3,4-Phenylenedioxythiophene (PheDOT) Based Hole-Transporting Materials for Perovskite Solar Cells

Article abstract of DOI:10.1002/asia.201501423

Two new electron-rich molecules based on 3,4-phenylenedioxythiophene (PheDOT) were synthesized and successfully adopted as hole-transporting materials (HTMs) in perovskite solar cells (PSCs). X-ray diffraction, absorption spectra, photoluminescence spectra, electrochemical properties, thermal stabilities, hole mobilities, conductivities, and photovoltaic parameters of PSCs based on these two HTMs were compared with each other. By introducing methoxy substituents into the main skeleton, the energy levels of PheDOT-core HTM were tuned to match with the perovskite, and its hole mobility was also improved (1.33×10^-4 cm² V^-1 s^-1, being higher than that of spiro-OMeTAD, 2.34×10^-5 cm² V^-1 s^-1). The PSC based on MeO-PheDOT as HTM exhibits a short-circuit current density (J_sc) of 18.31 mA cm^-2, an open-circuit potential (V_oc) of 0.914 V, and a fill factor (FF) of 0.636, yielding an encouraging power conversion efficiency (PCE) of 10.64 % under AM 1.5G illumination. These results give some insight into how the molecular structures of HTMs affect their performances and pave the way for developing high-efficiency and low-cost HTMs for PSCs.

Full text of DOI:10.1002/asia.201501423

DOI: 10.1002/asia.201501423
Full Paper
Hole-Transporting Materials
3,4-Phenylenedioxythiophene (PheDOT) Based Hole-Transporting
Materials for Perovskite Solar Cells
Jian Chen+, Bai-Xue Chen+, Fang-Shuai Zhang, Hui-Juan Yu, Shuang Ma, Dai-Bin Kuang,*
Guang Shao,* and Cheng-Yong Su[a]
Abstract: Two new electron-rich molecules based on 3,4-
phenylenedioxythiophene (PheDOT) were synthesized and
successfully adopted as hole-transporting materials (HTMs)
in perovskite solar cells (PSCs). X-ray diffraction, absorption
spectra, photoluminescence spectra, electrochemical proper-
ties, thermal stabilities, hole mobilities, conductivities, and
photovoltaic parameters of PSCs based on these two HTMs
were compared with each other. By introducing methoxy
substituents into the main skeleton, the energy levels of
PheDOT-core HTM were tuned to match with the perovskite,
and its hole mobility was also improved (1.33”
10À4 cm2 VÀ1 sÀ1, being higher than that of spiro-OMeTAD,
2.34”10À5 cm2 VÀ1 sÀ1). The PSC based on MeO-PheDOT as
HTM exhibits
a short-circuit current density (Jsc) of
18.31 mAcmÀ2, an open-circuit potential (Voc) of 0.914 V, and
a fill factor (FF) of 0.636, yielding an encouraging power con-
version efficiency (PCE) of 10.64% under AM 1.5G illumina-
tion. These results give some insight into how the molecular
structures of HTMs affect their performances and pave the
way for developing high-efficiency and low-cost HTMs for
PSCs.
Introduction
opment of effective HTMs for transporting the holes and
blocking the electrons from the light absorbents to the metal
counter electrode.[10,12] Several new types of HTMs based on
small organic molecules, polymers, and inorganic salts provid-
ing reasonable efficiencies have been reported. Inorganic
HTMs were included in PSCs due to their high conductivity,
and the highest efficiency of 17.3% can be achieved, however,
the disadvantages of limited selection and deposition method
hinder their further development.[13–15] Organic HTMs including
polymers and small molecules display diverse molecular struc-
tures that can be modified by chemically tailored methods to
fit different technological purposes.[16–19] In comparison with
polymeric HTMs, small molecular HTMs hold several outstand-
ing advantages such as convenient synthesis that is compati-
ble for large-scale manufacture, easy purification by chroma-
tography, crystallization or vacuum sublimation, easy character-
ization of molecular structure with definite molecular weight,
and good pore filling into the nanostructured materials by a so-
lution process.[20–23] Although 2,2’,7,7’-tetrakis(N,N’-di-p-methoxy-
phenylamine)-9,9’-spirobifluorene (spiro-OMeTAD) continues to
be the most effective small-molecule HTM for PSCs, previous
studies have demonstrated that the onerous synthesis and low
charge-carrier mobility of spiro-OMeTAD significantly limit its
potential for further application.[24–26] Therefore, it is imperative
to develop more economical and efficient alternatives for suc-
cessful commercialization of PSCs. The principal considerations
for choosing HTMs generally include low cost, high hole mobi-
lity, tunable energy of the frontier molecular orbitals (HOMO
and LUMO), which need to match well with the valence band
(VB) and conduction band (CB) of perovskite to enable hole ex-
Photovoltaic technology, directly converting sunlight into elec-
tricity, is one of the most effective ways to utilize solar
energy.[1,2] PSCs using hybrid organic–inorganic perovskite as
light absorbent have emerged as the forerunner in the next-
generation photovoltaic technology due to their superb PCE
along with very low material costs.[3–7] The light absorbents
based on hybrid organolead trihalide (CH3NH3PbX3, X=Cl, Br
or I) exhibit a good light absorption over the whole visible
solar emission spectrum,[6,8] a long diffusion length of charge
carriers and an excellent charge-carrier mobility, making them
all-round players in the field of PSCs.[9,10] Although a certified
PCE of up to 20.1% was demonstrated in 2015,[11] it is highly
desirable to improve the already remarkable efficiencies of
PSCs by searching for better materials and through device op-
timization.[9]
For further enhancement of PSCs performance as well as
their commercialization, one of the crucial issues is the devel-
[a] J. Chen,+ B.-X. Chen,+ F.-S. Zhang, H.-J. Yu, S. Ma, Prof. Dr. D.-B. Kuang,
Dr. G. Shao, Prof. Dr. C.-Y. Su
MOE Key Laboratory of Bioinorganic and Synthetic Chemistry
School of Chemistry and Chemical Engineering
Sun Yat-sen University
Guangzhou, 510275 (PR China)
E-mail: kuangdb@mail.sysu.edu.cn
shaog@mail.sysu.edu.cn
[+] These authors contributed equally to this work.
