Benzotriazole-bridged sensitizers containing a furan moiety for dye-sensitized solar cells with high open-circuit voltage performance

Article abstract of DOI:10.1002/asia.201100967

Two new benzotriazole-bridged sensitizers are designed and synthesized (BTA-I and BTA-II) containing a furan moiety for dye-sensitized solar cells (DSSCs). Two corresponding dyes (BTA-III and BTA-IV) with a thiophene spacer were also synthesized for comparison. All of these dyes performed as sensitizers for DSSCs, and the photovoltaic performance data of these benzotriazole-bridged dyes showed a high open-circuit voltage (V_oc: 804-834 mV). Among the four dyes, DSSCs based on BTA-II, with a furan moiety and branched alkyl chain, showed the highest V_oc (834 mV), a photocurrent density (J _sc) of 12.64 mA cm^-2, and a fill factor (FF) of 0.64, corresponding to an overall conversion efficiency (η) of 6.72 %. Most importantly, long-term stability of the BTA-I-IV-based DSSCs with ionic-liquid electrolytes under 1000 h light-soaking was demonstrated, and BTA-II exhibited better photovoltaic performance of up to 5.06 % power conversion efficiency.

Full text of DOI:10.1002/asia.201100967

FULL PAPERS
DOI: 10.1002/asia.201100967
Benzotriazole-Bridged Sensitizers Containing a Furan Moiety for Dye-
Sensitized Solar Cells with High Open-Circuit Voltage Performance
Jiangyi Mao, Fuling Guo, Weijiang Ying, Wenjun Wu, Jing Li, and Jianli Hua*[a]
Abstract: Two new benzotriazole-
bridged sensitizers are designed and
synthesized (BTA-I and BTA-II) con-
taining a furan moiety for dye-sensi-
tized solar cells (DSSCs). Two corre-
sponding dyes (BTA-III and BTA-IV)
with a thiophene spacer were also syn-
thesized for comparison. All of these
dyes performed as sensitizers for
DSSCs, and the photovoltaic perfor-
mance data of these benzotriazole-
bridged dyes showed a high open-cir-
cuit voltage (Voc: 804–834 mV). Among
the four dyes, DSSCs based on BTA-II,
with a furan moiety and branched alkyl
chain, showed the highest Voc
(834 mV), a photocurrent density (Jsc)
of 12.64 mAcmÀ2, and a fill factor (FF)
of 0.64, corresponding to an overall
conversion efficiency (h) of 6.72%.
Most importantly, long-term stability of
the BTA-I–IV-based DSSCs with ionic-
liquid electrolytes under 1000 h light-
soaking was demonstrated, and BTA-II
exhibited better photovoltaic perfor-
mance of up to 5.06% power conver-
sion efficiency.
Keywords: dyes/pigments · electro-
chemistry
·
electron transfer
·
heterocycles · solar cells
Introduction
Research activities have been focused on creating dyes with
broad light absorption, but no satisfying results have been
achieved to date.[6] Second, the open-circuit voltage (Voc) for
DSSCs based on organic dyes is still lower than that for
ruthenium dyes.[7] Benzotriazole, as a very cheap and com-
mercially available chemical material, has been used in elec-
troplating the surface of purified silver, copper, and zinc. In
recent years, benzotriazole-based p-conjugated polymers
have been widely used in photovoltaic cells because of their
chemical and environmental stability as well as their elec-
tronic tenability.[8] Recently, a fluorine-substituted benzotria-
zole conjugated polymer with a medium band gap yielded
7% efficiency in polymer–fullerene solar cells, which were
designed to possess a high hole mobility.[9] Also, Wang and
co-workers incorporated a benzotriazole moiety attached to
a thiophene into an organic sensitizer for DSSCs and yield-
ed a power conversion efficiency of 8.02% with an open-cir-
cuit voltage of 780 mV.[10] Particularly, benzotriazole is a
close analogue of benzothiadiazole; the lone pair on the ni-
trogen atom is more basic than the lone pairs on sulfur and
is more easily donated into the triazole ring.[9] This differ-
ence causes dyes employing benzotriazole as the p-conjuga-
tion unit to be more electron-rich, which leads to a higher
LUMO energy level.[8] Moreover, pyrimidine, and benzimi-
dazole have been tested as additives in the electrolyte for
the sake of increasing Voc, so the alkyl-containing benzotria-
zole group can be expected to improve Voc.[10] Therefore,
benzotriazole-based p-conjugated organic sensitizers have
stronger electron injection ability than their benzothiadia-
zole-based counterparts, and a high open circuit voltage
may be obtained with them.
Dye-sensitized solar cells (DSSCs) based on organometallic
and metal-free organic sensitizers have attracted considera-
ble attentions since the seminal report by Grꢀtzel and co-
workers.[1] On the one hand, DSSCs based on ruthenium(II)
polypyridyl organometallic complex photosensitizers, such
as N3, N719, and the black dye, have achieved record light-
to-power conversion efficiencies exceeding 12% under AM
1.5 simulated sunlight within the past 20 years.[2] On the
other hand, in view of the high cost associated with the pro-
duction and purification of the ruthenium dyes, metal-free
organic dyes are considered to be an alternative due to their
high molar absorption coefficient, simple synthesis, low cost,
and easy molecular tailoring. A large number of studies
have been devoted to the molecular engineering of organic
chromophores to direct their interaction with the wide-
band-gap semiconductors and to improve the light-harvest-
ing of the DSSCs.[3–5]
For most of the pure organic sensitizers, the donor–
(p conjugation)–acceptor (D-p-A) system is the basic fea-
ture, because it facilitates effective photoinduced intramo-
lecular charge transfer. Compared with the ruthenium(II)
polypyridyl organometallic complexes, organic sensitizers
have some drawbacks for DSSCs. Firstly, organic sensitizers
have poor light response in the NIR (near-infrared) region.
[a] J. Mao, F. Guo, W. Ying, Dr. W. Wu, Dr. J. Li, Prof. J. Hua
Key Laboratory for Advanced Materials
Institute of Fine Chemicals and Department of Chemistry
East China University of Science and Technology
130 Meilong Road, Shanghai 200237 (China)
Fax : (+86)21-64252758
Most of the metal-free organic sensitizers with high effi-
ciency and good stability reported to date rely on thiophene
or thiophene-based heterocycles as the p spacer. This trend
E-mail: jlhua@ecust.edu.cn
982
ꢁ 2012 Wiley-VCH Verlag GmbH & Co. KGaA, Weinheim
Chem. Asian J. 2012, 7, 982 – 991

could be explained by the fact that holes in such dyes were
located on the thiophene moieties. And furan, as oxygen an-
alogue of thiophene, which has a higher oxidation potential,
would be more efficient for the hole location and reinforce
the stability of the dye sensitizers.[11] However, furan has re-
ceived much less attention than the thiophene unit. Recent-
ly, furan units have also been incorporated into some conju-
gated polymers and oligomers as an alternative to thio-
phenes for photovoltaics and have revealed that the optical
and charge-carrier mobility can be comparable to that of
thiophenes.[12] There have been reports showing that the in-
corporation of a furan moiety can somewhat improve poly-
mer solubility and gain high molecular weight.[13] Moreover,
furan can provide more effective conjugation and lower the
energy of the charge-transfer transition because of its small-
er resonance energy (furan 16 kcalmolÀ1, thiophene 29 kcal
molÀ1) in the spacer.[14] Organic sensitizers containing a
furan unit applied in DSSCs have also been reported and
showed relatively high efficiency.[15]
Scheme 1. Molecular structures of the dyes BTA-I–IV.
