Co-sensitization of organic dyes for efficient dye-sensitized solar cells

Article abstract of DOI:10.1002/cssc.201200655

Novel cyanine dyes, in which a tetrahydroquinoline derivative is used as an electron donor and 1-butyl-5-carboxy-3, 3-dimethyl-indol-1-ium moiety is used as an electron acceptor and anchoring group, were designed and synthesized for application in dye-sensitized solar cells. The photovoltaic performance of these solar cells depends markedly on the molecular structure of the dyes in terms of the n-hexyl chains and the methoxyl unit. Retardation of charge recombination caused by the introduction of n-hexyl chains resulted in an increase in electron lifetime. As a consequence, an improvement of open-circuit photovoltage (V _oc) was achieved. Also, the electron injection efficiencies were improved by the introduction of methoxyl moiety, which led to a higher short-circuit photocurrent density (J_sc). The highest average efficiency of the sensitized devices (η) was 5.6 % (J_sc=13.3 mA cm^-2, V_oc=606 mV, and fill factor FF=69.1 %) under 100 mW cm^-2 (AM 1.5G) solar irradiation. All of these dyes have very high absorption extinction coefficients and strong absorption in a relatively narrow spectrum range (500-650 nm), so one of our organic dyes was explored as a sensitizer in co-sensitized solar cells in combination with the other two other existing organic dyes. Interestingly, a considerably improved photovoltaic performance of 8.2 % (J_sc=20.1 mA cm^-2, V_oc=597 mV, and FF=68.3 %) was achieved and the device showed a panchromatic response with a high incident photon-to-current conversion efficiency exceeding 85 % in the range of 400-700 nm. Sensitive dyes absorb it all: Co-sensitization of three spectrally complementary dyes on a TiO₂ film in a well-designed sequence significantly improves the photovoltaic performance of the device, and an efficiency of 8.2 % is achieved. The devices demonstrate a panchromatic response with an incident photon-to-current conversion efficiency >80 % over the entire visible spectral region from 400 to 700 nm. Copyright

Full text of DOI:10.1002/cssc.201200655

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DOI: 10.1002/cssc.201200655
Co-sensitization of Organic Dyes for Efficient Dye-
Sensitized Solar Cells
Ming Cheng,[a] Xichuan Yang,*[a] Jiajia Li,[a] Fuguo Zhang,[a] and Licheng Sun*[a, b]
Novel cyanine dyes, in which a tetrahydroquinoline derivative
is used as an electron donor and 1-butyl-5-carboxy-3, 3-di-
methyl-indol-1-ium moiety is used as an electron acceptor and
anchoring group, were designed and synthesized for applica-
tion in dye-sensitized solar cells. The photovoltaic performance
of these solar cells depends markedly on the molecular struc-
ture of the dyes in terms of the n-hexyl chains and the me-
thoxyl unit. Retardation of charge recombination caused by
the introduction of n-hexyl chains resulted in an increase in
electron lifetime. As a consequence, an improvement of open-
circuit photovoltage (Voc) was achieved. Also, the electron in-
jection efficiencies were improved by the introduction of me-
thoxyl moiety, which led to a higher short-circuit photocurrent
density (Jsc). The highest average efficiency of the sensitized
devices (h) was 5.6% (Jsc =13.3 mAcmÀ2, Voc =606 mV, and fill
factor FF=69.1%) under 100 mWcmÀ2 (AM 1.5G) solar irradia-
tion. All of these dyes have very high absorption extinction co-
efficients and strong absorption in a relatively narrow spec-
trum range (500–650 nm), so one of our organic dyes was ex-
plored as a sensitizer in co-sensitized solar cells in combination
with the other two other existing organic dyes. Interestingly,
a considerably improved photovoltaic performance of 8.2%
(Jsc =20.1 mAcmÀ2, Voc =597 mV, and FF=68.3%) was achieved
and the device showed a panchromatic response with a high
incident photon-to-current conversion efficiency exceeding
85% in the range of 400–700 nm.
