune the properties of layered perovskites, a group of crystals that could replace silicon in solar cells, light-emitting diodes (LEDs) and many other applications, provided their behaviour can be made more predictable.
Perovskites are materials named after a mineral discovered in Russia in 1839, with which they all share a basic crystal structure. Those of the ‘two-dimensional layered’ variety, comprising several inorganic and organic layers, are particularly promising for photovoltaic cells and as light sources. The inorganic, semi-conducting part is very efficient at absorbing sunlight and turning it into electricity, and the organic layers offer protection against moisture. They are also easier and cheaper to manufacture than silicon, the current material of choice for solar cells. Their applications could also include LEDs (where they can be used to emit light, rather than absorb it), and sensors and components for robotics.
There are myriad possible ways to make layered perovskites, with different chemical elements for the organic and inorganic parts. Scientists would like to have a manual telling them what is the best choice for each application, and how a change in chemical composition affects the material’s properties.
In a study1 published in Advanced Materials, Milena P. Arciniegas from Istituto Italiano di Tecnologia in Genoa and her colleagues have started writing that manual. They used lead and bromine for the inorganic layer, and tried out various amines (a class of compounds based on nitrogen, hydrogen and carbon) for the organic part. “It is like a millefoglie cake,” Arciniegas says. “The crust layers keep the cake together, and the cream layers give the flavour.” In this case, the cream is the organic layer, and the flavour is the colour of the light emission.
Most known bromine-based perovskites emit blue light, but the researchers thought that by tweaking the way hydrogen atoms in the amines bind to the semiconducting part, it would be possible to get other colours from the same material. “We worked with computational scientists and asked them to help us predict how a change in the anchor site would impact the light emission, and how the length of the molecule would impact the robustness and efficiency of the material,” Arciniegas explains.
They narrowed the search to three families of amines with different hydrogen bonds, and used the results of the simulation to guide laboratory experiments. Eventually, they managed to create a new set of layered perovskites with blue, yellow and white emission. The set was made at room temperature, using relatively simple molecules and environmentally friendly solvents – which bodes well for future manufacturing. “This is an initial step, but it shows a method to make the design of these materials more systematic, and the library of possible compounds to use is huge,” Arciniegas explains. Other organic molecules, for example, would change the way the material conducts electricity, or would make it foldable.
The team plans to explore other materials for the organic part, and to try to replace lead with other non-toxic elements for the inorganic one, while preserving efficiency.
