Thiophene-Based Two-Dimensional Dion-Jacobson Perovskite Solar Cells with over 15percent Efficiency

Article abstract of DOI:10.1021/jacs.0c03363

Two-dimensional (2D) perovskites are emerging photovoltaic materials because of their highly tunable photophysical properties and improved environmental stability in comparison with 3D perovskites. Here, a thiophene-based bulky dication spacer, namely, 2,5-thiophenedimethylammonium (ThDMA), was developed and applicated in 2D Dion-Jacobson (DJ) perovskite. High-quality 2D DJ perovskite, (ThDMA)(MA)n-1PbnI3n+1 (nominal n = 5), with improved crystallinity, preferred vertical orientation, and enlarged spatially resolved carrier lifetime could be achieved by a one-step method using a mixed solvent of DMF/DMSO (v/v, 9:1). The optimized device exhibits a high efficiency of 15.75percent, which is a record for aromatic spacer-based 2D DJ perovskite solar cells (PSCs). Moreover, the unencapsulated 2D DJ perovskite devices sustained over 95percent of their original efficiency after storage in N2 for 1655 h. Importantly, both the light-soaking stability and thermal stability (T = 80 °C) of the 2D DJ perovksite devices are dramatically improved in comparison with their 3D counterparts. These results indicate that highly efficient and stable 2D DJ PSCs could be achieved by developing thiophene-based aromatic spacers as well as device engineering.

Full text of DOI:10.1021/jacs.0c03363

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Article
Thiophene-based Two-Dimensional Dion–Jacobson
Perovskite Solar Cells with over 15% Efficiency
Di Lu, Guangwei Lv, Zhiyuan Xu, Yixin Dong, Xiaofei Ji, and Yongsheng Liu
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Thiophene-based Two-Dimensional Dion–Jacobson Perovskite Solar
Cells with over 15% Efficiency
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†
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Di Lu, Guangwei Lv, Zhiyuan Xu, Yixin Dong, Xiaofei Ji, and Yongsheng Liu*
†
The Centre of Nanoscale Science and Technology and Key Laboratory of Functional Polymer Materials, Institute of
Polymer Chemistry, College of Chemistry, Nankai University, Tianjin 300071, China.
‡
Renewable Energy Conversion and Storage Center (RECAST), Nankai University, Tianjin 300071, China
KEYWORDS: two-dimensional perovskite, solar cells, trap density, spacer cations, mobility.
ABSTRACT: Two-dimensional (2D) perovskites are emerging photovoltaic materials because of their highly tunable
photophysical properties and improved environmental stability in comparison with 3D perovskites. Here, a thiophene-based bulky
dication spacer, namely 2,5-thiophenedimethylammonium (ThDMA), was developed and applicated in 2D Dion–Jacobson (DJ)
perovskite. High quality 2D DJ perovskite, (ThDMA)MAn-1Pb I3n+1 (nominal n = 5), with improved crystallinity, preferred vertical
n
orientation and enlarged spatially resolved carrier lifetime could be achieved by one-step method using mixed solvent of
DMF/DMSO (v:v, 9:1). The optimized device exhibits a high efficiency of 15.75%, which is a record for aromatic spacer-based 2D
DJ perovskite solar cells (PSCs). Moreover, the unencapsulated 2D DJ perovskite devices sustained over 95% of its original
o
efficiency after storage in N
2
for 1655 h. Importantly, both the light soaking stability and thermal stability (T = 80 C) of the 2D DJ
perovksite devices are dramatically improved in comparison with their 3D counterparts. These results indicate that highly efficient
and stable 2D DJ PSCs could be achieved by developing thiophene-based aromatic spacers as well as device engineering.
INTRODUCTION
well as device engineering to obtain high-quality perovskite
films with crystal preferred vertical orientation. So far,
aliphatic diammonium cations with different length of alkyl
chains have been studied in 2D DJ PSCs and shown promising
With natural multi-quantum well structure, two-dimensional
(2D) metal halide perovskites are a class of emerging high-
performance semiconductors due to their impressive structural
diversity, tunable optoelectronic properties and excellent
environment stability. The Ruddlesden-Popper (RP) and
Dion-Jacobson (DJ) 2D perovskites have the general formula
1
0-12
photovoltaic performance.
