Formation mechanism of freestanding CH3NH3PbI3 functional crystals: In situ transformation vs dissolution-crystallization

Article abstract of DOI:10.1021/cm5028817

To date, the formation mechanism of organolead halide CH₃NH₃PbI₃ perovskites based on the efficient sequential reaction route has remained virtually unexplored. Such a synthetic method usually yields high-performance solar cells with an efficiency over 15%, and the identification of the crystal growth mechanism is crucial for understanding the chemical reaction process and further improving the light converting efficiency. Herein, we develop a versatile and facile approach based on sequential reaction to produce freestanding CH₃NH₃PbI₃ crystals as a model for crystal growth mechanism studies. It was found that the in situ transformation and dissolution-crystallization mechanisms play competing roles in determining the characteristics of products that are largely depend on the chemical reaction kinetics. Such a method can also be readily used for synthesis of freestanding CH₃NH₃PbI₃ crystals with controllable morphological characteristics, such as cuboids, rods, wires, and plates. The synthetic strategy as well as the crystal growth mechanisms exemplified here can also serve in the design and development of more sophisticated organolead halide perovskites as well as further optimization across a range of possible domains of applications.

Full text of DOI:10.1021/cm5028817

Subscriber access provided by Library, Special Collections and Museums, University of Aberdeen
Article
On the Formation Mechanism of Freestanding CH3NH3PbI3 Functional
Crystals: in situ Transformation vs Dissolution-Crystallization
Shuang Yang, Yi Chu Zheng, Yu Hou, Xiao Chen, Ying Chen, Yun Wang, Huijun Zhao, and Hua Gui Yang
Chem. Mater., Just Accepted Manuscript • DOI: 10.1021/cm5028817 • Publication Date (Web): 14 Nov 2014
Downloaded from http://pubs.acs.org on November 14, 2014
Just Accepted
“Just Accepted” manuscripts have been peer-reviewed and accepted for publication. They are posted
online prior to technical editing, formatting for publication and author proofing. The American Chemical
Society provides “Just Accepted” as a free service to the research community to expedite the
dissemination of scientific material as soon as possible after acceptance. “Just Accepted” manuscripts
appear in full in PDF format accompanied by an HTML abstract. “Just Accepted” manuscripts have been
fully peer reviewed, but should not be considered the official version of record. They are accessible to all
readers and citable by the Digital Object Identifier (DOI®). “Just Accepted” is an optional service offered
to authors. Therefore, the “Just Accepted” Web site may not include all articles that will be published
in the journal. After a manuscript is technically edited and formatted, it will be removed from the “Just
Accepted” Web site and published as an ASAP article. Note that technical editing may introduce minor
changes to the manuscript text and/or graphics which could affect content, and all legal disclaimers
and ethical guidelines that apply to the journal pertain. ACS cannot be held responsible for errors
or consequences arising from the use of information contained in these “Just Accepted” manuscripts.
Chemistry of Materials is published by the American Chemical Society. 1155 Sixteenth
Street N.W., Washington, DC 20036
Published by American Chemical Society. Copyright © American Chemical Society.
However, no copyright claim is made to original U.S. Government works, or works
produced by employees of any Commonwealth realm Crown government in the course
of their duties.

Page 1 of 7
Chemistry of Materials
1
2
3
4
5
6
On the Formation Mechanism of Freestanding CH NH PbI
7
8
9
1
1
1
1
1
1
1
1
1
1
2
2
2
2
2
2
2
2
2
2
3
3
3
3
3
3
3
3
3
3
4
4
4
4
4
4
4
4
4
4
5
5
5
5
5
5
5
5
5
5
6
3
3
3
Functional Crystals: in situ Transformation vs Dissolution-
0
1
2
3
4
5
6
7
8
9
0
1
2
3
4
5
6
7
8
9
0
1
2
3
4
5
6
7
8
9
0
1
2
3
4
5
6
7
8
9
0
1
2
3
4
5
6
7
8
9
0
Crystallization
†
†
†
†
†
‡
‡
Shuang Yang, Yi Chu Zheng, Yu Hou, Xiao Chen, Ying Chen, Yun Wang, Huijun Zhao, and
, ,
† ‡
Hua Gui Yang*
†
Key Laboratory for Ultrafine Materials of Ministry of Education School of Materials Science and Engineering East
China University of Science and Technology, 130 Meilong Road, Shanghai, 200237 (China)
‡
Centre for Clean Environment and Energy, Gold Coast Campus Griffith University, Queensland, 4222, (Australia)
KEYWORDS: perovskite, organic-inorganic hybrid composites, in situ transformation, dissolution-crystallization,
crystal growth
ABSTRACT: To date, the formation mechanism of organolead halide CH NH PbI perovskites based on the efficient
3
3
3
sequential reaction route, has remained virtually unexplored. Such a synthetic method usually yields high-performance
solar cells with an efficiency over 15%, and the identification of the crystal growth mechanism is crucial for understanding
the chemical reaction process and further improving the light converting efficiency. Herein, we develop a versatile and
facile approach based on sequential reaction to produce freestanding CH NH PbI crystals as a model for crystal growth
mechanism studies. It was found that the in situ transformation and dissolution-crystallization mechanisms play
competing roles in determining the characteristics of products that are largely depend on the chemical reaction kinetics.
