Ligand-Mediated Control of ZnxSey Intermediates for Defect-Free ZnSe Heteroepitaxy on Quantum Dots

ZnSe is a cornerstone shell material for enhancing the efficiency and stability of quantum dots (QDs). However, the chemical mechanisms governing detrimental zinc vacancy (VZn) formation remain unclear, limiting the predictive synthesis of high-quality heterostructures. Herein, we demonstrate that rational manipulation of ZnxSey intermediates via free oleic acid (OA) effectively suppresses both VZn and morphological inhomogeneity in CdSe/ZnSe core/shell QDs. Under OA-deficient conditions, sluggish precursor conversion yields a broad distribution of ZnxSey intermediates, including Zn-deficient heavy clusters like Zn2Se3(TOP), that lead to VZn incorporation. Conversely, excess OA shifts the intermediate landscape toward Zn-rich light species and suppresses the shift of intermediates into oxidized forms. This intermediate-level control enables the growth of VZn-free, morphologically uniform ZnSe shells with near-unity photoluminescence quantum yield. Our findings establish intermediate stoichiometry as a deterministic handle for the defect-free heteroepitaxy.