Introduction
Dye-sensitized solar cells (DSSCs) are regarded as a low-cost
next-generation solar cells, and significant progress has been
made since their inception in 1991.[1] However, it is necessary
to further improve the energy conversion efficiency of DSSCs
to enable successful commercialization. To achieve this goal,
the photosensitizer needs to capture as much incident light as
possible, both in the absorption intensity and the absorption
breadth. Many attempts, such as tandem DSSCs and co-sensi-
tized DSSCs, have been conducted to broaden the absorption
spectra of the cells.[2–17] For example, the co-sensitization of
a porphyrin dye YD2-o-C8 and a metal-free dye Y123 with
complementary spectral responses showed an efficiency of
12.3%, a considerably higher photovoltaic performance than
the devices fabricated with the individual dye.[6] A phthalocya-
nine dye (TT1 or PcS15) co-sensitized with various organic dyes
(JK2, D2, or D131) exhibited an enhanced device performance
through the improved light-harvesting efficiency of the
cell.[9,10,16] The co-sensitization of TiO2 films by a black dye and
organic dyes (D131 or Y1) resulted in a significantly enhanced
photocurrent, leading to a device performance of 11.0–
11.4%.[11,12] These works have shown a clear advance towards
efficient DSSCs based on the system with an extended spec-
trum response in the red to near-IR region. Cyanine dyes have
very high absorption extinction coefficients (about
105 mÀ1 cmÀ1), an intense but narrow absorption band in the
long wavelength region. This makes them good candidates for
co-sensitizers owing to the less competitive absorption with
dyes absorbing in the short wavelength region and the near
infrared (NIR) region. We have designed and synthesized four
cyanine dyes CM201–CM204 (see Figure 1), in which a tetrahy-
droquinoline derivative is used as an electron donor and 1-
butyl-5-carboxy-3, 3-dimethyl-indol-1-ium moiety is used as an
electron acceptor and anchoring group, and applied these
dyes to DSSCs. The dye CM203 was also applied to co-sensitize
with the other two organic dyes CMR103 and HY113 (see
Figure 7).
[a] Dr. M. Cheng, Prof. X. Yang, Dr. J. Li, Dr. F. Zhang, Prof. L. Sun
State Key Laboratory of Fine Chemicals
DUT-KTH Joint Education and Research Centre on Molecular Devices
Dalian University of Technology (DUT)
2 Linggong Rd., 116024 Dalian (P.R. China)
Fax: (+86)411-84986250
Results and Discussion
Photophysical and electrochemical properties of CM201–
CM204
E-mail: yangxc@dlut.edu.cn
[b] Prof. L. Sun
School of Chemical Science and Engineering
Center of Molecular Devices, Department of Chemistry
Royal Institute of Technology (KTH)
The absorption spectra recorded for the dyes in dichlorome-
thane solution are displayed in Figure 2. All of the dyes exhibit
a prominent peak around 578–604 nm (Table 1 and Figure 2)
with a molar extinction coefficient from 3.9ꢀ104 to 4.0ꢀ
104 mÀ1 cmÀ1. Figure 3 shows the absorption spectra of four
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0.96, 0.80, 0.84, and 0.74 V
versus standard hydrogen elec-
trode (NHE), respectively. These
values are more positive than
the potential of S2À/Sx2À couple
(+0.5 V versus NHE),[18] indicat-
ing the oxidized dyes can be re-
generated
thermodynamical-
ly.[19–21] The estimated excited-
state potential corresponding to
the LUMO levels of the dyes
CM201–CM204 are À0.83 V,
À0.93 V, À0.89 V, and À0.95 V
versus NHE, respectively, which
are more negative than the
conduction band edge of TiO2
Figure 1. Structure of the cyanine dyes CM201–CM204.
Figure 2. Absorption spectra of CM201–CM204 in CH2Cl2 (2.0ꢀ10À5 m).
Figure 3. Absorption spectra of CM201–CM204 on TiO2 films.
(about À0.5 V versus NHE).[19] Therefore, the energy surplus of
the LUMO in four dyes allows the injection of electrons into
the conduction band of TiO2.
Table 1. UV/Vis absorption and electrochemical properties of the dyes
CM201–CM204.
[d]
[e]
Dye
lmax[a] in
CH2Cl2 [nm] [MÀ1 cmÀ1
e at lmax
lmax[b] on TiO2 E0–0
[nm]
Eox
[V][c] [V]
ELUMO
[V]
]
CM201 578
CM202 593
CM203 586
CM204 604
38600
40100
38500
40300
583
607
593
610
1.79 0.96 À0.83
1.74 0.80 À0.94
1.73 0.84 À0.89
1.69 0.74 À0.95
Photocurrent–voltage characteristics of devices sensitized
by CM201–CM204
The dye-sensitized solar cells using these dyes as sensitizers for
nano-crystalline anatase TiO2 were fabricated, and the device
performance parameters under AM 1.5G illumination are
shown in Table 2. Figure 4 and Figure 5 show the photocur-
[a] Absorption spectra in solution were measured in CH2Cl2 (2ꢀ10À5 m).
