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.本工作报道了胶体CsPbX3–Pb4S3Br2（X=Cl、Br、I）纳米晶异质结构的合成，该体系展示了金属卤化物钙钛矿与非钙钛矿晶格之间清晰且具有原子级分辨的外延界面的构建实例。研究采用预制的亚纳米CsPbBr3团簇，通过两步直接合成法制备了CsPbBr3–Pb4S3Br2纳米晶。密度泛函理论（Density Functional Theory）计算表明，该异质界面处形成了准II型能带对齐与局域陷阱态，可促进光生激子的超快分离与载流子俘获，该结论得到了光谱实验的验证。通过与Cl–或I–离子进行后合成反应，可得到对应的CsPbCl3–Pb4S3Br2与CsPbI3–Pb4S3Br2异质结构，从而实现仅在钙钛矿结构域内的阴离子交换。当钙钛矿晶格与硫卤化物晶格形成界面时，其结构刚性得以提升，这一点可通过CsPbI3–Pb4S3Br2异质结构中亚稳γ相（或称“黑相”）CsPbI3稳定性的显著改善得到证实。