Halide Perovskite–Lead Chalcohalide Nanocrystal Heterostructures

We report the synthesis of colloidal CsPbX3-Pb4S3Br2 (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 CsPbBr3-Pb4S3Br2 nanocrystals are prepared by a two-step direct synthesis, using pre-formed sub-nm CsPbBr3 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, respectively promoting ultrafast separation of photogenerated excitons and carrier trapping, as confirmed by spectroscopic experiments. Post-synthesis reaction with either Cl- or I- ions delivers the corresponding CsPbCl3-Pb4S3Br2 and CsPbI3-Pb4S3Br2 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 g phase (or “black” phase) of CsPbI3 in the CsPbI3-Pb4S3Br2 heterostructure.