Stable and low-cost mesoscopic CH3NH3PbI2Br perovskite solar cells by using a thin poly(3-hexylthiophene) layer as a hole transporter

Article abstract of DOI:10.1002/chem.201404427

Mesoscopic perovskite solar cells using stable CH₃NH₃PbI₂Br as a light absorber and low-cost poly(3-hexylthiophene) (P3HT) as hole-transporting layer were fabricated, and a power conversion efficiency of 6.64% was achieved. The partial substitution of iodine with bromine in the perovskite led to remarkably prolonged charge carrier lifetime. Meanwhile, the replacement of conventional thick spiro-MeOTAD layer with a thin P3HT layer has significantly reduced the fabrication cost. The solar cells retained their photovoltaic performance well when they were exposed to air without any encapsulation, presenting a favorable stability. The combination of CH₃NH₃PbI₂Br and P3HT may render a practical and cost-effective solid-state photovoltaic system. The superior stability of CH3NH3PbI2Br is also promising for other photoconversion applications.

Full text of DOI:10.1002/chem.201404427

DOI: 10.1002/chem.201404427
Full Paper
&
Solid-State Solar Cells
Stable and Low-Cost Mesoscopic CH3NH3PbI2Br Perovskite Solar
Cells by using a Thin Poly(3-hexylthiophene) Layer as a Hole
Transporter
Meng Zhang, Miaoqiang Lyu, Hua Yu, Jung-Ho Yun, Qiong Wang, and Lianzhou Wang*[a]
Abstract: Mesoscopic perovskite solar cells using stable
CH3NH3PbI2Br as a light absorber and low-cost poly(3-hex-
ylthiophene) (P3HT) as hole-transporting layer were fabricat-
ed, and a power conversion efficiency of 6.64% was ach-
ieved. The partial substitution of iodine with bromine in the
perovskite led to remarkably prolonged charge carrier life-
time. Meanwhile, the replacement of conventional thick
spiro-MeOTAD layer with a thin P3HT layer has significantly
reduced the fabrication cost. The solar cells retained their
photovoltaic performance well when they were exposed to
air without any encapsulation, presenting a favorable stabili-
ty. The combination of CH3NH3PbI2Br and P3HT may render
a practical and cost-effective solid-state photovoltaic system.
The superior stability of CH3NH3PbI2Br is also promising for
other photoconversion applications.
Introduction
ited number of reports on the use of CH3NH3PbI2Br as a light
absorber. Seok and co-workers have studied the solar cells of
CH3NH3PbI3ꢀxBrx perovskite with tunable band gaps, using
polytriarylamine (PTAA) as HTM.[4b] The results showed im-
proved stability of CH3NH3PbI3ꢀxBrx compared to the
CH3NH3PbI3 under the same humidity conditions. Moreover,
the CH3NH3PbI2Br has also been found to have a higher ab-
sorption coefficient and an upper conduction band (CB) posi-
tion, enabling a greater driving force to inject electrons into
the CB of TiO2.[9] Thus, compared with Cl, Br substitution in per-
ovskite CH3NH3PbI3 is of great advantage in free arrangement
of bromine atoms, which can be allocated to both apical and
equatorial position.[8] The free arranged bromine atoms in the
perovskite absorber make it possible for onset adjustment of
optical absorption, leading to optimized multi-junction photo-
voltaic devices and color management applications.[4b,10]
Driven by the demand of developing low-cost and high-effi-
ciency solar cells, mesoscopic dye-sensitized solar cells have
been widely studied.[1] In recent years, a great breakthrough
was made by replacing dye with organometal halide perov-
skite as light harvesting materials.[2] A typical triiodide perov-
skite (CH3NH3PbI3)-based solar cell with an expensive organic
spiro-MeOTAD as the hole-transporting material (HTM) has
been demonstrated to be very promising, with efficiencies of
more than 15.0%.[3] In spite of the high efficiency, there are
some issues existing for the CH3NH3PbI3-based perovskite solar
cell systems. One major drawback of CH3NH3PbI3 is its poor sta-
bility when exposed to moisture in air,[4] which can be easily
decomposed and lose its function as light absorber. To develop
air-stable perovskite materials, many approaches have been
studied, and among them, mixed halide perovskites
CH3NH3PbI3ꢀyXy (X=Cl and Br) have shown better humidity re-
sistance when prepared in air,[4b,5] which could facilitate solar
cell processing in air and subsequently lead to long-term sta-
bility of solar cells.