Supporting information and the ORCID identification number(s) for the au-
thor(s) of this article can be found under http://dx.doi.org/10.1002/
asia.201501423.
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traction and electron blocking, dopability, as well as high proc-
essability and stability.[27–29] PheDOT, a benzenic analogue of
3,4-ethylenedioxythiophene (EDOT), usually serves as a building
block for construction of various classes of functional or low-
band-gap conducting polymers due to its unique combination
of conductivity and stability.[30,31] Unlike the core structures
based on EDOT, PheDOT-based derivatives are quite stable
under atmospheric conditions by increasing the highest occu-
pied molecular orbital (HOMO) level.[32,33] In addition, the incor-
poration of a flat phenylene ring eliminates the problems of
out-of-plane substituents and potentially enables better order-
ing and packing.[34] Unfortunately, the development and appli-
cation of PheDOT-based HTMs in PSCs have been neglected.
In this work, we report the design and synthesis of two new
PheDOT-based small-molecule HTMs denoted as H-PheDOT
and MeO-PheDOT (Scheme 1) and their successful application
in PSCs. The methoxy group in MeO-PheDOT is used to adjust
the electronic properties of the hole conductor and H-PheDOT
is synthesized for comparison. X-ray diffraction, absorption
spectra, electrochemical properties, thermal stabilities, hole
mobilities, conductivities, and photovoltaic parameters of PSCs
based on these two HTMs are extensively investigated for de-
veloping high-efficiency HTMs. To the best of our knowledge,
this is the first case for adoption of HTMs with a PheDOT struc-
ture in fabricating PSCs.
S6), elemental analysis, and X-ray diffraction. All the analytical
data are consistent with the proposed structures. Both HTMs
have good solubility in commonly used solvents, such as di-
chloromethane (DCM), chloroform, tetrahydrofuran, toluene,
and chlorobenzene.
As shown in Figures S7–S14, X-ray diffraction analyses unam-
biguously clarify the molecular structures of two HTMs. For the
core of PheDOT, the measured dihedral angle between the
thiophene and benzene rings is only 7.068 and 1.968 for H-
PheDOT and MeO-PheDOT (Figures S15, S16), respectively, ba-
sically a planar structure. The quasi-planar core of PheDOT can
induce a stronger intermolecular interaction than that of spiro-
OMeTAD, which normally presents as an amorphous solid.[36]
Both HTMs were observed to crystallize in a triclinic crystal
system. For H-PheDOT, the CH/p hydrogen bonds were mea-
sured to about 2.96, 3.04 and 3.14 Š (Figure 1a), respectively.
Similarly, each MeO-PheDOT molecule has CH/p hydrogen
bonds with surrounding molecules (ca. 2.93 Š, Figure 1b).
These close-stacked molecular arrangements are favorable for
hole transport among HTM molecules and might be able to ef-
fectively protect the perovskite layer.[36–38] To the best of our
knowledge, there is only one report on the crystal structure
and packing of HTMs in PSCs.[36]
Wide-angle X-ray diffraction (WAXD) spectra of three HTMs
in film state are shown in Figure S17. Sharp and intense reflec-
tions of H-PheDOT and MeO-PheDOT can be observed, indi-
cating their crystalline structures. By contrast, spiro-OMeTAD
showed a weak, broad, and diffused peak that indicated an
amorphous structure, which was consistent with the result
from a previous report.[36] Compared to amorphous HTMs, crys-
talline HTMs possess an abundance of short contacts that pro-
vide ample pathways for hole transfer among molecules.
