Dye-sensitized solar cells based on a donor-acceptor system with a pyridine cation as an electron-withdrawing anchoring group

Article abstract of DOI:10.1002/chem.201200826

New hemicyanine dyes (CM101, CM102, CM103, and CM104) in which tetrahydroquinoline derivatives are used as electron donors and N-(carboxymethyl)-pyridinium is used as an electron acceptor and anchoring group were designed and synthesized for dye-sensitized solar cells (DSSCs). Compared with corresponding dyes that have cyanoacetic acid as the acceptor, N-(carboxymethyl)-pyridinium has a stronger electron-withdrawing ability, which causes the absorption maximum of dyes to be redshifted. The photovoltaic performance of the DSSCs based on dyes CM101-CM104 markedly depends on the molecular structures of the dyes in terms of the n-hexyl chains and methoxyl. The device sensitized by dye CM104 achieved the best conversion efficiency of 7.0 % (J_sc=13.4 mA cm^-2, V_oc=704 mV, FF=74.8 %) under AM 1.5 irradiation (100 mW cm^-2). In contrast, the device sensitized by reference dye CMR104 with the same donor but the cyanoacetic acid as the acceptor gave an efficiency of 3.4 % (J_sc=6.2 mA cm ^-2, V_oc=730 mV, FF=74.8 %). Under the same conditions, the cell fabricated with N719 sensitized porous TiO₂ exhibited an efficiency of 7.9 % (J_sc=15.4 mA cm^-2, V_oc=723 mV, FF=72.3 %). The dyes CM101-CM104 show a broader spectral response compared with the reference dyes CMR101-CMR104 and have high IPCE exceeding 90 % from 450 to 580 nm. Considering the reflection of sunlight, the photoelectric conversion efficiency could be almost 100 % during this region.

Full text of DOI:10.1002/chem.201200826

DOI: 10.1002/chem.201200826
Dye-Sensitized Solar Cells Based on a Donor–Acceptor System with a
Pyridine Cation as an Electron-Withdrawing Anchoring Group
Ming Cheng,[a] Xichuan Yang,*[a] Jiajia Li,[a] Cheng Chen,[a] Jianghua Zhao,[a]
Yu Wang,[a] and Licheng Sun*[a, b]
Abstract: New hemicyanine dyes
(CM101, CM102, CM103, and CM104)
in which tetrahydroquinoline deriva-
tives are used as electron donors and
N-(carboxymethyl)-pyridinium is used
as an electron acceptor and anchoring
group were designed and synthesized
for dye-sensitized solar cells (DSSCs).
Compared with corresponding dyes
that have cyanoacetic acid as the ac-
ceptor, N-(carboxymethyl)-pyridinium
markedly depends on the molecular
structures of the dyes in terms of the n-
hexyl chains and methoxyl. The device
sensitized by dye CM104 achieved the
best conversion efficiency of 7.0%
(Jsc =13.4 mAcmÀ2, Voc =704 mV, FF=
74.8%) under AM 1.5 irradiation
(100 mWcmÀ2). In contrast, the device
sensitized by reference dye CMR104
with the same donor but the cyanoace-
tic acid as the acceptor gave an effi-
ciency of 3.4% (Jsc =6.2 mAcmÀ2, Voc =
730 mV, FF=74.8%). Under the same
conditions, the cell fabricated with
N719 sensitized porous TiO2 exhibited
an
efficiency
of
7.9%
(Jsc =
FF=
15.4 mAcmÀ2,
Voc =723 mV,
72.3%). The dyes CM101–CM104
show a broader spectral response com-
pared with the reference dyes
CMR101–CMR104 and have high
IPCE exceeding 90% from 450 to
580 nm. Considering the reflection of
sunlight, the photoelectric conversion
efficiency could be almost 100%
during this region.