Another obstacle that may hinder the possible commerciali-
zation of perovskite solar cells is the high cost of spiro-
MeOTAD which is the most commonly used HTM.[5,6] Since the
birth of the first perovskite solar cell, the exploration for cost-
effective HTMs has been continuously performed.[11] P3HT is
one of the most widely used semiconducting polymers in or-
ganic photovoltaics devices.[12] In comparison with spiro-
MeOTAD, P3HT is-dopant free and can be prepared without an
extra oxidation process when applied in perovskite solar cells.
As a result of its facile processing method and desirable hole
conductivity, P3HT has been regarded as a good option for
HTM.[11a,13] In the early stage, the efficiencies of the P3HT em-
ployed perovskite solar cells were less satisfactory.[11a,13a,14] Very
recently, comparable photovoltaic performance to spiro-
MeOTAD was realized in planar-structured CH3NH3PbI3ꢀxClx-
based devices using P3HT.[15] This shows great potential of
P3HT as a cost-effective HTM in perovskite solar cells. In prac-
tice, the fabrication cost of P3HT layer can be only a fraction of
Solar cells using CH3NH3PbI3ꢀxClx as light absorber have ach-
ieved promising efficiencies;[6] however, it was also noted that
the formation of continuous solid phase CH3NH3PbI3ꢀxClx
cannot be realized both experimentally and theoretically,[7]
possibly because the chlorine atoms can only be doped at the
apical positions of the PbI4X2 (X=I, Br and Cl) octahedron in
the perovskite structure.[8] Meanwhile, there are a relatively lim-
[a] M. Zhang, M. Lyu, Dr. H. Yu, Dr. J.-H. Yun, Q. Wang, Prof. L. Wang
Nanomaterials Centre, School of Chemical Engineering
The University of Queensland, St Lucia, Qld 4072 (Australia)
E-mail: l.wang@uq.edu.au
Supporting information for this article is available on the WWW under
http://dx.doi.org/10.1002/chem.201404427.
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that of spiro-MeOTAD,[16] which made P3HT an important can-
didate for HTM in terms of developing low-cost perovskite
solar cells.
Herein we report a new configuration of perovskite solar cell
using CH3NH3PbI2Br as light absorber and a thin P3HT layer as
HTM. This system combines the superior stability of
CH3NH3PbI2Br and the low-cost property of P3HT, and finally
presents a stable photovoltaic performance in practical condi-
tions.
Figure 2. Cross-sectional SEM image of the solar cell using CH3NH3PbI2Br
and P3HT.
Results and Discussion
Material characterizations
of mesoporous TiO2/CH3NH3PbI2Br composite layer is about
500 nm, which is in the optimized range for efficient light har-
vesting and electron transfer.[11a,17] The compact TiO2 worked as
a hole-blocking layer and simultaneously provides path ways
for electron transfer together with a thicker mesoporous TiO2
layer. For the system, P3HT acts as a hole-conducting layer and
blocks electrons, so that the photogenerated electrons and
holes from CH3NH3PbI2Br can be efficiently separated.
The XRD pattern of CH3NH3PbI2Br film is shown in Figure 1.
