A new layered nano hybrid perovskite film with enhanced resistance to moisture-induced degradation

Article abstract of DOI:10.1016/j.cplett.2016.05.054

In this paper, a new layered hybrid perovskite film ((EDA)(MA)₂[Pb₃I₁₀]) was synthesized through one-step method. Ethylenediamine (EDA) cation was introduced into the perovskite lattice to synthesize a layered structure with improved resistance to degradation by humidity. The effects of humidity and time on crystal structure, composition, morphology and absorption spectra of (EDA)(MA)₂[Pb₃I₁₀] were analyzed by in situ grazing incidence X-ray diffraction (GIXRD), scanning electron microscope (SEM), and UV-Vis spectroscope. The results reveal that a (EDA)(MA)₂[Pb₃I₁₀] film is more moisture resistant than a CH₃NH₃PbI₃ film which is widely used in the perovskite solar cell now. UV-Vis spectroscopy result also shows that the layered structure film is a suitable solar absorber with a bandgap (1.67 eV), which is close to the optimum value for solar photoelectric conversion. Compared to CH₃NH₃PbI₃, the low-cost perovskite structure offers greater tunability on a molecular level for further material optimization and possibility for widely used in the future.

Full text of DOI:10.1016/j.cplett.2016.05.054

Accepted Manuscript
A New Layered Nano Hybrid Perovskite Film with Enhanced Resistance to
Moisture-Induced Degradation
Wenlong Jiang, Jifei Ying, Wei Zhou, Kongchao Shen, Xing Liu, Xingyu Gao,
Fuqiang Guo, Yanmin Gao, Tieying Yang
PII:
S0009-2614(16)30363-3
DOI:
http://dx.doi.org/10.1016/j.cplett.2016.05.054
CPLETT 33894
Reference:
To appear in:
Chemical Physics Letters
Received Date:
Accepted Date:
15 March 2016
25 May 2016
Please cite this article as: W. Jiang, J. Ying, W. Zhou, K. Shen, X. Liu, X. Gao, F. Guo, Y. Gao, T. Yang, A New
Layered Nano Hybrid Perovskite Film with Enhanced Resistance to Moisture-Induced Degradation, Chemical
Physics Letters (2016), doi: http://dx.doi.org/10.1016/j.cplett.2016.05.054
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A New Layered Nano Hybrid Perovskite Film with Enhanced
Resistance to Moisture-Induced Degradation
a,b
a
a
b
b
b
Wenlong Jiang , Jifei Ying , Wei Zhou , Kongchao Shen , Xing Liu , Xingyu Gao , Fuqiang
c
a
b
Guo , Yanmin Gao *, Tieying Yang *
a
Jiangsu University of Science and Technology, Zhenjiang 100190, China
b
Shanghai Institute of Applied Physics, Chinese Academy of Sciences, Shanghai 201204, China
c
Zhengzhou University of Industrial Technology, Zhengzhou, Henan 451150, China
Abstract
In this paper, a new layered hybrid perovskite film((EDA)(MA)
2
[Pb I10]) was
3
synthesized through one-step method. Ethylenediamine(EDA) cation was introduced
into the perovskite lattice to synthesize a layered structure with improved resistance to
degradation by humidity. The effects of humidity and time on crystal structure,
composition, morphology and absorption spectra of (EDA)(MA)
2
[Pb I10] were
3
analyzed by in situ grazing incidence X-ray diffraction(GIXRD), scanning electron
microscope(SEM), and UV-Vis spectroscope. The results reveal that a
(
EDA)(MA)
2
[Pb
3
I
10] film is more moisture resistant than a CH
3
NH
3
PbI film which is
3
widely used in the perovskite solar cell now. UV-Vis spectroscopy result also shows
that the layered structure film is a suitable solar absorber with a bandgap(1.67 eV),
which is close to the optimum value for solar photoelectric conversion. Compared to
CH
3
NH
3
PbI , the low-cost perovskite structure offers greater tunability on a
3
molecular level for further material optimization and possibility for widely used in the
future.
1
. Introduction
Solar energy is seen as one of the most promising renewable energy forms in the

