Layered hybrid lead perovskite single crystals: Phase transformations and tunable optical properties

Article abstract of DOI:10.1039/d0ce00753f

Based on the disadvantages of crystal processing and device fabrications of 3D halide perovskites, there is a need to introduce aromatic ammonium into CH3NH3PbI3 to address these concerns. Herein, we report the controllable growth of layered perovskite (C6H5CH2CH2NH3)2(CH3NH3)n-1PbnI3n+1 (n = 1-3) single crystals realised by controlling the proper molar ratio of reactants in the ambient atmosphere. Interestingly, two polymorphs of (C6H5CH2CH2NH3)2PbI4 single crystals coexisted, and their phase transformation were achieved by different strategies. Moreover, the crystal structure determinations, band gap, optical properties, and thermal stability of the (C6H5CH2CH2NH3)2(CH3NH3)n-1PbnI3n+1 (n = 1-3) single crystals were studied in detail. The (C6H5CH2CH2NH3)2(CH3NH3)n-1PbnI3n+1 (n < 3) single crystals with quantum well structures exhibited strong photoluminescent properties. These intriguing features may lay the foundation for optoelectronic applications of the layered perovskite materials.

Full text of DOI:10.1039/d0ce00753f

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Layered hybrid lead perovskite single crystals:
phase transformations and tunable optical
properties†
Cite this: DOI: 10.1039/d0ce00753f
Jiewu Song, Yangyang Dang, *abc Xiao Long Liu and Xutang Tao *a
a
a
Based on the disadvantages of crystal processing and device fabrications of 3D halide perovskites, there is
a need to introduce aromatic ammonium into CH
the controllable growth of layered perovskite (C
crystals realised by controlling the proper molar ratio of reactants in the ambient atmosphere. Interestingly,
two polymorphs of (C CH CH NH PbI single crystals coexisted, and their phase transformation were
achieved by different strategies. Moreover, the crystal structure determinations, band gap, optical
properties, and thermal stability of the (C CH CH NH (CH NH 3n+1 (n = 1–3) single crystals
were studied in detail. The (C CH CH NH (CH NH 3n+1 (n < 3) single crystals with quantum
3
NH
3
PbI
3
to address these concerns. Herein, we report
6 5
H CH
2
CH
2
NH (CH NH 3n+1 (n = 1–3) single
3
)
2
3
3 n
)n−1Pb I
H
6 5
2
2
3
)
2
4
Received 22nd May 2020,
Accepted 20th August 2020
6
H
5
2
2
3
)
2
3
3 n
)n−1Pb I
6
H
5
2
2
3
)
2
3
3 n
)n−1Pb I
DOI: 10.1039/d0ce00753f
well structures exhibited strong photoluminescent properties. These intriguing features may lay the
foundation for optoelectronic applications of the layered perovskite materials.
rsc.li/crystengcomm
syntheses,
crystal
structure
determinations,
and
Introduction
optoelectronic properties research of layered perovskites BA -
2
6a
Organic–inorganic hybrid lead layered perovskite materials
have gained significant attention in the field of
optoelectronics due to their high stability and optical
MA Pb I
(n = 1–3) were investigated by Kanatzidis et al.
n−1
n 3n+1
2 n
Recently, BA MAn−1Pb I3n+1 based solar cells, reported by
6b
Mohite et al. exhibited the PCE of 12.52% with high stability.
However, there have been only few reports available on the
PEA MAn−1Pb 3n+1 material. Karunadasa et al. have reported
enhanced moisture-stable PEA MA Pb I solar cells with the
1
–7
tunability.
perovskites ABX
materials A MA Pb I
Contrary
Ruddlesden–Popper layered perovskite
(where A is n-butyl-ammonium
to
three-dimensional
hybrid
3
,
2
n
I
2
n−1
n 3n+1
2
2
3 10
7
(BA)
or
phenethyl-ammonium
(PEA);
MA
is
PCE of 4.73%. Kanatzidis group have reported the white-
light emission and structural distortions based on the two
polymorphs of (DMEN)PbBr4 (DMEN = 2-(dimethylamino)
2
+
2+
methylammonium; M is ordinarily Sn or Pb ; X is usually
−
−
−
Cl , Br or I , and n is an integer) exhibit the excellent
stability and have thus attracted considerable interest. In
ethylamine) single crystals as well as the structural diversity
8
1
957, the Ruddlesden–Popper layered perovskite structured
of
layered
perovskite
single
crystal
materials.