The single peak at 28.88 is a key indication of a cubic perov-
It is noted that the HTM layer is quite thin (ca. 50 nm) com-
pared to the thickness in the reported devices, which is nor-
mally about 100–300 nm.[3a,6a,15] Based on the same coating so-
lution usage per unit area, we applied 10 mgmLꢀ1 P3HT coat-
ing solution instead of the commonly applied concentration of
15–20 mgmLꢀ1 [11a,13a,15,18]
reducing the material cost without
,
sacrificing the hole transporting property of the P3HT HTM
layer. In comparison with the widely used spiro-MeOTAD coat-
ing
solution
with
concentrations
of
about
72–
208 mgmLꢀ1 [6b,19]
,
the P3HT coating solution used for the devi-
Figure 1. XRD pattern of the CH3NH3PbI2Br film deposited on a glass sub-
strate.
ces in this study thus can be over 10 times cheaper than that
of spiro-MeOTAD (AU$8mLꢀ1 versus AU$93–267mLꢀ1; Table 1).
Considering HTM is the most expensive component in perov-
skite solar cells, the use of a thin P3HT layer can significantly
reduce the cost of the whole device.
skite phase as previously reported.[4b] The sharp diffraction
peaks at 14.2, 20.3, 24.8, 28.8, 32.3, 35.5, 41.2, and 43.88 can be
assigned to the (100), (110), (111), (200), (210), (112), (220), and
(300) planes of the cubic phase perovskite, respectively, which
indicate a pure crystallinity of the perovskite. The calculated
corresponding lattice constant is 6.19 ꢁ, which is in consistent
with the linear relationship between lattice constant of the
cubic phase structure and Br composition as reported.[4b] The
chemical composition of the
Optical properties
To characterize the optical properties of the CH3NH3PbI2Br light
absorber, UV/Vis absorption and steady-state photolumines-
cence (PL) measurement were conducted. The UV/Vis absorp-
CH3NH3PbI2Br perovskite film
were also confirmed to have
Table 1. Cost comparison of HTM coating solutions for different device configurations.
a ratio of about 1:2:1 for Pb:I:Br
by X-ray energy-dispersive spec-
troscopy (EDS; Supporting Infor-
mation, Figure S1).
Device structure
Light absorber
HTM
Concentration(HTM)
Cost(HTM) mLꢀ1
[AU$]
[mgmLꢀ1
]
Mesoscopic
Mesoscopic
Planar
Mesoscopic
Nanowire
Mesoscopic
Planar
Mesoscopic
Mesoscopic (our device)
CH3NH3PbI3
CH3NH3PbI3ꢀxClx
CH3NH3PbI3
CH3NH3PbI3
CH3NH3PbI2Br
CH3NH3PbI3
CH3NH3PbI3ꢀxClx
CH3NH3PbI3
CH3NH3PbI2Br
spiro[a]
spiro[a]
spiro[a]
spiro[a]
spiro[a]
P3HT
P3HT
P3HT
P3HT
72.3[3b]
93
113
231
267
267
12
13
16
8
88 (8 wt.%[6b]
180[19b]
)
Figure 2 presents the cross-
sectional scanning electron mi-
croscopy (SEM) image of the
208 (0.170 M[3a]
)
208 (0.170 M[9]
15[11a]
)
device, showing
a
FTO/TiO2/
16.6 (1.5 wt.%[15]
)
CH3NH3PbI2Br/P3HT/Au sandwich
structure, which is a typical layer
structure for mesoscopic perov-
skite solar cells.[3a,5] The thickness
20[13a]
10
[a] Spiro-MeOTAD.
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Figure 3. a) UV/Vis absorpation spectrum of TiO2 film coated with
CH3NH3PbI2Br. b) Transformed Kubelka–Munk spectrum of TiO2 film coated
with CH3NH3PbI2Br.
~
Figure 4. a) Time-integrated PL emission spectra for CH3NH3PbI2Br ( ) and
!
CH3NH3PbI2Br/P3HT ( ). Excitation wavelength: 450 nm. b) Time-resolved PL
decay detected at peak wavelength of emission for CH3NH3PbI3 ( ),
&
~
!