To decrease dye aggregation
and enhance tolerance towards
water in the electrolyte, a hy-
drophobic alkyl chain (octyl or
2-ethylhexyl) was introduced
À
to modify the N H bond of
the benzotriazole group; the 2-
ethylhexyl group has more
steric hindrance than octyl and
might lead to a better open-cir-
cuit voltage. On the basis of
the
above
consideration,
herein we have designed and
synthesized two new benzo-
triazole-bridged
sensitizers
(BTA-I and BTA-II) contain-
ing a furan moiety for DSSCs.
Scheme 2. Synthesis of the dyes BTA-I–IV.
Two
corresponding
dyes
(BTA-III and BTA-IV) with
thiophene spacers were also synthesized for the purpose of
comparison. Consequently, we expect to introduce benzo-
triazole and furan as p spacer to organic dyes for improving
their photovoltaic performance and long-term stability. Mo-
lecular structures of BTA-I–IV are presented in Scheme 1.
nylboronic acid gave a strong yellowish green compound 3
(or 4). Then Suzuki coupling of 3 (or 4) with 5-formylthio-
phen-2-boronic acid (in the synthesis of BTA-III,IV) or 5-
formylfuran-2-boronic acid (BTA-I,II), respectively, afford-
ed monoaldehyde-substituted precursors 5–8. Finally, com-
pounds 5–8 were treated with cyanoacetic acid under typical
Knoevenagel condensation conditions to obtain the target
dyes BTA-I–IV. All the intermediates and target dyes were
characterized by standard spectroscopic methods. Clearly,
the synthetic process is easy, because all the intermediates
and target compounds are stable and the synthesis method
is very common.
Results and Discussion
Synthesis
The synthetic route to the four dyes BTA-I–IV containing
the benzotriazole moiety is depicted in Scheme 2. The octyl
or 2-ethylhexyl chain attached to the benzotriazole group
can improve the solubility, form a tightly packed insulating
Optical and Electrochemical Properties
À
monolayer blocking the I3 or cations approaching the TiO2,
and enhance the open-circuit voltage. The syntheses of
BTA-I–IV started from compound 1 (in the synthesis of
BTA-I,III) or 2 (BTA-II,IV). Asymmetrical Suzuki coupling
reaction of compound 1 (or 2) with 4-(diphenylamino)phe-
UV/Vis absorption spectra of the four dyes in a diluted solu-
tion of CH2Cl2 are shown in Figure 1a and their absorption
data are listed in Table 1. In the UV/Vis spectra, the dyes
exhibit two major absorption bands, appearing at 300 and
Chem. Asian J. 2012, 7, 982 – 991
ꢁ 2012 Wiley-VCH Verlag GmbH & Co. KGaA, Weinheim
www.chemasianj.org
983

Jianli Hua et al.
FULL PAPERS
450–460 nm. All of the dyes have a relatively broad and
strong absorption, with the maximum absorption at 450,
449, 458, and 454 nm, respectively. The absorption band
around 300 nm was ascribed to the localized aromatic p–p*
transition of triphenylamine, and the maximum absorption
at around 450–460 nm can be attributed to the intramolecu-
lar charge transfer (ICT) between the triphenylamine donor
and the cyanoacetic acid acceptor.[16] As this series of sensi-
tizers contains the same electron donor and acceptor and
similar conjugated bridges, the absorption peaks for BTA-I–
IV are almost the same. It is well known that sunlight at the
wavelength of 475 nm has a maximum radiation energy, so
BTA-I–IV should possess excellent light-harvesting ability
in DSSCs. The corresponding maximum molar extinction co-
efficients of the four dyes are 2.14ꢂ104, 3.33ꢂ104, 3.31ꢂ104,
and 3.96ꢂ104 mÀ1 cmÀ1, respectively. Notably, BTA-IV has a
higher molar extinction coefficient than the other three
dyes, which may be due to the introduction of the thiophene
moiety and the branched alkyl chain can effectively improve
its light-harvesting ability.[17]
The absorption spectra of BTA-I–IV on thin transparent
TiO2 films (4 mm thick) after 12 h adsorption in CH2Cl2 solu-
tion are shown in Figure 1b. The maximum absorption
peaks for BTA-I–IV on the TiO2 film are located at 432,
435, 426, and 425 nm, respectively. The absorption peaks are
blue-shifted by 18, 14, 32, and 29 nm, respectively, from the
solution spectra. The blue shift of the absorption spectra of
BTA-I–IV on TiO2 could be ascribed to deprotonation and
formation of H-aggregates (extended head-to-tail stack-
ing).[18] It is worth noting that the absorption maximum of
BTA-II is blue-shifted less than that of BTA-I, suggesting
that BTA-II with branched alkyl may have a lower tendency
to form H-aggregates than BTA-I. The same phenomenon
can be observed between BTA-III and BTA-IV.
In addition to the resemble absorption spectra, the four
dyes display very similar electrochemical oxidation charac-
teristics as well. Cyclic voltammetry (CV) was employed to
measure the electrochemical properties and evaluate the
possibility of electron transfer from the excited dye to the
conduction band of TiO2. The examined highest occupied
molecular orbital (HOMO) levels and the lowest unoccu-
pied molecular orbital (LUMO) levels are collected in
Table 1. Cyclic voltammetry was performed in acetonitrile/
tetrahydrofuran solution, using 0.1m tetrabutylammonium
hexafluorophosphate as the supporting electrolyte, Pt as
working electrode and counter electrode, saturated, calomel
electrode (SCE) as reference electrode. The HOMO levels
of BTA-I–IV are 1.03, 0.94, 0.91, and 0.92 V (vs. NHE), re-
spectively. Their HOMO levels show only minor differences
as all four dyes have the same electron donor. The band-gap
energies (E0À0) of the four dyes are 2.16, 2.11, 2.13, and
2.15 eV for BTA-I–IV, respectively, which were estimated
from the absorption onset of the UV/Vis absorption spectra
of the dyes. The estimated excited-state potentials for BTA-
I–IV calculated from EHOMOÀE0À0, are À1.13, À1.17, À1.22,
and À1.23 V, respectively. These dyes can be reversibly oxi-
dized at proper oxidation potentials, which are more posi-
Figure 1. a) UV/Vis absorption spectra of BTA-I–IV in CH2Cl2 and
b) UV/Vis absorption spectra of BTA-I–IV adsorbed on 4 mm TiO2 trans-
parent films.
Table 1. Optical and electrochemical properties of the dyes BTA-I–IV.
[b]
[d]
Dye
lmax[a] [nm]
lmax
HOMO[c]
[V]
E0À0
LUMO[e]
[V]
(eꢂ104 MÀ1 cmÀ1
)
[nm]
[eV]
A
ACHTUNGTRENN(UNG vs. NHE)
BTA-I
BTA-II
BTA-III 454 (3.31)
BTZ-IV 449(3.96)
458 (2.14)
450 (3.33)
432
435
426
425
1.03
0.94
0.91
0.92
2.16
2.11
2.13
2.15
À1.13
À1.17
À1.22
À1.23
À
tive than ferrocene/ferrocenium (Fc/Fc+) and IÀ/I3 redox
couples, suggesting sufficient driving force for dye regenera-
tion. The LUMO levels of these dyes are sufficiently more
ACHTUNGTRENNUNG
[a] Absorption maximum in CH2Cl2 (1.5ꢂ10À5 m). [b] Absorption maxi-
mum on 4 mm TiO2 transparent films. [c] HOMO energy levels were mea-
sured in CH2Cl2 with 0.1m tetra-n-butylammonium hexafluorophosphate
(TBAPF6) as electrolyte (working electrode: Pt; reference electrode:
SCE; calibrated with ferrocene/ferrocenium (Fc/Fc+) as an external refer-
ence. Counter electrode: Pt. [d] E0À0 was estimated from the onset of
UV/Vis absorption of the dyes. [e] LUMO energy levels were estimated
by subtracting E0À0 from the HOMO energy level. NHE=normal hydro-
gen electrode.
negative than the conduction band edge energy level (ECB
)
of the TiO2 semiconductor (À0.5 V vs. NHE),[5c] indicating
that the electron injection process from the excited dye mol-
ecule to the TiO2 conduction band is more efficient.
