Solution-Phase Synthesis of Cesium Lead Halide Perovskite Nanowires

Article abstract of DOI:10.1021/jacs.5b05404

Halide perovskites have attracted much attention over the past 5 years as a promising class of materials for optoelectronic applications. However, compared to hybrid organic-inorganic perovskites, the study of their pure inorganic counterparts, like cesium lead halides (CsPbX₃), lags far behind. Here, a catalyst-free, solution-phase synthesis of CsPbX₃ nanowires (NWs) is reported. These NWs are single-crystalline, with uniform growth direction, and crystallize in the orthorhombic phase. Both CsPbBr₃ and CsPbI₃ are photoluminescence active, with composition-dependent temperature and self-trapping behavior. These NWs with a well-defined morphology could serve as an ideal platform for the investigation of fundamental properties and the development of future applications in nanoscale optoelectronic devices based on all-inorganic perovskites.

Full text of DOI:10.1021/jacs.5b05404

Communication
pubs.acs.org/JACS
Solution-Phase Synthesis of Cesium Lead Halide Perovskite
Nanowires
Dandan Zhang,†,§,⊥ Samuel W. Eaton,†,⊥ Yi Yu, Letian Dou, and Peidong Yang*,†,‡,§,∥
†
†,§
†
‡
Department of Chemistry and Department of Materials Science and Engineering, University of California, Berkeley, California
9
4720, United States
§
Materials Sciences Division, Lawrence Berkeley National Laboratory, Berkeley, California 94720, United States
∥Kavli Energy NanoSciences Institute, Berkeley, California 94720, United States
*
S Supporting Information
perovskite produces large morphological variations, making it a
non-ideal platform for understanding these materials’ funda-
mental properties.
ABSTRACT: Halide perovskites have attracted much
attention over the past 5 years as a promising class of
materials for optoelectronic applications. However,
compared to hybrid organic−inorganic perovskites, the
study of their pure inorganic counterparts, like cesium lead
Controlled synthesis of materials with high quality and well-
defined morphology not only benefits fundamental research but
3
also offers great promise for practical applications. Examples
halides (CsPbX ), lags far behind. Here, a catalyst-free,
3
include the development of semiconducting quantum dots
solution-phase synthesis of CsPbX nanowires (NWs) is
3a
3b
3
(QDs), one-dimensional (1D) nanowires (NWs), and two-
reported. These NWs are single-crystalline, with uniform
growth direction, and crystallize in the orthorhombic
phase. Both CsPbBr and CsPbI are photoluminescence
3c
dimensional (2D) nanosheets, which can have optical and
electrical properties superior to those of their bulk counterparts.
In terms of inorganic halide perovskites, with the exception of
3
3
active, with composition-dependent temperature and self-
trapping behavior. These NWs with a well-defined
morphology could serve as an ideal platform for the
investigation of fundamental properties and the develop-
ment of future applications in nanoscale optoelectronic
devices based on all-inorganic perovskites.
2a
single-crystalline QDs, there have been no reports of 1D or
2
D nanostructures. Semiconductor NWs, in particular,
currently attract widespread interest due to the great potential
to advance fundamental and applied research toward new
classes of inherently 1D photonic and electronic nanostruc-
tures.
Here, a catalyst-free, solution-phase synthesis of CsPbX3
NWs is reported. Detailed structural characterization reveals
that these NWs are single-crystalline, with uniform growth
direction, and crystallize in an orthorhombic phase. Optical
measurements show that both CsPbBr3 and CsPbI3 are
alide perovskites have been demonstrated to be a
H
promising class of materials for optoelectronic applica-
1
1a
tions, including high-efficiency photovoltaic cells, light-
1
b
1c
1d
emitting diodes, lasers, and photodetectors. The advan-
tages of these compounds include their excellent charge-
transport properties and broad chemical tunability. While
recent studies have been mostly focused on hybrid organic−
inorganic compounds, the study of their inorganic analogues,
photoluminescence (PL) active, with CsPbBr showing strong
3
PL, CsPbI exhibiting a self-trapping effect, and both displaying
1e
1f
3
temperature-dependent PL. These single-crystalline NWs could
serve as an ideal platform for further investigation of structure−
function relationships critical to the development of future
applications in nanoscale optoelectronics.
like AMX (A = Rb, Cs; M = Ge, Sn, Pb; X = Cl, Br, I), is
3
2
limited.