However, the aliphatic
1
-4
diammoniums are electrically insulating due to its low
dielectric constant. In contrast, with delocalized π-electrons
along the molecular backbone, the aromatic spacer exhibits a
larger dielectric constant in comparison with the aliphatic one
of the same size, which could reduce the dielectric mismatch
6
between the organic layer and adjacent corner-sharing [PbI ]
2 n-1 n n
of A B M X3n+1 and ABn-1M X3n+1, respectively. Here, A
and A are monovalent and divalent organic cations,
respectively, B is a monovalent cation, X is a halide anion, M
is a divalent metal, and n is defined as the layer number of
corner-sharing [PbI ] inorganic slabs. Much work has been
6
done on 2D RP perovskite solar cells (PSCs) by developing
new spacers and device engineering to improve their
4-
4
-
4
slabs and weaken the corresponding dielectric confinement
13-15
effect in the well.
Recently, Kanatzidis and co-workers
reported that the pyridinium-based aromatic dication spacers
exhibit smaller exciton binding energy compared to aliphatic
series due to the increased dielectric constant, resulting in a
4-9
photovoltaic performance. 2D RP perovskites have pairs of
interdigitated organic spacers between adjacent corner-sharing
1
6, 17
4
-
champion efficiency of 12.04%.
Grätzel et al. reported the
6
[PbI ] sheets, in which a van der Waals gap appeared in the
first phenyl-based aromatic spacer for 2D DJ perovskite with
efficiencies exceeding 7% and excellent stability in humid
bulky spacers bilayer structure. In contrast, there is no van der
Waals gap in the 2D DJ perovskites since the diammonium
groups of organic spacer layer could bridge the neighboring
inorganic slabs by hydrogen bonding interactions, thus
1
8
ambient air. Although 2D DJ perovskite has shown great
potential in solar cells with improved stability, the
development of new organic spacers as well as device
engineering are highly necessary to further boosting their
photovoltaic performance. The thiophene unite is a basic and
among the most important building blocks in organic
semiconductor materials and high photovoltaic performance
has been demonstrated when thiophene-based spacers were
4
eliminates the disadvantages of RP perovskites. The strong
hydrogen bonding interactions between spacer and inorganic
slabs would lead to a more rigid structure and shortened
interslab distance, which may reduce the barrier of organic
layer and facilitate efficient charge transport in the 2D
3
perovskites. These advantages make 2D DJ perovskite a
1
9-21
used in 2D RP PSCs.
D DJ PSCs using thiophene derivatives as organic spacers
have rarely been studied.
However, as a newly research field,
promising candidate for efficient and stable PSCs.
2
To realized high performance 2D DJ PSCs, it’s highly
necessary to rational design bulky dication spacer materials as
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In this work,
a
thiophene derivative, namely 2,5-
PEDOT:PSS, indicate its potential application in photovoltaic
cells.
The film surface morphology of the 2D DJ perovskite with
DMF as solvent (we named it control film) and the 2D DJ
perovskite with optimized DMF/DMSO ratio (9:1, v:v) (we
named it target film) were evaluated by scanning electron
microscope (SEM). Figure 1c,d show that both films possess
full surface coverage but different grains morphology.
Compared to the control film, the improved film quality of the
target film could be attributed to the strong coordination
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thiophenedimethylammonium iodide (ThDMAI), was
successfully synthesized and applicated in 2D DJ PSCs. A
high quality 2D DJ perovskite film based on (ThDMA)(MA)n-
1
n
Pb I3n+1 (nominal n = 5) were fabricated by DMSO-assisted
film growth technique. It is found that the crystal growth and
orientation of the 2D DJ perovskites could be induced by the
strong coordination molecule DMSO when it was used in the
precursor solution, leading to enlarged grain size, decreased
trap-state density and more efficient charge transport
compared to the 2D DJ perovskite film without DMSO. The
optimized device exhibits a champion power conversion
efficiency (PCE) of 15.75%, which is the highest efficiency so
far for aromatic spacer-based 2D DJ PSCs to the best of our
knowledge. Furthermore, the optimized 2D perovskites exhibit
superior film and device stability compared to their 3D
counterparts. For example, the unencapsulated 2D devices
interaction between DMSO and PbI
2
, which, as a result, retard
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crystallization, leading to increased grain size of 2D DJ
23, 24
perovskites.
Figure S4 shows the cross-section SEM of
control and target 2D DJ perovskite devices, which exhibit
layer-by-layer structures. The densely packed morphology and
obviously enlarged grain size of the target film in the cross-
section SEM is consistent with the top-view SEM images.
sustain over 95% of their original PCE after storage in N
655 hours, while only ~54% of their initial values left for 3D
MAPbI PSCs. Furthermore, the light and thermal stability of
3
D DJ PSCs were also dramatically improved in comparison
2
for
1
2
with MAPbI -based devices.
