Syntheses of needle-shaped layered perovskite (C6H5CH2NH3)2PbI4bundles via a two-step processing technique

Article abstract of DOI:10.1016/j.jallcom.2016.12.090

Similar to the three-dimensional perovskites, two-dimensional (2D) layered lead halide perovskites constitute a particular class of semiconductor materials in the family of perovskites. This article reports syntheses of needle-like bundles of 2D perovskite (C₆H₅CH₂NH₃)₂PbI₄by a two-step processing technique. The concentration of C₆H₅CH₂NH₃I precursor has a great influence on the product, structural and compositional analyses prove the phase and stoichiometry of 2D perovskite (C₆H₅CH₂NH₃)₂PbI₄with high crystallinity for the needle bundles synthesized with concentration of C₆H₅CH₂NH₃I higher than 25 mg/mL. Intensive studies on the growth mechanism of the products were carried out; we believe the involvement of C₆H₅CH₂NH₃⁺group determines the layered structure and the final morphology of the products. Photoluminescence measurement show that the needles possess a band-edge emission peak centering around 540 nm and a narrow full width at half maximum of about 30 nm.

Full text of DOI:10.1016/j.jallcom.2016.12.090

Accepted Manuscript
Syntheses of needle-shaped layered perovskite (C H CH NH ) PbI bundles via a
6 5 3 2
2
4
two-step processing technique
Dewei Ma, Yidan He
PII:
S0925-8388(16)34008-7
DOI:
10.1016/j.jallcom.2016.12.090
JALCOM 40012
Reference:
To appear in: Journal of Alloys and Compounds
Received Date: 12 October 2016
Revised Date: 30 November 2016
Accepted Date: 6 December 2016
Please cite this article as: D. Ma, Y. He, Syntheses of needle-shaped layered perovskite
(C H CH NH ) PbI bundles via a two-step processing technique, Journal of Alloys and Compounds
6 5
2
3 2
4
(2017), doi: 10.1016/j.jallcom.2016.12.090.
This is a PDF file of an unedited manuscript that has been accepted for publication. As a service to
our customers we are providing this early version of the manuscript. The manuscript will undergo
copyediting, typesetting, and review of the resulting proof before it is published in its final form. Please
note that during the production process errors may be discovered which could affect the content, and all
legal disclaimers that apply to the journal pertain.

ACCEPTED MANUSCRIPT

ACCEPTED MANUSCRIPT
Syntheses of needle-shaped layered perovskite
(C6H5CH2NH3)2PbI4 bundles via a two-step
processing technique
Dewei Ma*, Yidan He
Department of Applied Physics, Zhejiang University of Technology, Hangzhou
310023, PR China
*Corresponding author: Dewei Ma
E-mail: dwma@zjut.edu.cn
ABSTRACT
Similar to the three-dimensional perovskites, two-dimensional (2D) layered lead
halide perovskites constitute a particular class of semiconductor materials in the
family of perovskites. This article reports syntheses of needle-like bundles of 2D
perovskite (C6H5CH2NH3)2PbI4 by a two-step processing technique. The
concentration of C6H5CH2NH3I precursor has a great influence on the product,
structural and compositional analyses prove the phase and stoichiometry of 2D
perovskite (C6H5CH2NH3)2PbI4 with high crystallinity for the needle bundles
synthesized with concentration of C6H5CH2NH3I higher than 25 mg/mL. Intensive
studies on the growth mechanism of the products were carried out; we believe the
+
involvement of C6H5CH2NH3 group determines the layered structure and the final
morphology of the products. Photoluminescence measurement show that the needles
possess a band-edge emission peak centering around 540 nm and a narrow full width
at half maximum of about 30 nm.
1

ACCEPTED MANUSCRIPT
Keywords: Nanostructured materials; Chemical synthesis; Crystal growth; Optical
properties
1. Introduction
Organic–inorganic lead halide perovskites, particularly the three-dimensional
(3D) perovskites represented by methylammonium (MA) lead iodide, have been
under intense investigation due to their applications in high efficiency solar cells and
efficient light emitters [1-4]. Similar to the 3D perovskites, two-dimensional (2D)
layered lead halide perovskites with the general formula (RNH3)2PbX4 or
(NH3-R-NH3)PbX4, where R is an organic group, and X a halogen such as Cl, Br, or I,
constitute a particular class of semiconductor materials in the family of perovskites [5,
6]. The structure of this kind of hybrid consists of an extended network of
corner-sharing metal halide octahedra [PbX6]4- alternating with a bilayer or monolayer
organic moiety, exhibiting a multi-quantum well structure [7]. In terms of the
considerable contrast of the dielectric constants between the metal halide layer and the
organic layer, the 2D hybrid perovskite exhibits a very large exciton binding energy of
a few hundred meV, much larger than those in a quasi-2D analog PbX2 [8, 9]. The
confined excitons in the inorganic layer, consequently, display unique optical
properties such as sharp exciton emission even at room temperature [10], efficient
electroluminescence [11-13], increased scintillation [14], and distinguished
third-order optical nonlinearity [15, 16] etc.
Generally, the 2D layered perovskites possess excellent film process-ability. So
far, a large variety of methods, including spin coating [17, 18], vacuum vapor
2