*
CH3NH3PbBr3 ( ), CH3NH3PbI2Br ( ), and CH3NH3PbI2Br/P3HT ( ).
tion spectrum can tell us the light absorbing property of the
perovskite, while the PL measurement is aimed at determining
the charge carrier recombination behavior in the bulk perov-
skite and also in the interface of perovskite/HTM heterojunc-
tion. As shown in Figure 3a, the UV/Vis absorbance spectrum
of the CH3NH3PbI2Br deposited on the mesoporous TiO2 layer
shows an onset absorption band at around 700 nm, which is in
line with the light absorption resulted from the dark brown
color of the CH3NH3PbI2Br layer. In the region of 350 nm to
650 nm, a much stronger absorption of CH3NH3PbI2Br over
CH3NH3PbI3 is observed (Supporting Information, Figure S2), in-
dicating a larger absorption coefficient of CH3NH3PbI2Br.[9] The
direct optical band gap energy (Eg) of CH3NH3PbI2Br was deter-
mined by converting the corresponding reflectance spectrum
according to the Kubelka–Munk relation (Figure 3b). It is found
that the calculated Eg value of CH3NH3PbI2Br was about 1.77–
1.78 eV, which is in a good agreement with the previously re-
ported values.[4b,9]
P3HT layer can be observed in the time-resolved PL decay plot
as well (Figure 4b). The presences of P3HT layer dramatically
accelerate the PL decay process. It elucidates an efficient
charge transfer of the CH3NH3PbI2Br/P3HT interface.
It was reported that a longer charge carrier lifetime contrib-
utes to a longer charge carrier diffusion length, which en-
hanced photovoltaic performance of the devices.[20,21] For in-
stance, the Cl substitution prolongs the charge carrier lifetime
of CH3NH3PbX3 (X=I or Br).[22] Consequently, the solar cells
based on CH3NH3PbX3ꢀyCly (X=I or Br) have presented im-
proved power conversion efficiencies.[23] Here, the average life-
time different CH3NH3PbI3ꢀxBrx perovskite absorber has been
estimated by time-resolved PL decay. The decay curves of dif-
ferent perovskite are fitted with a triexponential function of
time t [Eq. (1)]:
The PL spectra of the CH3NH3PbI2Br samples with and with-
out the presence of P3HT are shown in Figure 4a. An obvious
emission peak of CH3NH3PbI2Br at around 700 nm is observed,
showing a little Stocks shift in comparison with the absorbance
spectrum in Figure 3a.[20] By coating with a thin P3HT layer, the
emission peak is quenched to a very low level. The obvious
quenching in PL emission suggests an efficient charge separa-
tion between CH3NH3PbI2Br and P3HT. It is suggested that the
photogenerated holes can be quickly extracted to the P3HT
layer before bulk recombination.[21] The PL quenching effect of
X
Ai eꢀt=t ; i ¼ 1,2,3
ð1Þ
i
FðtÞ ¼
where Ai is prefactor and ti is time constant. And the average
charge carrier lifetime (tav) is estimated with Ai and ti according
to Equation (2).[24]
X
X
tav
¼
Ai ti2=
Aiti; i ¼ 1,2,3
ð2Þ
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MeOTAD as one of the most efficient hole-transporting materi-
als have been widely used for the perovskite solar cells. We
also applied spiro-MeOTAD in CH3NH3PbI2Br based perovskite
solar cells under the same conditions for comparison (Support-
ing Information, Figure S3), which have shown lower efficien-
cies than P3HT based devices (5.7% versus 6.6%). We under-
stand the efficiency of the spiro-MeOTAD-based devices could
be improved by further optimization. But in comparison with
the facile processed P3HT, spiro-MeOTAD requires more re-
stricted processing conditions, including the doping and oxi-
dizing processes. Considering that the fabrication cost of the
thin P3HT layer is much lower than spiro-MeOTAD, the config-
uration of CH3NH3PbI2Br/P3HT can be considered to be more
cost-effective. Meanwhile, the photovoltaic performance of de-
vices employing CH3NH3PbI2Br is better than that of using
CH2NH3PbBr3 and CH3NH3PbI3 (Supporting Information, Fig-
ure S4 and Table S1). It is considered that the superior per-
formance of CH3NH3PbI2Br stems from the high absorption co-
efficient in visible light region together with its prolonged
charge carrier lifetime.
