Lead-based colloidal semiconductors, in the form of lead chalcogenide and lead-halide perovskite nanocrystals, are extensively studied for applications in the infrared and visible spectral ranges respectively. Yet, these materials suffer from limitations, motivating the search for alternatives: lead-halide perovskites quickly degrade in operando conditions, and the more robust lead chalcogenides can be hardly pushed in the visible range due to the narrow band gaps. However, there is a class of materials that bridge between lead chalcogenides and perovskites, which has been little explored so far and may hold promises for optoelectronic properties. They are the lead chalcohalides, ternary compounds with general formula PbaEbXc (E = S, Se, Te; X = F, Cl, Br, I). In an attempt to investigate these materials, we synthesized and solved the structure of two lead sulfohalides unknown to date (Pb4S3Br2 and Pb3S2Cl2), which proved to be indirect bandgap semiconductors. When tested in photodetectors and solar cells, Pb4S3Br2 demonstrated a photoresponse that, albeit modest, encouraged deeper investigations into this class of compounds. Further experiments led us to the synthesis of lead chalcohalide – perovskite heterostructures, which are nanoparticles composed of two connected crystalline domains. Their interface represents the first reported epitaxial connection of lead-halide perovskites with a phase outside the family of cesium lead halides, and is made possible by the intimate structural similarities that Pb4S3X2 shares with some of the Cs-Pb-X compounds. The formation of lead chalcohalide – lead perovskite heterostructures has a strong impact on the behaviour of both materials. On the one hand, it quenches the otherwise bright photoluminescence of the perovskite, suggesting a delocalization of carriers on the chalcohalide domain that might be exploited for photo-harvesting. Moreover, the Pb4S3Br2-CsPbI3 epitaxial connection stabilizes the labile CsPbI3 perovskite, potentially solving a well-known of perovskite-based photovoltaics. On the other hand, the perovskite exerts a strong templating effect on the chalcohalide domain, producing a complete phase selectivity for the case of lead sulfochlorides: Pb3S2Cl2 forms when the perovskite is absent, Pb4S3Cl2 when it is present. These results motivate further research on lead chalcohalides, and pave the road for the advanced control over the synthesis of colloidal inorganic nanomaterials through epitaxial templating.

Lead chalcohalides nanocrystals and chalcohalide-perovskite heterostructures

ACS Spring 2022

The official archive and repository for all ACS Meetings & Expositions abstracts and select posters or presentations.