3
RESULTS AND DISCUSSION
In consideration of the strategy for developing aromatic
ring-based divalent (+2) organic spacers, we designed and
synthesized an electron-rich thiophene-based derivative
(
ThDMAI). The synthetic routes can be found in Scheme 1
and the synthesis procedure is shown in the Supporting
Information. Thiophene-2,5-dicarbaldehyde was first
reduced by NaBH to obtain compound 2 in a yield of 99.2%.
1
4
Figure 1. (a) 3D structure of MA and ThDMA. (b) Schematic
The hydroxyls in compound 2 were then converted to azides
using 1,8-Diazabicyclo[5.4.0.]undec-7-ene (DBU) and
diphenylphosphosphoryl azide (DPPA). By reducing the
compound 3 with PPh
diamine compound 4 was achieved with a yield of 96.5%. To
get pure target compound, the compound 4 was further
2
protected with di-tert-butyl dicarbonate (Boc O). Finally, the
target molecules ThDMAI was obtained by using HI to
deprotect and generate target salt ThDMAI (Figure S1, S2).
crystal structure of (ThDMA)(MA)
4 5
Pb I16. (c, d) SEM top-view
images of the control and target films.
2
2
To study the effect of DMSO on the crystallinity of the 2D
(ThDMA)(MA) Pb 16 perovskite films, X-ray diffraction
3
through the Staudinger reaction, the
4
5
I
(XRD) measurements were performed. As illustrated in
Figure 2a, the control film without DMSO shows very weak
diffraction peaks, suggesting poor crystallinity. Interestingly,
the diffraction peak intensity was dramatically improved for
target film with optimized DMF/DMSO ratio of 9:1. The
dominant (111) and (202) diffraction peaks, corresponding to
related crystallographic plane of perovskite, were observed at
Scheme 1. Synthetic routes of ThDMAI.
OHC
S
CHO
NaBH4
S
DBU, DPPA
S
PPh3
S
HO
OH
N3
N3
H2N
NH2
1
4.6° and 28.9°, respectively. The intensity of (111) peak in
1
2
(99%)
3
(81%)
4
(97%)
target film was approximately 24 times higher than that of
control film. Moreover, the target film shows a decreased full
O
O
O
O
O
O
S
HI
O
O
S
N
N
O
H
H
I H3N
NH3 I
o
Et3N
width at half-maximum (FWHM) of (0.11 ) for the (111) peak
5
(51%)
ThDMAI (77%)
in comparison with control film (0.14°). The smaller FWHM
and stronger diffraction intensity of (111) peak for the target
film indicate its dramatically increased crystallinity, in well
agreement with the enlarged size of grains shown in SEM top-
view images above and the accelerated film formation process
show in Figure S5.
Figure 1a and 1b display 3D chemical structure of
methylammonium (MA), ThDMA and a schematic crystal
structure of (ThDMA)(MA) Pb 16, in which the adjacent
octahedron layers were separated by one
4
5
I
4
-
6
inorganic [PbI ]
sheet of organic spacer ThDMA. The lack of van der Waals
gap in DJ perovskites in comparison with RP perovskites
would reduce the distance between two inorganic layers and
enhance the structure stability. As illustrated in Figure S3, the
valence band maximum (VBM) of ThDMA-based 2D DJ
In addition to film crystallinity, crystal orientation also
plays a key role for charge transport between bottom and top
electrodes in the devices owing to the anisotropic nature of
4
layered perovskite system. To evaluate the crystal orientation
perovskite, (ThDMA)(MA)n-1Pb
n
I
3n+1 (nominal n=5)
,
was
of the 2D DJ perovskite in the films, the grazing incidence
wide angle X-ray scattering (GIWAXS) of our samples were
investigated (Figure 2b, c). The control film reveals weak
(111) and (202) diffraction rings as well as discrete Bragg
spots with dispersive edges, suggesting partial layered crystals
are randomly orientated in the grains of 2D DJ perovskite. The
randomly orientated crystals will hinder the efficient charge
measured to be 5.54 eV from ultra-violet photoelectron
spectroscopy (UPS). The conduction band maximum (CBM)
was calculated to be 3.96 eV by subtracting the VBM from the
optical bandgap. The well-matched energy levels of the 2D DJ
perovskite with charge transport materials, such as PCBM and
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thickness.28 A schematic diagram of morphology and charge
transport model of the control and target films in the
photovoltaic devices were further proposed. As illustrated in
Figure 2e, the control film exhibits smaller and randomly
orientated grains, where the phases with paralleled orientation
would retard the charge transport between two electrodes. In
contrast, after introducing DMSO in the precursor solutions,
larger and more vertical orientated grains could be formed in
the obtained target film due to the retarded crystallization.
transport in the devices. When proper amount of DMSO was
introduced, the target film shows discrete and sharp Bragg
spots (Figure 2c), suggesting a high degree of preferential
1
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5, 26
vertical orientation with respect to the substrate.
results indicate that suitable DMSO could effectively regulate
the crystal growth and orientations of the grains due to the
coordination of DMSO and PbI in the precursor solution.