4
models were put forward by S. N. Ruddlesden and P. Popper.
Photoconductors based on PEA MA Pb I
(n = 1–3) single
2
n−1
n 3n+1
Later, Mitzi et al. reported the synthesis and properties of
crystals with significant light-detection have been investigated
in detail by Bakr et al. Photosensors based on a large-area
5
9
2 n
layered perovskite materials BA MAn−1Sn I3n+1. Subsequently,
flexible single-crystalline membrane (SCM) and bulk single-
1
0
a
crystals of PEA PbI were investigated. In many cases, the
2 4
State Key Laboratory of Crystal Materials & Institute of Crystal Materials,
Shandong University, No. 27 Shanda South Road, Jinan, 250100, P. R. China.
E-mail: txt@sdu.edu.cn
layered perovskite-based optoelectronic devices such as solar
7
,11
12
cells,
LEDs),
films. In particular, PEA
field-effect transistors (FETs), light-emitting diodes
b
13–15
School of Physics and Physical Engineering, Shandong Provincial Key Laboratory
(
and photodetectors are based on powders and thin
MAn−1Pb 3n+1 materials with quantum
of Laser Polarization and Information Technology, Qufu Normal University,
2
n
I
2
c
73165, Qufu, P. R. China
well structures are extensively utilized in perovskite light-
emitting diodes (LEDs) due to their strong photoluminescence.
Single crystals with the absence of grain boundaries and
low density traps provide an ideal test platform for
fundamental studies on properties of layered perovskites.
However, there has been previous reports
C-CP/MAS NMR, ionic motion, and local
structures as well as confinement effects of the
Tianjin Key Laboratory of Molecular Optoelectronic Sciences & Department of
Chemistry, School of Sciences, & Collaborative Innovation Center of Chemical
Science and Engineering, Tianjin University, Tianjin, 300072, P. R. China.
E-mail: yeung_dang@tju.edu.cn
†
Electronic supplementary information (ESI) available: Additional data for
fluorescence photo, green emissive, red emissive, calculated and PXRD patterns,
TGA/DSC, UV-vis spectra, PL decay lifetime, crystal data and structure
refinements. CCDC 1815922–1815926. For ESI and crystallographic data in CIF
or other electronic format see DOI: 10.1039/d0ce00753f
1
6–19
focused on the
13
preparation,
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PEA MA PbnI3n+1. Recently, based on the previous research,
CrystEngComm
20–23
2
n−1
the layered perovskite PEA MA Pb I
in the form of
2
n−1 n 3n+1
nano- or micro-crystals, polycrystalline powders, and thin
films have been thoroughly investigated. Until now, there
have been only few reports on the bulk crystal growth and
relevant intrinsic properties of the layered perovskite PEA
2
-
MA PbnI3n+1. In this work, we reported the bulk growth and
n−1
crystal structure determinations of PEA MA Pb I
(n = 1–
2
n−1 n 3n+1
3) single crystals in detail. Interestingly, we observed that
PEA PbI had two polymorphs (monoclinic and triclinic
2
4
lattice structures) with green and red emissions, when
exposed to UV irradiation. The phase transformation
processes of PEA PbI polymorphs by different strategies
2
4
demonstrated that the two polymorphs get transformed
mutually. Further, their tunable bandgap, PL and PL decay
time, and thermal stability were also systematically
investigated. The interesting results may provide chances of
further study on optoelectronic device applications of these
layered hybrid perovskite single crystals.
Experimental
Reagents
Fig. 1 Bulk single crystals of PEA
the control of molar ratio. (a) PEA
single crystals; (c) PEA MAPb
single crystals. Inset: Scale bar: mm.
2
MAn−1Pb
PbI
single crystals; (d) PEA
n
I
3n+1 (n = 1–3) obtained by
All starting reagents including PbO, CH NH , C H CH CH -
NH Cl (PEACl), and HI solution obtained from Sino-pharm
3
Co. Ltd were of analytical grade and used without further
purification.