[b] Absorption spectra on TiO2 film were measured with dye-loaded TiO2
films immerged in CH2Cl2 solution. [c] The energy gap E0–0 was deter-
mined from the intersection of the tangent of absorption on TiO2 film
and the X axis at 1240/l. [d] The oxidation potentials of the dyes were
measured in CH2Cl2 solutions with tetrabutylammonium hexafluorophos-
phate (TBAPF6, 0.1m) as electrolyte, ferrocene/ferrocenium (Fc/Fc+) as an
internal reference and converted to NHE by adding 440 mV. [e] ELUMO
Table 2. Photovoltaic performances[a] of the DSSCs sensitized by CM201–
CM204.
(versus NHE) was calculated according to ELUMO =EoxÀE0–0
.
Dye[b]
Jsc [mAcmÀ2
]
Voc [mV]
FF [%]
h [%]
CM201
CM202
CM203
CM204
11.7Æ0.2
12.4Æ0.1
12.2Æ0.1
13.3Æ0.2
580Æ5
588Æ4
596Æ3
606Æ4
70.1Æ1.2
68.7Æ1.0
68.9Æ0.5
69.1Æ0.8
4.7Æ0.1
5.0Æ0.2
5.0Æ0.1
5.5Æ0.1
dyes adsorbed on the surfaces of the TiO2 films. It can be seen
that upon anchoring the dyes to the TiO2 surface, the absorp-
tion spectra red shifted around 5–14 nm and became broader
than those in solution.
[a] Performances of DSSCs were measured by using a 0.159 cm2 working
area under 100 mWcmÀ2. [b] The concentration of the dye bath is 2ꢀ
The cyclic voltammograms (CV) of the four dyes show quasi-
reversible couples. The HOMO levels of CM201, CM202, CM203,
and CM204 corresponding to their first redox potentials are
10À4
m
in CH2Cl2. Electrolyte: 0.6m 1,2-dimethyl-3-propylimidazolium
iodide (DMPII), 0.3m LiI, 0.02m Sx2À, 0.02m S in acetonitrile (AN).
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CM204, was just caused by the alkyl chain and was not related
to CDCA).
Electrochemical impedance spectroscopy analysis of devices
sensitized by CM201–CM204
Electrochemical Impedance Spectroscopy (EIS) analysis was
used to study the interfacial charge transfer processes in
DSSCs. The measurements were scanned from 106 to 10À2 Hz
at room temperature in dark condition with an applied bias
voltage of À0.70 V. Nyquist plots and Bode phase plots for the
devices sensitized by CM201–CM204 are shown in Figure 6.
Figure 4. J–V curves of DSSCs sensitized by CM201–CM204.
Figure 5. IPCE spectra of DSSCs sensitized by CM201–CM204.
rent-voltage (J–V) curves and the incident photon-to-current
conversion efficiencies (IPCE). Under standard global AM 1.5G
solar conditions, the devices using dye CM204 exhibited the
best efficiency giving a short-circuit photocurrent density (Jsc)
of 13.3 mAcmÀ2, an open- circuit voltage (Voc) of 606 mV, and
a fill factor (FF) of 69.1%, corresponding to an overall conver-
sion efficiency (h) of 5.5%. According to the IPCE spectra, the
integral current density is 13.7 mAcmÀ2, which considering the
error is in good agreement with the measured photocurrent
density. The devices sensitized by the dyes CM201, CM202, and
CM203 showed efficiencies in the range of 4.7–5.0% (see
Table 2). Kroeze et al.[22] reported that, in the presence of alkyl
substitution in the dye structure, Voc can be improved owing
to the inhibition of charge recombination resulting from the
blocking effect of the substituent on the TiO2 surface. There-
fore, we introduced the n-hexyl chains into the dyes CM203
and CM204. From the test results (Table 2), we indeed ob-
served that the Voc of the device sensitized by CM203 is higher
(16 mV) than that of the device sensitized by CM201, yielding
a higher efficiency for CM203. A similar result was found in the
devices sensitized by CM202 and CM204. The Voc of the device
sensitized by CM204 was 18 mV higher than that of the device
sensitized by CM202. These results indicate that the charge re-
combination was effectively suppressed by the blocking effect
of the long alkyl chain.(CDCA was added in every case, so the
Voc difference between CM201 and CM203, or CM202 and
Figure 6. a) Nyquist plots and b) Bode phase plots of DSSCs sensitized by
CM201–CM204.