Such a method can also be readily used for synthesis of freestanding CH NH PbI crystals with controllable morphological
characteristics, such as cuboids, rods, wires, and plates. The synthetic strategy as well as the crystal growth mechanisms
exemplified here can also serve in the design and development of more sophisticated organolead halide perovskites as
well as further optimization across a range of possible domains of applications.
3
3
3
3
3
3
Conventionally, this sequential reaction is ideally deemed
to be an in situ intercalation mechanism via the insertion
1. INTRODUCTION
19
Organic-inorganic perovskites have drawn intensive
research interests for their successfully coupling of the
advantages of organic and inorganic components.
Among these materials, the CH NH PbX (X=Cl, Br or I)
of organic ammonium cations. However, the previous
understandings ignored the complexity of this reaction,
such as the solvation or dissolution of lead halides,
coordinative change of metal ions, insertion of the
organic cations and structural reconstruction. In fact, all
these issues are still absent in the literature, and thus we
sought to systematically probe the crystal growth
mechanism which can provide further advancement of
these functional materials. In addition, freestanding
perovskite crystals are also essential due to the ease of
being measured as basic prototype for the fundamental
research compared with thin films as well as their
potential applications.
1
-5
3
3
3
perovskites have made a breakthrough as the sensitizer of
6-11
solar cells recently.
In pursuit of high-performance
devices, several synthetic methods have been explored to
prepare organolead halide perovskite films. Generally,
there are two ways for preparing organolead halide
perovskite films. One is the one-step spin-casting route
which usually yields inhomogeneous morphological
structures because of the uncontrollable precipitation.
Another is the sequential deposition route by reacting
pre-deposited PbX2 film with CH NH X isopropanol
1
2-15
3
3
Herein, we firstly developed a versatile and facile
method based on sequential reaction for preparing
solution-processed freestanding CH NH PbI crystals
which acted as the experimental prototype for studying
the crystal formation mechanism. Our further
experimental results illustrated that crystal growth is in
6
, 16-18
solution or gaseous molecules.
has led to the impressive efficiency over 15% with
optimized pore filling and full coverage of the films.
This simple method
6
3
3
3
Despite the success of sequential reaction in
photovoltaic devices, the corresponding knowledge of the
inherent process of crystal growth is highly desired and
crucial for the synthesis of organic-inorganic perovskites
and further designing improved functional materials.
line with
transformation
mechanisms, which is largely dependent on the reaction
ACS Paragon Plus Environment
a
competing relation between in situ
and dissolution-crystallization

Chemistry of Materials
Page 2 of 7
2
.2. Synthesis of freestanding
1
2
3
4
5
6
7
8
9
1
1
1
1
1
1
1
1
1
1
2
2
2
2
2
2
2
2
2
2
3
3
3
3
3
3
3
3
3
3
4
4
4
4
4
4
4
4
4
4
5
5
5
5
5
5
5
5
5
5
6
CH NH PbI crystals. CH NH I
was synthesized according to
the literature by solution
reaction of 24 mL methylamine
solution (33 wt% in ethanol,
Aldrich), 10 mL hydroiodic acid
3
3
3
3
3
a
(
HI, 57 wt%, Aldrich) and 100
mL ethanol (99.7%, Shanghai
Lingfeng Chemical reagent) in
0
1
2
3
4
5
6
7
8
9
0
1
2
3
4
5
6
7
8
9
0
1
2
3
4
5
6
7
8
9
0
1
2
3
4
5
6
7
8
9
0
1
2
3
4
5
6
7
8
9
0
250 mL round bottomed flask
under nitrogen atmosphere at 0
0
C for 2 h with stirring at 400
1
1
rpm.
