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-block-poly(2-vinylpyridine) (PS-b-P2VP) on the formation of cesium lead bromide (CsPbBr₃) nanocrystals. The process involves four stages: (i) PS-b-P2VP micellization, (ii) PbBr₂ complexation, (iii) coordination interaction with P2VP, and (iv) burst nucleation of CsPbBr₃ nanocrystals. Toluene, a good solvent for PS but a nonsolvent for P2VP, PbBr₂, and CsBr, facilitates the formation of PS-b-P2VP spherical micelles. Adding PbBr₂ to these micelles in toluene results in multiple emulsion, dispersing PbBr₂ microstructures (microemulsion) and forming [PbBr₃]^- 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, [PbBr₄]^2- complexes also form, driving CsPbBr₃ to CsPb₂Br₅ transformation via Ostwald ripening, resulting in large CsPb₂Br₅ microcrystals that precipitate due to gravitational forces overcoming Brownian motion, destabilizing their dispersion in the solution.