984
www.chemasianj.org
ꢁ 2012 Wiley-VCH Verlag GmbH & Co. KGaA, Weinheim
Chem. Asian J. 2012, 7, 982 – 991

Benzotriazole Sensitizers with a Furan Moiety
sensitize the semiconductor electrode, the DSSCs obtained
optimized h values of 6.85, 6.72, 7.02, and 7.05%, respective-
ly. This variation is mainly due to differences in solubility
and in the incident photon-to-current conversion efficiency
(IPCE) spectra. For example, the IPCE of BTA-II-based
DSSCs (Figure 3b) is higher in CH2Cl2 than in the other
three solutions.
Molecular Orbital Calculations
To gain an insight into the molecular structure and electron
distribution, density functional theory (DFT) calculations
were performed at the B3LYP/6-31G* level of theory with
[19]
Gaussian03.
The electron distributions of the HOMOs
and LUMOs of the dyes are shown in Figure 2. In the
ground state for all the dyes, electrons are homogeneously
Table 2. Current–voltage characteristics obtained from BTA-I–IV-sensi-
tized solar cells in various solvents with CDCA.
Dye
Solvent
Jsc [mAcmÀ2
]
Voc [mV]
FF
h [%]
BTA-I
DMF
THF
CH2Cl2
toluene
DMF
8.96
714
773
824
784
722
793
834
808
708
754
804
741
685
732
806
778
0.67
0.65
0.66
0.69
0.62
0.62
0.64
0.62
0.67
0.64
0.66
0.67
0.70
0.62
0.66
0.67
4.29
5.12
6.85
5.90
4.50
5.44
6.72
6.15
4.43
5.47
7.02
5.65
3.73
5.36
7.05
6.39
10.20
12.58
10.93
10.11
11.04
12.64
12.33
9.38
11.27
13.26
11.47
7.84
BTA-II
BTA-III
BTA-IV
THF
CH2Cl2
toluene
DMF
THF
CH2Cl2
toluene
DMF
THF
CH2Cl2
toluene
11.75
13.36
12.24
Figure 2. Calculated HOMOs and LUMOs of BTA-I–IV.
distributed in the donor (triphenylamine), and upon illumi-
nation with light, electrons move from the HOMO to the
LUMO by intramolecular charge transfer and are finally lo-
cated in anchoring group (cyanoacetic acid) through the
p bridge. The results indicated that the high electron density
from the donor unit moved to the cyanoacrylic acid moiety
in the HOMO–LUMO excitation induced by light, thus al-
lowing an efficient photoinduced electron transfer from the
dye to the TiO2 electrode.
Effect of Different Dye Baths on the Performance of
DSSCs
In different solvents, dyes exhibit diversified interactions
with the solvents,[20] which could cause changes of the physi-
cal and chemical properties between the dyes and semicon-
ductor surface. Therefore, the suitable solvent for semicon-
ductor sensitization is important to obtain good overall con-
version efficiency (h). To optimize the dye baths of these
dyes for TiO2 sensitization, BTA-I–IV in different solvents
(toluene, CH2Cl2, THF and DMF) with coadsorbent (cheno-
deoxycholic acid, CDCA) were employed to sensitize TiO2;
the photovoltaic performance of BTA-I–IV-based DSSCs
were measured and are shown in Table 2 and Figure 3a. The
data reveal large differences in the performance of BTA-I–
IV-based DSSCs fabricated in various dye-bath solutions.
When CH2Cl2 solutions of BTA-I–IV were introduced to
Figure 3. a) Overall conversion efficiency spectra for DSSCs based on
BTA-I–IV in different solvents and b) IPCE spectra of DSSCs based on
BTA-II sensitized in different solvents with CDCA.
Chem. Asian J. 2012, 7, 982 – 991
ꢁ 2012 Wiley-VCH Verlag GmbH & Co. KGaA, Weinheim
www.chemasianj.org
985

Jianli Hua et al.
FULL PAPERS
comparison, and the dyes exhibited inferior conversion effi-
ciency of 5.77, 6.17, 6.26, and 6.35%, respectively. Therefore
co-adsorbents are still needed to improve the photovoltaic
performance, although long or branched alkyl chains have
been introduced to these sensitizers.
Photovoltaic Performance of DSSCs
To reduce aggregation, nonchromophoric adsorbates, such
as deoxycholic acid (DCA) or chenodeoxycholic acid
(CDCA), have been co-deposited onto semiconductor surfa-
ces. In this work, CDCA was used as the co-adsorbent for
BTA-I–IV to effectively improve the photoelectric conver-
sion efficiency. Figure 4 shows the photovoltaic performance
Figure 4b shows the current–voltage characteristics of
DSSCs fabricated with these benzotriazole dyes BTA-I–IV
as sensitizers under standard global AM 1.5 solar light. The
detailed parameters of short-circuit current density (Jsc),
open-circuit voltage (Voc), fill factor (FF), and photovoltaic
conversion efficiency (h) are summarized in Table 2. In gen-
eral, the short-circuit current Jsc is related to the molar ex-
tinction coefficient of the dye, in which a higher molar ex-
tinction coefficient correlates with good light-harvesting
ability and a higher short-circuit current density. Among the
four dyes, BTA-III- and BTA-IV-based DSSCs (with the
thiophene group) show higher short-circuit currents than
BTA-I- and BTA-II-based ones (with furan) due to the
better molar extinction coefficient and IPCE value. On the
other hand, BTA-II- and BTA-IV-sensitized devices with
branched alkyl chains exhibit larger open-circuit voltages
than those sensitized with the corresponding dyes with
linear alkyl chains, BTA-I and BTA-III. The addition of dif-
ferent alkyl chains to the p-conjugated linkers suppressed
electron recombination in DSSCs by blocking the approach
À
of I3 to the TiO2 surface, and the branched alkyl chain
could suppress dye aggregation and retard charge recombi-
nation in DSSCs more effectively than the linear alkyl
chain.[21]
Significantly, the BTA-I,II-sensitized devices incorporat-
ing a furan moiety exhibit a higher open-circuit voltage than
BTA-III,IV-sensitized devices with a thiophene unit, and
the significant improvement of Voc from 804 mV (BTA-III)
to 834 mV (BTA-II) should be attributed to the reduction of
charge recombination. To understand the role of furan-
bridged dyes in improving Voc, their effect on dark current
was studied (Figure 4b). It is obvious that the dark current
onset potential of the furan-bridged dyes shifted to a larger
value from that of the thiophene-bridged dyes. This dark-
current change indicates that the introduction of furan
chains into bridged rings can inhibit charge recombination
between injected electrons and I3À ions in the electrolyte.
