Nanocrystal Heterostructures Based on Halide Perovskites and Metal Sulfides

We report the synthesis of nanocrystal heterostructures composed of CsPbCl₃ and PbS domains sharing an epitaxial interface. We were able to promote the growth of a PbS domain (in competition with the more commonly observed Pb₄S₃Cl₂ one) on top of the CsPbCl₃ domain by employing Mn²⁺ ions, the latter most likely acting as scavengers of Cl^- ions. Complete suppression of the Pb₄S₃Cl₂ domain growth was then achieved by additionally selecting an appropriate sulfur source (bis(trimethylsilyl)sulfide, which also acted as a scavenger of Cl^- ions) and reaction temperature. In the heterostructures, emission from the perovskite domain was quenched, while emission from the PbS domain was observed, pointing to a type-I band alignment, as confirmed by calculations. These heterostructures, in turn, could be exploited to prepare second-generation heterostructures through selective ion exchange on the individual domains (halide ion exchange on CsPbCl₃ and cation exchange on PbS). We demonstrate the cases of Cl^- → Br^- and Pb²⁺ → Cu⁺ exchanges, which deliver CsPbBr₃-PbS and CsPbCl₃-Cu_2-xS epitaxial heterostructures, respectively.