2
Meanwhile, traces of weak Bragg spots appeared at q < 1,
suggesting a small quantity of low-n phases exist in the 2D DJ
The
2
7, 28
perovskite film.
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Figure 3. (a) J-V characteristics of the control and target 2D DJ
PSCs. (b) EQE spectra and integrated photocurrent density of the
corresponding devices. (c) PCE distribution (40 individual
devices were collected) of the control and target devices. (d)
Stabilized power output and current density of the target device.
(e) Double-logarithmic plots of JSC versus light intensity. (f)
Figure 2. (a) XRD patterns of the control and target films. (b, c)
GIWAXS data of control and target films. (d) HRTEM image of
the target film. Insets are FFT images of the corresponding area.
(e) Schematic diagram of morphology and charge transport model
of the control and target devices.
Seminatural-logarithmic plots of VOC versus light intensity.
The p-i-n type photovoltaic devices were fabricated with a
architecture of ITO/PEDOT: PSS/perovskite/PCBM/BCP/Ag
to study the device performance of control and target 2D DJ
perovskites. Figure 3a shows the current density–voltage (J–
V) curves of the optimized devices. The detailed photovoltaic
parameters are summarized in Table 1. The control device
exhibits a low efficiency of 6.11%, with an open-circuit
voltage (VOC) of 1.00 V, a low short-circuit current density
To investigate the phase distribution in optimized 2D DJ
perovskite film, high-resolution transmission electron
microscope (HRTEM) was investigated. As illustrated in
Figure 2d, the HRTEM images show well-defined lattice
spacings with different fingerprint, which were further
analyzed using the fast Fourier transform (FFT) analysis. The
narrow inter-planar spacing of 3.10 Å in region (i) suggest the
-2
(JSC) of 9.83 mA cm , and an inferior fill factor (FF) of
62.01%. In contrast, the best performing target device exhibits
-
an improved VOC of 1.07 V, an increased JSC of 19.55 mA cm
2
9
existance of 3D MAPbI
3
phase in the film. The relatively
2
,
and a notable FF of 75.46%, yielding a champion PCE of
wider interplanar spacing of 20.80 Å in region (ii) and 7.58 Å
in region (iii) could be assigned to the (040) reflection of the n
1
5.75%, which is a record for aromatic spacer-based 2D DJ
16-18
PSCs to the best of our knowledge.
The dramatically
=
6 phase and the (060) reflection peak of the n=3 phase,
enhanced photovoltaic performance could be attributed to the
high film quality with improved crystallinity and preferred
vertical orientation of layered perovskites. As shown in Figure
respectively (Figure S6 and Table S1). Moreover, other inter-
planar spacings could also be observed in the 2D DJ
perovskite film (Figure S7), which could be ascribed to
different layered phases. The randomly distributed 2D DJ
perovskite phases maybe related to the different
thermodynamic stability of layered DJ phases with different
3
b, the calculated JSC from EQE data are 9.71 and 19.18 mA
-2
cm for the control and target devices, respectively, in well
agreement with the J-V data. Note that the devices based on
2D DJ perovskite exhibit hysteresis under different scanning
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condition (Figure S8, Table S2), similar to previous reports.18
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Importantly, as shown in Figure 3c and Figure S9, the target
2D DJ PSCs shows excellent reproducibility with average
PCE of 14.76%, much higher compared to that of control
devices (average PCE = 5.40%), indicating the positive effect
of DMSO on the photovoltaic performance of 2D DJ
perovskite because of the improved film quality and
suppressed charge recombination. We note that the efficiency
was decreased when more DMSO was used to fabricate the 2D
DJ perovskite films, as shown in Figure S8b and Table S3.