Figure 4. a) IPCE action spectra for DSSCs based on dyes BTA-I–IV co-
adsorbed with CDCA and b) current–voltage characteristics of DSSCs
based on BTA-I–IV co-adsorbed with CDCA.
of DSSCs based on BTA-I–IV co-adsorbed with CDCA
using
0.1m
1,2-dimethyl-3-propylimidazolium
iodide
(DMPII), 0.1m LiI, 0.05m I2 , and 0.5m 4-tertbutylpyridine
(TBP) as redox electrolyte. Figure 4a shows the action spec-
tra of incident photon-to-current conversion efficiency
(IPCE) as a function of incident wavelength for DSSCs. In
good agreement with absorption spectra, the IPCE action
spectra for DSSCs based on BTA-I–IV keep a high plateau
in the visible region up to 600 nm. Taking the absorption
and reflection of the conductive glass and dye aggregation
into account, all the four dyes have a maximum of IPCE of
about 80%. The strong absorption band of the four dyes is
located at 350–600 nm, where incident photon-to-current
conversion exhibits great efficiency. These features explain
why the dyes can achieve high photoelectric conversion effi-
ciency. We have also measured the photovoltaic perfor-
mance of BTA-I–IV-based DSSCs without co-adsorbents for
Electrochemical Impedance Spectroscopy
Charge recombination and electron injection efficiency are
correlated with the open circuit voltage (Voc).[22] To further
demonstrate that the introduction of conjugated furan can
effectively improve the open-circuit voltage, electrochemical
impedance spectroscopy (EIS) was employed to study the
electron recombination in DSSCs based on these BTA-I–IV
dyes under À0.70 V bias applied voltage in the dark. The
Nyquist plot, Bode plot, and equivalent circuit are shown in
Figure 5. Some important parameters can be obtained by fit-
ting the EIS spectra with an electrochemical model.[23] RS,
Rrec, and RCE represent series resistance and charge-transfer
resistances at the dye/TiO2/electrolyte interface and counter
986
www.chemasianj.org
ꢁ 2012 Wiley-VCH Verlag GmbH & Co. KGaA, Weinheim
Chem. Asian J. 2012, 7, 982 – 991

Benzotriazole Sensitizers with a Furan Moiety
Table 3. Parameters obtained by fitting the impedance spectra of the
DSSCs with sensitizers BTA-I–IV, using the equivalent circuit (Fig-
ure 4c).
Dye
RS [WcmÀ2
]
Rrec [WcmÀ2
]
RCE [WcmÀ2
]
te [ms]
BTA-I
39.3
35.5
40.6
31.7
850.7
971.3
384.9
635.7
29.7
13.8
13.1
19.2
87
93
59
63
BTA-II
BTA-III
BTA-IV
[a] The reaction resistance of the DSSCs consisting of TiO2/dye/electro-
lyte and Pt/electrolyte interface based on BTA-I–IV were analyzed by
software (ZSimpWin) using an equivalent circuit.
on the benzotriazole unit. This result is in agreement with
the observed shift in the Voc value under standard global
AM 1.5 illumination.
Photovoltaic Performance of Solvent-Free Ionic Liquid
Electrolyte DSSCs
Long-term stability is also a vital parameter for sustained
cell operation for future applications. However, the use of
organic solvents is undesirable as they are likely to be vola-
tile, so we substituted the liquid electrolyte with a solvent-
free ionic liquid electrolyte.[25] BTA-I–IV were evaluated as
sensitizers for the ionic liquid electrolyte DSSCs using 1-
butyl-3-methylimidazolium, 1-methyl-3-trimethylsilylimida-
zolium, iodine, benzimidazole, and guanidine thiocyanate
(BMII:MSII:I2:BI:GNCS=20:20:1.67:0.67:3.33) as redox
electrolyte.[26] Figure 6a shows the IPCE spectra of DSSCs
based on BTA-I–IV with a solvent-free ionic liquid electro-
lyte. We can see that the four dyes can efficiently convert
visible light to photocurrent in the region from 350 to
650 nm, in which the maximum IPCE is 71.7% for BTA-I at
520 nm, 75.0% for BTA-II at 520 nm, 69.2% for BTA-III at
480 nm, and 69.8% for BTA-IV at 540 nm. In the spectral
range 450–550 nm, the conversion efficiency of BTA-I,II is
higher than that of BTA-III,IV, but the IPCE value of
BTA-III,IV is higher than that for BTA-I,II in the range of
550–650 nm. As a result, the IPCE performance of the ionic
liquid electrolyte DSSCs based on BTA-I–IV is similar. Pho-
tovoltaic performances of BTA-I–IV-sensitized TiO2 film
electrodes with a solvent-free ionic liquid electrolyte under
standard global AM 1.5 solar condition are listed in Table 4,
and the corresponding photocurrent–voltage curves are
shown in Figure 6b. Obviously, BTA-I,II show higher open-
circuit voltages than BTA-III,IV, which can be tentatively
attributed to the prevention of dye aggregation on the semi-
conductor when a furan moiety is incorporated into the or-
ganic sensitizer. Also, the conversion efficiency of the sol-
vent-free ionic liquid DSSC based on BTA-II is the highest,
while the opposite result is found for liquid electrolyte. This
difference could be explained by the highest IPCE value
and open-circuit voltage of BTA-II. Long-term stability
measurements of devices with solvent-free ionic liquid elec-
trolyte were tested, and Figure 7 shows the photovoltaic per-
formance recorded over a period of 1000 h. The overall effi-
ciency for BTA-I–IV-based DSSCs remained at 95% of the
Figure 5. a) Nyquist plot, b) Bode plot, and c) equivalent circuit of
DSSCs based on BTA-I–IV dyes. The lines of (a) and (b) show theoreti-
cal fits using the equivalent circuits (c).
electrode (CE), respectively. The series resistance (RS) and
electrolyte reduction resistance (RCE) corresponding to the
first semicircle show almost the same value in the four dyes-
based DSSCs, because the devices use the same electrode
material and same electrolyte, and Rrec corresponds to the
middle semicircle (Figure 5a). From the EIS measurements,
the electron lifetime (te) expressing the electron recombina-
tion between the electrolyte and TiO2 may be extracted
from the angular frequency (wrec) at the mid-frequency peak
in the Bode phase plots using the relation te =1/wrec (Fig-
ure 5b). The reaction resistance of the DSSCs consisting of
TiO2/dye/electrolyte and Pt/electrolyte interface based on
BTA-I–IV were analyzed by software (ZSimpWin) using an
equivalent circuit.[24] As shown in Table 3, the Rrec of the
BTA-I–IV dyes are 850.7, 971.3, 384.9, and 635.7 WcmÀ1
,
respectively. Estimated from te =1/wrec, the electron lifetime
of the BTA-I–IV dyes are 87, 93, 59, and 63 ms, respectively.
BTA-II has the longest electron lifetime among the four
dyes, indicating that the electron recombination rate be-
tween the TiO2 film and the electrolyte is indeed suppressed
by introduction of a furan group and branched alkyl chain
Chem. Asian J. 2012, 7, 982 – 991
ꢁ 2012 Wiley-VCH Verlag GmbH & Co. KGaA, Weinheim
www.chemasianj.org
987

Jianli Hua et al.
FULL PAPERS
Figure 6. a) The IPCE spectra of DSSCs based on BTA-I–IV with a sol-
vent-free ionic liquid electrolyte and b) current–voltage characteristics of
DSSCs based on BTA-I–IV with solvent-free ionic liquid electrolyte.
Table 4. Photovoltaic performance of DSSCs based on BTA-I–IV with
solvent-free ionic liquid electrolyte.
Dye
Jsc [mAcmÀ2
]
Voc [mV]
FF
h [%]
BTA-I
10.24
11.23
11.88
11.73
708
709
672
673
0.64
0.64
0.62
0.62
4.66
5.06
4.97
4.92
BTA-II
BTA-III
BTA-IV
initial value after 1000 h of visible-light illumination. On
continuous 1000 h of light soaking, the Jsc and Voc for BTA-
I–IV-sensitized solar cells showed fluctuation during the ini-
tial 600 h and then remained almost constant for 1000 h.
This result demonstrates that BTA-I–IV sensitizers are effi-
cient in solvent-free ionic liquid electrolyte DSSCs, and they
have comparable long-term stability. The results demon-
strate that benzotriazole-bridged sensitizers containing a
furan moiety are promising candidates for improving the
performance and long-term stability of DSSCs.
Conclusions
Figure 7. Variations of photovoltaic parameters (Jsc, Voc, FF, and h) with
aging time for the DSSC devices based on BTA-I–IV and ionic liquid
electrolyte under visible-light soaking.
