DOI: https://doi.org/10.29363/nanoge.incnc.2021.011
Publication date: 8th June 2021
Caesium lead halide perovskite nanocrystals, owing to high oscillator strength of bright triplet excitons, slow dephasing (coherence times of up to 80 picoseconds) and minimal inhomogeneous broadening of emission lines, are promising building blocks for creating superlattice structures that exhibit collective phenomena in their optical spectra. Thus far, only single-component superlattices with the simple cubic packing have been devised from these novel nanocrystals, which have been shown to exhibit superfluorescence – a collective emission resulting in a burst of photons with ultrafast radiative decay (ca. 20 ps) that could be tailored for use in ultrabright (quantum) light sources [1]. However, far broader structural engineerability of superlattices, required for programmable tuning of the collective emission and for building a theoretical framework can be envisioned from the recent advancements in colloidal science [2]. We show that co-assembly of cubic and spherical steric-stabilized nanocrystals is experimentally possible and that the cubic shape of perovskite nanocrystals leads to a vastly different outcome compared to all-spherical systems. We present perovskite-type (ABO3) binary nanocrystal superlattices, besides expected NaCl-type or common AlB2-type superlattices. In binary ABO3 superlattices, larger spherical nanocrystals occupy the A sites and smaller cubic CsPbBr3 nanocrystals reside on B and O sites. The deformability of ligand shell on cube corners makes the lattice stable over broad nanocrystal size ratio range. Targeted substitution of B-site nanocubes by truncated cuboid PbS nanocrystals leads to the exclusive formation of ternary ABO3 superlattice. All synthesized superlattices exhibit a high degree of orientational ordering of the CsPbBr3 nanocubes. We also demonstrate the effect of superlattice structure on superfluorescent behaviour. Our work paves the way for further exploration of complex, ordered and functionally useful perovskite mesostructures.
This work was primarily supported by the European Union through Horizon 2020 Research and Innovation Programme (ERC CoG Grant, grant agreement number 819740, project SCALE-HALO) and, in part, by the Swiss National Science Foundation (grant number 200021_192308, project Q-Light). We acknowledge the funding received from EU-H2020 under grant agreement number 654360 supporting the Transnational Access Activity within the framework NFFA-Europe to the TUG’s ELETTRA SAXS beamline of CERIC-ERIC. We acknowledge the funding received from NSF, DMR-CMMT 1606336 (USA). We thank Y. Shynkarenko for assistance with high-resolution SEM imaging.
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