The Making and Breaking of Lead-Free Double Perovskite Nanocrystals of Cesium Silver–Bismuth Halide Compositions

• Published in: Nano letters Vol. 18; no. 6; pp. 3502 - 3508
• Main Authors: Bekenstein, Yehonadav, Dahl, Jakob C, Huang, Jianmei, Osowiecki, Wojciech T, Swabeck, Joseph K, Chan, Emory M, Yang, Peidong, Alivisatos, A. Paul
• Format: Journal Article
• Language: English
• Published: United States American Chemical Society 13-06-2018
• Subjects: cesium silver bismuth halides; double perovskites; INORGANIC, ORGANIC, PHYSICAL, AND ANALYTICAL CHEMISTRY; Lead-free halide perovskites; perovskite nanocrystals; Lead-free halide perovskites; perovskite nanocrystals; cesium silver bismuth halides; double perovskites
• ISSN: 1530-6984; 1530-6992
• DOI: 10.1021/acs.nanolett.8b00560

Replacing lead in halide perovskites is of great interest due to concerns about stability and toxicity. Recently, lead free double perovskites in which the unit cell is doubled and two divalent lead cations are substituted by a combination of mono- and trivalent cations have been synthesized as bulk single crystals and as thin films. Here, we study stability and optical properties of all-inorganic cesium silver­(I) bismuth­(III) chloride and bromide nanocrystals with the double perovskite crystal structure. The cube-shaped nanocrystals are monodisperse in size with typical side lengths of 8 to 15 nm. The absorption spectrum of the nanocrystals presents a sharp peak, which we assign to a direct bismuth s–p transition and not to a quantum confined excitonic transition. Using this spectroscopic handle combined with high-resolution transmission electron microscopy (TEM) based elemental analysis, we conduct stoichiometric studies at the single nanocrystal level as well as decomposition assays in solution and observe that Ag+ diffusion and coalescence is one of the pathways by which this material degrades. Drying the nanocrystals leads to self-assembly into ordered nanocrystal solids, and these exhibit less degradation than nanocrystals in solution. Our results demonstrate that Cs2AgBiX6 (X = Cl, Br) nanocrystals are a useful model system to study structure–function relationships in the search for stable nontoxic halide perovskites.