In summary, two new benzotriazole-bridged sensitizers
(BTA-I and BTA-II) containing a furan moiety for DSSCs
have been designed and synthesized; the corresponding dyes
(BTA-III and BTA-IV) with thiophene spacer were also
988
www.chemasianj.org
ꢁ 2012 Wiley-VCH Verlag GmbH & Co. KGaA, Weinheim
Chem. Asian J. 2012, 7, 982 – 991

Benzotriazole Sensitizers with a Furan Moiety
tion (0.02m in 2-propanol solution) with heat treatment at 4008C for
20 min. A hole (0.8 mm diameter) was drilled on the counter electrode
by a drill press. The perforated sheet was cleaned by ultrasound in an
ethanol bath for 15 min. The dye-covered TiO2 electrode and Pt counter
electrode were assembled into a sandwich-type cell and sealed with a
hot-melt gasket of 25 mm thickness made of the ionomer Surlyn 1702
(Dupont). The electrolyte consisting of 0.1m 1,2-dimethyl-3-propylimida-
zolium iodide (DMPII), 0.1m LiI, 0.05m I2, and 0.5m 4-tertbutylpyridine
(TBP) in a mixture of acetonitrile and methoxypropionitrile (volume
ratio 7:3) was introduced into the cell via vacuum backfilling from the
hole in the back of the counter electrode. Finally, the hole was sealed by
a film of Surlyn 1702 and a cover glass (0.1 mm thickness) using a hot
iron bar. The cell active area was tested with a mask, the size of which
was about 1.5 mm lager than the side length of the TiO2 electrode.
synthesized for comparison. Significantly, the Voc values of
BTA-I,II with a furan moiety are higher than those of BTA-
III,IV with a thiophene group. BTA-II-based DSSCs with a
furan moiety and a branched alkyl chain exhibit the highest
Voc of 834 mV. Most importantly, the long-term stability of
the BTA-I–IV-based DSSCs with ionic liquid electrolytes
under 1000 h illumination was demonstrated, and BTA-II
exhibited better conversion efficiency of 5.06%. As an alter-
native to thiophene, the furan moiety can be advantageously
incorporated into the dye sensitizer as a p spacer and im-
prove the cell efficiency and stability. It should be noted
that the benzotriazole unit could become a simple and effi-
cient building block for the future sensitizer molecular
design in DSSCs due to favorable optical and electronic
properties.
Materials and Reagents
Optically transparent FTO conducting glass (fluorine doped SnO2, trans-
mission >90% in the visible, sheet resistance 15 W per square) was ob-
tained from the Geao Science and Educational Co. Ltd. of China and
cleaned by a standard procedure. Methoxypropionitrile (MPN) was pur-
chased from Aldrich. Tetra-n-butylammonium hexafluorophosphate
(TBAPF6), 4-tert-butylpyridine (4-TBP), and lithium iodide were bought
from Fluka and iodine (99.999% purity) was purchased from Alfa Aesar.
Triphenylamine-4-boronic acid was bought from Sun Chemical Technolo-
gy (Shanghai) Co, Ltd. Tetrahydrofuran (THF) was pre-dried over 4 ꢄ
molecular sieves and distilled under argon atmosphere from sodium ben-
zophenone ketyl immediately prior to use. Dichloromethane was distilled
under normal pressure and dried over calcium hydroxide. All other
chemicals were purchased from Aldrich and used as received without fur-
ther purification. The starting materials 4,7-dibromo-2-octyl-2H-
benzo[d]-[1,2,3]-triazole (1) and 4,7-dibromo-2-(2-ethylhexyl)-2H-
Experimental Section
Instruments and Characterization
NMR spectra were obtained on a Brꢃcker AM 400 spectrometer. The ab-
sorption spectra of the dyes in solution and adsorbed on TiO2 films were
measured with a Varian Cary 500 spectrophotometer. Mass spectra were
recorded on an ESI mass spectrometer. The cyclic voltammograms of
dyes were obtained with a Versastat II electrochemical workstation
(Princeton applied research) using a normal three-electrode cell with a
Pt working electrode, a Pt wire counter electrode, and a regular calomel
reference electrode in saturated KCl solution.
benzo[d]ACTHUNRTGNEUNG[1,2,3]-triazole (2) were prepared according to published proce-
dures.[8]
The photocurrent action spectra were measured with a Model SR830
DSP Lock-In Amplifier, a Model SR540 Optical Chopper (Stanford Re-
search Corporation, USA), a 7IL/PX150 xenon lamp with power supply,
and a 7ISW301 Spectrometer. The irradiation source for the photocur-
rent density–voltage (J–V) measurement is an AM 1.5 solar simulator
(91160, Newport Co., USA). The photocurrent action spectra were mea-
sured with an IPCE test system consisting of a model SR830 DSP Lock-
In Amplifier and a model SR540 Optical Chopper (Stanford Research
Corporation, USA), a 7IL/PX150 xenon lamp and power supply, and a
7ISW301 spectrometer. The electrochemical impedance spectroscopy
(EIS) measurements of all the DSSCs were performed using a Zahner
IM6e Impedance Analyzer (ZAHNER-Elektrik GmbH & CoKG, Kro-
nach, Germany). The frequency range is 0.1 Hz–100 kHz. The applied
voltage bias is À0.70 V. The magnitude of the alternative signal is 10 mV.
Synthesis
4-(7-bromo-2-octyl-2H-benzo[d]
(3): Compound 1 (390 mg, 1.00 mmol), [Pd
ACHTUNGTRENNUNG
AHCTUNGTRENNUNG
and K2CO3 (1.00 g, 7.25 mmol) in THF (30 mL) and H2O (5 mL) were
heated to 558C under a nitrogen atmosphere for 30 min. A solution of 4-
(diphenylamino)phenylboronic acid (288 mg, 1.00 mmol) in THF (10 mL)
was added slowly, and the mixture was heated at reflux for further 12 h.
After cooling to room temperature, the mixture was extracted with
CH2Cl2 (3ꢂ50 mL). The organic portion was combined and dried over
MgSO4, and volatile components were removed by rotary evaporation.
The residue was purified by column chromatography on silica gel
(CH2Cl2/petroleum ether=1:3, v/v) to give a green solid (230 mg). Yield:
1
41.6%. H NMR (CDCl3; 400 MHz): d=7.91 (d, J=8.8 Hz, 1H), 7.60 (d,
Fabrication of Dye-Sensitized Solar Cells
J=2.0 Hz, 1H), 7.29 (d, J=7.7 Hz, 4H), 7.21–7.15 (m, 8H), 7.06 (dd, J=
4.4, 2.8 Hz, 2H), 4.77 (dd, J=10.3, 4.5 Hz, 2H), 2.19–2.08 (m, 2H), 1.27
(d, J=11.9 Hz, 10H), 0.87 ppm (t, J=6.9 Hz, 3H). HRMS (ESI, m/z):
[M]+ calcd for C32H33BrN4 552.1889; found 552.1876.
A screen-printed TiO2 particle was used as photoelectrode. The thickness
of TiO2 film (4 mm paste, T/SP) was controlled by the mesh size (0.5 cmꢂ
0.5 cm) of screen printing and then dried for 6 min at 1258C. This proce-
dure was repeated twice (to give a thickness of ca. 8 mm), and the result-
ing surface was finally coated by a layer (ca. 5 mm) of TiO2 paste (Ti-
nanoxide 300) as the scattering layer. The three-layer TiO2 electrodes
were gradually heated under an air flow at 2758C for 5 min, 3258C for
5 min, 3758C for 5 min, 4508C for 15 min, and 5008C for 15 min. Before
immersion in the dye solution, these films were soaked in 0.05m aqueous
TiCl4 overnight in a closed chamber and washed with water and ethanol,
which can significantly increase the short-circuit photocurrent. Then sin-
tering was carried out at 4508C for 30 min. After the film was cooled to
room temperature, it was immersed in a 3ꢂ10À4 m dye bath in CH2Cl2 (or
other solvent) and maintained in the dark for 24 h at room temperature.