ACCEPTED MANUSCRIPT
deposition [19, 20] and two-step dip processing method [21], have been used to
prepare the 2D layered perovskite thin films. Although the 2D perovskite thin films
have excellent optical properties [10, 11, 14-16] together with important applications
in device fabrications [22-26], in general ideas, single crystals possess exceptionally
low trap-state densities and long charge-carrier diffusion lengths [27], thus leading to
better device performance over polycrystalline films. On the other hand, single
crystals are often the most useful medium for examining structural and physical
properties of the compounds [28]. Yet synthesis of hybrid materials is often
challenging because of the distinctly different physical and chemical characters of the
organic and inorganic components [19]. Furthermore, allowing for the decomposition
of the hybrid perovskite at an elevated temperature, organic-inorganic perovskite
single crystals are normally synthesized by crystal growth from a solution phase, the
most employed method was solvent evaporation or cooling down the saturated
precursor solution [20].
Due to superior optoelectronic properties compared to their bulk counterparts,
one-dimensional (1D) nanostructural materials (nanorods, nanowires and nanoneedles)
of single-crystal semiconductors have attracted heightened attention for the
applications in nanoelectronics and nanophotonics [29, 30]. However, there has been
little reports on syntheses of 2D perovskites with controlled morphology like 1D
nanorods/nanoneedles [31]. Furthermore, to our knowledge, little references on
(C6H5CH2NH3)2PbI4 (abbreviated as (PMA)2PbI4 hereafter for convenience) were
reported previously [32-34]. In this article, we report syntheses of needle-like bundles
3

ACCEPTED MANUSCRIPT
of 2D perovskite (PMA)2PbI4 by a two-step processing technique, namely, thin film of
lead salt was prepared first, and then the pre-deposited thin film was dipped into a
solution containing the desired organic ammonium cation for a period of time with the
aim to get the final product. Then we studied the growth mechanism of these
needle-like bundles intensively. Optical measurements show that the needles possess a
band-edge emission peak centering around 540 nm and a narrow full width at half
maximum (FWHM) of about 30 nm.
2. Experimental details
All chemicals and reagents were purchased from Sigma-Aldrich and used as
received unless specified otherwise.
2.1. Synthesis of benzylammonium iodide (C6H5CH2NH3I, PMAI)
The benzylammonium iodide was synthesized by a similar method reported
previously [24]. Briefly, HI (57 wt.% in water) was added slowly to equal molar ratio
of benzylamine in a flask at 0 °C. Then the mixture was evaporated at an elevated
temperature until benzylammonium iodide crystals precipitated from the solution.
After the solution was cooled, the powder product was filtered and rinsed with diethyl
ether several times before it was dried at 80 °C in a vacuum oven for ∼24 h to remove
the residual water.
2.2. Growth of needle-like bundles of (PMA)2PbI4
First, PbAc2 thin film was prepared by drop-casting 100 mg/mL PbAc2.3H2O
aqueous solution on FTO glass substrate, and then dried in an oven for 30 min at
60 °C. Then the needle-like bundles of (PMA)2PbI4 were synthesized by placing the
4

ACCEPTED MANUSCRIPT
PbAc2 film into PMAI solution in isopropanol (IPA) with concentration higher than
25 mg/mL at room temperature. After a specified reaction time, the FTO substrate was
taken out and dipped into IPA to remove any leftover solution on the sample, and then
dried under a stream of nitrogen flow. For the samples with PbI2 as the Pb source,
PbI2 film was prepared by spin-coating a solution of 400 mg/mL PbI2 (99.99%) in
dimethylformamide (DMF) at 3000 rpm for 15 s in air, and then the spin-coated PbI2
film was immersed in PMAI/IPA solution for a period of time.
2.3. Structural, morphological and optical characterizations
Optical images were obtained with an Olympus BX51M optical microscope.
Scanning electron microscope (SEM) images were acquired on a LEO SUPRA 55 VP
field-emission SEM operated at 3.0 kV. Energy-dispersive X-ray spectroscopy (EDX)
was performed on samples transferred onto a Si wafer using a LEO 1530
field-emission SEM equipped with an EDS detector operating at 15.0 kV. X-ray
diffraction (XRD) data were collected using Cu Kα radiation on a Siemens STOE
diffractometer (40 kV, 40 mA). The photoluminescence (PL) of single needle was
collected with an Aramis Confocal Raman/PL microscope excited by a 442 nm laser.
The sample was transferred to a Si substrate by a dry-transfer method before the PL
measurement.
3. Results and discussion
For the two-step processing technique to synthesize 2D perovskite (PMA)2PbI4,
the concentration of PMAI in IPA has a great influence on the product. XRD
measurements show that the as-synthesized products keep the same crystal structure
5