Thermogravimetric analysis (TGA) and differential scanning
calorimetry (DSC) measurements show that H-PheDOT and
MeO-PheDOT have high decomposition temperatures (Td, 475
and 4338C for H-PheDOT and MeO-PheDOT, respectively) (Fig-
ures S18, S19) and glass transition temperature (Tg, 1048C for
MeO-PheDOT) (Figure S21). However, H-PheDOT did not give
an obvious Tg (Figure S20). The Tg value of MeO-PheDOT is sig-
nificantly higher than that of the previously reported H101 (Tg,
Results and Discussion
The PheDOT-core HTMs were synthesized through a simple
process by use of inexpensive starting materials based on
a Suzuki coupling reaction. The synthetic route is depicted in
Scheme 1. The detailed synthetic procedures and spectroscop-
ic data of compounds 1–3 were reported.[33,35] The precursor
(compound 1) is air-stable, unlike 2,5-dibromo-EDOT used to
prepare H101, which is rapidly oxidized in air and must be
used immediately upon in situ formation or else kept under an
inert atmosphere.[32] The molecular structures of new HTMs (H-
1
PheDOT and MeO-PheDOT) were characterized by H/13C NMR
spectroscopy (Figures S1, S2, S4, and S5, Supporting Informa-
tion), high-resolution mass spectrometry (HR-MS) (Figures S3,
Scheme 1. Synthetic procedures of HTMs.
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Figure 2. (a) UV/Vis absorption and photoluminescence of H-PheDOT and
MeO-PheDOT in DCM (1.0”10À5 m). (b) UV/Vis absorption spectra of HTMs
coated on TiO2/CH3NH3PbI3 films.
Figure 1. Dashed red lines illustrate CH/p hydrogen bonds in the crystal of
(a) H-PheDOT (ca. 2.96, 3.04 and 3.14 Š) and (b) MeO-PheDOT (ca. 2.93 Š).
ble property of HTM since the loss of incident photons from
absorption of HTM can be minimized.
738C)[32] because the replacement of the ethylene bridge in
H101 by a phenyl group increases the molecular size. A higher
Tg value is favorable for the practical application in a device.[39]
All the results reveal that these two new HTMs have excellent
thermal stability to be fabricated in PSCs.
Cyclic voltammetry (CV) of HTMs was recorded to determine
the ground-state oxidation potential (Figures S23–S26). On the
basis of the reported HOMO level of spiro-OMeTAD
(À5.22 eV),[20] the HOMO levels of H-PheDOT and MeO-
PheDOT are À5.45 eV and À5.32 eV, respectively. Figure 3a
shows the relevant energy level diagram of the materials used
to prepare the PSCs. H-PheDOT exhibits a slightly lower HOMO
than that of CH3NH3PbI3 (À5.44 eV), which is unfavorable for
the hole transportation. The antagonistic contribution of hole
transport leads to a relatively low PCE. However, the HOMO of
MeO-PheDOT is 0.12 eV higher than that of CH3NH3PbI3, indi-
cating that MeO-PheDOT has energetics favorable for hole
transfer. Thus, the introduction of ÀOMe groups on the pri-
mary ligand can increase the HOMO energy because of their
strong electron-donating effect. The DEg (H-PheDOT, 2.87 eV
(431 nm) and MeO-PheDOT, 2.79 eV (444 nm), Table 1) is ob-
tained from the intersection of the emission and absorption
spectra (Figures S27, S28). The lowest unoccupied molecular
orbital (LUMO) energy is calculated by adding the DEg to the
corresponding HOMO energy. The LUMO levels of H-PheDOT
(À2.58 eV) and MeO-PheDOT (À2.53 eV) are higher than the
conduction band edge of CH3NH3PbI3 (À3.93 eV), which could
block the electron transportation from CH3NH3PbI3 to Au and
hence suppress carrier recombination.[40,41]
The UV/Vis absorption spectra of H-PheDOT and MeO-
PheDOT in DCM are depicted in Figure 2a. The absorption
spectra indicate that H-PheDOT starts to absorb light from
448 nm, which is 15 nm blue-shifted relative to that of MeO-
PheDOT (463 nm). The absorption onset wavelength (lonset
)
that reflects the optical band-gap energy (DEg) of the material
helps in identifying the influence of the substitution position.
Thus, MeO-PheDOT has a lower DEg. The molar absorption co-
efficient (e) values of H-PheDOT and MeO-PheDOT are 5.01”
104 LmolÀ1 cmÀ1 (394 nm) and 4.80”104 LmolÀ1 cmÀ1 (401 nm),
respectively, calculated at the respective lmax value. The fluo-
rescence spectra of H-PheDOT and MeO-PheDOT show maxi-
mum emission at 449 and 477 nm, respectively. The Stokes
shift of H-PheDOT (60 nm) is almost identical to that of MeO-
PheDOT (61 nm) (Figure S22), indicating a similar structural
change in the excited state of both HTMs. The fluorescence
quantum yields (FF) of H-PheDOT and MeO-PheDOT in DCM
(1.0”10À5 m) are 24.9% (lex =389 nm) and 51.0% (lex =
416 nm), respectively. Figure 2b shows the UV/Vis absorption
spectra of the perovskite-coated compact TiO2 films with these
two HTMs, which absorb a broad range of light from visible to
the near-infrared. Two HTM-coated photoactive films exhibit
an enhanced absorption band due to the superposed absorp-
tion characteristic of their constituents. Moreover, MeO-
PheDOT shows a lower absorbance, which would be a favora-
As previously highlighted, charge transport is another signifi-
cant parameter to consider in the design of new HTMs for
PSCs. Herein, the hole mobility was measured by space-
charge-limited currents (SCLCs).[42,43] Fitting the current–voltage
curves (Figures S29–S31) for each material to the Mott–Gurney
square law (see the Supporting Information for details) gave
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tion of hole mobility are described in the Supporting Informa-
tion.
