Researchers from KU Leuven from the Roeffaers Lab and the Hofkens Group have discovered a new way to create the sought-after dark alpha-phase perovskite. They used direct laser writing (tuned intense laser light) to locally heat the perovskite surface, making it change from the (useless) delta state to the (highly desirable) alpha state.
Furthermore, they also found that the material now remained in this state for many weeks, even at room temperature, without further need of a stabilizing treatment. The scientists further managed to use the laser beam to rapidly micro-fabricate complex patterns of the dark FAPbI3 state. "These findings are a big step forward in locally tailoring the structural, electrical, and optical properties of an important new class of materials and provides an avenue for making customised optical devices, all on demand".
This work pertains to one of the challenges that remain to be resolved regarding the stability of perovskite crystals under real-world conditions. At room temperature, certain perovskite materials arrange themselves in the yellow-colored delta phase, with little practical value for technological applications. But when heated above 150° C, the material rearranges itself into a different black structure, called the alpha state, before reverting to the delta phase after a few days under ambient conditions. It is usually this dark alpha state that is most interesting for researchers and technology.