has
a stronger electron-withdrawing
ability, which causes the absorption
maximum of dyes to be redshifted. The
photovoltaic performance of the
DSSCs based on dyes CM101–CM104
Keywords: cyanoacetic acid · do-
nor–acceptor systems
· dyes/pig-
ments · pyridine cation · sensitizers
Introduction
nyl)amino]phenyl,[17–20] and triphenylamine,[21–29] units as
donors, and cyanoacetic acid as the acceptor, which show
promising efficiencies ranging from 5 to 10%. Cyanine dyes
and hemicyanine dyes have high molar extinction coeffi-
cients (about 105 mÀ1 cmÀ1), capture the sunlight well, and
therefore have attracted extensive attention. But the conver-
sion efficiency and the incident photon-to-current conver-
sion efficiency (IPCE) of the reported cyanine dyes and
hemicyanine dyes are not very high. Herein, we report the
design, synthesis of four hemicyanine dyes CM101–CM104
(see Figure 1), in which tetrahydroquinoline derivatives are
used as a donor, and N-(carboxymethyl)-pyridinium is
adopted as the acceptor and anchoring group. For compari-
son, we also synthesized four dyes CMR101–CMR104 (see
Figure 1) with the same donor, but the cyanoacetic acid as
acceptor and anchoring group. The dyes CM101–CM104 ex-
hibited promising efficiencies ranging from 5.9 to 7.0%
through a unidirectional flow of electrons on excitation.
Meanwhile, all these dyes CM101–CM104 show high IPCE
exceeding 90% at 450–580 nm. In contrast, under the same
conditions, the DSSCs sensitized by the reference dyes
CMR101–CMR104 shown efficiencies in the range of 2.9–
3.5%. The devices sensitized by dyes CM101–CM104 show
higher efficiencies than that of the devices sensitized by
CMR101–CMR104, of particular importance is the obvious
increase in short-circuit photocurrent density (Jsc). The sig-
nificant increase in Jsc is mainly attributed to the wider spec-
tra response of the dyes CM101–CM104.
Dye-sensitized solar cells (DSSCs) are regarded as the next
generation of low-cost solar cells, and significant progress
has been made since Grꢀtzel and co-workers reported good
solar cell performances for DSSCs based on a Ru-complex
dye in 1991.[1,2] So far, these devices have achieved power
conversion efficiencies of over 12%.[3] However, the use of
precious metal Ru increases the cost of the device. Thus,
many scientists have committed to develop effective metal-
free organic dyes, and impressive photovoltaic performances
have been reported on various organic dyes that contain
coumarin,[4–6] indoline,[7,8] cyanine,[9,10] phenothiazine,[11,12]
tetrahydroquinoline,[13,14] carbazole[15,16] [bis(dimethylfluore-
[a] Dr. M. Cheng, Prof. X. Yang, Dr. J. Li, Dr. C. Chen, Dr. J. Zhao,
Y. Wang, 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
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), Teknikringen 30
10044 Stockholm (Sweden)
Supporting information for this article is available on the WWW
under http://dx.doi.org/10.1002/chem.201200826.
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FULL PAPER
Figure 3. Absorption spectra of CM101, CM102, CM103, CM104, and
CMR104 on TiO2 films.
Table 1. UV/Vis absorption and electrochemical properties of the dyes
CM101, CM102, CM103, CM104, and CMR104.
[a]
[b]
Dye
lmax in
e
lmax
E0À0
Eox
ELUMO
CH2Cl2
[nm]
[mÀ1 cmÀ1
]
on
[V][c]
[V][d]
[V][e]
TiO2
[nm]
(vs.
NHE)
(vs.
NHE)
ACHTUNGTRENNUNG(vs.
NHE]
CM101
CM102
CM103
CM104
503
514
504
521
49000
45900
47300
40400
23800
511
525
521
532
442
1.98
1.93
1.91
1.87
2.42
1.00
0.80
0.87
0.73
0.82
À0.98
À1.13
À1.04
À1.14
À1.60
À
Figure 1. Structures of sensitizers CM101, CM102, CM103, CM104, and
reference sensitizers CMR101, CMR102, CMR103, and CMR104.
CMR104 435
[a] Absorption spectra were measured in CH2Cl2 solution (2ꢂ10 5 m).
[b] Absorption spectra on TiO2 film were measured with dye-loaded
TiO2 films immerged in CH2Cl2 solutions. [c] E0-0 was determined from
intersection of the tangent of absorption on TiO2 film and the X axis by
1240/l. [d] The oxidation potentials of the dyes were measured in CH2Cl2
solutions with TBAPF6 (0.1m) as electrolyte, ferrocene/ferrocenium (Fc/
Fc+) as an internal reference and converted to NHE by addition of
Results and Discussion
Absorption spectra of the four dyes CM101–CM104 in a di-
luted solution of CH2Cl2 and TiO2 films were shown in
Figure 2 and Figure 3, respectively. To evaluate the viability
of electron transfer from the excited-state of the dyes to the
TiO2 conduction band, cyclic voltammetry (CV) was em-
440 mV. [e] ELUMO was calculated by EoxÀE0À0
.