The precipitate was
recovered by evaporation at 50
o
C for 2 h, washed with diethyl
Figure 1. Schematic illustration of the plausible formation mechanisms of (A) in situ transformation and (B)
dissolutionꢀcrystallization of CH
3
NH
3
PbI
3
crystals via sequential reaction route. The insets in the right images are the ether three times and finally
o
atomic structure of CH NH PbI
3
3
3
crystals.
dried at 60 C in vacuum oven
overnight. The synthesis of
CH NH PbI was conducted via a sequential reaction
route at room temperature. In a typical synthesis, 2 mg of
PbI was firstly added in 2 ml isopropanol (IPA, 99.7%,
Aldrich). These PbI crystals can not be dissolved and to
ensure well dispersion, the obtained suspension was
further treated in ultrasonic bath for 15 min. Then 8 mL of
0.06 mM CH NH I isopropanol solution was dropwise
kinetics by governing the chemical coordination between
Pb and I atoms. To the best of our knowledge, such
crystal growth mechanism has not been reported for this
important sequential reaction process of organic-
inorganic perovskite crystals. Moreover, the freestanding
perovskite crystals can not only be kept parallel
3
3
3
2
2
geometries to PbI , but reconstructed into cube-shaped
2
2
3 3
perovskite crystals as well at certain CH NH I
3
3
added into the PbI suspension under magnetic stirring at
2
concentration. Our synthesis strategy would enable the
availability of freestanding perovskite crystals with
controllably geometries as well as understanding the
intrinsic crystal growth of organic-inorganic perovskites.
400 rpm. The colour of the precipitates changed from
yellow to dark brown and finally to black. After stirring
for 2 h, the products were separated by centrifugation at
7000 rpm for 6 min, washed three times with hexane or
o
chlorobenzene (10 ml each time) and finally dried at60 C
2
.
EXPERIMENTAL SECTION
for 2h in a vacuum oven.
2
.1. Synthesis of PbI crystals. Lead iodine crystals were
2
2.3.
Material
characterization. Crystallographic
information of CH NH PbI crystals was investigated by
synthesized by a modified method according to the
literature. Typically, 0.971 g lead nitrate (Pb(NO ) , 99%,
25
3
3
3
3
2
powder X-ray diffraction (PXRD, Bruker D8 Advanced
Diffractometer, Cu Kα radiation, 40 kV). The morphology
and structure of the samples were characterized by field
emission scanning electron microscopy (FESEM,
HITACHI S4800) and transmission electron microscopy
Aldrich) and certain amount of the capping agents were
dissolved in 25 ml deionized water. Here, the capping
agents for the synthesis of sample PbI -S1 and PbI -S2 are
2
2
0
0
.06 g of polyvinyl pyrrolidone (PVP, M=40000, Aldrich),
.10 g of cetyltrimethylamonium bromide (CTAB, 99%,
(
TEM, JEOL JEM-1400, 100 kV). PbI2 and perovskite
Aldrich), respectively, and the sample PbI -S3 is
2
samples were dispersed in deionized water or hexane,
respcetively, and then dropped on a conductive SEM
sample holder, or a carbon-coated copper grid with
irregular holes for electron microscopy (SEM/TEM)
analysis. The Pb content dissolved in solution was
determined by inductively coupled plasma spectroscopy
synthesized without capping agents. Then 5 mL of 0.6 M
potassium iodide (KI, 99%, Aldrich) aqueous solution
which acted as iodine precursor was slowly dropped into
the Pb(NO ) solution under vigorous stirring at 700 rpm,
3
2
and a yellow coloured precursor was obtained. The
mixture of 30 ml was transferred into a Teflon-lined
autoclave with a filling ratio of 60%. The vessel was then
(
ICP). The optical absorption spectra were measured by
using
a
Cary
500
Spectrophotometer.
The
a
o
sealed and treated at 120 C for 12 h in an oven. After
photofluorescence spectra were obtained from
Fluorolog-3-P molecular fluorescence spectrometer with
excitation wavelength of 460 nm.
cooled to room temperature, the clear solution at the
upper section was carefully removed by plastic dropper
and a precipitate (PbI product) formed at the bottom of
2
the Teflon reactor. The solid products obtained were
3
.