Some important parameters can be obtained by fitting the EIS
spectra to an electrochemical model.[23] RS, Rrec, and RCE repre-
sent the series resistance and the charge-transfer resistances at
the dye/TiO2/electrolyte interface (recombination resistance)
and the counter electrode (CE), respectively. From the EIS
measurements, the electron lifetime (te) expressing the elec-
tron recombination between the electrolyte and TiO2 may be
extracted from the angular frequency (wrec) at the mid frequen-
cy peak in the Bode phase plots using the relation te =1/wrec.
The diameters of the medium-frequency semicircle, corre-
sponding to Rrec, decrease in the order CM204 (37.8 W)>
CM203 (32.6 W)>CM202 (26.7 W)>CM201 (20.1 W), implying
that the recombination reaction between the conduction band
electrons in TiO2 film and electrolyte is better inhibited for
CM203 and CM204 than for CM201 and CM202 because of the
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introduction of n-hexyl. As a consequence, an improvement in
Voc was achieved. The electron recombination lifetimes (t) cal-
culated from the angular frequency (wmin) at the intermediate-
frequency peak in the Bode phase plots (Figure 6b) using t=
1/wmin also indicated the trend (see Figure 6b and Table 3).
Table 3. Parameters obtained by fitting the EIS spectra to an electro-
chemical model.
Dye
Rs
[W]
Rrec
[W]
Rce
[W]
Lifetimes
[s]
CM201
CM202
CM203
CM204
19.4
19.3
19.5
19.5
20.1
26.7
32.6
37.8
3.2
3.2
4.0
4.2
0.28
0.45
0.46
0.47
Figure 8. Absorption spectra of CMR103, CM203, HY113, and co-adsorption
on TiO2 films.
The J–V curves of solar cells with CMR103, CM203, HY113,
and the co-sensitization of three dyes are shown in Figure 9.
The corresponding photovoltaic parameters of these solar cells
Photophysical, photocurrent–voltage characteristics of co-
sensitized DSSCs
As mentioned above, in spite of the high e of organic dyes
CM201–CM204, the narrow spectrum response (500–650 nm)
limits the light absorption to the visible region leading to
lower DSSC efficiencies compared to the ruthenium complex
N719. So the other two metal-free organic dyes CMR103 and
HY113 reported by our group earlier[24,25] were selected as co-
sensitizers with CM203 to enhance the light harvesting effi-
ciency in DSSC applications. The structures of CMR103 and
HY113 are shown in Figure 7. The absorption spectrum of
CMR103, CM203, HY113, and the co-absorption of the three
dyes on TiO2 films are shown in Figure 8. Dye CMR103 has
a strong absorption in the range of 400–500 nm, and HY113
shows intense absorption in the NIR region (600–700 nm). The
co-sensitized TiO2 film exhibits three absorption peaks and
broad absorption in 400–700 nm regions.
Figure 9. J–V curves and photos of DSSCs sensitized by CMR103, CM203,
HY113, and co-sensitization.
are presented in Table 4. The power conversion efficiencies (at
AM 1.5G illumination) of devices based on individual CMR103,
CM203, and HY113 were 3.1, 5.0, and 4.4%, respectively. Impor-
tantly, the co-sensitized solar cell showed much higher photo-
Table 4. Photovoltaic performances[a] of DSSCs sensitized by TQ1, M203,
HY113, and co-sensitization.
Dye[b]
Jsc
Voc
[mV]
FF
[%]
h
[mAcmÀ2
]
[%]
CMR103
CM203
HY113
Co1
Co2
Co3
6.6Æ0.2
12.2Æ0.1
11.3Æ0.1
18.3Æ0.3
20.1Æ0.2
19.1Æ0.2
660Æ3
596Æ4
570Æ5
595Æ5
597Æ5
595Æ4
71.1Æ1.0
68.9Æ0.6
69.3Æ0.5
69.1Æ0.5
68.3Æ1.0
68.7Æ0.6
3.1Æ0.2
5.0Æ0.2
4.4Æ0.2
7.5Æ0.2
8.2Æ0.2
7.8Æ0.2
[a] Performances of the DSSCs were measured by using a 0.159 cm2 work-
ing area under 100 mWcmÀ2 (AM 1.5G) condition. Electrolyte: 0.6m
DMPII, 0.3m LiI,0.02m Sx2À,0.02m S. [b] The concentration of the dye bath
is 2ꢀ10À4 m in CH2Cl2.