If chenodeoxycholic acid (CDCA) was used as a co-adsorbent, the TiO2
film was soaked in a 20 mm CDCA bath in ethanol for 8 h and then in a
3ꢂ10À4 m dye bath in CH2Cl2 (or other solvent) for 16 h at room tempera-
ture. The electrode was then rinsed with CH2Cl2 and dried. To prepare
the counter electrode, the Pt catalyst was deposited on the cleaned fluo-
rine-doped tin oxide (FTO) glass by coating with a drop of H2PtCl6 solu-
4-(7-bromo-2-(2-ethylhexyl)-2H-benzo[d]ACTHUNTGRNEUNG[1,2,3]triazol-4-yl)-N,N-dipheny-
laniline (4): The synthesis method resembles that of compound 3, but
using 2 as starting material, and the product was purified by column chro-
matography on silica gel (CH2Cl2/petroleum ether=1:3, v/v) to give a
green solid (450 mg). Yield: 48.5%. 1H NMR (CDCl3; 400 MHz): d=
7.94 (d, J=8.7 Hz, 1H), 7.87–7.82 (m, 1H), 7.55–7.51 (m, 1H), 7.32 (d,
J=7.7 Hz, 1H), 7.22–7.17 (m, 5H), 7.11 (dd, J=5.1, 3.9 Hz, 6H), 7.02–
6.96 (m, 2H), 4.61 (d, J=7.2 Hz, 2H), 2.27–2.17 (m, 1H), 1.30–1.21 (m,
8H), 0.88–0.79 ppm (m, 6H). HRMS (ESI, m/z): [M]+ calcd for
C32H33BrN4 552.1889; found 552.1828.
5-(7-(4-(diphenylamino)phenyl)-2-octyl-2H-benzo[d]
furan-2-carbaldehyde (5): Compound 3 (120 mg, 0.22 mmol), [PdACHTUNGTRENNUNG
ACHTUNGTRENNUNG
(100 mg, 0.087 mmol), and K2CO3 (1.00 g, 7.25 mmol) in THF (30 mL)
and H2O (5 mL) were heated to 558C under a nitrogen atmosphere for
30 min. A solution of 2-formylfuran-5-boronic acid (31 mg, 0.22 mmol) in
THF (5 mL) was added slowly, and the mixture was heated at reflux for
further 12 h. After cooling to room temperature, the mixture was extract-
Chem. Asian J. 2012, 7, 982 – 991
ꢁ 2012 Wiley-VCH Verlag GmbH & Co. KGaA, Weinheim
www.chemasianj.org
989

Jianli Hua et al.
FULL PAPERS
ed with CH2Cl2 (3ꢂ30 mL). The organic portion was combined and dried
over MgSO4, and volatile components were removed by rotary evapora-
tion. The residue was purified by column chromatography on silica gel
(CH2Cl2/petroleum ether=2:1, v/v) to give a yellow solid (100 mg).
Yield: 80.6%. 1H NMR (CDCl3; 400 MHz): d=9.71 (s, 1H), 8.10 (d, J=
7.7 Hz, 1H), 8.03–8.00 (m, 2H), 7.67 (d, J=3.7 Hz, 1H), 7.63 (d, J=
7.7 Hz, 1H), 7.42 (d, J=3.7 Hz, 1H), 7.32–7.27 (m, 4H), 7.22–7.16 (m,
7H), 7.07 (t, J=7.3 Hz, 2H), 4.80 (t, J=7.3 Hz, 2H), 2.22–2.13 (m, 2H),
1.35–1.19 (m, 10H), 0.88–0.85 ppm (m, 3H). HRMS (ESI, m/z): [M]+
calcd for C37H36N4O2 568.2838; found 568.2842.
(DMSO; 400 MHz): d=8.10 (d, J=8.8 Hz, 2H), 7.97 (d, J=7.7 Hz, 1H),
7.83 (s, 1H), 7.79 (d, J=7.7 Hz, 1H), 7.54 (d, J=3.6 Hz, 1H), 7.39–7.33
(m, 4H), 7.32 (d, J=3.6 Hz, 1H), 7.16–7.02 (m, 8H), 4.76 (d, J=6.6 Hz,
2H), 2.20–2.12 (m, 1H), 1.30–1.21 (m, 8H), 0.91 (t, J=7.4 Hz, 3H),
0.80 ppm (t, J=7.2 Hz, 3H). 13C NMR (DMSO; 100 MHz): d=177.49,
154.73, 152.29, 149.10, 147.54, 146.75, 142.13, 140.50, 133.45, 131.85,
131.32, 129.83, 129.67, 129.58, 129.3, 124.60, 123.64, 123.31, 122.06, 113.34,
59.24, 29.92, 29.25, 27.71, 23.78, 22.34, 13.80, 10.40 ppm. HRMS (ESI, m/
z): [M+H]+ calcd for C40H38N5O3 636.2975; found 636.2979.
2-Cyano-3-(5-(7-(4-(diphenylamino)phenyl)-2-octyl-2H-benzo[d]-
AHCTUNGTERG[NNUN 1,2,3]triazol-4-yl)thiophen-2-yl)acrylic acid (BTA-III): The synthesis
5-(7-(4-(diphenylamino)phenyl)-2-(2-ethylhexyl)-2H-benzo[d]-
method resembles that of compound BTA-I but starts from 7, and the
product was purified by column chromatography on silica gel (CH2Cl2/
ethanol=10:1, v/v) to give a red solid (80 mg). Yield: 75.5%. 1H NMR
(DMSO; 400 MHz): d=8.16 (d, J=4.0 Hz, 1H), 8.15 (s, 1H), 8.06 (d, J=
8.7 Hz, 2H), 7.87 (d, J=7.6 Hz, 1H), 7.81 (d, J=4.1 Hz, 1H), 7.71 (d, J=
7.7 Hz, 1H), 7.36 (t, J=7.9 Hz, 4H), 7.10 (m, 8H), 4.83 (t, J=6.8 Hz,
2H), 2.08 (s, 2H), 1.26–1.15 (m, 10H), 0.78 ppm (t, J=6.8 Hz, 3H).
13C NMR (DMSO; 100 MHz): d=170.93, 153.47, 149.11, 148.27, 146.80,
142.27, 141.52, 141.10, 137.05, 129.73, 129.67, 129.47, 127.32, 124.53,
123.65, 122.32, 121.25, 117.81, 115.13, 114.09, 59.58, 31.08, 29.33, 28.47,
28.23, 26.10, 21.99, 14.22 ppm. HRMS (ESI, m/z): [M+H]+ calcd for
C40H38N5O2S 652.2746; found 652.2745.
ACHTUNGTRENNUNG[1,2,3]triazol-4-yl)furan-2-carbaldehyde (6): The synthesis method resem-
bles that of compound 5, but starts from 4, and the product was purified
by column chromatography on silica gel (CH2Cl2/petroleum ether=2:1,
v/v) to give a yellow solid (74 mg). Yield: 69.2%. 1H NMR (CDCl3;
400 MHz): d=9.71 (s, 1H), 8.11 (d, J=7.7 Hz, 1H), 8.04–7.99 (m, 2H),
7.65 (dd, J=10.7, 5.7 Hz, 2H), 7.43 (d, J=3.7 Hz, 1H), 7.33–7.27 (m,
4H), 7.21–7.16 (m, 6H), 7.07 (t, J=7.3 Hz, 2H), 4.73 (d, J=6.9 Hz, 2H),
2.31–2.22 (m, 1H), 1.41–1.30 (m, 8H), 0.97 (t, J=7.4 Hz, 3H), 0.88 ppm
(t, J=6.2 Hz, 3H). HRMS (ESI, m/z): [M]+ calcd for C37H36N4O2
568.2838; found 568.2852.