The conductivities of films were determined by use of
a two-contact electrical conductivity set-up, which was per-
formed by following a published procedure.[38] We note that
the conductivity of pristine H-PheDOT (4.17”10À7 ScmÀ1) is
higher than that of pristine MeO-PheDOT (3.04”10À7 ScmÀ1).
Experimental details of fabrication and characterization of con-
ductivity are described in the Supporting Information.
Figure 3b shows a cross-sectional scanning electron micros-
copy (SEM) image of an FTO/TiO2/CH3NH3PbI3/MeO-PheDOT/
Au device, exhibiting a well-defined hybrid structure with clear
interfaces. The thicknesses of perovskite and HTM layers were
observed to be about 230 and 210 nm, respectively.
The photocurrent–voltage (J–V) curves for solar cells are pre-
sented in Figure 4a and the detailed photovoltaic parameters
are summarized in Table 2. Further, the statistical data for
a batch of ten devices are shown in Tables S2 and S3. Under
Figure 3. (a) Energy level diagram of each component. (b) Cross-sectional
SEM image of a representative device.
Table 1. Thermal stability, electrochemical and electrical properties of
HTMs.
[a]
HTMs
Td Tg
DEg HOMO LUMO Hole mobili-
Conductivity[b]
[ScmÀ1
[8C] [8C] [eV] [eV]
[eV]
ty[b]
]
(cm2 VÀ1 sÀ1
)
H-
PheDOT
MeO-
475 –
2.87 À5.45 À2.58 2.89”10À5
4.17”10À7
3.04”10À7
433 104 2.79 À5.32 À2.53 1.33”10À4
PheDOT
[a] H-PheDOT showed no Tg. [b] Pure HTM without doping.
the mobility data listed in Table 1. The results show that the
hole mobilities of H-PheDOT and MeO-PheDOT are 2.89”10À5
and 1.33”10À4 cm2 VÀ1 sÀ1, respectively.
The higher FF (Table 2) of the cell with MeO-PheDOT could
be explained by its higher hole mobility. The value (2.34”
10À5 cm2 VÀ1 sÀ1) obtained here for pristine spiro-OMeTAD is
similar to the data reported in the literature.[29,44] Thus, the
hole mobility of MeO-PheDOT is higher than that of spiro-
OMeTAD. Experimental details of fabrication and characteriza-
Figure 4. (a) Photocurrent–voltage (J–V) characteristics of solar cells. (b) Cor-
responding IPCE spectra.
similar conditions, the average PCEs for the cells with H-
PheDOT and MeO-PheDOT are 5.34% and 9.46%, respectively.
The best-performing device with H-PheDOT and MeO-PheDOT
gave a Jsc of 16.58 and 18.31 mAcmÀ2, a Voc of 0.782 and
0.914 V, and a FF of 0.516 and 0.636, affording a PCE of 6.69%
and 10.64%, respectively. The PCE value for the MeO-PheDOT
based cell is higher than that for the cell with H-PheDOT due
to higher Jsc, Voc and FF values. To gain a deeper insight into
the HTM variations, the incident monochromatic photon-to-
current conversion efficiency (IPCE) spectra of PSCs were re-
corded (Figure 4b). The MeO-PheDOT based device enhanced
the photocurrent in the whole visible region between 400 and
Table 2. Photovoltaic parameters of the solar cells employing different
HTMs.
HTM
Jsc
Voc
FF
PCE
[%]
Rs
Rsh
[WcmÀ2
]
[mAcmÀ2] [V]
[WcmÀ2
]
Average 15.52
0.693 0.496 5.34 37.1
0.782 0.516 6.69 21.2
0.885 0.588 9.46 11.1
0.914 0.636 10.64 8.7
229.4
129.0
825.8
686.7
H-PheDOT
Best
Average 18.19
Best 18.31
16.58
MeO-
PheDOT
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800 nm relative to that of H-PheDOT by improving charge col-
lection/extraction due to its higher hole mobility and more
suitable energy level alignment.[45] An integral photocurrent
from the overlap of the IPCE spectrum is 15.11 and
17.38 mAcmÀ2 for H-PheDOT and MeO-PheDOT, respectively,
basically in agreement with the experimentally obtained Jsc
value (Table 2). Under the same illumination, the fully opti-
mized device based on spiro-OMeTAD achieved an average
PCE of 13.17% in a parallel experiment. Our study also showed
that the device fabricated without HTM gave a PCE of only
around 1.71%, which confirmed that an HTM must be an inte-
gral component of the above-studied device configuration to
obtain a high PCE.