ACCEPTED MANUSCRIPT
at a PMAI/IPA concentration higher than 25 mg/mL (Fig. S1). The typical XRD
pattern in Fig. 1(a) (upper XRD pattern) shows that the diffraction peaks can be
indexed to (00l) (l=2, 4, 6, 8, 10 …) reflections of two-dimensional (2D) layered
perovskite of (PMA)2PbI4, crystalizing in an orthorhombic crystal system with space
group of Pbca and lattice parameters of a=8.689 Å, b=9.162 Å and c=28.78 Å [32, 34].
The observation of sharp and high diffraction orders proves the high crystallinity of
the as-synthesized 2D perovskite of (PMA)2PbI4. We also noticed the as-synthesized
products crystalized in other crystal structures obviously different from above 2D
perovskite of (PMA)2PbI4 with the PMAI/IPA concentration decreasing down to
10-20 mg/mL or around 5 mg/mL (Fig. S1), indicating different phases form under
this condition. Fig. 1(b) shows the extended crystal structure of (PMA)2PbI4. The
basic structural unit of this compound consists of a layer of corner-sharing PbI6
octahedra, with a layer of benzylammonium cations capping on both sides of the
[PbI4]2- layer through hydrogen bonds between the ammonium group and halogen
atoms (N-H•••X). The crystal of this 2D perovskite is then formed via stacking the
neutral (PMA)2PbI4 layers along the c axis via weak van der Waals interactions [32].
SEM measurements were then carried out to investigate the morphological
evolution of the product with the PMAI/IPA concentration (Fig. S2). Note that the
product, namely 2D perovskite of (PMA)2PbI4, forms in needle-like hyper-branched
bundles at a PMAI/IPA concentration ranging from 30 mg/mL to 80 mg/mL, and the
needle becomes wider in diameter, while changes little in length with increasing
PMAI/IPA concentration. When the PMAI/IPA concentration deceases down to 10-20
6

ACCEPTED MANUSCRIPT
mg/mL, ribbon-like bundles develop in solution; at around 5mg/mL, hexagonal plates
stacked pagoda-like structure comes into being. Herein, we focus on studies of 2D
perovskite (PMA)2PbI4, namely the crystal growth of needle-like bundles. The typical
SEM and optical images of needle-like bundles of (PMA)2PbI4 are illustrated in Fig.
2(a-b), here the PMAI/IPA concentration of 40 mg/mL was used as an example. The
needles are measured to be 1000~1500 ꢀm in length and 10 ~ 20 ꢀm in sectional
dimension, the aspect ratio is supposed to be ~100. Besides the formation of
needle-like hyper-branched bundles with sector-like morphology, we noticed a few
individual needles exhibiting the feature of “two sharp ends”, as encircled by an
ellipse in Fig. 2(a). A magnified SEM image displayed in Fig. 2(c) further verifies the
“sharp tip” character of the needle. The middle section of the needle exhibits a flat
morphology and smooth surface, as clearly indicated in Fig. 2(d-e). Combined with
the XRD pattern in above Fig. 1(a), we can conclude that the flat surface of
(PMA)2PbI4 needle corresponds to the (00l) reflections, namely the crystallographic
ab plane of layered compound (PMA)2PbI4, in other words, the c-axis is perpendicular
to the substrate [35]. Fig. 2(f) displays a picture of the sample growing in an 80 mg/ml
PMAI/IPA solution after a reaction time of 2.5 h, which shows orange-colored needles
growing to diverse directions to form hyper-branched bundle with one ends of the
needles adhered together.
To further confirm the element constituents in the (PMA)2PbI4 needle, the needle
was made a direct dry transfer to Si substrate and conducted EDX test, the results are
displayed in Fig. 3. Elements Pb and I were found obviously in a representative EDX
7

ACCEPTED MANUSCRIPT
spectra of a single (PMA)2PbI4 needle, the elements C and O may come from the
surface contamination and oxidation of the SEM sample. Qualitative results of 30
individual needles give an average atomic ratio of 3.65/1 for I/Pb, in reasonable
agreement with the (PMA)2PbI4 stoichiometry. EDX element mapping in a selected
area of an individual (PMA)2PbI4 needle shows uniform spatial distribution of Pb and
I throughout the needle. As for the products synthesized in a PMAI/IPA solution with
concentration smaller than 25 mg/mL, quantitative elemental analyses yield average
I/Pb molar ratios close to 3 and 2 for the PMAI/IPA concentration of 20 mg/mL and 5
mg/mL respectively (Fig. S3), maybe ascribed to the formation of (PMA)PbI3 [32, 36]
and PbI2 [37] rather than 2D perovskite of (PMA)2PbI4 in a low PMAI/IPA
concentration, which is consistent with above XRD and SEM results.
In order to reveal the growth process of needle-like (PMA)2PbI4 bundles in
PMAI/IPA solution, time-dependent experiments were carried out. Fig. 4(a-f) show
SEM images of (PMA)2PbI4 superstructures synthesized at different reaction times
with the PMAI/IPA concentration fixed at 40 mg/mL, and the corresponding XRD
patterns were displayed in Fig. 4(g). The characterizations of as dip-coated PbAc2 thin
film on FTO substrate were also provided for comparison. Though it’s hard to see
clearly the morphology of the PbAc2 phase merely from the SEM image in Fig. 4(a),
the XRD pattern in Fig. 4(g) (black curve) clearly proves its existence. After a short
reaction time of 1 min, we noticed some regions of the substrate were densely covered
with irregular aggregates, while other areas were sparsely covered with needle-like
aggregates. Compared with the XRD pattern of as dip-coated PbAc2 film, the XRD
8