(e=49000mÀ1 cmÀ1), 514 nm (e=45900mÀ1 cmÀ1), 504 nm
(e=47300mÀ1 cmÀ1) and 521 nm (e=40400mÀ1 cmÀ1), respec-
tively, in a diluted solution of CH2Cl2. However, the refer-
ence dyes CMR101–CMR104 have absorptions with maxima
at 411 nm (e=22200mÀ1 cmÀ1), 422 nm (e=32300mÀ1 cmÀ1),
424 nm (e=23900mÀ1 cmÀ1) and 435 nm (e=23800mÀ1 cmÀ1)
in a diluted solution of CH2Cl2, respectively (see the Sup-
porting Information, Figure S2, Figure S3, and Table S1).
The molar extinction coefficients of dyes CM101–CM104
are obviously higher than that of reference dyes CMR101–
CMR104, indicating that the dyes CM101–CM104 have a
better light-harvesting ability. Also, due to the stronger elec-
tron-withdrawing ability of the N-(carboxymethyl)-pyridini-
um, the dyes CM101–CM104 are redshifted by about 80–
100 nm compared with the corresponding dyes CMR101–
CMR104 that have cyanoacetic acid as the acceptor. Com-
pared with the spectra in CH2Cl2 solution, the absorption
spectra of the four dyes attached to TiO2 film (see Figure 3)
were broadened significantly and redshifted to a different
extent, which can be attributed to the formation of a J-type
aggregate. The absorption spectrum of CM102 is redshifted
by 11 nm, corresponding to a 0.05 V decrease in energy,
which was attributed to the introduction of methoxyl com-
Figure 2. Absorption spectra of CM101, CM102, CM103, CM104, and
CMR104 in CH2Cl2 (2.0ꢂ10À5 m).
ployed to determine the highest occupied molecular orbital
(HOMO) levels and the lowest unoccupied molecular orbi-
tal (LUMO) levels of the dyes. The characteristic data are
collected in Table 1.
As shown in Figure 2, all of the dyes (CM101–CM104)
have relatively strong absorptions with maxima at 503 nm
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X. Yang, L. Sun et al.
pared with that of CM101. A similar result was also found
between the absorption spectra of CM103 and CM104. The
introduction of methoxyl made the absorption spectrum of
CM104 redshift by 17 nm compared with that of CM103.
Electrochemical tests also proved that the introduction of
methoxyl made the potential of HOMO levels more nega-
tive, about 0.2 V. The lmax of CM104 is the most redshifted
of the four dyes prepared. The main reason is maybe the
synergy effect of long alkyl-chains and the methoxyl group.
The cyclic voltammograms (CV) of the four dyes show
quasi-reversible couples. The HOMO levels of CM101,
CM102, CM103, and CM104 corresponding to their first
redox potential are 1.00, 0.80, 0.87 and 0.73 V versus NHE,
respectively. The potentials are more positive than the po-
tential of triiodide/iodide couple (+0.5 V vs. NHE), which
can lead to fast dye generation.[31] The estimated excited-
state potential corresponding to the LUMO levels of the
dyes CM101–CM104 are À0.98, À1.13, À1.04, and À1.14 V
versus NHE, respectively, which are more negative than the
conduction band level of TiO2 (about À0.5 V vs. NHE).[31a]
Therefore, the energy surplus of the LUMO in four dyes
allow for the addition of the 4-tert-butylpyridine (TBP) in
the electrolyte, which can make the conduction band of
TiO2 more negative and consequently improve the Voc and
total solar energy conversion efficiency.[32] As shown in
Figure 4, the dye CM104 has narrower band-gap compared
Figure 5. Isodensity surface plots of the HOMOÀ1, HOMO, LUMO, and
LUMO+1 of CM103.
are shown in the Supporting Information. All of these dyes
have good charge separation. The HOMO of CM103 is de-
localized over the tetrahydroquinoline unit and the LUMO
of CM103 contains the delocalized p* framework, with a siz-
able electron-density distribution arising from the N-(car-
boxymethyl)-pyridinium.
