Isotropic-Grown Ultrasmall CsPbBr₃ Nanocrystals in an Enlarged Synthesis toward Efficient Blue Electroluminescence

Enlarged synthesis of monodisperse colloidal nanocrystals is essential for practical applications. However, the scalable synthesis of perovskite nanocrystals remains challenging due to the fast crystallization nature of perovskites, which allows for only an extremely short time window for mass and heat transfer. Specifically, the difficulties in the enlarged synthesis of ultrasmall and monodisperse CsPbBr₃ nanocrystals are amplified, usually accompanied by the formation of nanoplate byproducts. Here, we demonstrate a multibranched ligand-assisted synthetic strategy to control the isotropic growth of ultrasmall CsPbBr₃ nanocrystals in an enlarged synthesis. The multibranched ligand with large steric hindrance breaks the close alignment of alkylammonium cations at a specific facet during the nucleation stage, which synergistically suppresses anisotropic growth and extends the crystallization time window to several min. This allows for synthesis volumes up to 200 mL without compromising monodispersity and optical quality, which also avoids the generation of nanoplate byproducts. The enlarged-synthesized CsPbBr₃ nanocrystals exhibit blue emission at 480 nm with a narrow full-width at half-maximum of 21 nm. Corresponding blue light-emitting diodes achieve an external quantum efficiency of 22.4% with great spectral stability and reproducibility. This work provides a solution for scalable preparation of ultrasmall nanocrystals and presents a generalizable ligand design approach for morphology control, facilitating the practical development of highly efficient perovskite optoelectronic devices.