This could be ascribed to the changed film morphology after
introducing more DMSO, which exhibits higher boiling point
and stronger coordination capability with PbI2 in comparison
with DMF. The high PCE of the optimized target device was
further verified by the stabilized power outputs measurements
under the maximum power point (0.88 V), which shows an
(1)
where A
1
and A
2
are the relative amplitudes, and τ and τ are
1 2
the best-fit PL decay times for fast and slow recombination of
the charge carrier, respectively. The fitted TRPL parameters of
the 2D DJ perovskite films are summarized in Table S4. The
calculated average decay time (τavg) for the target film is 200.1
38
ns, which is associated with the overall recombination and is
larger than that of control film (110.5 ns), further suggesting
enlarged charge carrier lifetime due to the suppressed
nonradiative recombination loss in the target film, consistent
with the transient photovoltage (TPV) results shown in Figure
S11 and Table S5.
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0
-2
average PCE of 15.01% and a JSC of 17.06 mA cm (Figure
3
d).
To study the carrier recombination in the control and target
D DJ PSCs, light intensity (I) dependent J-V characteristics
2
α
was performed. Figure 3e shows the linear relation of J  I in
a double-logarithmic scale. When the value of α is close to 1,
the device shows weak space charge effects and almost all
3
0, 31
charge could be collected prior to recombination.
The
fitted α value is 0.88 and 0.91 for control and target devices,
respectively. The larger α value of the target device suggests
its weaker nongeminate recombination, leading to improved
3
2, 33
FF and JSC
.
We further studied the recombination kinetics
in the devices by light intensity dependence of Voc in a
seminatural logarithm scale. In general, the trap-assisted
Shockley–Read–Hall recombination plays the role when the
slope deviating from unity kT/q, where q is elementary charge,
3
4
k is Boltzmann constant, and T is temperature. Figure 3f
shows the target device with a slop of 1.08 kT/q, which is
lower than that of control device (1.14 kT/q), suggesting the
suppressed trap-assisted recombination loss in the target
device, consistent with its enhanced crystal quality as
demonstrated by XRD results and reduced trap density
3
5
discussed below. Note that a slope close to one could also
3
6
indicate surface recombination. The results suggest that the
targed device may exist slightly higher surface recombination
in comparison with control device, in agreement with the
increased roughness of target film shown in SEM image
above.
Figure 4. (a) Optical properties (absorption and PL) of the control
and target 2D DJ perovskite films. (b) TPRL spectra of
corresponding films. (c) Jph-Veff characteristics of the photovoltaic
devices. (d) I-V curves of hole-only devices under dark. (e) I-V
curves of electron-only devices under dark.
Figure 4a shows the absorption spectra of the 2D DJ
perovskite films. In comparison with the bandgap of 1.60 eV
for the control film, the target film shows slightly reduced
bandgap of 1.58 eV due to the improved film quality with
enhanced crystallinity, consistent with the EQE data shown in
Figure 3b. The steady-state photoluminescence (PL) and time-
resolved photoluminescence (TPRL) measurements were
performed to investigate the charge recombination kinetics in
2D DJ perovskite films. As shown in Figure 4a, the target film
exhibited more than 3 times stronger PL intensity than that of
the control film, indicating the suppressed nonradiative
recombination due to the reduced trap density. Moreover, the
target film exhibits a slightly red-shifted PL peak of 769 nm
compared to that of the control film (764 nm) due to the
improved crystallinity, in agreement with their absorption
spectra. The TPRL curves (Figure 4b) were fitted using an
Considering the dramatically improved photovoltaic
performance, the photocurrent density
versus effective
voltage (Jph-Veff) measurements were performed to investigate
the exciton dissociation and charge collection efficiency in the
Jph is defined as Jph = J − J , where J is
L D L
the photocurrent density measured under one-sun illumination
3
9
devices (Figure 4c).
−
2
(
AM 1.5G, 100 mW cm ) and J
dark. Veff is defined as Veff = V – Vapp, where V
the voltage when Jph equals zero and the applied bias,
D
is the current density in
0
0
and Vapp are
4
0
respectively. The saturation photocurrent density (Jsat
)
mainly related to the absorbed incident photons at high Veff
and it could be defined as the photocurrent, where the
photogenerated excitons could be separated into free charge
carriers and collected by corresponding electrodes.
Therefore, the charge collection efficiency under different Veff
At the maximum power
point, the Jph/Jsat ratios for target device was 0.836, which is
much larger than that of target device (0.492), suggesting the
41
4
2, 43
37
could be estimated by Jph/Jsat ratio.
empirical biexponential equation:
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Table 1. The parameters for 2D (ThDMA)MAn-1Pb
n
I
3n+1 (nominal n = 5) perovskite based control and target devices.
