Effects of Additives on the Mediated Synthesis of CsPbBr ₃ Nanocrystals via Soft Colloidal Templates of Block Copolymer Micelles

PS-b-P2VP (Polystyrene-block-poly(2-vinylpyridine) micellar nanoreactors offer a versatile platform for synthesizing cesium lead bromide (CsPbBr3) perovskite nanocrystals (NCs), yet the process is often hindered by the poor solubility of the cesium bromide (CsBr) precursor. Here, we demonstrate a simple and highly effective strategy to overcome this limitation by acidifying the CsBr precursor solution with hydrochloric acid (HCl), which provides tunable control over the crystallization pathway. A systematic investigation reveals a “Goldilocks” effect, where a controlled HCl concentration yields high-quality CsPbBr3 NCs with a photoluminescence quantum yield (PLQY) of up to 98%, while excess HCl produces abundant lead bromide complexes that arrest the conversion and quench emission. We show that HCl’s role extends beyond that of a simple solubilizer to that of a dual-function modulator of the nanoreactor itself. Protons from the strong acid protonate the basic P2VP core, kinetically controlling the stability of lead bromide complexes and governing the final NC quality. Furthermore, we show that the physical state of the core profoundly influences the reaction pathway. This work provides a simple and robust method for producing near-perfect perovskite emitters and deepens the fundamental understanding of polymer-templated nanocrystal synthesis.