To suppress the aggregation of dyes, 3a, 7a-dihydroxy-5b-
cholic acid (CDCA; 10 equiv) was used as a co-adsorbent.
The J–V curves and the IPCE spectra of the devices sensi-
tized by dyes CM101, CM102, CM103, and CM104 that
employ an acetonitrile electrolyte containing DMPII (0.6m),
LiI (0.25m), I2 (0.01m), TBAI (0.05m), TBP (0.2m) are
shown in Figure 6 and Figure 7, respectively. The photovol-
Figure 6. J–V curves of the DSSCs sensitized by CM101, CM102, CM103,
CM104, and CMR104.
Figure 4. The comparisons of HOMO and LUMO levels of CM104 and
CMR104.
with the reference dye CMR104 and the LUMO level of
CM104 are more positive than that of CMR104 , which can
attributed to the much stronger electron-withdrawing ability.
Similar results can also be identified between other CM
series dyes and their corresponding reference dyes.
To understand the geometrical configuration and electron
distributions, molecular orbital calculations of dyes CM101–
CM104 were performed with the TD-DFT on B3LYP/6-
31G(+d) and the isodensity surface plots of CM103 are
shown in Figure 5. The isodensity surface plots of other dyes
Figure 7. IPCE spectra of the DSSCs sensitized by CM101, CM102,
CM103, CM104, and CMR104.
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Dye-Sensitized Solar Cells
FULL PAPER
Table 2. Photovoltaic performances[a] of DSSCs sensitized by CM101,
CM102, CM103, CM104, CMR104 and N719.
suppressed by the blocking effect, due to the combination of
the long alkyl-chain unit and CDCA. This is also supported
by our preliminary electron-lifetime studies, which are pre-
sented in Figure 9. Comparing the electron lifetimes as a
function of Voc, DSSCs based on CM104 showed significant-
Dye
Jsc
[mAcmÀ2
Voc
[mV]
FF
[%]
h
G
]
[%]
CM101[b]
CM102[b]
CM103[b]
CM104[b]
CMR104[b]
N719[c]
12.2
13.6
12.7
13.4
6.2
675
682
695
704
730
720
74.8
73.3
73.1
74.8
74.8
71.3
5.9
6.8
6.4
7.0
3.4
7.9
15.4
[a] Performances of DSSCs were measured with 0.159 cm2 working area
under 100 mWcmÀ2 (AM 1.5) conditions. [b] The concentration of dye
bath is 2ꢂ10 À4 m in CH2Cl2. Electrolyte: DMPII (0.6m), LiI (0.25m), I2
(0.01m), TBAI (0.05m), and TBP (0.2m) in CH3CN. [c] The concentration
of the dye bath is 2ꢂ10À4 m in EtOH. Electrolyte: 0.6m DMPII, 0.063m
LiI, 0.03m I2, 0.28m TBP and 0.05m GuSCN CH3CN.
taic performance data were collected in Table 2. The per-
formance of the devices sensitized by dyes CMR101–
CMR104 are shown in the Supporting Information; Fig-
ure S4, Figure S5, and Table S2.
Figure 9. Electron lifetime as a function of extracted charge under open-
circuit conditions for DSSCs based on CM102, CM103, CM104, and
CMR104, respectively.
Under standard global AM 1.5 solar conditions, the
CM104-sensitized cells exhibited the best efficiencies, giving
a short-circuit photocurrent density (Jsc) of 13.4 mAcmÀ2, an
open-circuit voltage (Voc) of 704 mV, and a fill factor (FF) of
74.8%, corresponding to an overall conversion (h) of 7.0%.
According to the IPCE spectra, the integral current density
is 13.7 mAcmÀ2 (see Figure 8),[33] which is in good agree-
ly longer electron lifetimes compared with CM102. This pro-
vides support for the long alkyl-chains introduced in CM104
preventing electrons in TiO2 from recombining with redox
species yielding a high Voc. The Jsc of the devices sensitized
by CM102 and CM104 are much higher than that of the de-
vices sensitized by CM101 and CM103 and this is mainly at-
tributed to the introduction of methoxyl. The introduction
of methoxyl makes the HOMO and LUMO of dyes more
negative and increases the energy surplus for efficient elec-
tron injection. The devices sensitized by dyes CM101–
CM104 show much higher Jsc and efficiencies than that of
the devices sensitized by CMR101–CMR104 (see Figure 5,
Table 2, and the Supporting Information; Figure S4 and
Table S2). The significant increase in Jsc is mainly attributed
to the wider spectra response of the dyes CM101–CM104
compared with that of CMR101–CMR104 (see Figure 6 and
the Supporting Information; Figure S5). However, the cells
fabricated with dyes CM101– CM104 show lower Voc than
that of the cells fabricated with dyes CMR101–CMR104,
which can mainly attributed to the shorter electron lifetimes
of CM series dyes compared with the CMR series dyes (see
Figure 9).