3
2
6
5
2
2
2
4
single crystals; (b) MA: PEA
2 4
PbI
2
2
I
7
2
MA Pb I
2
3 10
Syntheses and crystal growth
The synthesis of MAI and crystal growth procedure was
2
4–26
performed according to previously reported methods.
PEACl (9.458 g, 0.06 mol) and PbO (6.696 g, 0.03 mol) were
dissolved in 200 ml HI mixed solution at 75 °C under
constant stirring, forming a yellow transparent solution.
Solutions were saturated at 55 °C. Two polymorphs of
orange-layered PEA PbI single crystals were grown via the
2 4
temperature-lowering method in an ambient atmosphere for
about two weeks, as evidenced in Fig. 1(a).
2 4
The mixtures of two polymorphous PEA PbI single
crystals (0.500 g) were weighed, dissolved in 6 ml CH OH
3
solution and then added into 10 ml HI solution, which
resulted in a light-yellow solution. Green emissive PEA PbI
2 4
single crystals appeared at the bottom of the flask under UV
irradiation condition at room temperature by the slow
evaporation method, as shown in Fig. 2 and S2.†
The mixtures of the two polymorphous PEA PbI single
2
4
crystals (2.00 g) were weighed and dissolved in 10 ml HI
solution, forming a light-yellow solution at 100 °C. Red
emissive PEA PbI single crystals appeared at the bottom of
2
4
the flask under UV irradiation condition via the temperature-
lowering method, as shown in Fig. 2 and S3.†
Fig. 2 The phase transformation processes of red and green emissive
PEA PbI single crystals. (a and f) The mixture of red and green
emissive PEA PbI single crystals or only green emissive PEA PbI
single crystals turned to red emissive via high temperature and high
concentration PEA PbI –HI solutions. (b–e) The mixture of red and
green emissive PEA PbI single crystals or only the red emissive
PEA PbI single crystals turned to green emissive via CH OH and HI
mixed solutions.
2
4
PEACl (4.729 g, 0.03 mol), MAI (4.77 g, 0.03 mol), and PbO
2
4
2
4
(6.696 g, 0.03 mol) were dissolved in 200 ml HI solution at 75
2
4
°C under constant stirring, forming a yellow transparent
2
4
solution. The solutions were saturated at 55 °C. Red plate
MA: PEAPbI4 single crystals were grown by using the
2
4
3
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1
–3) single crystals. First, PEACl was reacted with PbO in HI
solutions at 75 °C in air. Subsequently, MAI was added into
the formed PEA PbI solution to obtain different PEA
Pb I single crystals. Recently, Yin et al. reported the
2
4
2
MAn−1-
n 3n+1
modulation of broadband emissions of PEA PbI ; the
2
4
different emission peaks resulted from different precursor
materials (PbO and PbI ) due to the concentration of lead
2
iodide species in the reaction mixture that affected the final
product and contributed to the generation of iodine
2
7
vacancies. In our results, the two polymorphs of PEA PbI
2
4
easily crystallized in coexistence and exhibited green and red
fluorescence when exposed to UV irradiation, as shown in
Fig. 2. Under the UV irradiation, the red emissive PEA PbI
2
4
single crystals first appeared, followed by the green emissive
PEA PbI single crystals that covered the surface of the red
emissive PEA PbI single crystals, as shown in Fig. 2(a) and
2
4
2
4
S1.† The results indicated that the solubility of the red
emissive PEA PbI single crystals was lower than that of the
green emissive PEA PbI single crystals. More importantly,
2
4
2
4
2 n
Fig. 3 (a–e) Diagrams of crystal structures of PEA MAn−1Pb I3n+1 (n =
PEA
2
PbI
4
polymorphs were completely and mutually
1
–3) at room temperature. (a) Along the [100] direction, the layered
monoclinic crystal structure of PEA PbI (b–e) Along the [001]
direction, the layered triclinic crystal structures of PEA MAn−1Pb
n = 1–3); hydrogen atoms bonded to C or N atoms were omitted for
clarity.
transformed by different strategies (Fig. 2). The red emissive
PEA PbI single crystals completely transformed into green
2
4
;
2
n 3n+1
I
2
4
(
emissive PEA
method using CH
PbI
single crystals by the slow evaporation
OH and HI mixed solutions at room
2
4
3
temperature (Fig. 2 and S2†). Previously, Yang et al. employed
methanol as an additive in diethyl ether to control the
morphology and investigate the growth mechanism of
temperature-lowering method in an ambient atmosphere for
about two weeks, as shown in Fig. 1(b).
