Promoted Growth and Multiband Emission in Heterostructured Perovskites Through Cs+‐Sublattice Interaction

Abstract Precise control of exciton confinement in metal halide perovskites is critical to the development of high‐performance, stable optoelectronic devices. A significant hurdle is the swift completion of ionic metathesis reactions, often within seconds, making consistent control challenging. Herein, the introduction of different steric hindrances in a Cs + sublattice within CsYb 2 F 7 is reported, which effectively modulates the reaction rate of Cs + with lead (Pb 2+ ) and halide ions in solution, extending the synthesis time for perovskite nanostructures to tens of minutes. Importantly, the Cs + sublattice provides a crystal facet‐dependent preference for perovskite growth and thus exciton confinement, allowing the simultaneous occurrence of up to six emission bands of CsPbBr 3 . Moreover, the rigid CsYb 2 F 7 nano template offers high activation energy and enhances the stability of the resulting perovskite nanostructures. This methodology provides a versatile approach to synthesizing functional heterostructures. Its robustness is demonstrated by in‐situ growth of perovskite nanostructures on Cs + ‐mediated metal‐organic frameworks.