In the fabrication process, the researchers use lithography to etch a mask pattern on a substrate of hybrid perovskite bulk crystal. The design of the mask provides a visible process to control the growth of the ultra-thin crystal film formation. This single-crystal layer is then peeled off the bulk crystal substrate, and transferred to an arbitrary substrate while maintaining its form and adhesion to the substrate. A lead-tin mixture with gradually changing composition is applied to the growth solution, creating a continuously graded electronic bandgap of the single-crystal thin film.
The perovskite resides at the neutral mechanical plane sandwiched between two layers of materials, allowing the thin film to bend. This flexibility allows the single-crystal film to be incorporated into high-efficient flexible thin film solar cells, and into wearable devices, contributing toward the goal of battery-free wireless control.
Their method allows researchers to fabricate single-crystal thin films up to 5.5 cm by 5.5 cm squares, while having control over the thickness of the single-crystal perovskite--ranging from 600 nanometers to 100 microns--as well as the composition gradient in the thickness direction.
"Further simplifying the fabrication process and improving the transfer yield are urgent issues we're working on," said Xu. "Alternatively, if we can replace the pattern mask with functional carrier transport layers to avoid the transfer step, the whole fabrication yield can be largely improved."
Instead of working to find chemical agents to stabilize the use of polycrystalline perovskites, this study demonstrates that it's possible to make stable