1
2
3
4
5
6
7
8
9
e [a]
[b]
Device
V
OC (V)
J
SC
Integrated JSC
(mA cm-2)
FF
(%)
PCEmax/PCEavg
(%)
μ
e
μh
μ
e
/μ
h
N
t
Nth
-2
(cm v-1 s )
4.1810-4
1.0510-3
-2
-1
(cm v-1 s )
8.6310-5
7.7610-4
-2
-1
-3
-3
(mA cm )
(cm )
(cm )
Control
Target
1.00
1.07
9.83
9.71
62.01
75.46
6.11/5.40
4.84
1.36
9.051015
1.651015
5.901016
4.611015
19.55
19.18
15.75/14.76
[a]
Calculated from electron-only device. [b] Calculated from hole-only device.
more favored exciton dissociation and effective charge
transport in the target device. As for short circuit conditions,
the calculated Jph/Jsat ratio was 0.821 for control device and
fluctuations.46 Compared to the control film with a uniform
blue color in the TCFM image, the target film displays green
color, suggesting its spatially resolved longer carrier lifetime.
Figure 5c shows the corresponding PL occurs of different
carrier lifetime extracted from TCFM images. It reveals that
the control film exhibits a narrow charge carrier lifetime
distribution between 15 and 80 ns with a peak at 38 ns. In
contrast, an overall higher average PL lifetime from 23 to 187
ns with a peak at 92 ns was observed for the target film.
Moreover, the integrated area of the PL counts with different
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
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
0
.993 for target device. The larger Jph/Jsat value for target
device indicates a more efficient charge collection efficiency,
agree well with the transient photocurrent (TPC) results
(Figure S10, Table S4). Furthermore, the trap density and
charge mobility of the control and target devices were
evaluated by space charge limited current (SCLC) analysis.
The dark current–voltage (I–V) curves of hole-only and
6
6
electron-only
glass/ITO/PEDOT:PSS/perovskite/Spiro-OMeTAD/Ag
glass/ITO/SnO
shown in Figure 4d, 4e. The trap density (N
determined by the trap-filled limit voltage (VTFL) using
devices
with
the
structure
of
and
lifetimes are 1.46  10 and 3.54  10 for control and target
films, respectively. The distribution of PL counts indicates a
higher charge carrier concentration and a longer carrier
lifetime in the target film, in agreement with the PL and TPRL
results discussed above. The strong PL intensity and long PL
lifetime observed from the TCFM images further indicate the
high film quality of target 2D DJ perovskite, resulting in a low
trap density and thus suppressed nonradiative recombination
loss. Note that, in comparison with the macroscopic PL decays
2
/perovskite/PCBM/BCP/Ag, respectively, are
) could be
t
4
4
equation:
(
2)
where L is the thickness of 2D DJ perovskite films, q is the
elemental charge, Ɛ and Ɛ are the vacuum permittivity and
relative dielectric constant (Ɛ
in Figure 4d, the hole trap density was estimated to be 5.90 
(Figure 4b), the slightly faster microscopic PL lifetime
0
r
obtained from TCFM could be ascribed to the different
6
r
= 25), respectively. As shown
47
excitation fluences.
1
6
−3
1
0
cm for control film, which is about 12.7 times of the
1
5
target film (4.61  10 ). Similarly, the control film shows the
electron trap density of 9.05  10 cm , which is about 5.5
times of the target film (1.65  10 ). The decreased trap
density is agreement with the improved crystallinity and
enlarged grain size, which increases the charged transport
properties and supresses the charge recombination loss. The
mobility could be calculated by fitting the I−V curves to the
1
5
−3
1
5
4
5
Mott-Gureny Law:
(3)
where μ
0
is the electron or hole mobility, V is the internal
voltage in the device, and J is the current density. The electron
−4
and hole mobility were estimated to be 4.18  10 and 8.63 
−5
2
−1 −1
−3
1
7
0 cm V
s
for control 2D DJ perovskite, 1.05  10 and
−4
2
−1
−1
.76  10 cm
V
s
for target 2D DJ perovskite,
respectively. The enlarged and balanced mobility of target
film are consistent with its reduced trap density (Figure S11),
as summarized in Table 1, resulting in improved VOC and FF
of the corresponding device as discussed above.
Figure 5. (a, b) Time-resolved confocal fluorescence microscopy
images (20×20 µm) of the control and target films. (c) PL occurs
distribution of different carrier lifetime for the corresponding
films.