electron migration from CH3NH3PbI3 to the Au metal electrode,
which is responsible for the increased Rsh. Accordingly, the
higher FF value of the cell with MeO-PheDOT could be ration-
alized in terms of a lower Rs and a higher Rsh.[19,20]
The hysteresis characteristics in J–V curves (Figures S32, S33)
were evaluated under both forward and reverse bias sweep
with a scan speed of 0.15 VsÀ1, and are summarized in Table
S4. The device based on MeO-PheDOT gave
a Jsc of
17.49 mAcmÀ2, a Voc of 0.856 V, and a FF of 0.649, correspond-
ing to a PCE of 9.71% at forward-bias to short-circuit (FB-SC)
direction. At short-circuit to forward-bias (SC-FB) direction, the
device afforded a PCE of 8.06%. The PCE for SC-FB is 83.0% of
that for FB-SC. However, for the device with H-PheDOT, the
PCE for SC-FB is only 56.8% of that for FB-SC. Thus, the device
with H-PheDOT showed a serious hysteresis between the two
scan directions under similar conditions. This phenomenon
may originate from its lower hole mobility and insufficient driv-
ing force for hole injection.
The high voltage output in PSCs is determined by perovskite
materials and the HOMO level of the HTM.[46] As H-PheDOT ex-
hibits a slightly deeper HOMO level (À5.45 eV) than that of
CH3NH3PbI3 (À5.44 eV), the driving force might not be enough
for the hole injection from CH3NH3PbI3 to HTM. Such an insuffi-
cient hole extraction probably raises the carrier density within
the bulk perovskite material and brings up the increment of re-
combination rate. As a result, the Voc of the cell with H-
PheDOT is lower.
Conclusions
Herein, we report the syntheses and characterizations of two
new PheDOT-based HTMs as well as their application in PSCs.
The replacement of an ethylene bridge in an EDOT-based mol-
ecule (H101) by a phenyl group leads to a better thermal sta-
bility of the HTM. Further, by simply introducing methoxy
groups into the main skeleton, the energy levels of the
PheDOT-core HTM are tuned to match with the perovskite,
and its hole mobility is also improved (higher than that of
spiro-OMeTAD). The best-performing device, fabricated with
MeO-PheDOT as HTM, achieves an impressive PCE of 10.64%.
We believe that PheDOT-core arylamine derivatives can be
used as HTMs for fabrication of efficient and cost-effective
photovoltaic devices. Our results give some insight into how
the molecular structures of HTM affect their performances in
PSCs and shed light on the future rational design of high-effi-
ciency and low-cost HTMs for hybrid solar cells.
The FF is related to series resistance (Rs) and shunt resistance
(Rsh), which can be extracted from J–V curves (Figure 5). As
listed in Table 2, the ten cells based on H-PheDOT give an
average Rs of 37.1 WcmÀ2, whereas the ten cells based on
MeO-PheDOT show an average Rs of 11.1 WcmÀ2. The lower Rs
value of the cell with MeO-PheDOT can be explained by its
higher hole-transporting ability. For Rsh, the HTM functions as
both hole-transporting layer and electron-blocking layer in the
FTO/TiO2/CH3NH3PbI3/HTM/Au device (Figure 3a). MeO-
PheDOT with a higher LUMO can more effectively block the
Experimental Section
Materials and Measurements. All reactions were carried out under
an atmosphere of argon with freshly distilled THF. All the other re-
agents were purchased from commercial sources and used without
further purification unless otherwise noted. 1H and 13C NMR spectra
were recorded at 258C on a 400 MHz NMR spectrometer (Bruker,
1
AVANCE III). Chemical shifts were reported relative to Me4Si for H
and 13C. HRMS spectra were recorded on ESI-Q-TOF mass spec-
trometer (Bruker Daltonics, ESI-Q-TOF maXis 4G). X-ray intensities
were collected on an Agilent Gemini S Ultra CCD diffractometer
with enhanced X-ray source of Cu radiation (l=1.54178 Š) by use
of the w–f scan technique. Cyclic voltammetry (CV) measurements
were performed on a CHI-750 electrochemical workstation (CHI In-
struments, Chenhua Corporation, Shanghai, China) with a three-
electrode system: a Pt wire working electrode, Ag/AgNO3 reference
electrode and a Pt plate counter electrode. Quantum yields (FF)
were measured by using an absolute PL quantum yield measure-
ment system (Hamamatsu, C9920-02G) at room temperature. TGA
measurements were carried out from 358C to 9008C at a heating
Figure 5. (a) Series resistance (Rs) and (b) shunt resistance (Rsh) extracted
from J–V curves.
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rate of 10.08C minÀ1 under N2 atmosphere using a thermogravimet-
ric analyzer (Netzsch, STA449F3). DSC measurements were record-
ed on a differential scanning calorimeter (Netzsch, 204F1 Phoenix).