Figure 7. Structures of the dyes CMR103 and HY113.
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current and efficiency than those of the individual dye-sensi-
tized cells. The absorption and desorption of the sensitizer is
a balance during the sensitization. To obtain a high Jsc, it is
necessary to make full use of the NIR region. In our experi-
ment, we found that the dye HY113 is easily desorbed during
the sensitization of other dyes. Correspondingly, the photocur-
rent depends on the soaking sequence of the three dyes
CMR103, CM203, and HY113. For the co-sensitized device Co2,
a TiO2 film was firstly dipped in the CMR103 dye solution
(0.5 h), then dipped in the CM203 dye solution (0.5 h), followed
by dipping in the HY113 dye solution (4 h). The resulting pho-
tovoltaic parameters Jsc, Voc, FF, and
h were 597 mV,
20.1 mAcmÀ2, 68.3%, and 8.2%, respectively. According to the
IPCE spectra, the integral current density was 19.8 mAcmÀ2
(see Figure 10), which considering the error matches well with
the measured photocurrent density. These results show a supe-
rior photovoltaic performance for the co-sensitization of three
organic dyes compared to that of the individual dye-sensitized
solar cells.
Figure 11. IPCE spectra of DSSCs sensitized by CMR103, CM203, HY113, and
co-sensitization (photo of DSSCs inserted). The devices Co1, Co2, and Co3
were sensitized with different soaking sequences of the three dyes CMR103,
CM203, and HY113.
CMR103, CM203, and HY113 dyes have peak efficiencies of 94
(460 nm), 91 (560 nm), and 90% (660–680 nm), respectively.
The IPCE spectrum of the solar cell based on co-sensitization
by CMR103, CM203, and HY113 dyes exhibits an impressive
panchromatic response from 400 to 700 nm. This shows that
the three organic dyes were efficiently co-adsorbed on the sur-
face of TiO2. Co-sensitization of the TiO2 electrodes markedly
increased the current density as reported in Table 4 and ex-
tended the spectral response to the whole visible domain and
consequently enhanced the photocurrent performance.
Figure 10. IPCE and integral current density of the co-sensitized device Co2.
The IPCE spectra of devices sensitized by CMR103, CM203,
HY113, and co-sensitization were plotted as a function of exci-
tation wavelength and are presented in Figure 10. From the
experiments, it was found that the IPCE of the co-sensitized
devices depended greatly on the dipping sequence and time
of the electrode in different dye solutions. The largest increase
in the IPCE region was observed in the region in which the
final dye was deposited. The co-sensitized device Co1 was fab-
ricated by the following steps: co-sensitization of TiO2 films
was first done by dipping the in the HY113 dye solution (4 h),
then by dipping in the CM203 dye solution (1 h), followed by
dipping in the CMR103 dye solution (1 h). The co-sensitized
device Co3 was sensitized in the following sequence: co-sensi-
tization of TiO2 films was first achieved by dipping in the
CM203 dye solution (1 h), then by dipping in the CMR103 dye
solution (1 h), followed by dipping in the HY113 dye solution
(4 h). For the Co1 device, the IPCE value in the NIR region was
much lower but much higher in 400–550 nm region than the
other devices. The HY113 sensitized Co2 device showed the
highest IPCE value in the NIR region and the highest Jsc. The
IPCE spectrum shows that solar cells sensitized by individual
Electrochemical impedance spectroscopy analysis of co-sen-
sitized DSSCs
From the EIS spectra of DSSCs sensitized by CMR103, CM203,
HY113, and co-sensitization (see Figure 12), we can see that
the diameters of the medium frequency semicircle, corre-
sponding to Rrec, vary considerably. The Rrec values are 39.1,
32.6, and 21.1 W for DSSCs sensitized by CMR103, CM203, and
HY113, respectively. For the co-sensitized device Co2, Rrec was
32.7 W. The Rrec of DSSCs decrease in the order of CMR103>
Co2>CM203>HY113, corresponding to the decrease of volt-
age. The recombination reaction between the conduction-
band electron in TiO2 films and electrolyte is better inhibited
for the co-sensitized solar cells compared with the device sen-
sitized by CM203 and HY113. The Bode phase plots showed
the same trends.