2
8
MAPbI3 perovskite films. As described above, the CH OH
3
PEACl (9.458 g, 0.06 mol), MAI (7.155 g, 0.045 mol), and
PbO (20.088 g, 0.09 mol) were dissolved in 300 ml HI solution
solvent helps accelerate the perovskite crystallization due to
the lower Gibbs free energy, which possibly combines with
PEA PbI to produce the intermediate complex to promote
at 75 °C under constant stirring, forming
transparent solution. The solutions were saturated at 60 °C.
Dark red PEA MAPb single crystals were grown via the
a yellow
2
4
the formation of green emissive PEA
However, the green emissive PEA PbI
completely transformed into the red emissive PEA PbI single
2
PbI
4
single crystals.
2
2
I
7
2
4
single crystals were
temperature-lowering method in an ambient atmosphere for
about two weeks, as shown in Fig. 1(c).
2
4
2 4
crystals with a high concentration PEA PbI –HI solution or at
PEACl (9.458 g, 0.06 mol), MAI (11.925 g, 0.075 mol), and
PbO (33.480 g, 0.15 mol) were dissolved in 500 ml HI solution
high temperature (Fig. 2 and S3†). Moreover, the two
polymorphous phases of PEA PbI single crystals were stable
2
4
at 75 °C under constant stirring, forming
a
yellow
at room temperature in the ambient atmosphere. These
phase transformations could provide guidance for the
controlled crystal growth of the multi-component perovskite
transparent solution. The solutions were saturated at 65 °C.
Black PEA MA Pb I single crystals were grown via the
2
2
3 10
temperature-lowering method in an ambient atmosphere for
about two weeks, as shown in Fig. 1(d).
2 n
materials. Besides, PEA MAn−1Pb I3n+1 (n = 1–3) single crystals
exhibited an oriented morphology; the PXRD patterns were
same as their calculated XRD diffraction patterns, as shown
in Fig. S4.†
Characterizations
2 n
The PEA MAn−1Pb I3n+1 (n = 1–3) single crystals mostly
The measurements from single-crystal and powder X-ray
diffractions, TGA/DSC, PL spectroscopy, PL lifetime decay,
and UV-vis spectroscopy are described in detail in the ESI.†
represented a triclinic lattice structure at room temperature,
as revealed by the single-crystal X-ray diffraction technique
and is listed in Table S1.† More importantly, there have been
no reports about the crystal structures of MA: PEAPbI4 and
Result and discussions
PEA
refined the crystal structures of PEA
to the C2/m (no. 12) and P ¯1 (no. 2) space groups at −70 °C.
In our results, the green and red emissive PEA PbI
2 2 3
MA Pb I10. Previously, Calabrese et al. determined and
The bulk PEA
2
MAn−1Pb
n
I
3n+1 (n = 1–3) single crystals obtained
2
PbI
4
and PEA
2
MAPb
2
I
7
0
2
in ambient atmosphere via the temperature-lowering method
are shown in Fig. 1. Based on the disadvantages of obtaining
2
4
single
bulk-layered PEA
essential to master the proper molar ratio of PEACl, MAI, and
PbO in the HI solution to obtain bulk PEA MA Pb I (n =
2
MAn−1Pb
n
I
3n+1 (n = 1–3) single crystals, it is
crystals exhibited the monoclinic and triclinic space groups,
which was determined to be C2/m (no. 12) and P ¯1 (no. 2) at
room temperature, respectively. Especially, the new crystal
2
n−1
n 3n+1
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Fig. 4 (a) Fluorescence photos and PL spectra of monoclinic PEA
2
PbI
4
(1), triclinic PEA
2
PbI
4
(2), and MA: PEAPbI
4
(3) single crystals; (b) PL decay
lifetime of monoclinic PEA
irradiation and emission at 710 nm; (d) PL decay lifetime of MA: PEAPbI
2
PbI
4
under 445 nm irradiation and emission at 520 nm; (c) PL decay lifetime of triclinic PEA
under 445 nm irradiation and emission at 710 nm.