All CV measurements were carried out in freshly distilled DCM
calcd for C50H40N2O6S: C, 75.36; H, 5.06; N, 3.52; S, 4.02, found: C,
75.26; H, 5.18; N, 3.40; S, 3.93.
using
tetrabutylammonium
hexafluorophosphate (TBAPF6, Acknowledgements
0.1 molLÀ1
)
as the supporting electrolyte at
a scan rate of
50 mVsÀ1 at room temperature, and each solution (1.0”
10À4 molLÀ1) was purged with N2 for 5 min prior to measurement.
Ferrocene/ferrocenium (Fc/Fc+, 1.0”10À4 molLÀ1) couple was used
as an external standard. The J--V curves were recorded by use of
This work was financially supported by the National Natural
Science Foundation of China (21102187, 91433109), the Natural
Science Foundation of Guangdong Province (S2013010012128,
S2013030013474), the Science and Technology Planning Proj-
ect of Guangdong Province (2015A010105013), and the Sci-
ence and Technology Planning Project of Guangzhou City
(201504291110274, 201504010031).
a
Keithley 2400 source meter under simulated AM 1.5G
(100 mWcmÀ2) illumination provided by a solar light simulator
(Oriel, Model: 91192). A 1000 W xenon arc lamp (Oriel, Model:
6271) was used as a light source and the incident light intensity
was calibrated with an NREL standard Si solar cell. The J–V curves
of all devices were measured with an active area of 0.1256 cm2.
The IPCE spectra were recorded on a Keithley 2000 multimeter
under the illumination of a 150 W tungsten lamp with a monochro-
mator (Spectral Product DK240). The synthesis of CH3NH3I and ex-
perimental details of the fabrication of PSCs are described in the
Supporting Information.
Keywords: energy conversion · hole-transporting materials ·
organic electronics · perovskite solar cells · sulfur heterocycles
[1] G. Hodes, Science 2013, 342, 317–318.
[2] M. D. McGehee, Nat. Mater. 2014, 13, 845–846.
[3] A. Kojima, K. Teshima, Y. Shirai, T. Miyasaka, J. Am. Chem. Soc. 2009, 131,
6050–6051.
Synthesis of H-PheDOT. Under Ar atmosphere, compound
1 (348 mg, 1.0 mmol, 1.0 equiv), compound 2 (607 mg, 2.1 mmol,
2.1 equiv), K2CO3 aqueous solution (2.0m, 4 mL), and [Pd(PPh3)4]
(58 mg, 0.05 mmol, 0.05 equiv) were dissolved in freshly distilled
THF (16 mL). The reaction mixture was refluxed with stirring for
20.0 h (protected from daylight). After reaction, H2O (10 mL) was
added to quench the reaction. The reaction mixture was then ex-
tracted with DCM. The organic phase was then dried over magne-
sium sulfate and filtered. After evaporation at a reduced pressure,
the residue was subjected to column chromatography on silica gel
(eluent: petroleum ether/CH2Cl2/EtOAc=20/1/0.1, v/v/v), affording
H-PheDOT as a yellow solid (520 mg, 76.8%). The product was fur-
ther purified by recrystallization (solvents: petroleum ether/CH2Cl2)
[4] H. S. Jung, N. G. Park, Small 2015, 11, 10–25.
[5] N. J. Jeon, J. H. Noh, W. S. Yang, Y. C. Kim, S. Ryu, J. Seo, S. I. Seok,
Nature 2015, 517, 476–480.
[6] M. Grätzel, Nat. Mater. 2014, 13, 838–842.
[7] B. V. Lotsch, Angew. Chem. Int. Ed. 2014, 53, 635–637; Angew. Chem.
2014, 126, 647–649.
[8] P. Da, M. Cha, L. Sun, Y. Wu, Z. S. Wang, G. Zheng, Nano. Lett. 2015, 15,
3452–3457.
[9] D. Shi, V. Adinolfi, R. Comin, M. Yuan, E. Alarousu, A. Buin, Y. Chen, S.
Hoogland, A. Rothenberger, K. Katsiev, Y. Losovyj, X. Zhang, P. A.
Dowben, O. F. Mohammed, E. H. Sargent, O. M. Bakr, Science 2015, 347,
519–522.
[10] S. Kazim, M. K. Nazeeruddin, M. Grätzel, S. Ahmad, Angew. Chem. Int. Ed.
2014, 53, 2812–2824; Angew. Chem. 2014, 126, 2854–2867.
[11] R. F. Service, Science 2015, 347, 225.
1
for solar cell fabrication. H NMR (400 MHz, CDCl3): d=7.63 (d, J=
8.0 Hz, 4H), 7.30–7.26 (m, 8H), 7.15–7.09 (m, 12H), 7.06–6.99 (m,
4H), 6.98–6.93 ppm (m, 4H). 13C NMR (100 MHz, CDCl3): d=147.43,
146.84, 140.59, 134.64, 129.31, 127.10, 125.93, 124.60, 123.72,
123.38, 123.14, 116.92, 115.41 ppm. HRMS (ESI) m/z: [M]+ Calcd for
C46H32N2O2S: 676.2179; found: 676.2180. Elemental analysis (%)
calcd for C46H32N2O2S: C, 81.63; H, 4.77; N, 4.14; S, 4.74; found: C,
81.46; H, 4.80; N, 4.10; S, 4.85.