RESULTS AND DISCUSSION
collected by centrifugation at 7000 rpm for 6 min, raised
o
with H O twice (15 ml each time) and dried at 60 C in a
Typically, crystal growth in solution can be classified into
2
vacuum oven overnight.
ACS Paragon Plus Environment

Page 3 of 7
Chemistry of Materials
geometries based on a hydrothermal method by reacting
25
1
2
3
4
5
6
7
8
9
Pb(NO ) with KI in the presence of capping agents.
3
2
Then the PbI2 crystals were transferred into an
isopropanol solution with excess CH NH I, these crystals
3
3
were therefore turned from yellow to dark brown and
finally to black. There is also some difference between
PbI samples in the transformation rate which is probably
2
ascribed to the shape, size, and surface characteristics of
PbI and the CH NH I concentration.
2
3
3
During the formation of perovskite crystals, iodine
ions play crucial roles to determine the crystal growth
mechanism; it is thus necessary to investigate the
crystallographic variations of the products with different
10
11
12
13
14
15
16
17
18
19
20
21
22
23
24
25
26
27
28
29
30
31
32
33
34
35
36
37
38
39
40
41
42
43
44
45
46
47
48
49
50
51
52
53
54
55
56
57
58
59
60
-
I concentration. Figure 2 presents the PXRD patterns of
the products by reacting as-prepared sample PbI -S1 with
2
1
6.05 and 53.49 mM CH NH I in isopropanol. Diffraction
3 3
o
o
o
o
peaks at 12.67 , 25.51 , 38.66 and 52.39 match well with
the (001), (002), (003) and (004) lattice planes of
hexagonal 2H PbI2 polytype (space group: P3m1(164),
JCPDS file No. 07-0235), respectively. After reacting for 20
min in 16.05 mM CH NH I, the diffraction peaks shift to
Figure 2. PXRD patterns of the CH
different concentration of CH NH I: (A, B) 16.05, and (C) 53.49 mM. (B)
shows detailed patterns around 12 and 16 2θ values.
3 3 3
NH PbI crystals synthesized with
3
3
3
3
o
o
o
about 0.35 larger 2-theta values which may be as a
consequence of the coordinate variation of lead and
intercalation of interstitial molecules, ions or atoms
forming a transient state. Further reaction to 60 min, the
three basic types: precipitation from supersaturated
solution, in situ transformation, and dissolution-
crystallization. Regarding the reaction conditions for the
sequential process, it should be processed by in situ
transformation or dissolution-crystallization mechanisms
2
0
obtained crystals exhibit two separated phase of PbI and
2
CH NH PbI accompanied by the CH NH I intercalation.
3
3
3
3
3
We then observed the almost completely formation of
perovskite phase at 120 min, and the refined tetragonal
as shown in Figure 1. Here, PbI2 is
a layered
semiconductor contains a hexagonally closed-packed Pb
plane sandwiched between two layers of iodide ions. For
the in situ transformation mechanism, only trace amount
of PbI will be dissolved in solvent which suggests the
inorganic lead framework can be remained. The dissolved
iodine ions would drive edge-sharing PbI octahedrons to
corner-sharing structure along the equatorial direction,
together with the inserting of the organic ammonium
ions. Generally, PbI is almost completely insoluble in
isopropanol that the lead framework has been presumed
to be remained, however, in this case, it can be truly
coordinated with iodine ions to form lead complex.
Therefore, we
hypothesize that the
crystal
perovskites
lattice parameters, a=8.762(2) Å, c=12.449(5) Å, are
16, 26
slightly smaller than the previous reported values.
The
presence of vacancies on one or two of the three primitive
sites of perovskites may locally cause the alternating of
crystal lattice in an attempt to reestablish stoichiometry
2
6
27
across all the site, since the long reaction time for
+
-
CH NH PbI indicates the deficiency of CH NH and I
3
3
3
3
3
kinetically. Evidently, this crystallization process should
be an in situ transformation rather than dissolution-
crystallization due to the presence of the transient state
between the networks of edge sharing hexagonal and
2
21-23
growth
of
would
dissolution-
undergo
a
crystallization process in
iodine rich environment.
In the presence of
ammonium
cations,
coordinated lead complex
as building blocks can
further recrystallize into
a
thermodynamically
2
4
favored morphology.
Our synthetic strategy
of CH NH PbI crystals
3
3
3
typically involves initial
preparation of
crystals with expected
2 3 3 3
Figure 3. SEM images of the as prepared (AꢀC) PbI and (DꢀF) CH NH PbI crystals. The insets are the corresponding shape
models. All samples were synthesized with the reaction time of 2 h.
