Tuning Perovskite\nNanocrystal Synthesis via Amphiphilic\nBlock Copolymer Templates and Solvent Interactions

Amphiphilic block copolymer (a-BCP) micelles offer morphological\ndiversity and dimensional tunability, making them suitable for the\nfabrication of perovskite nanocrystals. However, precise control over\nthe nucleation and growth of perovskite nanocrystals using a-BCP colloidal\ntemplates remains underexplored. This study investigates the effects\nof toluene, methanol, and polystyrene-<i>block</i>-poly(2-vinylpyridine)\n(PS-<i>b</i>-P2VP) on the formation of cesium lead bromide\n(CsPbBr<sub>3</sub>) nanocrystals. The process involves four stages:\n(i) PS-<i>b</i>-P2VP micellization, (ii) PbBr<sub>2</sub> complexation, (iii) coordination interaction with P2VP, and (iv)\nburst nucleation of CsPbBr<sub>3</sub> nanocrystals. Toluene, a good\nsolvent for PS but a nonsolvent for P2VP, PbBr<sub>2</sub>, and CsBr,\nfacilitates the formation of PS-<i>b</i>-P2VP spherical\nmicelles. Adding PbBr<sub>2</sub> to these micelles in toluene results\nin multiple emulsion, dispersing PbBr<sub>2</sub> microstructures\n(microemulsion) and forming [PbBr<sub>3</sub>]<sup>−</sup> complexes\nencapsulated by the micelles (nanoemulsion). Prolonged stirring enhances\nthis nanoemulsion. CsBr, insoluble in toluene, must be dissolved in\nmethanol before being mixed with micelle-encapsulated complexes, promoting\nquick crystal nucleation. However, excess methanol weakens micellization,\nleading to the formation of fused micelles and irregular nanocrystals.\nAt a high methanol content, [PbBr<sub>4</sub>]<sup>2–</sup> complexes also form, driving CsPbBr<sub>3</sub> to CsPb<sub>2</sub>Br<sub>5</sub> transformation via Ostwald ripening, resulting in\nlarge CsPb<sub>2</sub>Br<sub>5</sub> microcrystals that precipitate\ndue to gravitational forces overcoming Brownian motion, destabilizing\ntheir dispersion in the solution.