Halide Perovskite–Lead Chalcohalide Nanocrystal Heterostructures

[Image: see text] We report the synthesis of colloidal CsPbX(3)–Pb(4)S(3)Br(2) (X = Cl, Br, I) nanocrystal heterostructures, providing an example of a sharp and atomically resolved epitaxial interface between a metal halide perovskite and a non-perovskite lattice. The CsPbBr(3)–Pb(4)S(3)Br(2) nanocrystals are prepared by a two-step direct synthesis using preformed subnanometer CsPbBr(3) clusters. Density functional theory calculations indicate the creation of a quasi-type II alignment at the heterointerface as well as the formation of localized trap states, promoting ultrafast separation of photogenerated excitons and carrier trapping, as confirmed by spectroscopic experiments. Postsynthesis reaction with either Cl(–) or I(–) ions delivers the corresponding CsPbCl(3)–Pb(4)S(3)Br(2) and CsPbI(3)–Pb(4)S(3)Br(2) heterostructures, thus enabling anion exchange only in the perovskite domain. An increased structural rigidity is conferred to the perovskite lattice when it is interfaced with the chalcohalide lattice. This is attested by the improved stability of the metastable γ phase (or “black” phase) of CsPbI(3) in the CsPbI(3)–Pb(4)S(3)Br(2) heterostructure.