Table 2. Estimated average charge carrier lifetime of different perovskites
at the emission wavelength (lem).
Perovskite
lem [nm]
tav [ns]
CH3NH3PbI3
CH3NH3PbI2Br
CH3NH3PbBr3
775
695
530
13.3
16.0
68.5
To achieve uniform films for the measurement and compari-
son, all the perovskite precursor solutions sharing a same con-
centration of Pb have been spin-coated on mesoporous Al2O3
scaffold layer. Among the tested perovskite materials
CH3NH3PbBr3 exhibits the longest tav up to 68.5 ns (Table 2).
Meanwhile, CH3NH3PbI2Br presents prolonged tave compared to
CH3NH3PbI3, indicating an improved charge carrier transport
property of CH3NH3PbI2Br. The improvement might be associat-
ed with its highly ordered cubic structure, whereas, in compari-
son, the tetragonal structure of CH3NH3PbI3 is less ordered.
To quantitatively evaluate the electron transfer process
under the incident light illumination of the devices, measure-
ment of incident photon-to-electron conversion efficiency
(IPCE) spectrum is performed using the Newport IPCE system.
As shown in Figure 5b, the device shows a wide range photo-
current response with IPCE over 40% from 350 nm to 600 nm
and a maximum IPCE approaching 60% around 400 nm to
500 nm. The IPCE value shown in the spectra is in good agree-
ment with the absorption spectra of CH3NH3PbI2Br as shown in
Figure 3a. Meanwhile, the IPCE
Photovoltaic performance
The photovoltaic performance of the devices was measured
under standard AM1.5 simulated sunlight adjusted using stan-
dard silicon solar cell. The result is shown in Figure 5a. Encour-
agingly, the CH3NH3PbI2Br/P3HT perovskite solar cell exhibits
a power conversion efficiency of 6.64% with a short circuit cur-
rent density (Jsc) of 12.93 mA/cm2, an open circuit voltage (Voc)
of 0.82 V and a fill factor (FF) of 0.628. Note that the spiro-
spectrum also presents a dip be-
tween 550 nm to 650 nm. This
quantitatively loss may be attrib-
utable to the light absorption of
the P3HT layer.[14b] In general,
the photovoltaic performance of
devices using CH3NH3PbI2Br and
P3HT shows comparably superior
light utilization efficiency among
the prepared perovskite materi-
als in visible light region[14a]
.
The stability of perovskite
solar cells has been remaining
a big issue for the reported devi-
ces. The reason may largely attri-
bute to the decomposition of
the perovskite when exposed to
moisture. Under ambient air con-
dition with regular humidity,
CH3NH3PbI2Br are much more
stable than CH3NH3PbI3, as we
can easily identify by the color
change of the films (Supporting
Information, Figure S5). Thus, the
CH3NH3PbI2Br devices are ex-
pected to have better stability
than those with CH3NH3PbI3. As
Figure 5. a) Representative J–V curve of TiO2/CH3NH3PbI2Br/P3HT solar cells measured under AM1.5 simulated sun-
light (100 mW/cm2 irradiance) and b) the corresponding IPCE spectrum. c) Stability of CH3NH3PbI2Br/P3HT solar
cells stored in air at room temperature without encapsulation.
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butoxide in 25 mL anhydrous ethanol) under vigorous stirring. The
resulting solution was kept aging for 24 h. A thin layer of compact
TiO2 on the FTO substrate was deposited by spin-coating the TiO2
sol at 1000 rpm for 30 s and then annealed at 5008C for 30 min.
