Putting the strain into engineering a more stable perovskite

Scientists at New York state’s Rensselaer Polytechnic Institute say they have created a more stable halide perovskite using strain engineering. The process refers to technologies used in the semiconductor industry to improve carrier transport, and therefore current drive, in transistors by means of causing mechanical deformation of the material used.

The problem with the halide perovskite the scientists worked on – the α-formamidinium lead iodide known as α-FAPbI₃ – is a tendency of its cubic perovskite lattice to take an hexagonal structure at the room temperatures needed for a PV device to operate properly. “This hexagonal structure cannot respond to most of the frequencies of light in solar radiation and hence is not of interest for technological applications,” wrote the scientists in the paper A structurally unstable semiconductor stabilized and enhanced by strain, published in Nature.

Taking the strain

To stabilize the crystal structure, the researchers used strain engineering to grow crystalline α-FAPbI₃ from a solution so it formed on another, more stable halide perovskite. “The FAPbI₃ atoms in the growing crystal align with the cubic structure of the atoms in the substrate, thereby forming a pseudocubic structure themselves,” stated the paper.

The Rensselaer team said the epitaxial process used to adjust the crystal structure locked it into the pseudocubic form, preventing the hexagonal shape. That was achieved by the strong chemical forces put in motion by the epitaxy. “The pseudocubic structure remains stable for at least a year at room temperature,” the scientists claimed.

The researchers said it was still unclear if their results would find an immediate application in perovskite cell development but added, similar strain engineering techniques could be applied to halide perovskite compounds which have similar atomic arrays to α-FAPbI₃ and which exhibit different technologically important electronic properties.