Angewandte
Communications
Chemie
Perovskite Nanostructures
Highly Luminescent Cesium Lead Halide Perovskite Nanocrystals with
Tunable Composition and Thickness by Ultrasonication
Yu Tong, Eva Bladt, Meltem F. Aygꢀler, Aurora Manzi, Karolina Z. Milowska,
Verena A. Hintermayr, Pablo Docampo, Sara Bals,* Alexander S. Urban,*
Abstract: We describe the simple, scalable, single-step, and
polar-solvent-free synthesis of high-quality colloidal CsPbX3
(X = Cl, Br, and I) perovskite nanocrystals (NCs) with tunable
halide ion composition and thickness by direct ultrasonication
of the corresponding precursor solutions in the presence of
organic capping molecules. High angle annular dark field
scanning transmission electron microscopy (HAADF-STEM)
revealed the cubic crystal structure and surface termination of
the NCs with atomic resolution. The NCs exhibit high photo-
luminescence quantum yields, narrow emission line widths,
and considerable air stability. Furthermore, we investigated the
quantum size effects in CsPbBr3 and CsPbI3 nanoplatelets by
tuning their thickness down to only three to six monolayers.
The high quality of the prepared NCs (CsPbBr3) was
confirmed by amplified spontaneous emission with low thresh-
olds. The versatility of this synthesis approach was demon-
strated by synthesizing different perovskite NCs.
lasers.[1] One of the main advantages of these materials is the
fact that the optical band gap can be easily tuned by
exchanging individual components.[2] The success of these
materials quickly led to the synthesis of nanocrystals (NCs),
first in the form of organic/inorganic hybrid perovskites,[1b,3]
and later also as purely inorganic cesium-based perovskites.[4]
Nanocrystals exhibit high photoluminescence quantum yields
(PLQYs) and offer an inherent way to tune the optical
properties through size- and dimensionality-dependent quan-
tum confinement.[5] Currently, unlike for conventional metal
chalcogenide based NCs, only a limited number of synthetic
methods are available for the preparation of CsPbX3 NCs.
The most widely adopted method for the preparation of
CsPbX3 nanocubes with very high PLQYs is based on high-
temperature hot injection, which was developed by Kova-
lenko and co-workers in 2015 and refined by Alivisatos and
co-workers to obtain nanoplatelets (NPLs).[4b,6] However, the
hot-injection approach is tedious, it is generally performed
under an inert atmosphere, and can currently only be applied
to control the thickness of bromine-based perovskites.
Indeed, an additional halide ion exchange step is necessary
to prepare NPLs based on iodide or chloride perovskites, as
shown simultaneously by the groups of Manna, Kovalenko,
and Alivisatos.[4b,6,7] Sun et al.[8] reported an approach for the
shape-controlled synthesis of CsPbBr3 NCs at room temper-
ature. However, this method requires the pre-synthesis of the
cesium precursor under inert atmosphere at higher temper-
atures. While being simple, room-temperature syntheses
generally lead to NCs with relatively low PLQYs.[8] Herein,
T
he outstanding optoelectronic properties of inexpensive
and solution-processable hybrid metal halide perovskites
have brought them to the forefront of many research fields,
such as solar cells, light-emitting diodes, photodetectors, and
[*] Y. Tong, A. Manzi, V. A. Hintermayr, Dr. A. S. Urban,
Dr. L. Polavarapu, Prof. Dr. J. Feldmann
Chair for Photonics and Optoelectronics
Department of Physics and Center for NanoScience (CeNS)
Ludwig-Maximilians-Universitꢀt
Amalienstrasse 54, 80799 Munich (Germany)
E-mail: urban@lmu.de
we describe
a versatile, polar-solvent-free, single-step
approach for the large-scale synthesis of highly luminescent
CsPbX3 perovskite NCs and NPLs. Both the halide compo-
sition and the NPL thickness can be tuned, namely by direct
ultrasonication of the corresponding precursors in the pres-
ence of organic ligands (Figure 1a). The ability to tune the
thickness revealed the quantum size effects operating in
CsPbX3 (X = Br and I) NPLs, which enabled us to investigate
the thickness dependence of the optical properties of CsPbI3
NPLs for the first time.
As shown in Figure 1a, our synthesis of CsPbX3 (X = Cl,
Br, and I) perovskite NCs is based on direct tip sonication of
mixtures of the corresponding precursor salts (Cs2CO3 and
PbX2) and capping ligands (oleylamine and oleic acid) in
a nonpolar solvent (mineral oil or octadecene) under ambient
atmospheric conditions. Such a sonication process has pre-
viously been used for the preparation of metal nanoparticles.
This method is based on metal–ligand complex formation
under ultrasonication; these complexes are then further
Y. Tong, A. Manzi, Dr. A. S. Urban, Dr. L. Polavarapu,
Prof. Dr. J. Feldmann
Nanosystems Initiative Munich (NIM)
Schellingstrasse 4, 80799 Munich (Germany)
E. Bladt, Prof. Dr. S. Bals
EMAT, University of Antwerp
Groenenborgerlaan 171, B-2020 Antwerp (Belgium)
E-mail: sara.bals@uantwerpen.be
M. F. Aygꢁler, Prof. Dr. P. Docampo
Department of Chemistry and Center for NanoScience (CeNS)
Ludwig-Maximilians-Universitꢀt (LMU)
Butenandtstrasse 5–13, 81377 Munich (Germany)
Dr. K. Z. Milowska
Department of Materials Science and Metallurgy
University of Cambridge
27 Charles Babbage Rd, Cambridge CB3 0FS (UK)
Supporting information and the ORCID identification number(s) for
the author(s) of this article can be found under:
Angew. Chem. Int. Ed. 2016, 55, 1 – 7
ꢀ 2016 Wiley-VCH Verlag GmbH & Co. KGaA, Weinheim
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