Water‐Mediated Ligand Dynamics Enable Solution‐Phase Self‐Assembly of Perovskite Nanocrystals Into 3D Ordered Architectures

ABSTRACT Conventional approaches to perovskite superlattice (SL) synthesis typically involve multi‐step processing with post‐synthetic treatments, which often suffer from limited control, poor reproducibility, and scalability issues. Herein, we report a one‐step solution‐phase protocol for the synthesis of structurally stable, 3D CsPbBr 3 nanocrystal SLs using an amphiphilic double‐tailed ligand (cesium bis(2‐ethylhexyl) sulfosuccinate, Cs‐AOT) in combination with conventional ligands, and precisely controlled amounts of water. This approach enables rapid, spontaneous, and highly uniform SL assembly directly in solution within seconds, without any additional post‐processing. Systematic investigations reveal that isotropic nanocrystal growth and ordered SL formation critically depend on the interplay between ligand–ligand interactions, nanoconfined water, and reverse micelle formation. Molecular dynamics simulations and structural analyses further show that water migration enhances ligand mobility through polarity compensation, thereby strengthening interparticle entanglement and stabilizing the SLs in solution. The as‐synthesized CsPbBr 3 SLs demonstrate exceptional structural stability and enhanced emission properties, thereby enabling practical applications such as high‐performance anti‐counterfeiting optical quick response codes. This work provides fundamental insights into ligand–water interactions governing perovskite SL assembly and offers a scalable synthetic pathway for advanced functional SL materials.