To elucidate the effect of microstructural changes on the
spatially resolved carrier lifetime and PL intensity distribution
in the control and target 2D DJ perovskite films, time-resolved
confocal fluorescence microscopy (TCFM) was measured.
The PL intensity map and in-situ spatially resolved PL lifetime
map are shown in the same image using gray and color scale,
respectively. As shown in Figure 5a,b, the obvious
heterogeneity of the PL intensity observed on a microscopic
scale is related to the spatial distribution and variation of trap
states, which could be attributed to the stoichiometry of local
The optimized 2D (ThDMA)(MA)n − 1Pb I
n 3n+1
(nominal n =
5
) perovskite film was stored in ambient conditions (in air,
room temperature (RT), 45±5% relative humidity (RH)) under
natural light for XRD measurements. The 3D MAPbI film
was also measured for comparison. As illustrated in Figure 6a,
3
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3 2
the aged 3D MAPbI shows a strong PbI diffraction peak after with a rapid PCE dropping and only retaining ~10% of the
Page 6 of 9
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144 h, which is over 3 times stronger than that of the (110)
peak because of the severe degradation of perovskite film. In
contrast, 2D DJ perovskite film shows no obvious changes,
suggesting its superior environmental stability due to the
improved hydrophobicity, which is verified by the enlarged
original PCE after 162 h, whereas the 2D DJ perovskite device
still sustained over 88% of its initial efficiency after 668 h.
Importantly, the thermal stability of 2D DJ PSCs, which were
stored at 80 °C in N under dark, were also dramatically
2
improved in comparison with 3D PSCs, as show in Figure 7c.
o
o
waster contact angle (51.6 for 3D and 81.9 for 2D DJ
perovskites) shown in Figure S12. To study the thermal
stability of 3D and 2D perovskite films, a thermal aging test
The excellent stabilities of 2D DJ PSCs are mainly attributed
+
to the incorporated bulky ThDMA spacer, in which the –NH
3
exhibit strong NH···I hydrogen-bonding interaction with
o
4-
was further performed at 100 C (in air, RH = 45±5%) under
6
adjacent corner-sharing [PbI ] octahedron layers. The organic
dark condition. Figure 6b shows a strong PbI
2
peak for 3D
layer could not only hinder the ion migration effectively but
also prevent the perovskite film from moisture and oxygen
invasion.
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
MAPbI film after 23 days, while no obvious changes for 2D
3
DJ perovskite film. The superior thermal stability of the
ThDMA-based 2D DJ perovskite film compared to 3D
MAPbI film could be attributed to the improved thermal
3
stability of ThDMA spacers compared to MA cation as well as
hindered ion migration because of the incorporated bulky
4
8
ThDMA spacer.
Figure 7. (a) Stability test of unencapsulated 3D MAPbI
3
and 2D
3n+1 (nominal n = 5) perovskite devices in
2
at RT. (b) Stability test of unencapsulated devices under
n
(ThDMA)(MA)n−1Pb I
N
-2
2
continues light soaking (100 mW cm , white LED) in N . (c)
2
Thermal ageing test of unencapsulated devices under 80 °C in N .
CONCLUSIONS
Figure 6. (a) XRD of 3D MAPbI
ThDMA)(MA)n − 1Pb 3n+1 (nominal n = 5) perovskite films
deposited on ITO/PEDOT:PSS substrates stored in ambient air
(RH = 45±5%) under nature light. The major PbI peaks are
3
perovskite and 2D
In summary, a thiophene-based bulky diammonium iodide,
namely ThDMAI, was successfully synthesized and applicated
(
n
I
in 2D DJ PSCs. High quality 2D (ThDMA)MAn-1Pb
n 3n+1
I
2
(nominal n = 5) film with improved crystallinity, preferred
marked by asterisks. (b) XRD of 3D and 2D DJ perovskite films
vertical orientation and reduced trap density could be achieved
by one-step method using mixed solvent of DMF/DMSO (v:v,
9:1). The small amount of DMSO mainly play the role of
o
stored in air (RH = 45±5%) at 100 C.
To study the device stability of optimized 2D DJ PSCs,
aging test under different conditions was further investigated.