5-(7-(4-(diphenylamino)phenyl)-2-octyl-2H-benzo[d]ACTHNUGTRNEUNG[1,2,3]triazol-4-yl)th-
ioph-ene-2-carbaldehyde (7): The synthesis method resembles that of
compound 5, but uses 2-formylthiophene-5-boronic acid as reagent, and
the product was purified by column chromatography on silica gel
(CH2Cl2/petroleum ether=2:1, v/v) to give a yellow solid (100 mg).
Yield: 41.1%. 1H NMR (CDCl3; 400 MHz): d=9.88 (s, 1H), 8.10 (d, J=
4.0 Hz, 1H), 7.93 (d, J=8.7 Hz, 2H), 7.78–7.73 (m, 2H), 7.51 (d, J=
7.6 Hz, 1H), 7.23 (t, J=7.8 Hz, 4H), 7.12 (dd, J=8.1, 4.1 Hz, 6H), 7.00
(t, J=7.3 Hz, 2H), 4.73 (t, J=7.3 Hz, 2H), 2.10 (dd, J=14.5, 7.3 Hz,
2H), 1.21 (dd, J=20.4, 11.1 Hz, 10H), 0.87 ppm (t, J=6.9 Hz, 3H).
HRMS (ESI, m/z): [M+H]+ calcd for C37H36N4OS 585.2692; found,
585.2690.
2-Cyano-3-(5-(7-(4-(diphenylamino)phenyl)-2-(2-ethylhexyl)-2H-
benzo[d]ACTHNUGRTENUNG[1,2,3] triazol-4-yl)thiophen-2-yl)acrylic acid (BTA-IV): The syn-
thesis method resembles that of compound BTA-I but starts from 8, and
the product was purified by column chromatography on silica gel
(CH2Cl2/ethanol=10:1, v/v) to give a red solid (80 mg). Yield: 72.7%.
1H NMR (DMSO; 400 MHz): d=8.15 (d, J=4.0 Hz, 1H), 8.15 (s, 1H),
8.06 (d, J=8.6 Hz, 2H), 7.86 (d, J=7.6 Hz, 1H), 7.81 (d, J=4.0 Hz, 1H),
7.71 (d, J=7.7 Hz, 1H), 7.36 (t, J=7.8 Hz, 4H), 7.15–7.04 (m, 8H), 4.77
(d, J=6.5 Hz, 2H), 2.24–2.10 (m, 1H), 1.26 (m, 8H), 0.91 (t, J=7.4 Hz,
3H), 0.80 ppm (t, J=7.2 Hz, 3H). 13C NMR (DMSO; 100 MHz): d=
163.08, 156.86, 147.76, 146.76, 142.48, 141.76, 135.76, 129.66, 129.63,
129.59, 129.27, 127.21, 124.55 (s), 123.92, 123.61, 122.19, 121.38, 119.07,
116.65, 113.53, 59.61, 30.25, 28.09, 27.81, 23.68, 22.33, 13.81, 10.43 ppm.
HRMS (ESI, m/z): [M+H]+ calcd for C40H38N5O2S 652.2746; found
652.2745.
5-(7-(4-(diphenylamino)phenyl)-2-(2-ethylhexyl)-2H-benzo[d]-
ACHTUNGTRENNUNG[1,2,3]triazol-4-yl) thiophene-2-carbaldehyde (8): The synthesis method
resembles that of compound 5, but starts from 4 and uses 2-formylthio-
phene-5-boronic acid as reagent; the compound was purified by column
chromatography on silica gel (CH2Cl2/petroleum ether=2:1, v/v) to give
a yellow solid (83 mg). Yield: 61.9%. 1H NMR (CDCl3; 400 MHz): d=
9.95 (s, 1H), 8.18 (d, J=4.0 Hz, 1H), 8.01 (d, J=8.8 Hz, 2H), 7.85–7.80
(m, 2H), 7.59 (d, J=7.6 Hz, 1H), 7.33–7.27 (m, 4H), 7.21–7.16 (m, 6H),
7.07 (t, J=7.3 Hz, 2H), 4.73 (d, J=6.9 Hz, 2H), 2.34–2.23 (m, 1H), 1.36
(ddd, J=22.6, 8.9, 4.0 Hz, 8H), 0.97 (t, J=7.4 Hz, 3H), 0.88 ppm (t, J=
7.1 Hz, 3H). HRMS (ESI, m/z): [M+H]+ calcd for C37H36N4OS 585.2692;
found 585.2688.
Acknowledgements
This work was supported by NSFC/China (2116110444, 21172073, and
61006048), the National Basic Research 973 Program (2011CB808400),
the Fundamental Research Funds for the Central Universities
(WJ0913001 and WJ1014025), Ph.D. Programs Foundation of the Minis-
try of Education of China (20090074110004) and Scientific Committee of
Shanghai (10520709700). We are grateful to Dr. Xin Li in the Depart-
ment of Theoretical Chemistry and Biology, School of Biotechnology,
KTH Royal Institute of Technology in Sweden for computational assis-
tance.
2-Cyano-3-(5-(7-(4-(diphenylamino)phenyl)-2-octyl-2H-benzo[d]-
ACHTUNGTRENNUNG[1,2,3]triazol-4-yl) furan-2-yl)acrylic acid (BTA-I): A mixture of aldehyde
5 (120 mg, 0.21 mmol) with cyanoacetic acid (178 mg, 2.10 mmol) in
acetic acid (15 mL) was heated at reflux in the presence of ammonium
acetate (300 mg) for 12 h under argon. After cooling the solution, water
was added to quench the reaction. The precipitate was filtered and
washed with water. The residue was purified by column chromatography
on silica gel (CH2Cl2/ethanol=10:1, v/v) to give a red solid (80 mg).
Yield: 60.1%. 1H NMR (DMSO; 400 MHz): d=8.11 (d, J=8.8 Hz, 2H),
7.99 (d, J=7.7 Hz, 1H), 7.81 (d, J=7.7 Hz, 1H), 7.79 (s, 1H), 7.56 (d, J=
3.6 Hz, 1H), 7.39–7.34 (m, 4H), 7.30 (d, J=3.6 Hz, 1H), 7.14–7.06 (m,
8H), 4.85 (t, J=7.0 Hz, 2H), 2.08 (d, J=6.7 Hz, 2H), 1.28–1.16 (m,
10H), 0.79 ppm (t, J=6.8 Hz, 3H). 13C NMR (DMSO; 100 MHz): d=
171.46, 152.48, 148.88, 147.44, 146.75, 142.10, 140.44, 139.57, 133.73,
129.75, 129.65, 129.60, 129.31, 124.56, 123.61, 123.28, 122.08, 119.34,
116.92, 113.44, 56.24, 31.0, 30.39, 29.30, 28.45, 25.84, 21.98, 13.86 ppm.
HRMS (ESI, m/z): [M+H]+ calcd for C40H38N5O3 636.2975; found
636.2980.
[1] B. O’Regan, M. Grꢀtzel, Nature 1991, 353, 737.
[2] J. H. Yum, I. Jung, C. Baik, J. Ko, M. K. Nazeeruddin, M. Grꢀtzel,
Energy Environ. Sci. 2009, 2, 100.
[3] a) K. J. Jiang, K. Manseki, Y. H. Yu, N. Masaki, J. B. Xia, L. M.
Yang, Y. L. Song, S. Yanagida, New J. Chem. 2009, 33, 1973; b) J.
Tang, W. J. Wu, J. L. Hua, J. Li, H. Tian, Energy Environ. Sci. 2009,
2, 982; c) M. Velusamy, Y. C. Hsu, J. T. Lin, C. W. Chang, C. P. Hsu,
Chem. Asian J. 2010, 5, 87; d) J. B. Xia, L. Chen, S. Yanagida, J.