2
1st century. The trend towards wide spread affordable use of solar energy has led to
the development of thin-film based solar cells [1-2]. Perovskite solar cell has attracted
increasing attention due to the superb photovoltaic performance thanks to the intrinsic
material properties with high absorption coefficient, balanced charge transport
behavior and low trap density. Since the first reports by Miyasaka et al in 2009,
solar-cell-devices based on hybrid perovskites of the CH
3
NH
3
PbX (X= I, Br, Cl) type
3
have been largely improved as their power conversion efficiencies (PCEs) have
drastically increased from 3.8 % to 22.1 % in only a few years [3-6]. However, the
lead–halide perovskites have two main drawbacks: the toxicity of the water-soluble
source of lead and the degradation of the material by atmospheric moisture [7]. After
replacing the lead perovskite with the significantly less toxic tin analogue, solar cells
reached efficiencies of up to about 6 % [8]. The moisture sensitivity, however,
remains a major obstacle to commercialization. In the presence of high moisture, the
degradation process and decay mechanism may be expressed as follows, which results
in a significant decline in device performance [9].
In contrast to the 3-D perovskites, the layered two dimensional (2-D) systems can
accommodate much larger and more complex organic cations. This is because the
cage into which the organic cation must fit is no longer confined in three dimensions
[
(
10-12].
PEA) (CH
Karunadasa
made
devices
using
a
layered
perovskite
2
3
NH [Pb 10] as the absorber. The perovskite stucture showed no
3
)
2
3
I
significant changes after a period of 46 days of exposure to humidity [13]. Alex M.
Ganose synthesized a new layered perovskite struvture (CH NH Pb(SCN)
3
3
)
2
I
2 2,

displaying improved chemical stability against phase separation when in high RH [14].
Here
EDA)(MA)
we
[Pb
reported
a
new
layered
perovskite
enhanced
+
+
+
(
2
3
I
10](EDA= NH
3
(CH
2
)
2
NH
3
,MA=CH
3
NH
3
)
with
resistance to moisture-induced degradation by combining (EDA)I
2
, (MA)I, and PbI in
2
a 1:2:3 stoichiometric ratio in a solvent mixture of N,N-dimethylformamide(DMF).
The successful preparation and application of the new layered perovskite material
suggests that such materials may have a promising future in large-scale industrial
applications.
2
. Experimental
2
.1 Materials
(
EDA)I : HI solution was added dropwise to a cold(0 °C), stirred solution of
2
Ethylenediamine(5.0 mL, 75 mmol) in ethanol(5.0 mL) until a colorless precipitate
formed. The solid was filtered through paper and washed repeatedly with diethyl ether.
Cooling a 60 °C, saturated isopropanol solution of the solid to 0°C afforded (EDA)I
in ca. 90 % yield. MAI(99%) was purchased from Materwin Techology from China.
2
(
EDA)(MA)
.578 mmol), and PbI
0 °C for 6h and filtered through paper PTFE filters(0.45 mm) prior to use.
MAPbI : MAI and lead chloride (PbI , 99.99%, Alfa) powder were mixed in
2
[Pb
3
I
10]: Solid (EDA)I
2
(73.4 mg, 0.289 mmol), (MA)I(92.0 mg,
0
6
2
(400 mg, 0.868 mmol) were dissolved in DMF(0.87 mL) at
3
2
DMF (99.9%, Aldrich) with a molar ratio of 1:1. The perovskite precursor solution
was stirred at 60 °C for 6h and filtered through PTFE filters (0.45 mm) prior to use.
2
.2 Device fabrication