The solution of mesoporous TiO2 for spin-coating was prepared by
diluting the commercial TiO2 paste (Dyesol, 18NR-T) with ethanol
by a weight ratio of 1:7. The mesoporous TiO2 layer was spin
coated at 2000 rpm for 30 s and followed by an annealing process
at 5008C for 30 min. After cooling, a small amount of perovskite
precursor solution was dispensed onto the mesoporous electrode
film and soaked for 60 s to allow complete infiltration. The post
spin-coating process was conducted at 3000 rpm for 30 s in air.
The deposited films were then placed on a hot plate setting at
1008C for 5 min. P3HT coating solution was prepared by dissolving
P3HT (10 mgmLꢀ1, MW 54000–75000, Sigma–Aldrich) in 1,2-di-
chlorobenzene and filtering with 0.22 mm pore PVDF syringe filter
(Merck). For comparison, spiro-MeOTAD (68 mm, Merck) was with
dissolved in chlorobenzene for HTM coating with lithium bis(tri-
fluoromethanesulfonyl)imide (9 mm) and 4-tert-butylpyridine
(55 mm) as additives. The HTM layer was deposited by spin-coat-
ing. 35 mL of HTM coating solution was dispensed onto the perov-
skite layer, allow soaking for 15 s, and then spin at 2000 rpm for
30 s in air. Finally, the device was completed by deposition of
60 nm thick Au layer with an electron-beam evaporator at
10ꢀ6 torr. The cell active area of 0.12 cm2 was determined by apply-
ing a metal mask.
shown in Figure 5c, the stability test indicates that the efficien-
cy of the CH3NH3PbI2Br devices is well retained after exposing
for 250 h in air without any encapsulation. The Jsc has shown
a peak value at nearly 15 mAcmꢀ2 and been stabilized at
12 mAcmꢀ2. During the stability test, the Voc is kept increasing
and reached to 0.84 V, while FF remained similar at around 0.6.
Therefore, the stability performance of these devices is consid-
ered to be fairly good in practical consideration. Furthermore,
the photoconversion efficiency improvement of the perovskite
solar cells with time is observed in the first several days after
fabrication, which is in consistent with previously reported re-
sults.[3a,4b,25] The possible reason may be associated with the in-
terface state between the perovskite layer and HTM layer.
However, the detailed mechanism is still not clear and needs
to be further investigated.
Conclusion
In summary, we have successfully fabricated stable and low-
cost all-solid-state solar cells using a low-cost and facile
CH3NH3PbI2Br/P3HT system. The optimized device has achieved
a power conversion efficiency of 6.64% with Voc of 0.82 V and
FF of 0.628. The use of thin P3HT layer as HTM will remarkably
reduce the fabrication cost of the whole device. Compared to
the triiodine perovskite CH3NH3PbI3, the incorporation of bro-
mine in mixed halide perovskite led to an impressively longer
charge carrier lifetime, which is beneficial to the photovoltaic
performance. Finally, the fabricated solar cells present a good
stability in exposure to ambient air without any encapsulation.
Characterization
The cross-sectional morphology were recorded using a scanning
electron microscope (7001, JEOL). X-ray diffraction (XRD) data was
obtained from a Bruker Advanced X-ray diffractometer (40 kV and
30 mA) with CuKa radiation. UV/Vis absorption spectra of the re-
sulting films were measured by a spectrophotometer (V-650, Jasco)
with an integrating sphere. The room-temperature photolumines-
cence measurements were conducted with a fluorescence spec-
trometer (FLS 920, Edinburgh Instruments Ltd). The emission spec-
tra and electron lifetime were measured by exciting the samples
with a light beam from 450 W Xe lamp at 450 nm and a nanosec-
ond flash laser beam at 377 nm, respectively. All samples for the PL
measurement are coated on mesoporous Al2O3 substrates with
same thickness.