2
Lewis base due to its strong coordination capability with PbI ,
The device stability of 3D MAPbI
for comparison. The storage stability of unencapsulated
devices, which were stored in N at RT under dark, are shown
3
PSCs was also measured
thus retard crystallization rate, leading to increased grain size,
preferred vertical orientation and high film quality of 2D DJ
perovskite. In comparison with the low PCE of 6.11% of the
control device using DMF as solvent, the optimized target 2D
PSCs exhibit a champion PCE of 15.75%, which is a record
for aromatic spacer-based 2D DJ PSCs to the best of our
knowledge. Furthermore, the environmental stability of 2D DJ
films and devices were dramatically improved compared to its
3D counterpart because of the hydrophobic property of the
bulky ThDMA spacer. Therefore, the development of bulky
thiophene-based dication spacers such as ThDMA provides a
2
in Figure 7a and Figure S13. It is found that the 2D perovskite
device shown great improved stability with over 95% of its
original efficiency maintained after 1655 h (~69 days),
whereas only ~53% of its initial efficiency left for the 3D
perovskite device. We also conducted stability tests under
-2
continues light soaking (100 mW cm , white light-emitting
diode (LED)) in N atmosphere at RT. Figure 7b shows that
the 3D perovskite device encountered a severe degradation
2
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new strategy to boost efficiency and environmental stability
for 2D DJ PSCs.
Perovskites for Solar Cells with Ultrahigh Stability. Joule 2019, 3,
794-806.
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Chen, Y.; Huang, W., Reduced-Dimensional Perovskite Enabled by
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Perovskites with Short Interlayer Distance for High-Performance
Solar Cell Application. Adv. Mater. 2018, 30, e1800710.
ASSOCIATED CONTENT
Supporting Information. This material is available free of
charge via the Internet at http://pubs.acs.org. Experimental
1
13
procedures and characterization data, including H, C NMR
spectra, HRTEM, UPS, cross-section SEM, J-V curves, water
contact angle.
(13) Li, X.; Ke, W.; Traore, B.; Guo, P.; Hadar, I.; Kepenekian, M.;
Even, J.; Katan, C.; Stoumpos, C. C.; Schaller, R. D.; Kanatzidis, M.
G., Two-Dimensional Dion-Jacobson Hybrid Lead Iodide Perovskites
with Aromatic Diammonium Cations. J. Am. Chem. Soc. 2019, 141,
AUTHOR INFORMATION
Corresponding Author
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2880-12890.
14) Muljarov, E. A.; Tikhodeev, S. G.; Gippius, N. A.; Ishihara,
(
*
Y. Liu: liuys@nankai.edu.cn
T., Excitons in self-organized semiconductor/insulator superlattices:
PbI-based perovskite compounds. Phys. Rev. B 1995, 51, 14370.
(15) Hong, X.; Ishihara, T.; Nurmikko, A. V., Dielectric
confinement effect on excitons in Pbl -based layered semiconductors.
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Phys. Rev. B 1992, 45, 6961-6964.
(16) Ke, W.; Mao, L.; Stoumpos, C. C.; Hoffman, J.; Spanopoulos,
I.; Mohite, A. D.; Kanatzidis, M. G., Compositional and Solvent
Engineering in Dion-Jacobson 2D Perovskites Boosts Solar Cell
Efficiency and Stability. Adv. Energy Mater. 2019, 9, 1803384.
Author Contributions
#
D.L. and G. L. contributed equally to this work.
Notes
The authors declare no competing financial interest.
ACKNOWLEDGMENT
This work was financially supported by National Natural Science
Foundation of China (Grants No. 21875122, 51673097). We
would like to thank the beam time provided by the 1W1A station
(17) Mao, L.; Ke, W.; Pedesseau, L.; Wu, Y.; Katan, C.; Even, J.;
Wasielewski, M. R.; Stoumpos, C. C.; Kanatzidis, M. G., Hybrid
Dion-Jacobson 2D Lead Iodide Perovskites. J. Am. Chem. Soc. 2018,
140, 3775-3783.
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Kim, H. S.; Liu, Y.; Dar, M. I.; Zakeeruddin, S. M.; Wang, P.;
Hagfeldt, A.; Gratzel, M., Bifunctional Organic Spacers for
Formamidinium-Based Hybrid Dion-Jacobson Two-Dimensional
Perovskite Solar Cells. Nano Lett. 2019, 19, 150-157.
(19) Lai, H.; Kan, B.; Liu, T.; Zheng, N.; Xie, Z.; Zhou, T.; Wan,
X.; Zhang, X.; Liu, Y.; Chen, Y., Two-Dimensional Ruddlesden-
Popper Perovskite with Nanorod-like Morphology for Solar Cells
with Efficiency Exceeding 15%. J. Am. Chem. Soc. 2018, 140, 11639-
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(Beijing Synchrotron Radiation Facility) for GIWAXS
characterization.
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