Synthesis of CsPbX NWs. The preparation of CsPbX
3
3
Previous studies on the all-inorganic halide perovskites have
revealed that these materials have great potential in
optoelectronic applications. CsGeX3 are known for their
nonlinear optical properties and are potentially useful for
NWs was performed under air-free conditions using standard
Schlenk techniques, by reacting cesium oleate with lead halide
in the presence of oleic acid and oleylamine in octadecene
(ODE) at 150−250 °C. To analyze the NWs’ formation
mechanism, the reaction was quenched to room temperature at
different points in time, and the respective intermediates were
separated by centrifugation and examined using X-ray
diffraction (XRD) and transmission electron microscopy
2c,d
nonlinear optics in the mid-infrared and infrared regions.
CsSnI F has been demonstrated to be an effective hole-
3‑x x
transport material and is able to replace the problematic organic
2e
liquid electrolytes in dye-sensitized solar cells. Theoretical
calculations on ASnX (A = Cs, CH NH , NH CHNH ; X =
3
3
3
2
2
(
TEM).
Cl, I) suggested that their electronic properties strongly depend
2f
For CsPbBr NWs synthesis, the reaction dynamics have
3
on the structure of the inorganic SnX octahedral cage, which
6
been studied at 150 °C. At the initial stage (t < 10 min), the
reaction is dominated by the formation of nanocubes (NCs)
implies good prospects for the all-inorganic halide perovskites.
However, most of these studies were based on polycrystalline
perovksite films deposited on substrates using vapor-phase co-
2
e
2b
evaporation or solution deposition of a mixture of AX and
Received: May 25, 2015
BX . The uncontrolled precipitation or evaporation of the
2
©
XXXX American Chemical Society
A
DOI: 10.1021/jacs.5b05404
J. Am. Chem. Soc. XXXX, XXX, XXX−XXX

Journal of the American Chemical Society
Communication
Figure 1. Shape evolution of the as-prepared CsPbBr nanostructures synthesized with different reaction times. Scale bar, 100 nm.
3
Figure 2. Structural characterizations of CsPbBr nanowires. (a) Representative HR-TEM image of CsPbBr NWs. Scale bar, 10 nm. (b)
3
3
Experimental XRD spectrum (top two) of CsPbBr nanocubes and NWs, and standard XRD patterns (bottom two) for orthorhombic and cubic
3
phases of CsPbBr . Extra peaks (labeled *) are caused by the XRD aluminum stage.
3
with size ranging from 3 to 7 nm (Figure 1a). After 10 min, a
few thin NWs with diameters around 9 nm are found in the
product (Figure 1b). With increasing time, more NWs form
while the amount of NCs decreases; in addition, there are some
square-shaped nanosheets (NSs) in the product (Figure 1c and
Supporting Information (SI), Figure S7a). At a later stage (40−
the large crystals (Figure 1f). Notably, these morphologies do
not represent discrete intermediates formed at specific reaction
times, but evolve sequentially from each other. Consequently,
different intermediates can coexist in the product at a given
time during the reaction (SI, Scheme S1). The growth of
CsPbI NWs requires elevated temperatures (T > 180 °C) and
3
6
0 min) in the reaction, the NSs dissolved, and NWs with
demonstrates much faster kinetics. As such, the reaction is less
controllable and the size distribution of the NWs is wider,
ranging from tens to hundreds of nanometers (SI, Figure S2).
diameters uniformly below 12 nm (Figure 1d,e) and lengths up
to 5 μm (SI, Figure S1a−c) account for a greater proportion of
the product, along with the formation of crystals with sizes
larger than 200 nm (SI, Figure S1c). With longer time, the
NWs gradually disappear, and the product consists mainly of
The CsPbCl NWs have also been synthesized at 150 °C, but
3
the proportion of the NWs in the product at different reaction
stages is always relatively low (SI, Figure S3).
B
DOI: 10.1021/jacs.5b05404
J. Am. Chem. Soc. XXXX, XXX, XXX−XXX

Journal of the American Chemical Society
Communication
Figure 3. Optical characterizations of CsPbI and CsPbBr nanowires. Typical optical absorption and PL spectra for (a) CsPbBr NWs and (b)
3
3
3
CsPbI NWs. Inset: optical images of CsPbBr and CsPbI NWs under the laser beam.