The TiO
isopropoxide (Sigma-Aldrich, 99.999%) and 0.01M HCl. Dense TiO
was coated onto F-doped SnO (FTO) substrate by spinning titanium precursor at
000 rpm, followed by annealing at 500 °C for 1 h. The precursor solution was
2
compact film precursor solution in ethanol consists of 0.3 M titanium
2
film (≈40 nm)
2
5
deposited onto TiO /FTO substrate by spin-coating at 3000 rpm for 60 s. After drying
2
the film on a hotplate at 100 °C for 0.5 h, the color of the film turned from yellow to
dark brown, indicating the formation of perovskite. Subsequently, the spiro-OMeTAD
−
1
(
Sigma-Aldrich) solution (80 mg mL
chlorobenzene) with 17.5 µL
−
1
Li-bis(trifluoromethanesulfonyl) imide (Li-TFSI)/acetonitrile (500 mg mL ) and 28.5
µL TBP as additives was spin coated at 3000 rpm for 35 s. Finally, a 70 nm Au
electrode was thermally evaporated as an electrode. All of the layers were fabricated
inside an N
.3 Characterization methods
X-ray diffraction (XRD) including GIXRD was performed at BL14B1 beamline
2
-filled glove box.
2
of the Shanghai Synchrotron Radiation Facility (SSRF) using X-rays with a
wavelength of 1.24 Å. The morphology of the films was studied using a JEOL
PT008462 scanning electron microscope (SEM). The UV−vis absorption spectra of
the thin films were measured with a Hewlett UV-3010 spectrophotometer. The J–V
data were acquired with a Keithley 2400 source–meter unit. The light J–Vcurves were
measured under illumination with a Newport-Oriel (Sol3A Class AAA Solar
2
Simulator, 94043A) AM 1.5G light source operating at an intensity of 100 mW cm .
3
. Results and discussion

Confirmation of the crystallographic data would be desirable to explore
EDA)(MA) [Pb 10]. Crystal structure data obtained from one-dimensional (1D)
(
2
3
I
powder X-ray diffraction provides only limited structural information, in particular
for the highly oriented perovskite thin films. Therefore, we carried out in situ GIXRD
measurements on the perovskite film that is subjected to about 80% RH. Snapshots of
the in situ GIXRD experiments at various points in time are shown in Figure 1. All of
the GIXRD patterns exhibited a relatively strong scattering background from the
-1
amorphous glass substrate in the range of q=10-25 nm , where q is the scattering
vector (q=4πsin(θ)/λ). After calibration, key features of the perovskite diffraction
-1
pattern could be observed at q≈10.04, 19.74 and 22.21 nm . These are consistent with
reflection from the (110), (220) and (310) lattice planes, respectively [15]. Fig 1(a) is
the diffraction pattern of (EDA)(MA)
2
[Pb I10] without water vapor around the sample,
3
which reveals that the film is polycrystalline with preferred orientation along the
normal direction. As shown in Fig. 2(b), with the time increasing in a relative
-1
humidity of 80 %, new features in the diffraction pattern at q≈9 nm become more
and more intense and can be assigned to reflections from the (001) planes of PbI
2
(
PDF#07-0235)[16].
According to Fig. 1(c) and Fig. 1(d), it can be found that, when the CH
3
NH PbI
3
3
-1
film was exposed to moisture, PbI diffraction spots began to appear at q≈9 nm .
2
They eventually form a more complete ring pattern as the decomposition process
continued and completed after 30 min. This suggests that the crystalline phase
decomposes immediately when it is exposed to water vapor. On the other hand, for the

(
EDA)(MA)
crystalline phase does not decompose too much. So, (EDA)(MA)
higher resistance to humidity than the CH NH PbI film.
SEM images of (EDA)(MA) [Pb NH PbI
and differences on morphology between the two kinds of films could be seen clearly
through SEM images. It could be seen from Fig. 2(a), by controlling the ratio of
EDA)I , (MA)I and PbI , we obtain the (EDA)(MA) [Pb 10] film which is in the
form of flake microstructure and different layers are closely together with each other.
While CH NH PbI film is composed of independent micrometer-sized grains as
shown in Fig. 2(b). External dense layer of (EDA)(MA) [Pb 10] film can protect
inner layer from degradation and it consists with the GIXRD result that
EDA)(MA) [Pb 10] shows better resistance to high RH than CH NH PbI films.
The contact angle is the angle at which a liquid meets a solid surface.
2
[Pb
3
I
10] film – see Fig. 1(a),(b), little PbI
2
appears after 150 min and the
2
[Pb 10] film shows
3
I
3
3
3
2
3
I
10] and CH
3
3
3
films were shown in Fig.
2
(
2
2
2
3
I
3
3
3
2
3
I
(
2
3
I
3
3
3
Conventionally, the hydrophilicity and hydrophobicity of a surface is characterized by
the contact angle (CA) of a single droplet of water on the surface. The larger angle
represents better hydrophobicity. Fig. 3(a) shows the hydrophobic characteristics of
the CH
3
NH
3
PbI film according to the contact angle measurements. For this film, a
3
small droplet of water (∼8μL) formed a relatively hydrophilic contact, as indicated
by the estimated CA of 40°. However, considerably higher hydrophobic behavior was
observed on the film with the (EDA)(MA)
(b), which is larger than for the CH NH
moisture, it can be seen that CH NH PbI film would be influenced easier than the
2
[Pb
3
I
10] film, showing a CA of 73°, see Fig.
3
3
3
PbI
3
film. Therefore, when faced with
3
3
3

