α-CsPbI₃ Nanocrystals by Ultraviolet Light-Driven Oriented Attachment

Size and crystallinity of building units in the perovskite layer are of great significance to photovoltaic performance. Thus, to fabricate large-grain-size perovskite materials with the advantage of good crystallinity is quite necessary. The oriented attachment strategy has been proofed as an efficient method to control crystal growth. Herein, we reported on oriented attachment of α-CsPbI₃ quantum dots (QDs) into a large-grain-size nanocrystal under moderate ultraviolet (UV) light. By virtue of atomic-resolution TEM and X-ray absorption fine structure (XAFS) spectroscopy, we observed the UV-directed structure-evolution and growth process. This is trigged by UV-light illumination (7 W, 365 nm), which drives the oriented assembly of QDs into a large nanoparticle along {110} facets. Moreover, we also visualized a damage process of the α-CsPbI₃ QDs to photoinactive-Î-phase ones and finally into PbI₂ under high-power UV-light (100 W, 365 nm) exposure. The findings provide a prototype for fabricating large-size perovskite nanostructures with promising properties.