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Published January 27, 2021 | Supplemental Material + Published
Journal Article Open

Monodisperse Long-Chain Sulfobetaine-Capped CsPbBr₃ Nanocrystals and Their Superfluorescent Assemblies

Abstract

Ligand-capped nanocrystals (NCs) of lead halide perovskites, foremost fully inorganic CsPbX₃ NCs, are the latest generation of colloidal semiconductor quantum dots. They offer a set of compelling characteristics—large absorption cross section, as well as narrow, fast, and efficient photoluminescence with long exciton coherence times—rendering them attractive for applications in light-emitting devices and quantum optics. Monodisperse and shape-uniform, broadly size-tunable, scalable, and robust NC samples are paramount for unveiling their basic photophysics, as well as for putting them into use. Thus far, no synthesis method fulfilling all these requirements has been reported. For instance, long-chain zwitterionic ligands impart the most durable surface coating, but at the expense of reduced size uniformity of the as-synthesized colloid. In this work, we demonstrate that size-selective precipitation of CsPbBr₃ NCs coated with a long-chain sulfobetaine ligand, namely, 3-(N,N-dimethyloctadecylammonio)-propanesulfonate, yields monodisperse and sizable fractions (>100 mg inorganic mass) with the mean NC size adjustable in the range between 3.5 and 16 nm and emission peak wavelength between 479 and 518 nm. We find that all NCs exhibit an oblate cuboidal shape with the aspect ratio of 1.2 × 1.2 × 1. We present a theoretical model (effective mass/k·p) that accounts for the anisotropic NC shape and describes the size dependence of the first and second excitonic transition in absorption spectra and explains room-temperature exciton lifetimes. We also show that uniform zwitterion-capped NCs readily form long-range ordered superlattices upon solvent evaporation. In comparison to more conventional ligand systems (oleic acid and oleylamine), supercrystals of zwitterion-capped NCs exhibit larger domain sizes and lower mosaicity. Both kinds of supercrystals exhibit superfluorescence at cryogenic temperatures—accelerated collective emission arising from the coherent coupling of the emitting dipoles.

Additional Information

© 2020 American Chemical Society. This is an open access article published under an ACS AuthorChoice License, which permits copying and redistribution of the article or any adaptations for non-commercial purposes. Received: August 26, 2020; Published: December 29, 2020. The authors thank Dr. Frank Krumeich for acquisition of the cryo-HAADF-STEM and SEM images, Dr. Simon C. Böhme for measuring tr-PL traces, and Yuliia Berezovska for assistance with SAXS measurements. The authors are thankful for the access to NFFA and CERIC-ERIC, the Scientific Center for Optical and Electron Microscopy (ScopeM) at ETH Zurich and the Empa Electron Microscopy Center for use of their facilities. This work was financially supported by the Swiss Innovation Agency (Innosuisse, No. 32908.1 IP-EE) and, in part, by the European Union through the Horizon 2020 research and innovation program (grant agreement No. 819740, project SCALE-HALO). The authors are thankful for the funding received from the EU-H2020 research and innovation program under grant agreement No 654360 supporting the Transnational Access Activity within the framework NFFA-Europe to the TUG's ELETTRA SAXS beamline of CERIC-ERIC. Theoretical calculations of exciton level structure and radiative lifetime were supported as part of the Center for Hybrid Organic Inorganic Semiconductors for Energy (CHOISE), an Energy Frontier Research Center funded by the Office of Basic Energy Sciences, Office of Science, within the U.S. Department of Energy. The authors declare no competing financial interest.

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Created:
August 20, 2023
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October 23, 2023