ACCEPTED MANUSCRIPT
pattern at 1 min reaction (Fig. 4(g), red curve) shows an intensity shift between the
two diffraction peaks of PbAc2 at 7.5 ° and 9 °, which may be ascribed to the densely
dispersed irregular aggregates mentioned above and suggests the structural
rearrangement in crystal planes of PbAc2. In addition, a low intensive diffraction peak
at around 6.1 ° should be attributed to the needle-like aggregates, indicating the
formation of (PMA)2PbI4 superstructures at the very beginning. Extending the
reaction time to 10 min, needle-like bundles with clearly defined geometry formed on
most areas of the substrate, the needle was measured ~ 50 ꢀm in length and ~ 2 ꢀm in
width. High resolution SEM image on bottom panel of Fig. 4(c) reveals the rough
surface of the needle. The corresponding XRD pattern in Fig. 4(g) shows no existence
of PbAc2 phase, suggesting a complete conversion of PbAc2 to (PMA)2PbI4 at this
time. At 30 min, the needle size continues to increase; meanwhile, magnified SEM
image on bottom panel of Fig. 4(d) shows some pinholes on the needle surface, and
the corresponding XRD pattern displays dramatic increase of the (002) diffraction
peak in intensity, which may suggests the readjustment and improvement of the
crystal structure of (PMA)2PbI4 needles. Further prolonging the reaction time, the
needle surface becomes flatter, and the corresponding diffraction peaks continues to
increase, indicating the enhancement of crystallinity of (PMA)2PbI4.
The chemical reactions responsible for these syntheses may be described as
follows [37-40]:
ꢉꢅ
ꢁ ꢃ
ꢁ
ꢃ
ꢅ ꢁ
ꢃ
ꢁ
ꢃ
ꢅꢁ
ꢃ
PbAcꢀ ꢂ + 2 + ꢄ I ꢂꢆꢇ ↔ PbIꢀꢈꢉ ꢂꢆꢇ + 2Ac ꢂꢆꢇ ꢁꢄ = 0, 1, 2ꢃ
(1)
ꢉꢅ
ꢁ
ꢃ
ꢈꢁ
ꢃ
ꢁ
ꢃ
ꢁ ꢃ
ꢂ
PbI
ꢂꢆꢇ + ꢄPMA ꢂꢆꢇ ↔ PMA PbIꢀꢈꢉ
(2)
ꢉ
ꢀꢈꢉ
9

ACCEPTED MANUSCRIPT
At low concentration of PMAI in IPA (< 25 mg/mL), the pre-deposited PbAc2 thin
film gets dissolved and reacts with I- anion in solution to form PbI2 (see black curve in
-
Fig. S1 and Fig. S3(b)) or to produce PbI3 complex first followed by the formation of
(PMA)PbI3 (see red and blue curves in Fig. S1 and Fig. S3(a)). While at higher
concentration of PMAI precursor (≥ 25 mg/mL), the PbAc2 thin film firstly reacts
with I- anion to form dissolved PbI42- complex-ion, then the dissolved PbI42- anion and
PMA+ cation in solution organize into layered perovskite (PMA)2PbI4 (Fig. S1 and
Fig. 1). The driving forces for the ions assembling into layered perovskite include
2-
ionic bond linking the dissolved PbI4 to form extended octahedral network,
+
hydrogen bond between NH3 head in organic molecule and halogen atom in
inorganic perovskite sheet, and van der Waals interaction between the inorganic sheets.
+
The hydrogen bonding interaction between the NH3 heads and inorganic perovskite
sheets play an important role for forming the layered structure and the final structure
[41].
Schematic illustration can be given to depict the formation of (PMA)2PbI4
needle-like bundle, as shown in Fig. 5. When the pre-deposited PbAc2 thin film is
immersed into PMAI/IPA solution, the superficial PbAc2 contacting with solution will
be dissolved and react with I- ions to form free standing PbI6 octahedral structure; on
the other hand, it is assumed the precursor I- ions are consumed faster than the mass
transport rate, the interior PbAc2 will re-arrange its primary structure and assemble to
some aggregates to reduce the energy, as mentioned above (see Fig. 4(b) for SEM
image). The free-standing PbI6 octahedrons then organize into extended perovskite
10

ACCEPTED MANUSCRIPT
sheet via strong ionic bond, with organic ligand of PMA sheathing on both sides of
+
the perovskite sheet through the hydrogen bond between the NH3 head and the I-
anions in the perovskite sheet. On one hand, PMA holds the neighboring perovskite
sheets together to form stacked organic-inorganic-organic (PMA)2PbI4 sandwich
structures with van der Waals interactions between the tails of PMA. On the other
hand, as a capping agent, the presence of PMA limits the crystal growth in the
attachment side, and the steric hindrance effect of PMA ions determines the growth
speed of different crystal planes and thus resulting in anisotropic crystal growth [31].
From this point of view, the involvement of PMA group determines the layered
structure and the final morphology of the products. In the next step, the needles
assemble together because of their interaction forces, and then thermally induced
recrystallization may cause fusion on one side of each needle to minimize surface
energy, leading to the formation of present hierarchical structure.
We also tried PbI2 as the Pb source of desired perovskite. Herein, PbI2 film was
prepared by spin-coating a solution of PbI2 in DMF first, and then the spin-coated
PbI2 film was immersed in 40 mg/ml PMAI/IPA solution for 19 h. As a result, we
found needle-like rods with length of 20~30 ꢀm and diameter of 2~3 ꢀm together
with a resultant aspect ratio of ~ 10 formed on top of substrate (Fig. S4), both the
needle-like ends look not very sharp, and the needle size is much smaller in contrast
with the sample with PbAc2 source discussed above (see Fig. 2 for SEM images),
presumably PbAc2 is much more soluble than PbI2 in solution, thus leading to faster
sequential nucleation and crystal growth when PbAc2 is used as the precursor [42, 43].
11

