Tuning Perovskite Nanocrystal Synthesis via Amphiphilic Block Copolymer Templates and Solvent Interactions.

Amphiphilic block copolymer (a-BCP) micelles offer morphological diversity and dimensional tunability, making them suitable for the fabrication of perovskite nanocrystals. However, precise control over the nucleation and growth of perovskite nanocrystals using a-BCP colloidal templates remains underexplored. This study investigates the effects of toluene, methanol, and polystyrene--poly(2-vinylpyridine) (PS--P2VP) on the formation of cesium lead bromide (CsPbBr) nanocrystals. The process involves four stages: (i) PS--P2VP micellization, (ii) PbBr complexation, (iii) coordination interaction with P2VP, and (iv) burst nucleation of CsPbBr nanocrystals. Toluene, a good solvent for PS but a nonsolvent for P2VP, PbBr, and CsBr, facilitates the formation of PS--P2VP spherical micelles. Adding PbBr to these micelles in toluene results in multiple emulsion, dispersing PbBr microstructures (microemulsion) and forming [PbBr] complexes encapsulated by the micelles (nanoemulsion). Prolonged stirring enhances this nanoemulsion. CsBr, insoluble in toluene, must be dissolved in methanol before being mixed with micelle-encapsulated complexes, promoting quick crystal nucleation. However, excess methanol weakens micellization, leading to the formation of fused micelles and irregular nanocrystals. At a high methanol content, [PbBr] complexes also form, driving CsPbBr to CsPbBr transformation via Ostwald ripening, resulting in large CsPbBr microcrystals that precipitate due to gravitational forces overcoming Brownian motion, destabilizing their dispersion in the solution.