Polymer-templated mesoscale assembly directs synthesis of centimetre-scale perovskite single crystals.

The synthesis of high-quality single crystals is essential for revealing intrinsic structure-property relationships, as they provide an ideal model system free from grain boundaries and other extrinsic defects, enabling precise studies of electronic, optical, and charge-transport properties. In metal halide perovskites, an emerging family of semiconductors that have rapidly become a focal point of optoelectronic materials research, single crystal studies provide direct access to intrinsic processes such as defect formation, ion migration, and interfacial behavior. However, producing large, high-quality perovskite single crystals remains challenging because their multicomponent precursor solutions sustain dynamic solvation and coordination equilibria. The coexistence of fast ion dynamics and unstable coordination often drives uncontrolled multi-nucleation and disordered aggregation, making the nucleation stage a critical determinant of final crystal quality. Here, we introduce a general nucleation-control framework that regulates transient precursor species into mesoscale clusters via reversible, non-covalent interactions. Such weak and dynamic interactions provide soft confinement at the pre-nucleation stage, suppress random aggregation, promote selective nucleation, and permit ordered lattice formation without permanent additive incorporation. Implemented through a polymer-templated strategy, the approach enables the formation of centimetre-scale perovskite single crystals within hours and is broadly applicable across various perovskite compositions, demonstrating its universality.