ACCEPTED MANUSCRIPT
In addition, for the sample from PbI2 route, the seemingly short stumpy morphology
of the needles enables them towards a thermodynamic equilibrium state, thus prefer to
exit independently rather than assemble to bundles (Fig. S4).
To explore optical applications of the above synthesized (PMA)2PbI4 needles,
preliminary photoluminescence (PL) studies on these (PMA)2PbI4 needles were
carried out. Prior to optical tests, the (PMA)2PbI4 needles were made a dry transfer to
a Si substrate. The microscopic PL of a single needle was collected with a confocal
Raman microscope using a 442 nm laser source, and the representative PL spectra
from a single (PMA)2PbI4 needle synthesized with two different Pb sources were
displayed in Fig. 6. The sample using PbAc2 source displays a PL peak at 536 nm and
a broad shoulder around 546 nm, presumably arising from free exciton and bound
exciton transitions, respectively [44]; while for the sample using PbI2 source, a PL
peak centering at 544 nm together with a very weak emission around 595 nm can be
detected, in which the weak emission may be attributed to the crystal defects in
(PMA)2PbI4 needle. The emission maxima from the above two samples lie in the
range of 528∼575 nm for previous reported (PMA)2PbI4 [32-34]. The relatively large
variation of the peak maxima reflects the structural complexity of the layered
perovskite (PMA)2PbI4, assembled by the inorganic sheets containing corner-sharing
PbI6-octahedra and the organic aromatic ligands. Different preparation methods and
growth conditions cause different distortions and strain states in the inorganic
perovskite sheets of the synthesized (PMA)2PbI4, thus resulting in the changes of the
electronic structures and the band-gap energies [34, 45].
12

ACCEPTED MANUSCRIPT
4. Conclusions
In summary, we successfully synthesized hyper-branched needle-like bundles of
2D layered perovskite of (PMA)2PbI4 by a two-step processing technique. The
concentration of PMAI in IPA solution greatly affects the crystal structure and
morphology of the products. Needle-bundles of (PMA)2PbI4 can be synthesized at a
high concentration of PMAI precursor (≥ 25 mg/mL), while at a low PMAI/IPA
concentration (<25 mg/mL), the products crystalize in other phases with a low Pb/I
stoichiometric ratio (< 4). Time-dependent experiments were then carried out to reveal
the evolution of needle-like (PMA)2PbI4 bundles. Based on experimental observations,
we put forward a reasonable explanation to the formation of the needle-like bundles.
+
The hydrogen bonding interaction between the NH3 heads and inorganic perovskite
sheets is deemed to play an important role for forming needle-like perovskite
morphology. Using PbI2 as the Pb source, we obtained needle-like (PMA)2PbI4 rods,
the morphology is similar to the product with PbAc2 route. PL test show that the
needles possess a band-edge emission peak centering around 540 nm and a narrow
FWHM of about 30 nm. Our investigations will provide a new way to synthesize 2D
perovskites with controlled morphology and benefit to understand the crystal growth
kinetics of this kind of materials.
Acknowledgement
This work was financially supported by the Natural Science Foundation of
Zhejiang Province of China (No. LY13F040002).
13

ACCEPTED MANUSCRIPT
References
[1] J. Burschka, N. Pellet, S.J. Moon, R. Humphry-Baker, P. Gao, M.K. Nazeeruddin,
M. Gratzel, Sequential deposition as route to high-performance
a
perovskite-sensitized solar cells, Nature, 499 (2013) 316-319.
[2] M.M. Lee, J. Teuscher, T. Miyasaka, T.N. Murakami, H.J. Snaith, Efficient hybrid
solar cells based on meso-superstructured organometal halide perovskites,
Science, 338 (2012) 643-647.
[3] S.D. Stranks, H.J. Snaith, Metal-halide perovskites for photovoltaic and
light-emitting devices, Nat. Nanotechnol., 10 (2015) 391-402.
[4] Z.K. Tan, R.S. Moghaddam, M.L. Lai, P. Docampo, R. Higler, F. Deschler, M.
Price, A. Sadhanala, L.M. Pazos, D. Credgington, F. Hanusch, T. Bein, H.J.
Snaith, R.H. Friend, Bright light-emitting diodes based on organometal halide
perovskite, Nat. Nanotechnol., 9 (2014) 687-692.
[5] G.C. Papavassiliou, Three- and low-dimensional inorganic semiconductors, Prog.
Solid State Chem., 25 (1997) 125-270.
[6] T. Ishihara, Optical properties of Pb-based inorgainc-organic perovskites, in: T.
Ogawa, Y. Kanemitsu (Eds.) Optical Properties of Low-Dimensional Materials,
World Scientific, 1996, pp. 288-339.
[7] T. Umebayashi, K. Asai, T. Kondo, A. Nakao, Electronic structures of lead iodide
based low-dimensional crystals, Phys. Rev. B, 67 (2003).
[8] X. Hong, T. Ishihara, A.V. Nurmikko, Dielectric confinement effect on excitons
inPbI4-based layered semiconductors, Phys. Rev. B, 45 (1992) 6961-6964.
14