Figure 8. IPCE and integral current density of the devices sensitized by
dyes CM104 and CMR104.
ment with the measured photocurrent density, considering
the error. The devices sensitized by the dyes CM101,
CM102, and CM103 showed efficiencies in the range of 5.9–
6.8% (see Table 2). From the test results (Table 2), we ob-
served that the efficiencies of the devices sensitized by
CM103 are higher than that of the devices sensitized by
CM101. Of particular importance is the 20 mV increase in
Voc of the devices sensitized by CM103. We also found the
similar results between the devices sensitized by CM102 and
CM104; the Voc of the devices sensitized by CM104 is
22 mV higher than that of the device sensitized by CM102.
These results indicate that the charge recombination was
From the IPCE spectra (Figure 7) we can see that the de-
vices sensitized by the four dyes showed very high plateau
of over 90% from 450–580 nm. Considering the light-reflect-
ing and absorption loss by the conducting glass, the maxi-
mum efficiency for absorbed photon-to-collected electron
conversion efficiency (APCE) is almost 100%, suggesting a
very high charge collection yield. The increased IPCE
values of the devices sensitized by CM102 and CM104 rela-
tive to that of the devices sensitized by CM101 and CM103
are attributed to the introduction of the methoxyl group.
Compared with the IPCE of reference dyes CMR101–
CMR104, the dyes CM101–CM104 show broader spectra re-
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X. Yang, L. Sun et al.
sponse (see Figure 7, Figure 8 and the Supporting Informa-
tion; Figure S5).
Conclusion
Electrochemical impedance spectroscopy (EIS) analysis
was used to study the interfacial charge transfer processes in
DSSCs sensitized by CM101, CM102, CM103, and CM104
and they were scanned from 10À2 to 106 Hz at room temper-
ature in dark condition (Figure 10): Nyquist plots (a) and
Four hemicyanine sensitizers (CM101–CM104), in which tet-
rahydroquinoline derivatives were used as the donor and N-
(carboxymethyl)-pyridinium were used as the acceptor, were
designed, synthesized, and applied to DSSCs. With the intro-
duction of long alkyl chain and methoxyl, the devices sensi-
tized by dyes CM104 exhibits the best efficiency of 7.0%. In
comparison, among the reference dyes, the dye CMR104 as
sensitizer got the best efficiency of 3.4%. The photovoltaic
performance of the DSSCs based on dyes CM101–CM104
markedly depends on the molecular structures of the dyes in
terms of the n-hexyl chains and methoxyl. The introduction
of long alkyl chain suppresses the charge recombination so
improves the Voc. The introduction of methoxyl in the donor
part raises the HOMO levels and LUMO levels of sensitiz-
ers, and enhances the drive force to inject electrons to the
conduct band of TiO2, so leading to higher Jsc values. Com-
pared with the devices sensitized by dyes CMR101–
CMR104 with the cyanoacetic acid as acceptor and anchor-
ing group, the devices fabricated with dyes CM101–CM104
show wider spectra response and give obvious higher Jsc.
Further improvement of the dye structures based on CM104
by molecular engineering aiming for even better perform-
ance of DSSCs and the stability is in progress.
Experimental Section
The structures of the dyes CM101, CM102, CM103, and CM104 are
shown in Figure 1. These dyes were synthesized by a stepwise synthetic
protocol, shown in Scheme 1, Scheme 2, and Scheme 3. The synthesis of
dyes CMR101–CMR104 are shown in Figure S1 (the Supporting Informa-
tion). The detailed procedures for the syntheses of dye molecules are de-
scribed in the Supporting Information based on several references.[12,13]
1H NMR spectra were recorded on a VARIAN INOVA 400 MHz spec-
trometer (USA) with the chemical shifts by using TMS as standard. MS
data were obtained with GCT CA156 (UK), HP1100 LC/MSD (USA),
and LC/Q-TOF MS (UK). The absorption spectra were recorded on
HP8453 (USA). Electrochemical redox potentials were obtained by
cyclic voltammetry (CV) on electrochemistry workstation (BAS100B,
USA). Electrochemical impedance spectroscopy (EIS) was measured
with an impedance/gain-phase analyzer (PARSTAT 2273, USA) under
dark condition, with forward bias À0.7 V.