[12] T. C. Sum, N. Mathews, Energy Environ. Sci. 2014, 7, 2518–2534.
[13] J. H. Park, J. Seo, S. Park, S. S. Shin, Y. C. Kim, N. J. Jeon, H. W. Shin, T. K.
Ahn, J. H. Noh, S. C. Yoon, C. S. Hwang, S. I. Seok, Adv. Mater. 2015, 27,
4013–4019.
[14] J. A. Christians, R. C. M. Fung, P. V. Kamat, J. Am. Chem. Soc. 2014, 136,
758–764.
[15] S. Ye, W. Sun, Y. Li, W. Yan, H. Peng, Z. Bian, Z. Liu, C. Huang, Nano Lett.
2015, 15, 3723–3728.
[16] H. W. Chen, X. Pan, W. Q. Liu, M. L. Cai, D. X. Kou, Z. P. Huo, X. Q. Fang,
S. Y. Dai, Chem. Commun. 2013, 49, 7277–7279.
[17] Z. Yu, L. Sun, Adv. Energy Mater. 2015, 5, 1500213.
[18] M. Cai, V. T. Tiong, T. Hreid, J. Bell, H. Wang, J. Mater. Chem. A 2015, 3,
2784–2793.
[19] N. J. Jeon, J. Lee, J. H. Noh, M. K. Nazeeruddin, M. Grätzel, S. I. Seok, J.
Am. Chem. Soc. 2013, 135, 19087–19090.
[20] N. J. Jeon, H. G. Lee, Y. C. Kim, J. Seo, J. H. Noh, J. Lee, S. I. Seok, J. Am.
Chem. Soc. 2014, 136, 7837–7840.
[21] H. Choi, S. Paek, N. Lim, Y. H. Lee, M. K. Nazeeruddin, J. Ko, Chem. Eur. J.
2014, 20, 10894–10899.
[22] T. Krishnamoorthy, F. Kunwu, P. P. Boix, H. Li, T. M. Koh, W. L. Leong, S.
Powar, A. Grimsdale, M. Grätzel, N. Mathews, S. G. Mhaisalkar, J. Mater.
Chem. A 2014, 2, 6305–6309.
[23] A. Krishna, D. Sabba, H. Li, J. Yin, P. P. Boix, C. Soci, S. G. Mhaisalkar, A. C.
Grimsdale, Chem. Sci. 2014, 5, 2702–2709.
[24] W. H. Nguyen, C. D. Bailie, E. L. Unger, M. D. McGehee, J. Am. Chem. Soc.
2014, 136, 10996–11001.
Synthesis of MeO-PheDOT. Under Ar atmosphere, a 50 mL flask
was charged with compound 1 (383 mg, 1.1 mmol, 1.0 equiv),
K2CO3 aqueous solution (2.0m, 5 mL), and [Pd(PPh3)4] (64 mg,
0.055 mmol, 0.05 equiv). Subsequently, compound 3 (2.37 mmol,
827 mg, 2.1 equiv) in THF (20 mL) was added slowly by using a sy-
ringe. The reaction mixture was refluxed with stirring for 15.0 h
(protected from daylight). After reaction, H2O (10 mL) was added
to quench the reaction. The reaction mixture was then extracted
with DCM. The organic layer was then dried over magnesium sul-
fate and filtered. After evaporation at a reduced pressure, the resi-
due was subjected to column chromatography on silica gel
(eluent: petroleum ether/CH2Cl2 =2/1, v/v), affording MeO-PheDOT
as a yellow solid (630 mg, 71.8%). The product was further purified
by recrystallization (solvents: petroleum ether/CH2Cl2) for solar cell
fabrication. 1H NMR (400 MHz, CDCl3): d=7.55 (d, J=8.0 Hz, 4H),
7.08 (d, J=8.0 Hz, 8H), 6.98–6.91 (m, 8H), 6.84 (d, J=8.0 Hz, 8H),
3.80 ppm (s, 12H). 13C NMR (100 MHz, CDCl3): d=155.96, 147.70,
140.67, 140.61, 134.22, 126.94, 126.68, 124.07, 123.57, 120.30,
116.87, 115.27, 114.71, 55.49 ppm. HRMS (ESI) m/z: [M]+ Calcd for
C50H40N2O6S: 796.2602; found: 796.2588. Elemental analysis (%)
[25] A. Abate, D. J. Hollman, J. Teuscher, S. Pathak, R. Avolio, G. D’Errico, G.
Vitiello, S. Fantacci, H. J. Snaith, J. Am. Chem. Soc. 2013, 135, 13538–
13548.
[26] P. Qin, S. Paek, M. I. Dar, N. Pellet, J. Ko, M. Grätzel, M. K. Nazeeruddin, J.
Am. Chem. Soc. 2014, 136, 8516–8519.