ACCEPTED MANUSCRIPT
[9] K. Ema, K. Umeda, M. Toda, C. Yajima, Y. Arai, H. Kunugita, D. Wolverson, J.J.
Davies, Huge exchange energy and fine structure of excitons in an
organic-inorganic quantum well material, Phys. Rev. B, 73 (2006).
[10] T. Hattori, T. Taira, M. Era, T. Tsutsui, S. Saito, Highly efficient
electroluminescence from a heterostructure device combined with emissive
layered-perovskite and an electron-transporting organic compound, Chem. Phys.
Lett., 254 (1996) 103-108.
[11] M. Era, S. Morimoto, T. Tsutsui, S. Saito, Organic-inorganic heterostructure
electroluminescent device using
a
layered perovskite semiconductor
(C6H5C2H4NH3)2PbI4, Appl. Phys. Lett., 65 (1994) 676.
[12] A. Vassilakopoulou, D. Papadatos, I. Zakouras, I. Koutselas, Mixtures of
quasi-two and three dimensional hybrid organic-inorganic semiconducting
perovskites for single layer LED, J. Alloys Compd., (2016).
[13] I. Koutselas, P. Bampoulis, E. Maratou, T. Evagelinou, G. Pagona, G.C.
Papavassiliou,
Some
Unconventional
Organic−Inorganic
Hybrid
Low-Dimensional Semiconductors and Related Light-Emitting Devices, J. Phys.
Chem. C, 115 (2011) 8475-8483.
[14] S. Kishimoto, K. Shibuya, F. Nishikido, M. Koshimizu, R. Haruki, Y. Yoda,
Subnanosecond time-resolved x-ray measurements using an organic-inorganic
perovskite scintillator, Appl. Phys. Lett., 93 (2008) 261901.
15

ACCEPTED MANUSCRIPT
[15] A. Brehier, R. Parashkov, J.S. Lauret, E. Deleporte, Strong exciton-photon
coupling in a microcavity containing layered perovskite semiconductors, Appl.
Phys. Lett., 89 (2006) 171110.
[16] M. Shimizu, J.-i. Fujisawa, T. Ishihara, Nonlinear luminescence from an
inorganic–organic layered semiconductor, J. Lumin., 122-123 (2007) 485-487.
[17] S. Zhang, P. Audebert, Y. Wei, J.-S. Lauret, L. Galmiche, E. Deleporte, Synthesis
and optical properties of novel organic–inorganic hybrid UV (R–NH3)2PbCl4
semiconductors, J. Mater. Chem., 21 (2011) 466-474.
[18] K. Gauthron, J.S. Lauret, L. Doyennette, G. Lanty, A. Al Choueiry, S.J. Zhang, A.
Brehier, L. Largeau, O. Mauguin, J. Bloch, E. Deleporte, Optical spectroscopy of
two-dimensional layered (C6H5C2H4-NH3)2-PbI4 perovskite, Opt. Express, 18
(2010) 5912-5919.
[19] D.B. Mitzi, M.T. Prikas, K. Chondroudis, Thin Film Deposition of
Organic−Inorganic Hybrid Materials Using a Single Source Thermal Ablation
Technique, Chem. Mater., 11 (1999) 542-544.
[20] M. Era, T. Hattori, T. Taira, T. Tsutsui, Self-Organized Growth of PbI-Based
Layered Perovskite Quantum Well by Dual-Source Vapor Deposition, Chem.
Mater., 9 (1997) 8-10.
[21] K. Liang, D.B. Mitzi, M.T. Prikas, Synthesis and Characterization of
Organic−Inorganic Perovskite Thin Films Prepared Using a Versatile Two-Step
Dipping Technique, Chem. Mater., 10 (1998) 403-411.
16

ACCEPTED MANUSCRIPT
[22] H. Tsai, W. Nie, J.C. Blancon, C.C. Stoumpos, R. Asadpour, B. Harutyunyan, A.J.
Neukirch, R. Verduzco, J.J. Crochet, S. Tretiak, L. Pedesseau, J. Even, M.A.
Alam, G. Gupta, J. Lou, P.M. Ajayan, M.J. Bedzyk, M.G. Kanatzidis,
High-efficiency two-dimensional Ruddlesden-Popper perovskite solar cells,
Nature, 536 (2016) 312-316.
[23] L.N. Quan, M. Yuan, R. Comin, O. Voznyy, E.M. Beauregard, S. Hoogland, A.
Buin, A.R. Kirmani, K. Zhao, A. Amassian, D.H. Kim, E.H. Sargent,
Ligand-Stabilized Reduced-Dimensionality Perovskites, J. Am. Chem. Soc., 138
(2016) 2649-2655.
[24] D. Liang, Y. Peng, Y. Fu, M.J. Shearer, J. Zhang, J. Zhai, Y. Zhang, R.J. Hamers,
T.L. Andrew, S. Jin, Color-Pure Violet-Light-Emitting Diodes Based on Layered
Lead Halide Perovskite Nanoplates, ACS Nano, 10 (2016) 6897-6904.
[25] J. Byun, H. Cho, C. Wolf, M. Jang, A. Sadhanala, R.H. Friend, H. Yang, T.W. Lee,
Efficient Visible Quasi-2D Perovskite Light-Emitting Diodes, Adv. Mater., 28
(2016) 7515-7520.
[26] M. Yuan, L.N. Quan, R. Comin, G. Walters, R. Sabatini, O. Voznyy, S. Hoogland,
Y. Zhao, E.M. Beauregard, P. Kanjanaboos, Z. Lu, D.H. Kim, E.H. Sargent,
Perovskite energy funnels for efficient light-emitting diodes, Nat. Nanotechnol.,
11 (2016) 872-877.
[27] D. Shi, V. Adinolfi, R. Comin, M. Yuan, E. Alarousu, A. Buin, Y. Chen, S.
Hoogland, A. Rothenberger, K. Katsiev, Y. Losovyj, X. Zhang, P.A. Dowben, O.F.
Mohammed, E.H. Sargent, O.M. Bakr, Solar cells. Low trap-state density and
17

