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 CsYb2F7 is reported, which effectively modulates the reaction rate of Cs+ with lead (Pb2+) 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 CsPbBr3. Moreover, the rigid CsYb2F7 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