Figure 10. Electrochemical impedance spectra (EIS) of the CM101–
CM104-sensitized DSSCs.
bode phase plots (b). The bias voltage is À0.7 V. The alter-
nate current (AC) amplitude was set at 10 mV. The electron
recombination lifetimes (t) were calculated from the angu-
lar frequency (wmin) at the intermediate-frequency peak in
bode phase plot using t=1/wmin. The electron recombination
lifetimes of DSSCs sensitized by CM101, CM102, CM103,
and CM104 are 26.3, 27.4, 32.4, and 33.8 ms, respectively,
and decreased in the order of CM104>CM103>CM102>
CM101, indicating the charge recombination was suppressed
because of the introduction of long alkyl chain. From the
Nyquist plots we can see that the diameter of the medium
frequency semicircle, corresponding to the recombination
resistance (Rrec), also decreased in the order of CM104>
CM103> CM102> CM101. For the devices sensitized by
CM101, CM102, CM103 and CM104, the Rrec values are
17.4, 18.1, 21.1and 22.5 WcmÀ2, respectively. Corresponding-
ly, the devices sensitized by CM104 achieve the highest Voc.
The DSSCs sensitized by CM101–CM104 were fabricated according to a
previous literature procedure.[30] A layer of 2 mm TiO2 (13 nm paste, Hep-
tachroma, China) was coated on the F-doped tin oxide conducting glass
(TEC15, 15 W/square, Pilkington, USA) by screen printing and then
dried for 5 min at 1258C. This procedure was repeated 6 times (12 mm)
and finally coated by a layer (4 mm) of TiO2 paste (DHS-SLP1, Hepta-
AHCTUNTGREGNcNUN hroma, China) as the scattering layer. The double-layer TiO2 electrodes
(area: 6ꢂ6 mm) were heated under an air flow at 5208C for 30 min, and
then cooled to room temperature. The sintered film was further treated
with 40 mm TiCl4 aqueous solution at 708C for 30 min, then washed with
water, and annealed at 5208C for 30 min. After the film was cooled to
room temperature, it was immersed into a 2ꢂ10À4 m dye bath. The elec-
trode was then rinsed and dried with EtOH. The hermetically sealed
cells were fabricated by assembling the dye-loaded film as the working
electrode and Pt-coated conducting glass as the counter electrode sepa-
rated with a hot-melt surlyn 1702 film (25 mm, Dupont).
The photocurrent–voltage (J–V) properties were measured under AM 1.5
irradiation (100 mWcmÀ2) (16S-002, Solar Light Co. Ltd., USA). The in-
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Dye-Sensitized Solar Cells
FULL PAPER
Scheme 1. Synthetic routes of the donor: a) acetone, pTsOH, cyclohexane, 80–908C, 8–10 h; b) 2-octanone, pTsOH,toluene, 1258C,8–10 h; c) Raney-Ni,
H2, 1 MPa, 1208C; d) (CH3)2SO4, benzene, 858C, 24 h; e) DMF/POCl3, 558C, 6 h.
Acknowledgements
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),
Scheme 2. Synthetic routes of the acceptor part.
the Ministry of Science and Technology (MOST) (Grant
2001CCA02500), the Swedish Energy Agency, K & A Wallenberg Foun-
dation, and the State Key Laboratory of Fine Chemicals (KF0805), the
cident light intensity was 100 mWcmÀ2 calibrated with a standard Si solar
Program for Innovative Research Team of Liaoning Province (Grant No.
cell. The working areas of the cells were masked to 0.159 cm2. The date
LS2010042).
was collected by an electrochemical workstation (LK9805, Lanlike Co.
Ltd., China). The measurement of the incident photon-to-current conver-
sion efficiency (IPCE) was performed by a Hypermono-light (SM-25,
Jasco Co. Ltd., Japan).
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Received: March 12, 2012
Revised: August 14, 2012
Published online: October 18, 2012
16202
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Chem. Eur. J. 2012, 18, 16196 – 16202