ACCEPTED MANUSCRIPT
long carrier diffusion in organolead trihalide perovskite single crystals, Science,
347 (2015) 519-522.
[28] D.B. Mitzi, K. Chondroudis, C.R. Kagan, Organic-inorganic electronics, IBM J.
Res. Dev., 45 (2001) 29-45.
[29] N.P. Dasgupta, J. Sun, C. Liu, S. Brittman, S.C. Andrews, J. Lim, H. Gao, R. Yan,
P. Yang, 25th anniversary article: semiconductor nanowires--synthesis,
characterization, and applications, Adv. Mater., 26 (2014) 2137-2184.
[30] T.J. Kempa, R.W. Day, S.-K. Kim, H.-G. Park, C.M. Lieber, Semiconductor
nanowires: a platform for exploring limits and concepts for nano-enabled solar
cells, Energ. Environ. Sci., 6 (2013) 719-733.
[31] S. Aharon, L. Etgar, Two Dimensional Organometal Halide Perovskite Nanorods
with Tunable Optical Properties, Nano Lett., 16 (2016) 3230-3235.
[32] G.C. Papavassiliou, G.A. Mousdis, C.P. Raptopoulou, A. Terzis, Preparation and
Characterization of [C6H5CH2NH3]2PbI4, [C6H5CH2CH2SC(NH2)2]3PbI5 and
[C10H7CH2NH3]PbI3 Organic-Inorganic Hybrid Compounds, Z. Naturforsch. B,
54 (1999) 1405-1409.
[33] S. Zhang, G. Lanty, J.-S. Lauret, E. Deleporte, P. Audebert, L. Galmiche,
Synthesis and optical properties of novel organic–inorganic hybrid nanolayer
structure semiconductors, Acta Mater., 57 (2009) 3301-3309.
[34] M.E. Kamminga, H.-H. Fang, M.R. Filip, F. Giustino, J. Baas, G.R. Blake, M.A.
Loi, T.T.M. Palstra, Confinement Effects in Low-Dimensional Lead Iodide
Perovskite Hybrids, Chem. Mater., 28 (2016) 4554-4562.
18

ACCEPTED MANUSCRIPT
[35] A.T.M.N. Islam, Y. Tachiki, S. Watauchi, I. Tanaka, Growth mechanism of
EuBa2Cu3Ox single-crystalline whiskers from Ca and Te doped precursors, J.
Cryst. Growth, 289 (2006) 192-196.
[36] R.S. Black, Structure and optical properties of natural low dimensional,
semiconducting, organic inorganic hybrids, in, University of the Witwatersrand,
Johannesburg, 2012, pp. 308.
[37] S. Yang, Y.C. Zheng, Y. Hou, X. Chen, Y. Chen, Y. Wang, H. Zhao, H.G. Yang,
Formation Mechanism of Freestanding CH3NH3PbI3 Functional Crystals: In Situ
Transformation vs Dissolution–Crystallization, Chem. Mater., 26 (2014)
6705-6710.
[38] H. Zhu, Y. Fu, F. Meng, X. Wu, Z. Gong, Q. Ding, M.V. Gustafsson, M.T. Trinh,
S. Jin, X.Y. Zhu, Lead halide perovskite nanowire lasers with low lasing
thresholds and high quality factors, Nat. Mater., 14 (2015) 636-642.
[39] O.E. Lanford, S.J. Kiehl, The Solubility of Lead Iodide in Solutions of Potassium
Iodide-Complex Lead Iodide Ions, J. Am. Chem. Soc., 63 (1941) 667-669.
[40] O. Horváth, I. Mikó, Spectra, equilibrium and photoredox chemistry of tri- and
tetraiodoplumbate(II) complexes in acetonitrile, J. Photochem. Photobiol. A, 114
(1998) 95-101.
[41] Z. Cheng, J. Lin, Layered organic–inorganic hybrid perovskites: structure, optical
properties, film preparation, patterning and templating engineering,
CrystEngComm, 12 (2010) 2646.
19

ACCEPTED MANUSCRIPT
[42] W. Zhang, M. Saliba, D.T. Moore, S.K. Pathak, M.T. Horantner, T. Stergiopoulos,
S.D. Stranks, G.E. Eperon, J.A. Alexander-Webber, A. Abate, A. Sadhanala, S.
Yao, Y. Chen, R.H. Friend, L.A. Estroff, U. Wiesner, H.J. Snaith, Ultrasmooth
organic-inorganic perovskite thin-film formation and crystallization for efficient
planar heterojunction solar cells, Nat. Commun., 6 (2015) 6142.
[43] Y. Fu, F. Meng, M.B. Rowley, B.J. Thompson, M.J. Shearer, D. Ma, R.J. Hamers,
J.C. Wright, S. Jin, Solution growth of single crystal methylammonium lead
halide perovskite nanostructures for optoelectronic and photovoltaic applications,
J. Am. Chem. Soc., 137 (2015) 5810-5818.
[44] G.C. Papavassiliou, G.A. Mousdis, I.B. Koutselas, Some New Organic–Inorganic
Hybrid Semiconductors Based on Metal Halide Units: Structural, Optical and
Related Properties, Adv. Mater. Opt. Electron., 9 (1999) 265-271.
[45] P. Audebert, G. Clavier, V.r. Alain-Rizzo, E. Deleporte, S. Zhang, J.-S.b. Lauret,
G.t. Lanty, C.d. Boissière, Synthesis of New Perovskite Luminescent
Nanoparticles in the Visible Range, Chem. Mater., 21 (2009) 210-214.
20

