Direct Heteronucleation-Enabled Formation of Epitaxial Plasmonic CsPbBr₃-Cu_2-xSe Nanocrystal Heterostructures

The formation of epitaxial heterostructures between ionic halide perovskite and covalent chalcogenide semiconductor nanocrystals critically depends on interfacial coordination environments. Heteronucleation of chalcogenides on perovskite facets therefore requires precise control over reaction parameters, and most reported such systems rely on a shared Pb-based sublattice. Here, we report epitaxial plasmonic-semiconductor perovskite-chalcogenide CsPbBr₃-Cu_2-xSe nanocrystal heterostructures which do not share any common ions and are obtained with nucleation of Cu_2-xSe on preferred facets of CsPbBr₃ nanocrystals. This integration quenches the host photoluminescence but induces the plasmonic features yielding near-infrared absorption around ∼1000 nm. A cation-dominated synthetic pathway, in which copper precursor incorporation precedes selenium injection, suppresses undesired PbSe nucleation. High-resolution electron microscopy confirms favorable lattice matching and epitaxial growth at the interface. These results demonstrate that reaction chemistry can be engineered to access hybrid nanostructures of ionic and covalent interfaces and result in functional nanocrystal heterostructures.