Experimental Section
Materials synthesis
Methylammonium iodide/bromide (CH3NH3I/CH3NH3Br) was synthe-
sized as a precursor for preparing perovskites. Briefly, hydroiodic
acid (8 mL, 57 wt% in water, Sigma–Aldrich)/hydrobromic acid
(18 mL, 48 wt% in water, Sigma–Aldrich), and methylamine (20 mL,
33% in ethanol, Sigma–Aldrich) were mixed in anhydrous ethanol
(100 mL) and stirred in a glass bottle with ice bath. After stirring at
08C for 2 h, the resulting solution was evaporated at 508C by
a rotary evaporator. The product of CH3NH3I/CH3NH3Br powder was
washed with diethyl ether several times and dried in a vacuum
oven.
The J–V curve measurements were performed by employing an
AM1.5 solar simulator (91160_1000, Oriel) equipped with a 300 W
xenon light source (6258, Newport). The light intensity of the solar
simulator was measured by using a thermal power meter (1918-c,
Newport) with a detector (818P-040–25) and adjusted by a standard
silicon solar cell. J–V curves were obtained by scanning from
900 mV to ꢀ100 mV and measurements were recorded by a Keith-
ley model 2420 digital source meter. The voltage step and delay
time of photocurrent were 10 mV and 10 ms, respectively. The IPCE
spectrum was recorded on a Newport 1918-c power meter under
For perovskite preparation, readily synthesized CH3NH3I/CH3NH3Br
and PbI2/PbBr2 (Sigma–Aldrich) were mixed in N,N-dimethylform-
amide (anhydrous, Sigma–Aldrich) with molar ratio of 1.25:1 and
sonicated at 608C for 15 min to prepare CH3NH3PbI3 and
CH3NH3PbBr3 solutions. To prepare CH3NH3PbI2Br solution,
CH3NH3PbI3 (0.75m) and CH3NH3PbBr3 (0.75m) solutions were
mixed with a volume ratio of 2:1 in an amber glass bottle and
kept stirred for 30 min.
the irradiation of a 300 W xenon light tower (66902, Newport) with
1
an Oriel CornerstoneT 260 = m monochromator (74125, Oriel) in
4
DC mode.
Device fabrication
Acknowledgements
Fluorine-doped tin oxide (FTO) coated glass (Opvtech) was cut into
15 mmꢂ25 mm pieces and cleaned with soapy water, acetone,
and 2-propanol sequentially. The TiO2 sol for compact layer coating
was prepared by slowly adding solution A (0.2 mL, 3m HNO3 solu-
tion in 20 mL anhydrous ethanol) into solution B (2 mL, titanium
Financial support from CRC for Polymers, and ARC through its
DP and FF programs is acknowledged. This work was per-
formed in part at the Queensland node of the Australian Na-
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Keywords: hole-transporting materials · lead · low cost ·
perovskite · solid-state solar cells · stability · thiophenes
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Revised: September 22, 2014
Published online on && &&, 0000
&
&
Chem. Eur. J. 2014, 20, 1 – 7
www.chemeurj.org
6
ꢀ 2014 Wiley-VCH Verlag GmbH & Co. KGaA, Weinheim
ÝÝ These are not the final page numbers!

Full Paper
FULL PAPER
Cutting the cost: Mesoscopic
&
Solid-State Solar Cells
CH3NH3PbI2Br perovskite solar cells with
stable performance were fabricated. The
thin hole-transporting material layer of
poly(3-hexylthiophene) (P3HT) signifi-
cantly cuts down the cost of the device.
M. Zhang, M. Lyu, H. Yu, J.-H. Yun,
Q. Wang, L. Wang*
&& – &&
Stable and Low-Cost Mesoscopic
CH3NH3PbI2Br Perovskite Solar Cells by
using a Thin Poly(3-hexylthiophene)
Layer as a Hole Transporter
Chem. Eur. J. 2014, 20, 1 – 7
www.chemeurj.org
7
ꢀ 2014 Wiley-VCH Verlag GmbH & Co. KGaA, Weinheim
&
&
These are not the final page numbers! ÞÞ