(
EDA)(MA)
Fig. 4(a) showed that (EDA)(MA)
visual light spectrum compared with CH
the optical properties of the (EDA)(MA)
2
[Pb
3
I10] film.
2
[Pb
3
I10] film had a good absorption in the
3
NH
3
PbI
3
films. Time-dependent changes of
NH PbI films were
2
[Pb
3
I
10] and CH
3
3
3
observed by recording light absorption spectra – see Fig. 4. The ex situ light
absorption spectra of the (EDA)(MA) [Pb 10] film were measured immediately after
the film preparations and after 5, 10, 15 and 20 days of storage at 35% RH. The ex
situ light absorption spectra of the CH NH PbI films were measured immediately
2
3
I
3
3
3
after the film preparations and after 1, 2, and 3 days of storage in the same
environment. As shown in Fig. 4(a), 17days later, the film had degraded only a little
and still possessed good optical absorption. Eventually, the entire conversion of
perovskite into PbI
was confirmed again through visual observation. In contrast, as shown in Fig. 4(b),
the CH NH PbI films exhibit big changes of the absorption spectrum in short days at
5% RH due to dissolution-caused degradation. This shows a significantly weak
stability with regard to humidity. All results suggest that a promising solution for
overcoming the water sensitivity of the perovskite cell is replacing the CH NH PbI
with (EDA)(MA) [Pb 10]. In addition, we also obtained the photoluminescence (PL)
spectra of the (EDA)(MA) [Pb 10] film - see Fig. 4(a). We find a sharp PL peak at
740 nm. This wavelength corresponds to the band gap energy of ∼1.67 eV
according to the well-known relationship between band gap energy and wavelength:
EG = 1240/λonset), and it is suitable for use as the light absorbing component.
2
was observed after approximately 30 days. The enhanced stability
3
3
3
3
3
3
3
2
3
I
2
3
I
~
(

Fig. 5(a) shows the J–V characteristic of device with (EDA)(MA)
2
[Pb
3
I10] as the
light absorber. The champion device exhibits a high Voc of 1.24 V, a Jsc of 16.57 mA
-2
cm , and a FF of 0.56, yielding a PCE of 11.58 %. The encouraging result
demonstrate that (EDA)(MA) [Pb 10] is an efficient light absorber to obtain
high-performance perovskite solar cells. In order to study the role of
EDA)(MA) [Pb 10] in the device, we have designed a stability test using two
samples based on CH NH PbI and (EDA)(MA) [Pb 10] as light absorber. As
demonstrated in Fig. 5(b), the PCE of the perovskite solar cell with
2
3
I
(
2
3
I
3
3
3
2
3
I
(
EDA)(MA)
the CH NH
EDA)(MA)
2
[Pb
PbI
[Pb
3
I
10] drops only ~5 % after 18 days, which is much more stable than
one (~99 % drop). This experiment supports the importance of
10] in order to fabricate stable solar cells with high efficiency which
3
3
3
(
2
3
I
could endure high RH.
Conclusion
In summary, an EDA cation was introduced into the perovskite lattice to
synthesize a layered structure with high resistance to moisture degradation. GIXRD
result proves that the (EDA)(MA)
2
[Pb
3
I
10] film performs better than the CH
3
NH
3
PbI
3
film with regard to humidity caused degradation. Both water contact angle test and
SEM measurement consist with the GIXRD result. UV-Vis absorbance spectroscopy
result also indicates that the (EDA)(MA)
good replacement for the CH NH PbI film when used as light absorption layer in
solar cells. On the basis of this study, it could be possible to develop more stable PSCs
using (EDA)(MA) [Pb 10] films with the prospect of successful commercialization,
2
[Pb I10] film with a suitable band gap is an
3
3
3
3
2
3
I