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Experimental Section
The dyes were synthesized by the stepwise synthetic protocol
shown in Schemes 1–3 according to previous literature.[24–29]
1H NMR spectra were recorded (VARIAN INOVA 400 MHz spectro-
meter, USA) using tetramethylsilane as standard. MS data were ob-
tained by using GCT CA156 (UK), HP1100 LC/MSD (USA), and LC/Q-
TOF MS (UK). Absorption spectra were recorded on a HP8453
(USA). Electrochemical redox potentials were obtained by means of
cyclic voltammetry (CV) on an electrochemistry workstation
(BAS100B, USA). The working electrode was a glass carbon disk,
the auxiliary electrode was a Pt wire, and Ag/Ag+ was used as the
reference electrode. TBAPF6 was used as a supporting electrolyte
in AN. The Fc/Fc+ redox couple was used as an internal reference.
The potentials versus NHE were calibrated by adding 440 mV to
the potentials versus Fc/Fc+. EIS was measured with an impe-
dance/gain-phase analyzer (PARSTAT 2273, USA) under dark condi-
tions, with a forward bias of À0.7 V.
The DSSCs sensitized by dyes CM201–CM204 were fabricated ac-
cording to previous literature with modifications.[24] A layer of 2 mm
TiO2 (13 nm paste, Heptachroma, China) was coated on F-doped
tin oxide conducting glass (TEC15, 15 W/square, Pilkington, USA)
by screen printing and then dried for 5 min at 1258C. This proce-
dure was repeated six times (12 mm) and finally the electrode was
coated with a layer (4 mm) of TiO2 paste (DHS-SLP1, Heptachroma,
China) as the scattering layer. The double-layer TiO2 electrodes
(area: 6ꢀ6 mm) were heated under an air flow (5208, 30 min) and
then cooled to room temperature. The sintered film was further
treated with TiCl4 aqueous solution (40mm, 708C, 30 min), then
washed with water, and annealed (5208C, 30 min). After the film
was cooled to room temperature, it was immersed into a dye bath
Figure 12. a) Nyquist plots and b) Bode phase plots of DSSCs sensitized by
CMR103, CM203, HY113, and co-sensitized device Co2.
Conclusions
We designed, synthesized, and systematically investi-
gated four cyanine dyes CM201–CM204. Among the
four cyanine dyes, the devices sensitized by CM204
generated the highest efficiencies of 5.5%, with
a short-circuit photocurrent density of 13.3 mAcmÀ2
,
an open-circuit voltage of 606 mV, and a fill factor of
69.1%. All of the four dyes CM201–CM204 had very
high absorption extinction coefficients and a strong
absorption within a relatively narrow spectrum range
(500–650 nm). Upon exploration of CM203 as co-sen-
sitizer in combination with two other organic dyes,
CMR103 and HY113, a considerably improved effi-
ciency of 8.2% was achieved (Jsc =20.1 mAcmÀ2,
Voc =597 mV, and FF=68.3%). This is much higher
than that of an individual dye-sensitized solar cell.
More importantly, the co-sensitized devices having
complementary spectral responses provided a re-
markable increase in the photocurrent and hence en-
hanced the power conversion efficiency. The IPCE
spectra of cells based on co-sensitization showed
a panchromatic response with >80% efficiency over
the entire visible spectral region (400–700 nm). Using
this strategy, we can conveniently utilize a wide
region of the solar spectrum by co-sensitizing dyes
that have complementary spectral responses.
Scheme 1. Synthetic routes for the electron donor: a) acetone, p-TsOH, cyclohexane, 80–
908C, 8–10 h; b) 2-octanone, p-TsOH, toluene, 1258C, 8–10 h; c) Raney-Ni, H2, 1 MPa,
1208C; d) (CH3)2SO4, benzene, 858C, 24 h; e) dimethylformamide/POCl3, 558C, 6 h.
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Chemicals (KF0805), and the Pro-
gram for Innovative Research
Team of Liaoning Province (Grant
No. LS2010042).
Keywords: cyanines
·
dyes/
pigments · sensitizers · solar
cells
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858C, 24 h.
[2] L. Li, Y. Hao, X. Yang, J. Zhao, H.
Tian, C. Teng, A. Hagfeldt, L. Sun,
ChemSusChem 2011, 4, 609–612.
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We gratefully acknowledge the financial support of this work
from China Natural Science Foundation (Grant 21076039, Grant
20120102036), the National Basic Research Program of China
(Grant No. 2009CB220009), the Ministry of Science and Technolo-
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