PbI2
ACS Paragon Plus Environment

Chemistry of Materials
Page 4 of 7
kept constant in these experiments, a small amount of
1
2
3
4
5
6
7
8
9
1
1
1
1
1
1
1
1
1
1
2
2
2
2
2
2
2
2
2
2
3
3
3
3
3
3
3
3
3
3
4
4
4
4
4
4
4
4
4
4
5
5
5
5
5
5
5
5
5
5
6
PbI is still existed in Pero-S3, which may be due to the
2
difference in crystal geometries (Figure S3). Certainly, all
three samples prepared at low CH NH I concentration are
3
3
in good consistent with the in situ transformation
mechanism, and we have therefore demonstrated a new
synthetic strategy to prepare CH NH PbI crystals with
3
3
3
targeted geometric characteristics, in which the overall
crystal shapes are largely dependent on the morphology
of PbI crystals.
2
0
1
2
3
4
5
6
7
8
9
0
1
2
3
4
5
6
7
8
9
0
1
2
3
4
5
6
7
8
9
0
1
2
3
4
5
6
7
8
9
0
1
2
3
4
5
6
7
8
9
0
To
elucidate
the
dissolution-crystallization
mechanism, we then sought to increase the CH NH I
3
3
concentration, which is expected to destabilize PbI2
lattice and favor the recrystallization into
thermodynamically geometries. Inductively coupled
plasma (ICP) spectroscopy was employed to determine
the amount of Pb dissolved of PbI -S1 sample at different
2
CH NH I concentration as shown in Figure 4e. We found
3
3
that PbI is tend to be dissolved in iodine rich condition
2
and such phenomenon can be fulfilled by following
21
chemical equation,
Figure 4. (AꢀD) SEM images of the CH
different CH NH I concentration. (B) is at high magnification of the sample in
A). (E) Relationship between the dissolved Pb concentration (left axis) and
ratio (right axis) versus CH NH I concentration in the system after reaction. (F)
PXRD patterns of the CH NH PbI crystals synthesized with different
CH NH I concentration.
3
NH
3
PbI
3
crystals obtained with
The morphological and crystallographic information
in such process were further investigated by SEM and
PXRD, and the results are shown in Figure 4. With
CH NH I in the range between 2.67 and 5.34 mM, the
3
3
(
3
3
3
3
3
3
3
3
3
amount of dissolved lead was detected to be lower than
.0121 mM or 2.85% in the isopropanol solution that
0
resulted in incomplete formation of perovskites.
Curiously, when using 26.07 mM CH NH I, rod shaped
corner sharing tetragonal PbI octahedrons both at 20 and
6
3
3
6
0 min. Additionally, the scanning electron microscopy
crystals can not be observed, and alternatively, totally
new cube shaped CH NH PbI crystals with mean size of
(
SEM) images of the products harvested at different
3
3
3
reaction times clearly illustrated the in situ
transformation was firstly occurred at the crystal surface
by gradual ions intercalation with the original lead
framework (Figure S1). However, when 53.49 mM
CH NH I was used, the precipitate turned black within
3
3
seconds and in principle, such rapid crystal growth would
result in the collapse of the lead backbones. Only
tetragonal phase CH NH PbI occurred even in short
3
3
3
reaction time, and considering the extra iodine ions can
21
coordinate with Pb atoms, this process should be
classified as dissolution-crystallization.
One inherent difference between above mechanisms
lies in keeping or collapse of the lead framework before
and after reaction, which can be associated with the
morphological
change.
To
enable
systematical
observation of these changes, PbI -S1, PbI -S2, and PbI -S3
2
2
2
were synthesized with PVP, CTAB or without capping
agents by a hydrothermal method which present rod, wire
and plate shapes, respectively (Figure 3). After the
reaction in 16.05 mM CH NH I, the lead framework of
3
3
Pero-S1 is still kept as the rod shaped PbI -S1 with the
2
similar size and the crystals exhibits well-defined cuboid
surface with edges and corners. The sample Pero-S2 and
Pero-S3 are kept well of their overall wire and plate
shapes with PbI2 crystals and are also confirmed by
transmission electron microscopy (TEM) images (Figure
S2). Interestingly, although the reaction conditions were
Figure 5. (A) UV−vis absorption and (B) photoluminescence spectrum of the
as prepared CH NH PbI perovskites.
