Beyond Nano Building Blocks: The Influence of Mn(II) Doping on 3D Self‐Assembled Perovskite Supercrystals

The controlled assembly of nanocrystals (NCs) in 3D systems is an intriguing strategy to engineer innovative materials with advanced functionalities. Herein, undoped and manganese‐doped cesium lead mixed halide perovskite NCs are organized into ordered superstructures. The synthesis of CsPbCl _x Br _3–x NCs is carried out under mild conditions, achieving nanocubes with tunable composition emission and high quantum yields. Incorporating Mn(II) as a dopant induces the appearance of a red emission band and introduces a morphological diversity at the nanoscale. Well‐faceted micrometer‐sized supercrystals (SCs) on substrates without external templates are fabricated by a slow destabilization approach, based on capillary‐driven assembly in an antisolvent vapor environment. Through comprehensive structural and spectroscopic characterization, remarkable differences between doped and undoped systems are reveled in terms of their assembly behavior, morphology, and optical properties. Confocal microscopy, combined with fluorescence lifetime imaging microscopy, uncovers the unexpected spatial arrangement of emission within these superstructures, while diffraction analysis identifies distinct domains in co‐crystallized supercuboids. These findings provide crucial insights into how dopant incorporation influences the assembly processes and the collective optical behavior in perovskite SCs, establishing a foundation for designing functional NC architectures with tailored properties for next‐generation optoelectronic applications.