perhaps after some additional complementing studies.
Acknowledgments
The authors thank the staff of beamline BL14B1 at the Shanghai synchrotron
radiation facility. This work was financially supported by the National Natural
Science Foundation of China (Grant Nos. 11405253 and U1332205), the Youth
Innovation Promotion Association CAS and the research grant (No.14DZ2261200)
from the Science and Technology Commission of Shanghai Municipality.
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[
[
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(
Figure Captions
Fig. 1 2D GIXRD patterns of (EDA)(MA)
on glass, after (c) 0 min, (d) 30 min exposure to 80% RH.
Fig. 2 SEM topography of (a) (EDA)(MA) [Pb 10] and (b) CH
Fig. 3 Photograph of contact angle of water drop on (a) CH NH
[Pb 10] and (b) CH
2 3 3 3 3
[Pb I10] film on glass, after (a) 0 min (b) 150 min and CH NH PbI film
2
3
I
3
NH
3
PbI
and (b) (EDA)(MA) [Pb
3
NH PbI films in a 35 % RH
3
film
3
3
PbI
3
2
3
I10] film surfaces
Fig.4 UV–vis absorption spectra for (a) (EDA)(MA)
2
3
I
3
3
environment at different time point.
2 3
Fig.5 (a) J–V curves of solar cell with (EDA)(MA) [Pb I10] (b) Stability of the devices based on

(
2 3 3 3 3
EDA)(MA) [Pb I10] and CH NH PbI in an ambient environment after encapsulation using UV-epoxy

Figure 1 2D GIXRD patterns of (EDA)(MA)
2 3 3 3 3
[Pb I10] film on glass, after (a) 0 min (b) 150 min and CH NH PbI
film on glass, after (c) 0 min, (d) 30 min exposure to 80% RH.

2 3 3 3 3
Figure 2 SEM topography of (a) (EDA)(MA) [Pb I10] and (b) CH NH PbI film

3 3 3 2 3
Figure 3 Photograph of contact angle of water drop on (a) CH NH PbI and (b) (EDA)(MA) [Pb I10] film surfaces

a
4
3
2
1
1.0
0.5
0
5
1
1
2
d
d
0 d
5 d
0 d
3
0d
ITO
ITO
0
.0
0
400
500
600
700
800
Wavelength(nm)
6
4
2
0
1
2
3
h
b
d
d
d
0
4
00
500
600
700
800
Wavelength(nm)
Figure 4 UV–vis absorption spectra for (a) (EDA)(MA)
2 3 3 3 3
[Pb I10] and (b) CH NH PbI films in a 35 % RH
environment at different time point.

a 0
(
EDA)(MA) [Pb I ]
2 3 10
-
5
Voc(v) Jsc(mA cm-2 FF(%) PCE(%)
.24 16.57 56.37 11.58
1
-10
-15
-20
0.0
0.2
0.4
0.6
0.8
1.0
1.2
Bias(V)
1
4
(
EDA)(MA) [Pb I ]
b 12
2 3 10
CH NH PbI
3
3
3
1
0
8
6
4
2
0
0
2
4
6
8
10
12
14
16
18
20
Time/Day
Figure 5 (a) J–V curves of solar cell with (EDA)(MA)
2 3
[Pb I10] (b) Stability of the devices based on
(
EDA)(MA) [Pb 10] and CH NH PbI in an ambient environment after encapsulation using UV-epoxy
2
3
I
3
3
3

The effects of humidity and time on crystal structure of (EDA)(MA)
analyzed by in situ grazing incidence X-ray diffraction(GIXRD). The result reveals
that a (EDA)(MA) [Pb 10] film is more moisture resistant than a CH NH PbI film
which is widely used in the perovskite solar cell now.
2
[Pb I10] were
3
2
3
I
3
3
3

1
2
. An EDA cation was first introduced into the perovskite lattice to synthesize a
layered structure with high resistance to moisture degradation.
. The effects of humidity and time on crystal structure of (EDA)(MA)
2
[Pb I10]were
3
analyzed by in situ grazing incidence X-ray diffraction(GIXRD).