3
3
3
ACS Paragon Plus Environment

Page 5 of 7
Chemistry of Materials
4
.13 μm were generated, suggesting the intensive
in the visible range can not propagate through such
materials, and thus are localized and absorbed. However,
we note that there are some differences the absorbance
onset of the sample Pero-S3 as compared to Pero-S1 and
S2, which may be as a result of the different crystal
1
2
3
4
5
6
7
8
9
1
1
1
1
1
1
1
1
1
1
2
2
2
2
2
2
2
2
2
2
3
3
3
3
3
3
3
3
3
3
4
4
4
4
4
4
4
4
4
4
5
5
5
5
5
5
5
5
5
5
6
dissolution of PbI2 framework and the following
recrystallization into CH NH PbI crystals (Figure S4).
Furthermore, by using 53.49 mM CH NH I, the mean size
3
3
3
3
3
of obtained CH NH PbI crystals reaches a maximum of
3
3
3
28
3
0.2 μm with tetragonal structure as we expected in the
geometries. Moreover, Pero-S3 has an absorption peak
dissolution-crystallization growth. We finally raised the
CH NH I concentration to 106.98 mM, which inversely
reduces the cube shaped crystals to a mean size of 15.4
μm.
centered at 500 nm. This may be derived from the PbI as
2
a result of the incomplete reaction which is in consistence
3
3
2
9
with recent reports. The normalized near-infrared
photoluminescence of the perovskite crystals is shown in
Figure 4B. A 5 nm red shift in the emission peak from
Pero-S1 (λmax =766 nm) to Pero-S3 (λmax=771 nm) can be
observed in registry with the absorption spectrum. These
optical differences probably arise from the size, shape,
and polycrystalline of CH NH PbI crystals as well as the
0
1
2
3
4
5
6
7
8
9
0
1
2
3
4
5
6
7
8
9
0
1
2
3
4
5
6
7
8
9
0
1
2
3
4
5
6
7
8
9
0
1
2
3
4
5
6
7
8
9
0
As suggested above, our experimental results agree
well with the previous result that the PbI can be isolated
into PbI or PbI complex in iodine rich environment, as
the first dissolution step according to equation (1). The
formation of Pb complex would shift the equilibrium
forward to form perovskites via the recrystallization step
of equation (2).
2
-
2-
3
4
21
3
3
3
existence of PbI /CH NH PbI heterostructures. This
2
3
3
3
difference also hold promise for the further optimization
of this class of materials by crystal shape engineering or
incorporation of heterostructures.
On the basis of these findings, it can be reasonably
concluded that the kinetics of such crystal growth process
is greatly relied on the CH NH I concentration. At low
CH NH I concentration (<16.5 mM), only a small amount
of PbI can be bonded with iodine ions to form PbI
and/or PbI4 complex, and the lead framework can be
preserved. Subsequently, the recrystallization can not be
fully conducted and reversely, the CH NH I and I are
more prone to be directly intercalated into the lead
frameworks which give rise to CH NH PbI crystals with
original shapes by the in situ transformation. However,
the dissolved Pb concentration shows a slow change in
the presence of sufficient CH NH I (>26.7 mM),
CONCLUSION
3
3
In summary, we have developed for the first time a
versatile and simple synthetic strategy to prepare
3
3
-
2
3
2-
solution-processed freestanding CH NH PbI perovskite
3
3
3
crystals for revealing the intrinsic crystal growth
mechanism. Different from the previous views, the
experimental results presented here on cleaved samples
illustrate vividly that the in situ transformation and
dissolution-crystallization mechanisms play competing
roles in perovskite crystal growth, which largely depends
on iodine concentration that determine chemical reaction
+
-
3
3
3
3
3
3
3
kinetics. Crucially, by controlling the PbI morphology
indicating PbI may be well coordinated and existed as
PbI4 form in this condition. This also allows the
synthesis of new cube shaped CH NH PbI crystals whose
2
2
2-
21
and CH NH I concentration, we have succeed in tailoring
3
3
the crystal geometries including rods, wires, plates, and
cubes with tunable size. For the similarity of this type of
organic-inorganic perovskite based material, other
organic-inorganic hybrid perovskites can be, in principle,
obtained by this method accordingly. Furthermore, the
3
3
3
size was firstly increased to a maximum of 30.2 μm and
then reduced to 15.4 μm. Hence, the iodine ions act as
both lead ligands and reaction products at high CH NH I
concentration, which expedite the dissolution of lead
iodine, reversely retard the bonding between each
complex, and thus can finally regulate the crystal
characteristics. Since dissolution can be occurred partly
even in poor solvents, the main distinction between in
situ transformation and dissolution-crystallization
mechanism is the relative kinetic reaction rate of the
3
3
CH NH PbI crystals we synthesized exhibit significant
3
3
3
difference in optical properties. These results indicate this
method may help to understand the crystal growth
mechanism of organolead halide perovskites which have
potential applications such as catalysis, solar cells, field-
effect transistors, light-emitting devices as well as other
opto-electronic devices.