ACCEPTED MANUSCRIPT
Figure captions:
Fig. 1. (a) Typical XRD pattern of as-synthesized product grown in a PMAI/IPA
solution with concentration higher than 25 mg/mL; (b) Extended crystal structures of
(PMA)2PbI4, viewed approximately along the c axis. The unit cell outline is shown by
the dashed lines. The hydrogen atoms were removed for clarity.
Fig. 2. Morphologies of needle-like bundles of (PMA)2PbI4. (a-b) SEM images and
optical images of needle-like bundles synthesized in a PMAI/IPA solution with
concentration of 40 mg/ml for 15 h, the needle encircled by an ellipse in (a) shows a
“two sharp ends” feature; (c-e) Magnified SEM images of a typical needle tip and
middle sections; (f) Picture of needle-like bundles grown in an 80 mg/ml PMAI/IPA
solution after 2.5 h.
Fig. 3. EDX analysis of individual (PMA)2PbI4 needle. (a) A representative EDX
spectrum of a single (PMA)2PbI4 needle on Si substrate. (b) Quantitative elemental
analysis of these (PMA)2PbI4 needles yields an average I/Pb molar ratio of 3.65. (c)
The selected area SEM image of an individual (PMA)2PbI4 needle and (d, e) Element
mapping images of Pb and I for the selected area shown in (c).
Fig. 4. SEM images of (PMA)2PbI4 superstructures grown at different reaction times.
(a) As dip-coated PbAc2 film on FTO substrate for comparison, and at reaction times
of (b) 1 min, (c) 10 min, (d) 30 min, (e) 2 h and (f) 5 h respectively, with the
PMAI/IPA concentration fixed at 40 mg/mL. The bottom panels in Fig. (c-f) show
corresponding selected area high-resolution SEM images of (PMA)2PbI4 needles on
upper panels respectively.
Fig. 5. Schematic image showing the formation of (PMA)2PbI4 needle bundle.
Fig. 6. Confocal microscopic PL spectra of a single (PMA)2PbI4 needle synthesized
with different Pb sources of PbAc2 and PbI2 respectively.
21

ACCEPTED MANUSCRIPT
Figure 1
Fig. 1. (a) Typical XRD pattern of as-synthesized product grown in a PMAI/IPA
solution with concentration higher than 25 mg/mL; (b) Extended crystal structures of
(PMA)2PbI4, viewed approximately along the c axis. The unit cell outline is shown by
the dashed lines. The hydrogen atoms were removed for clarity.
22

ACCEPTED MANUSCRIPT
Figure 2
Fig. 2. Morphologies of needle-like bundles of (PMA)2PbI4. (a-b) SEM images and
optical images of needle-like bundles synthesized in a PMAI/IPA solution with
concentration of 40 mg/ml for 15 h, the needle encircled by an ellipse in (a) shows a
“two sharp ends” feature; (c-e) Magnified SEM images of a typical needle tip and
middle sections; (f) Picture of needle-like bundles grown in an 80 mg/ml PMAI/IPA
solution after 2.5 h.
23

ACCEPTED MANUSCRIPT
Figure 3
Fig. 3. EDX analysis of individual (PMA)2PbI4 needle. (a) A representative EDX
spectrum of a single (PMA)2PbI4 needle on Si substrate. (b) Quantitative elemental
analysis of these (PMA)2PbI4 needles yields an average I/Pb molar ratio of 3.65. (c)
The selected area SEM image of an individual (PMA)2PbI4 needle and (d, e) Element
mapping images of Pb and I for the selected area shown in (c).
24

ACCEPTED MANUSCRIPT
Figure 4
Fig. 4. SEM images of (PMA)2PbI4 superstructures grown at different reaction times.
(a) As dip-coated PbAc2 film on FTO substrate for comparison, and at reaction times
of (b) 1 min, (c) 10 min, (d) 30 min, (e) 2 h and (f) 5 h respectively, with the
PMAI/IPA concentration fixed at 40 mg/mL. The bottom panels in Fig. (c-f) show
corresponding selected area high-resolution SEM images of (PMA)2PbI4 needles on
upper panels respectively.
25

ACCEPTED MANUSCRIPT
Figure 5
Fig. 5. Schematic image showing the formation of (PMA)2PbI4 needle bundle.
26

ACCEPTED MANUSCRIPT
Figure 6
Fig. 6. Confocal microscopic PL spectra of a single (PMA)2PbI4 needle synthesized
with different Pb sources of PbAc2 and PbI2 respectively.
27

ACCEPTED MANUSCRIPT
ꢀ
ꢀ
ꢀ
Needle-like bundles of 2D layered perovskite of (C6H5CH2NH3)2PbI4 was synthesized.
The growth mechanism of the needle-like morphology was investigated.
The needles possess a band-edge emission peak centering around 540 nm.