2 4
PbI under 445 nm
4
structures of the red emissive PEA PbI , MA: PEAPbI , and
structures of triclinic PEA MA Pb I
(n = 1–3) were in
2
4
4
2
n−1
n 3n+1
PEA
2
MA
2
Pb
3
I
10 at room temperature were determined and
array along the [001] direction (Fig. 3(b–d)). All the I–Pb bond
lengths in the crystal structures of PEA MAn−1Pb
3) were found to be in perfect alignment, which made all
crystal structures of PEA MAn−1Pb 3n+1 (n = 1–3) symmetric.
The results of TGA and DSC of PEA MAn−1Pb 3n+1 (n = 1–
refined to be the triclinic system with the space group P ¯1 (no.
n
I3n+1 (n = 1–
2
2
). For triclinic PEA PbI , the cell parameters were a =
2 4
8
.7350(16) Å, b = 8.7359(16) Å, c = 16.673(3) Å, V = 1248.6(4)
2
n
I
3
Å , α = 99.694(5)°, β = 95.220(6)°, γ = 90.393(5)°, and Z = 2.
2
n
I
The cell parameters for MA: PEAPbI were a = 8.7497(8) Å, b =
3) are shown in Fig. S5.† All the single crystals showed
relatively good thermal stability. This advantage may promote
realistic optoelectronic applications of layered perovskite
materials in the temperature-variable environment.
4
3
8
9
.7510(8) Å, c = 16.6830(15) Å, V = 1253.4(2) Å , α =
9.7643(10)°, β = 95.2258(10)°, γ = 90.3394(10)° and Z = 2, and
PEA MA Pb I
3 10
exhibited the layered perovskite crystal
2
2
structure with cell parameters a = 8.8201(14) Å, b = 8.8198(14)
Å, c = 29.038(5) Å, V = 2245.0(6) Å , α = 93.198(2)°, β =
Subsequently, the optical band gap (E
the UV-vis absorption spectra combined with the Kubelka–
g
) was calculated from
3
2
9–31
9
5.495(2)°, γ = 90.123(2)° and Z = 2. The ball and stick
diagrams of PEA MAn−1Pb 3n+1 (n = 1–3) crystal structures
are shown in Fig. 3, in which all diagrams include the {PbI
Munk function (Fig. S6†).
was 2.13 eV, 1.97 eV, 1.86 eV, and 1.55 eV for PEA
PEAPbI , PEA MAPb , and PEA MA Pb 10, respectively. It is
demonstrated that PEA MA Pb I (n = 1–3) single crystals
The as-determined optical Eg
2
n
I
2
PbI , MA:
4
6
}
4
2
2
I
7
2
2
3
I
+
+
octahedral structured units. Moreover, PEA and MA organic
2
n−1
n 3n+1
+
cations were so disordered that the benzene ring and MA
exhibit an obvious tunable band gap. Due to the weak red
fluorescence of PEA MAPb and PEA MA Pb 10 single
crystals (Fig. S4†), we focused on PL spectra and the PL decay
time of the monoclinic phase of PEA PbI and the triclinic
cation could be hardly distinguished. Further, the monoclinic
PEA PbI single crystals showed a layered crystal structure
2
2
I
7
2
2
3
I
2
4
along the [100] direction (Fig. 3(a)), while the layered crystal
2
4
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phase of PEA PbI and MA: PEAPbI single crystals. The thick
Y. Dang acknowledges the project funded by China Postdoctoral
Science Foundation (No. 2017M621067 and 2018T110197).
2
4
4
single crystals exhibited shoulder and broad PL peaks, which
32–34
+
were similar to previous reports.
Interestingly, when MA
cation was added into PEA–Pb–I systems, all the PEA MA
-
n−1
2
Notes and references
Pb I
(n = 1–3) single crystals exhibited red emission. With
n 3n+1
+
the increase in the number of MA cation, PEA
MAn−1Pb I
2 n 3n+1
1 D. Shi, V. Adinolfi, R. Comin, M. Yuan, E. Alarousu, A. Buin, Y.
Chen, S. Hoogland, A. Rothenberger and K. Katsiev, Low trap-
state density and long carrier diffusion in organoleadtrihalide
perovskite single crystals, Science, 2015, 347, 519.