20
dissolution-crystallization process.
Based on these
systematically studies by measuring the solubility of PbI2,
the keep or collapse of lead backbone and the
intermediate state during the reaction, we can reasonably
concluded that in situ transformation and dissolution-
crystallization play the dominate role at low and high
CH NH I concentration, respectively. In addition, both
ASSOCIATED CONTENT
Supporting Information. Figures show SEM, TEM and
PXRD of the resultant samples. This material is available free
of charge via the Internet at http://pubs.acs.org.
3
3
AUTHOR INFORMATION
mechanisms work together at the medial CH NH I
concentration.
3
3
Corresponding Author
We then measured the UV-vis absorption and
* E-mail: hgyang@ecust.edu.cn
photoluminescence (PL) of the obtained CH NH PbI
3
perovskite crystals at room temperature as depicted in
Figure 5. All CH NH PbI crystals we synthesized have
3
3
ACKNOWLEDGMENT
This work was financially supported by National Natural
Science Foundation of China (21373083, 21203061), SRF for
ROCS, SEM, SRFDP, Programme for Professor of Special
3
3
3
broad optical absorption up to 800 nm and most photons
ACS Paragon Plus Environment

Chemistry of Materials
Page 6 of 7
Appointment (Eastern Scholar) at Shanghai Institutions of
(27) Neagu, D.; Tsekouras, G.; Miller, D. N.; Ménard, H.;
1
2
3
4
5
6
7
8
9
1
1
1
1
1
1
1
1
1
1
2
2
2
2
2
2
2
2
2
2
3
3
3
3
3
3
3
3
3
3
4
4
4
4
4
4
4
4
4
4
5
5
5
5
5
5
5
5
5
5
6
Higher Learning, Fundamental Research Funds for the
Central Universities (WD1313009, WD1214036), and China
Postdoctoral Science Foundation (2012M511056, 2013T60425).
Irvine, J. T. S. Nat. Chem. 2013, 5, 916-923.
(28) Pan, J.; Liu, G.; Lu, G. Q.; Cheng, H.-M., Angew. Chem.
Int. Ed. 2011, 123, (9), 2181-2185.
(
29) Chen, Q.; Zhou, H.; Song, T.ꢀB.; Luo, S.; Hong, Z.; Duan,
H.ꢀS.; Dou, L.; Liu, Y.; Yang, Y. Nano Letters 2014, 14, 4158ꢀ4163.
REFERENCES
(1)
Kagan, C.; Mitzi, D.; Dimitrakopoulos, C. Science 1999,
286, 945-947.
(2)
(3)
(4)
(5)
Mitzi, D. B. J. Chem. Soc., Dalton Trans. 2001, 1-12.
Mitzi, D. B. J. Mater. Chem. 2004, 14, 2355-2365.
Mitzi, D. B. Prog. Inorg. Chem. 2007, 48, 1-121.
Schmidt, L. C.; Pertegás, A.; González-Carrero, S.;
0
1
2
3
4
5
6
7
8
9
0
1
2
3
4
5
6
7
8
9
0
1
2
3
4
5
6
7
8
9
0
1
2
3
4
5
6
7
8
9
0
1
2
3
4
5
6
7
8
9
0
Malinkiewicz, O.; Agouram, S.; Minguez Espallargas, G.; Bolink,
H. J.; Galian, R. E.; Pérez-Prieto, J. J. Am. Chem. Soc. 2014, 136,
850–853.
(6)
Burschka, J.; Pellet, N.; Moon, S.-J.; Humphry-Baker,
R.; Gao, P.; Nazeeruddin, M. K.; Grätzel, M. Nature 2013, 499,
3
16-319.
7)
95–398.
8)
(
Liu, M.; Johnston, M. B.; Snaith, H. J. Nature 2013, 501,
Kojima, A.; Teshima, K.; Shirai, Y.; Miyasaka, T. J. Am.
