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 preformed
subnanometer 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,
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 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 γ phase (or “black” phase) of
CsPbI3 in the CsPbI3–Pb4S3Br2 heterostructure.