3
3
3
Catalyst-free, solution-phase syntheses are commonly used to
prepare nanostructures with low aspect ratio, such as rods and
it difficult to determine their exact phase, while the clear double
peak at ∼30° confirms that the CsPbBr NWs are grown in the
3
4
dots. The formation of high aspect ratio NWs in solution is
orthorhombic phase. The HR-TEM images (Figure 2a and SI,
5
usually achieved by oriented attachment of nanocrystals or by
Figure S6) show that the CsPbBr NWs are single crystalline
3
anisotropic growth driven by high monomer concentrations
with the assistance of surfactant capping. We believe that the
with uniform ⟨110⟩ growth direction. The XRD spectrum of
4
b,6
CsPbBr nanosheets also suffers severe peak broadening (SI,
3
formation of the CsPbX NWs here is not likely due to a
dipole-driven one-dimensional oriented attachment of NCs,
Figure S7c), making it difficult to tell its exact phase. Atomic
force microscopy (AFM) images show the thickness of the
nanosheets ranges from 0.5 to 2 nm (SI, Figure S8). HR-TEM
images of the sheets show lattice patterns with antiphase
3
5
since no dimers or “oligomers” of NCs are observed in the
products, and during the aging of a colloidal solution of the
nanocrystals, there is no nanorod formation due to the dipole-
driven attachment (SI, Figure S4). In order to get a better
understanding of the NWs’ growth mechanism, more experi-
ments have been conducted to investigate the influence of
temperature, time, surfactants, and precursor concentration on
the morphology of the product (SI, Table S1). A control
experiment done by changing the reaction solvent from ODE
to oleylamine shows much slow kinetics but with higher yield of
NWs, which suggests the NW formation most likely proceeds
through a surfactant-directed 1D growth mode (SI).
boundaries (SI, Figure S7b), which is commonly observed in
8
oxide perovskites. The exact phase of CsPbCl cannot be
3
determined by our X-ray diffractometer because the resolution
of the instrument cannot differentiate the closely spaced peaks.
Optical Properties of CsPbX NWs. The optical proper-
3
ties of the CsPbX (X = Br, I) NWs were studied by measuring
3
the UV−vis absorption and PL spectra of each material
dispersed on a substrate (Figure 3). The absorption onsets for
the CsPbBr and CsPbI NWs were found to be 521 nm (2.38
3
3
eV) and 457 nm (2.71 eV), respectively.
Structural Characterization of CsPbX NWs. CsPbX3
The narrow PL spectrum of CsPbBr (Figure 3a, dotted line)
3
3
bulk crystals exhibit a cubic perovskite structure in the highest
corresponds to excitonic emission with a small degree of
quantum confinement (60 meV blue-shift, SI, Figure S10) due
to the narrow wire diameter. A greater degree of confinement is
observed for the nanosheets (69 meV) due to an average sheet
thickness of only a few unit cells (SI, Figure S9). Temperature-
7
temperature phase. Upon lowering the temperature, CsPbI
3
7
a
undergoes one phase transition, cubic−orthorhombic
7c
(
328 °C), with a color change from dark to yellow. CsPbBr3
7b
has two phase transitions, cubic−tetragonal (130 °C)−
orthorhombic (88 °C), with hardly any color change
7d
dependent PL of the CsPbBr NWs reveals a small blue-shift
3
7
c
(
orange). CsPbCl shows three successive phase transitions,
(0.035 meV/K) with increasing temperature (SI, Figure S11).
While the opposite trend is typically observed, this behavior has
been reported for a range of materials, including Pb-doped
3
cubic−tetragonal (47 °C)−orthorhombic (42 °C)−monoclinic
7c
(
37 °C), with hardly any color change (pale yellow).
Both the yellow color of the crystal (SI, Figure S5b) and the
9
10
CsBr crystals as well as closely related cesium metal halide
11
XRD pattern (SI, Figure S5b) confirm that the CsPbI NWs are
and organometal halide pervoskites. The effect is attributed to
the balance between lattice expansion/contraction and
electron−phonon coupling; electron−phonon coupling typi-
cally dominates band gap behavior and results in a red-shift
with increasing temperature. Yu et al. reported, however, that
3
in the orthorhombic phase. The HR-TEM images (SI, Figure
S5a) show that the CsPbI NWs are single-crystalline, with
3
uniform ⟨100⟩ growth direction. The phase of CsPbBr NWs
3
needs more careful determination because of the small
difference between the XRD standard patterns of the
orthorhombic and cubic phases. As shown in Figure 2b, the
key difference in distinguishing the orthorhombic phase from
the cubic phase is the double peaks at ∼30°. The peak
10
the lattice term was dominant in CsSnI3; we hypothesize that
CsPbBr behaves similarly here.