Chem. Asian J. 2016, 11, 1043 – 1049
www.chemasianj.org
1048
ꢀ 2016 Wiley-VCH Verlag GmbH & Co. KGaA, Weinheim

Full Paper
[27] Z. Zhu, Y. Bai, H. K. H. Lee, C. Mu, T. Zhang, L. Zhang, J. Wang, H. Yan,
S. K. So, S. Yang, Adv. Funct. Mater. 2014, 24, 7357–7365.
[28] D. Bi, L. Yang, G. Boschloo, A. Hagfeldt, E. M. J. Johansson, J. Phys.
Chem. Lett. 2013, 4, 1532–1536.
[29] B. Xu, E. Sheibani, P. Liu, J. Zhang, H. Tian, N. Vlachopoulos, G. Boschloo,
L. Kloo, A. Hagfeldt, L. Sun, Adv. Mater. 2014, 26, 6629–6634.
[30] C. R. G. Grenier, W. Pisula, T. J. Joncheray, K. Müllen, J. R. Reynolds,
Angew. Chem. Int. Ed. 2007, 46, 714–717; Angew. Chem. 2007, 119, 728–
731.
[31] S. Roquet, P. Leriche, I. Perepichka, B. Jousselme, E. Levillain, P. Fr›re, J.
Roncali, J. Mater. Chem. 2004, 14, 1396–1400.
[32] H. Li, K. Fu, A. Hagfeldt, M. Grätzel, S. G. Mhaisalkar, A. C. Grimsdale,
Angew. Chem. Int. Ed. 2014, 53, 4085–4088; Angew. Chem. 2014, 126,
4169–4172.
[38] S. D. Sung, M. S. Kang, I. T. Choi, H. M. Kim, H. Kim, M. Hong, H. K. Kim,
W. I. Lee, Chem. Commun. 2014, 50, 14161–14163.
[39] H. Li, K. Fu, P. P. Boix, L. H. Wong, A. Hagfeldt, M. Grätzel, S. G. Mhaisal-
kar, A. C. Grimsdale, ChemSusChem 2014, 7, 3420–3425.
[40] Y. Xu, J. Shi, S. Lv, L. Zhu, J. Dong, H. Wu, Y. Xiao, Y. Luo, S. Wang, D. Li,
X. Li, Q. Meng, ACS Appl. Mater. Interfaces 2014, 6, 5651–5656.
[41] Y. Song, S. Lv, X. Liu, X. Li, S. Wang, H. Wei, D. Li, Y. Xiao, Q. Meng,
Chem. Commun. 2014, 50, 15239–15242.
[42] D. Poplavskyy, J. Nelson, J. Appl. Phys. 2003, 93, 341–346.
[43] R. Zhou, Q. D. Li, X. C. Li, S. M. Lu, L. P. Wang, C. H. Zhang, J. Huang, P.
Chen, F. Li, X. H. Zhu, W. C. H. Choy, J. B. Peng, Y. Cao, X. Gong, Dyes
Pigm. 2014, 101, 51–57.
[44] T. Leijtens, I. K. Ding, T. Giovenzana, J. T. Bloking, M. D. McGehee, A. Sell-
inger, ACS Nano 2012, 6, 1455–1462.
[33] I. F. Perepichka, S. Roquet, P. Leriche, J. M. Raimundo, P. Fr›re, J. Roncali,
Chem. Eur. J. 2006, 12, 2960–2966.
[45] H. Choi, S. Park, S. Paek, P. Ekanayake, M. K. Nazeeruddin, J. Ko, J. Mater.
Chem. A 2014, 2, 19136–19140.
[34] E. Poverenov, Y. Sheynin, N. Zamoshchik, A. Patra, G. Leitus, I. F. Pere-
pichka, M. Bendikov, J. Mater. Chem. 2012, 22, 14645–14655.
[35] C. Teng, X. Yang, C. Yang, S. Li, M. Cheng, A. Hagfeldt, L. Sun, J. Phys.
Chem. C 2010, 114, 9101–9110.
[46] S. Ryu, J. H. Noh, N. J. Jeon, Y. C. Kim, W. S. Yang, J. Seo, S. I. Seok,
Energy Environ. Sci. 2014, 7, 2614–2618.
[36] P. Ganesan, K. Fu, P. Gao, I. Raabe, K. Schenk, R. Scopelliti, J. Luo, L. H.
Wong, M. Grätzel, M. K. Nazeeruddin, Energy Environ. Sci. 2015, 8, 1986–
1991.
[37] M. Planells, A. Abate, D. J. Hollman, S. D. Stranks, V. Bharti, J. Gaur, D.
Mohanty, S. Chand, H. J. Snaith, N. Robertson, J. Mater. Chem. A 2013, 1,
6949–6960.
Manuscript received: December 21, 2015
Accepted Article published: February 3, 2015
Final Article published: March 2, 2016
Chem. Asian J. 2016, 11, 1043 – 1049
www.chemasianj.org
1049
ꢀ 2016 Wiley-VCH Verlag GmbH & Co. KGaA, Weinheim