3
(
Chem. Soc. 2009, 131, 6050-6051.
9) Jeon, N. J.; Lee, H. G.; Kim, Y. C.; Seo, J.; Noh, J. H.;
Lee, J.; Seok, S. I. J. Am. Chem. Soc. 2014, 136, 7837-7840.
(10) Xing, G.; Mathews, N.; Sun, S.; Lim, S. S.; Lam, Y. M.;
Grätzel, M.; Mhaisalkar, S.; Sum, T. C. Science 2013, 342, 344-347.
11) Stranks, S. D.; Eperon, G. E.; Grancini, G.; Menelaou,
(
(
C.; Alcocer, M. J.; Leijtens, T.; Herz, L. M.; Petrozza, A.; Snaith,
H. J. Science 2013, 342, 341-344.
(
12)
A.; Snaith, H. J. Adv. Funct. Mater. 2013, 24, 151–157.
13) Docampo, P.; Ball, J. M.; Darwich, M.; Eperon, G. E.;
Snaith, H. J. Nat. Commun. 2013, 4.
Eperon, G. E.; Burlakov, V. M.; Docampo, P.; Goriely,
(
(14)
Heo, J. H.; Im, S. H.; Noh, J. H.; Mandal, T. N.; Lim, C.-
S.; Chang, J. A.; Lee, Y. H.; Kim, H.-j.; Sarkar, A.;
NazeeruddinMd, K.; Gratzel, M.; Seok, S. I. Nat. Photon. 2013, 7,
4
86–491.
15)
Manca, J.; Boyen, H.-G. Adv. Mater. 2013, 26, 2041-2046.
16) Liang, K.; Mitzi, D. B.; Prikas, M. T. Chem. Mater. 1998,
0, 403-411.
(17) Chen, Q.; Zhou, H.; Hong, Z.; Luo, S.; Duan, H.-S.;
Wang, H.-H.; Liu, Y.; Li, G.; Yang, Y. J. Am. Chem. Soc. 2013, 136,
(
Conings, B.; Baeten, L.; De Dobbelaere, C.; D'Haen, J.;
(
1
6
22-625.
18)
81502.
(
Cohen, B. E.; Gamliel, S.; Etgar, L. APL Mat. 2014, 2,
Mitzi, D. B. Chem. Mater. 2001, 13, 3283-3298.
0
(19)
(20) Markov, I. V. Crystal growth for beginners. World
Scientific, 1995.
21)
(
Horváth, O.; Mikó, I. J. Photoch. Photobio. A 1998, 114,
95-101.
(22)
Shaopu, L.; Yi, L.; Zhonfan, L. Mikrochim. Acta 1983,
8
1, 355-366.
23) Clever, H. L.; Johnston, F. J. J. Phys. Chem. Ref. Data
980, 9, 751-784.
24) Lovette, M. A.; Browning, A. R.; Griffin, D. W.;
Sizemore, J. P.; Snyder, R. C.; Doherty, M. F. Ind. Eng. Chem. Res.
008, 47, 9812-9833.
25) Zhu, G.; Liu, P.; Hojamberdiev, M.; Zhou, J.-p.; Huang,
(
1
(
2
(
X.; Feng, B.; Yang, R. Appl. Phys. A Mater. Sci. Process. 2010, 98,
299-304.
(26) Colella, S.; Mosconi, E.; Fedeli, P.; Listorti, A.; Gazza,
F.; Orlandi, F.; Ferro, P.; Besagni, T.; Rizzo, A.; Calestani, G.;
Gigli, G.; De Angelis, F.; Mosca, R. Chem. Mater. 2013, 25, 4613-
4
618.
ACS Paragon Plus Environment

Page 7 of 7
Chemistry of Materials
1
2
3
4
5
6
7
8
9
Shuang Yang, Yi Chu Zheng,
Yu Hou, Xiao Chen, Ying
Chen, Yun Wang, Huijun Zhao
and Hua Gui Yang*
10
11
12
13
14
15
16
17
18
19
20
21
22
23
24
25
26
27
28
29
30
31
32
33
34
35
36
37
38
39
40
41
42
43
44
45
46
47
48
49
50
51
52
53
54
55
56
57
58
59
60
On the Formation Mechanism
of Freestanding CH NH PbI
Functional Crystals: in situ
Transformation vs Dissolution-
Crystallization
3
3
3
ACS Paragon Plus Environment