The preparation method used by the researchers is called "solution-based lithography-assisted epitaxial-growth-and-transfer". Specifically, a perovskite crystal (for example, MAPbI3) is used as a substrate, and a layer of polymer film (for example, Parylene) patterned by an imprinting method is covered on it as a mask for controlling crystal growth. Then use the epitaxy method to grow a new perovskite single crystal in the solution. The crystal will slowly "grow up" and expand above the mask, and finally connect into a single crystal film without grain boundaries. Subsequently, the grown perovskite single crystal film can be peeled off and then transferred to any other substrate. Tests such as XRD and photoluminescence spectroscopy show that the transferred single crystal film can maintain good crystallinity, have fewer surface defects, and can adhere well to the substrate. By controlling the film thickness, the mechanical properties of the single crystal perovskite film can also be adjusted. The single crystal perovskite film is sandwiched between two layers of polymer materials, and it can be bent to a certain extent. A thin film with a smaller thickness has a smaller bending radius, which indicates that this brittle crystal has significant flexibility. Although the flexibility of single-crystal perovskite films is not particularly good, there is already hope for applications in high-efficiency flexible thin-film solar cells and wearable devices.
Modern electronic products, such as mobile phones, computers and even satellites, are based on single crystal films made of materials such as silicon, gallium nitride and gallium arsenide. Single crystals have fewer defects and better electronic transmission performance, which further simplifies the manufacturing process and Improving the transfer yield is a problem they are trying to solve. If we can replace the patterned mask with a functional carrier transport layer to avoid the transfer step, the productivity of the entire process can be greatly improved.