3
Our CsPbI PL spectrum (Figure 3b, dotted line) consists of
3
two distinct peaks centered at 446 nm (2.78 eV) and 523 nm
(2.37 eV), with widths of 115 and 530 meV (fwhm),
broadening caused by the small size of the CsPbBr NCs makes
3
C
DOI: 10.1021/jacs.5b05404
J. Am. Chem. Soc. XXXX, XXX, XXX−XXX

Journal of the American Chemical Society
Communication
respectively. The narrow, high-energy peak likely stems from
Chang, W. H.; Li, G.; Yang, Y. Nat. Commun. 2014, 5, 5404. (e) Dong,
Q.; Fang, Y.; Shao, Y.; Mulligan, P.; Qiu, J.; Cao, L.; Huang, J. Science
excitonic emission similar to that of CsPbBr , but the broad,
3
2
015, 347, 967. (f) Noh, J. H.; Im, S. H.; Heo, J. H.; Mandal, T. N.;
Seok, S. I. Nano Lett. 2013, 13, 1764.
2) (a) Protesescu, L.; Yakunin, S.; Bodnarchuk, M. I.; Krieg, F.;
low-energy peak observed for CsPbI has been attributed
3
12
previously to the formation of self-trapped excitons (STEs).
(
Exciton self-trapping has been observed for a variety of ionic
compounds, including a number of recently studied organo-
Caputo, R.; Hendon, C. H.; Yang, R. X.; Walsh, A.; Kovalenko, M. V.
Nano Lett. 2015, 15, 3692. (b) Chung, I.; Song, J.-H.; Im, J.;
Androulakis, J.; Malliakas, C. D.; Li, H.; Freeman, A. J.; Kenney, J. T.;
Kanatzidis, M. G. J. Am. Chem. Soc. 2012, 134, 8579. (c) Tang, L. C.;
Huang, J. Y.; Chang, C. S.; Lee, M. H.; Liu, L. Q. J. Phys.: Condens.
Matter 2005, 17, 7275. (d) Tang, L.-C.; Chang, Y.-C.; Huang, J.-Y.;
Lee, M.-H.; Chang, C.-S. Jpn. J. Appl. Phys. 2009, 48, 112402.
1
1a,13
metal halide perovskite materials.
The temperature-
dependent PL of CsPbI3 NWs is also significantly more
complex than that of CsPbBr3 (SI, Figure S11). At low
temperatures, only STE emission is observed. Upon heating
past 100 K, the excitonic emission peak appears and grows
(e) Chung, I.; Lee, B.; He, J.; Chang, R. P. H.; Kanatzidis, M. G.
monotonically with temperature. Unlike CsPbBr , the excitonic
3
Nature 2012, 485, 486. (f) Borriello, I.; Cantele, G.; Ninno, D. Phys.
Rev. B: Condens. Matter Mater. Phys. 2008, 77, 235214.
peak red-shifts with increasing temperature, suggesting that a
strong electron−phonon coupling contribution dictates band
gap behavior. This is consistent with the self-trapping of
excitons; increased electron−phonon coupling results in greater
lattice distortion in the proximity of the exciton, thereby
(3) (a) Alivisatos, A. P. Science 1996, 271, 933. (b) Huang, M. H.;
Mao, S.; Feick, H.; Yan, H.; Wu, Y.; Kind, H.; Weber, E.; Russo, R.;
Yang, P. Science 2001, 292, 1897. (c) Wang, Q. H.; Kalantar-Zadeh, K.;
Kis, A.; Coleman, J. N.; Strano, M. S. Nat. Nanotechnol. 2012, 7, 699.
13a
increasing the probability of trapping. Additional discussion
of PL may be found in the SI, Table S2.
(4) (a) Peng, X.; Manna, L.; Yang, W.; Wickham, J.; Scher, E.;
Kadavanich, A.; Alivisatos, A. P. Nature 2000, 404, 59. (b) Peng, Z. A.;
In summary, a catalyst-free, solution-phase synthetic
approach has been developed to obtain single-crystalline,
Peng, X. J. Am. Chem. Soc. 2002, 124, 3343.
(5) Cho, K. S.; Talapin, D. V.; Gaschler, W.; Murray, C. B. J. Am.
Chem. Soc. 2005, 127, 7140.
orthorhombic CsPbX NWs with uniform growth direction.
3
(
2
(
2
6) Xi, L.; Tan, W. X. W.; Boothroyd, C.; Lam, Y. M. Chem. Mater.
008, 20, 5444.