(n = 1–3) single crystals gradually exhibited weaker emissions.
The monoclinic phase of PEA PbI was positioned at 520 nm.
2
4
Surprisingly, the triclinic PEA
PbI
2 4
and MA: PEAPbI
4
had two
fluorescent peak positions at 520 nm and 710 nm, respectively,
as shown in Fig. 4(a), which possibly resulted from edges of
the layered perovskite single crystals, as reported by Blancon
2 X. Chin, D. Cortecchia, J. Yin, A. Bruno and C. Soci, Nat.
Commun., 2015, 6, 7383.
3 X. Zhang, S. Bi, J. Zhou, S. You, H. Zhou, Y. Zhang and Z.
Tang, J. Mater. Chem. C, 2017, 5, 9376.
4 N. S. Ruddlesden and P. Popper, Acta Crystallogr., 1957, 10, 538.
5 D. B. Mitzi, C. A. Feild, W. T. A. Harrison and A. M. Guloy,
Nature, 1994, 369, 467.
35
30
et al. According to a previous report, the TRPL spectra of
the layered perovskites were well fitted by bi-exponential
decays, as shown in Fig. 4(b–d) and S7.† We found that the PL
decay time (τ) of monoclinic PEA PbI bulk crystals was 0.32
2
4
ns and 1.58 ns at 520 nm emission peak position. For triclinic
PEA PbI and MA: PEAPbI bulk crystals, the decay time was
reduced to 0.12 or 0.01 ns, and 0.63 or 0.44 ns at 520 nm
emission peak position, while their decay time at 710 nm
emission peak position was 1.81 or 1.64 μs and 9.39 or
6 (a) C. C. Stoumpos, D. H. Cao, D. J. Clark, J. Young, J. M.
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J. Even, M. A. Alam, G. Gupta, P. M. Ajayan, M. J. Bedzyk,
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2
4
4
9
.41 μs, respectively. The decreased band gaps and red-
shifted PL spectra compared with PEA PbI may be
attributed to the reduced disorder in dipoles of MA
2
4
+
3
6,37
cations within the crystal lattice.
is concluded that PEA MAn−1Pb
As mentioned above, it
3n+1 (n < 3) single crystals
2
n
I
exhibit the strong photoluminescent properties, which may
benefit the light-emitting diode (LED) applications.
Conclusions
In summary, we investigated the bulk growth, crystal structure
determinations, and tunable optical properties of layered hybrid
1
perovskite PEA
importantly, we observed that PEA
monoclinic and triclinic lattice structures) with green and red
2
MAn−1Pb
n
I
3n+1 (n = 1–3) single crystals. More
2
PbI had two polymorphs
4
(
emissions when exposed to UV irradiation. The phase
transformations of PEA PbI by different strategies demonstrated
2
4
1
1
1
that the two polymorphs transformed mutually. Further, the
tunable bandgap, PL spectra and PL decay time, and thermal
properties of PEA MA Pb I
(n = 1–3) single crystals were
2
n−1 n 3n+1
1
999, 286, 945.
investigated due to the changes in the compositional
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S. Hoogland, Y. Zhao, E. M. Beauregard, P. Kanjanaboos, Z. Lu,
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+
+
concentration of PEA and small MA cations. This work provides
an insightful guidance for the controlled growth of layered hybrid
perovskites and paves way for achieving high-performance and
stable layered perovskite optoelectronic devices.
1
1
1
Conflicts of interest
There are no conflicts of interest to declare.
Acknowledgements
This work is supported by the Development Program of China
17 T. Ueda, K. Shimizu, H. Ohkia and T. Okuda, Z. Naturforsch.,
A: Phys. Sci., 1998, 53, 983.
18 T. Ueda, K. Shimizu, H. Ohki and T. Okuda, Z. Naturforsch.,
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(
Grant No. 2016YFB1102201), the National Natural Science
Foundation of China (Grant No. 51932004, 61975098 and
1802215), and the 111 Project 2.0 (Grant No. BP2018013). Dr.
5
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