7) (a) Trots, D. M.; Myagkota, S. V. J. Phys. Chem. Solids 2008, 69,
520. (b) Sakata, M.; Nishiwaki, T.; Harada, J. J. Phys. Soc. Jpn. 1979,
7, 232. (c) Moeller, C. K. Nature 1958, 182, 1436. (d) Fujii, Y.;
Optical studies determined that both CsPbBr and CsPbI are
3
3
PL active, and exhibit unique compositional and temperature-
dependent behavior. Future studies with these NWs will
concentrate on the investigation of their electronic and
thermoelectronic properties as well as the development of
their optoelectronic applications. Additionally, while this work
4
Hoshino, S.; Yamada, Y.; Shirane, G. Phys. Rev. B 1974, 9, 4549.
8) Van Tendeloo, G.; Lebedev, O. I.; Amelinckx, S. J. Magn. Magn.
(
focuses on the CsPbX class of compounds, the synthetic
Mater. 2000, 211, 73.
3
method reported here can potentially be applied to other
inorganic perovskites, such as tin-based perovskites, which will
be less toxic.
(9) Aceves, R.; Babin, V.; Flores, M. B.; Fabeni, P.; Maaroos, A.; Nikl,
M.; Nitsch, K.; Pazzi, G. P.; Salas, R. P.; Sildos, I.; Zazubovich, N.;
Zazubovich, S. J. Lumin. 2001, 93, 27.
(
10) Yu, C.; Chen, Z.; J. Wang, J.; Pfenninger, W.; Vockic, N.;
Kenney, J. T.; Shum, K. J. Appl. Phys. 2011, 110, 063526.
11) (a) Dohner, E. R.; Jaffe, A.; Bradshaw, L. R.; Karunadasa, H. I. J.
ASSOCIATED CONTENT
Supporting Information
■
(
*
S
Am. Chem. Soc. 2014, 136, 13154. (b) Wu, K.; Bera, A.; Ma, C.; Du, Y.;
Yang, Y.; Li, L.; Wu, T. Phys. Chem. Chem. Phys. 2014, 16, 22476.
Experimental details and additional TEM, XRD, UV−vis, and
PL data. The Supporting Information is available free of charge
on the ACS Publications website at DOI: 10.1021/
jacs.5b05404.
(12) (a) Nikl, M.; Nitsch, K.; Somma, F.; Fabeni, P.; Pazzi, G. P.;
Feng, X. Q. J. Lumin. 2000, 87−89, 372. (b) Babin, V.; Fabeni, P.;
Nikl, M.; Nitsch, K.; Pazzi, G. P.; Zazubovich, S. Phys. Status Solidi B
2
001, 226, 419.
AUTHOR INFORMATION
Corresponding Author
p_yang@berkeley.edu
Author Contributions
(13) (a) Williams, R. T.; Song, K. S. J. Phys. Chem. Solids 1990, 51,
■
6
79. (b) Wu, X.; Trinh, M. T.; Niesner, D.; Zhu, H.; Norman, Z.;
Owen, J. S.; Yaffe, O.; Kudisch, B. J.; Zhu, X. Y. J. Am. Chem. Soc. 2015,
*
1
37, 2089.
⊥
D.Z. and S.W.E. contributed equally to this work.
Notes
The authors declare no competing financial interest.
ACKNOWLEDGMENTS
■
This work was supported by the Director, Office of Science,
Office of Basic Energy Sciences, Materials Science and
Engineering Division, U.S. Department of Energy, under
Contract No. DE-AC02-05CH11231 (PChem). S.W.E. thanks
the Camille and Henry Dreyfus Foundation for funding, award
no. EP-14-151.
REFERENCES
■
(
1) (a) Liu, M.; Johnston, M. B.; Snaith, H. J. Nature 2013, 501, 395.
b) Tan, Z.-K.; Moghaddam, R. S.; Lai, M. L.; Docampo, P.; Higler, R.;
(
Deschler, F.; Price, M.; Sadhanala, A.; Pazos, L. M.; Credgington, D.;
Hanusch, F.; Bein, T.; Snaith, H. J.; Friend, R. H. Nat. Nanotechnol.
2
014, 9, 687. (c) Zhang, Q.; Ha, S. T.; Liu, X.; Sum, T. C.; Xiong, Q.
Nano Lett. 2014, 14, 5995. (d) Dou, L.; Yang, Y. M.; You, J.; Hong, Z.;
D
DOI: 10.1021/jacs.5b05404
J. Am. Chem. Soc. XXXX, XXX, XXX−XXX