Mater. Chem. 2011, 21, 4644; e) A. B. F. Martinson, T. W. Hamann,
M. J. Pellin, J. T. Hupp, Chem. Eur. J. 2008, 14, 4458.
2-Cyano-3-(5-(7-(4-(diphenylamino)phenyl)-2-(2-ethylhexyl)-2H-
benzo[d]-[1,2,3] triazol-4-yl)furan-2-yl)acrylic acid (BTA-II): The synthe-
sis method resembles that of compound BTA-I but starts from 6, and the
product was purified by column chromatography on silica gel (CH2Cl2/
ethanol=10:1, v/v) to give a red solid (85 mg). Yield: 74.6%. 1H NMR
[4] a) J. Tang, J. L. Hua, W. J. Wu, J. Li, Z. G. Jin, Y. T. Long, H. Tian,
Energy Environ. Sci. 2010, 3, 1736; b) Y. Numata, I. Ashraful, Y.
Shirai, L. Y. Han, Chem. Commun. 2011, 47, 6159; c) L. Y. Han, A.
Fukui, Y. Chiba, A. Islam, R. Komiya, N. Fuke, N. Koide, R. Yama-
990
www.chemasianj.org
ꢁ 2012 Wiley-VCH Verlag GmbH & Co. KGaA, Weinheim
Chem. Asian J. 2012, 7, 982 – 991

Benzotriazole Sensitizers with a Furan Moiety
naka, M. Shimizu, Appl. Phys. Lett. 2009, 94, 013305; d) N. Xiang,
W. P. Zhou, S. H. Jiang, L. J. Deng, Y. J. Liu, Z. Tan, B. Zhao, P.
Shen, S. T. Tan, Sol. Energy Mater. Sol. Cells 2011, 95, 1174.
[5] a) H. N. Tian, X. C. Yang, R. K. Chen, Y. Z. Pan, L. Li, A. Hagfeldt,
L. C. Sun, Chem. Commun. 2007, 3741; b) W. J. Wu, J. B. Yang, J. L.
Hua, J. Tang, L. Zhang, Y. T. Long, H. Tian, J. Mater. Chem. 2010,
20, 1772; c) D. W. Chang, H. J. Lee, J. H. Kim, S. Y. Park, S. M.
Park, L. M. Dai, J. B. Baek, Org. Lett. 2011, 13, 3880; d) R. Chau-
han, M. Trivedi, L. Bahadur, A. Kumar, Chem. Asian J. 2011, 6,
1525; e) H. Wonneberger, N. Pschirer, I. Bruder, J. Schçneboom,
C. Q. Ma, P. Erk, C. Li, P. Buerle, K. Mꢃllen, Chem. Asian J. 2011,
6, 1744.
[6] Z. M. Tang, T. Lei, K. J. Jiang, Y. L. Song, J. Pei, Chem. Asian J.
2010, 5, 1911.
[7] H. Kusama, Y. Konishi, H. Sugihara, Sol. Energy Mater. Sol. Cells
2007, 91, 76.
[8] Z. H. Zhang, B. Peng, B. Liu, C. Y. Pan, Y. F. Li, Y. H. He, K. H.
Zhou, Y. P. Zou, Polym. Chem. 2010, 1, 1441.
[9] S. C. Price, A. C. Stuart, L. Q. Yang, H. X. Zhou, W. You, J. Am.
Chem. Soc. 2011, 133, 4625.
[18] a) T. Dentani, Y. Kubota, K. Funabiki, J. Jin, T. Yoshida, H. Min-
oura, H. Miura, M. Matsui, New J. Chem. 2009, 33, 93; b) H. N.
Tian, X. C. Yang, R. K. Chen, R. Zhang, A. Hagfeldt, L. C. Sun, J.
Phys. Chem. C 2008, 112, 11023.
[19] M. J. Frisch, G. W. Trucks, H. B. Schlegel, G. E. Scuseria, M. A.
Robb, J. R. Cheeseman, J. A. Montgomery Jr, T. Vreven, K. N.
Kudin, J. C. Burant, J. M. Millam, S. S. Iyengar, J. Tomasi, V.
Barone, B. Mennucci, M. Cossi, G. Scalmani, N. Rega, G. A. Peters-
son, H. Nakatsuji, M. Hada, M. Ehara, K. Toyota, R. Fukuda, J. Ha-
segawa, M. Ishida, T. Nakajima, Y. Honda, O. Kitao, H. Nakai, M.
Klene, X. Li, J. E. Knox, H. P. Hratchian, J. B. Cross, V. Bakken, C.
Adamo, J. Jaramillo, R. Gomperts, R. E. Stratmann, O. Yazyev, A. J.
Austin, R. Cammi, C. Pomelli, J. W. Ochterski, P. Y. Ayala, K. Mo-
rokuma, G. A. Voth, P. S alvador, J. J. Dannenberg, V. G. Zakrzew-
ski, S. Dapprich, A. D. Daniels, M. C. Strain, O. Farkas, D. K.
Malick, A. D. Rabuck, K. Raghavachari, J. B. Foresman, J. V. Ortiz,
Q. Cui, A. G. Baboul, S. Clifford, J. Cioslowski, B. B. Stefanov, G.
Liu, A. Liashenko, P. Piskorz, I. Komaromi, R. L. Martin, D. J. Fox,
T. Keith, M. A. Al-Laham, C. Y. Peng, A. Nanayakkara, M. Challa-
combe, P. M. W. Gill, B. Johnson, W. Chen, M. W. Wong, C. Gonza-
lez, J. A. Pople, Gaussian 03, Revision D.01; Gaussian, Inc.: Walling-
ford CT, 2004.
[10] Y. Cui, Y. Z. Wu, X. F. Lu, X. Zhang, G. Zhou, F. B. Miapeh, W. H.
Zhu, Z. S. Wang, Chem. Mater. 2011, 23, 4394.
[11] a) B. Walker, A. B. Tamayo, X. D. Dang, P. Zalar, J. H. Seo, A.
Garcia, M. Tantiwiwat, T. Nguyen, Adv Funct Mater. 2009, 19, 3063;
b) T. Umeyama, T. Takamatsu, N. Tezuka, Y. Matano, Y. Araki, T.
Wada, O. Yoshikawa, T. Sagawa, S. Yoshikawa, H. Imahori, J. Phys.
Chem. C 2009, 113, 10798.
[12] J. T. Lin, P. C. Chen, Y. S. Yen, Y. C. Hsu, H. H. Chou, M. P. Yeh,
Org. Lett. 2009, 11, 97.
[13] C. H. Woo, P. M. Beaujuge, T. W. Holcombe, O. P. Lee, J. M. J. Freꢅ-
chet, J. Am. Chem. Soc. 2010, 132, 15547.
[14] I. Y. Wu, J. T. Lin, J. Luo, C. S. Li, C. Tsai, Y. S. Wen, C. C. Hsu,
F. F. Yeh, S. Liou, Organometallics 1998, 17, 2188.
[15] S. Y. Qu, B. Wang, F. L. Guo, J. Li, W. J. Wu, C. Kong, Y. T. Long,
J. L. Hua, Dyes Pigm. 2012, 92, 1384.
[16] H. Y. Yang, Y. S. Yen, Y. C. Hsu, H. H. Chou, J. T. Lin, Org. Lett.
2010, 12, 16.
[20] N. Robertson, Angew. Chem. 2006, 118, 2398; Angew. Chem. Int.
Ed. 2006, 45, 2338.
[21] Y. Uemura, S. Mori, K. Hara, N. Koumura, Chem. Lett. 2011, 40,
872.
[22] F. F. Santiago, J. Bisquert, G. G. Belmonte, G. Boschloo, A. Hag-
feldt, Sol. Energy Mater. Sol. Cells 2005, 87, 117.
[23] F. S. Francisco, G. B. Germꢆ, M. S. Ivꢇn, J. Bisquert, Phys. Chem.
Chem. Phys. 2011, 13, 9083.
[24] Z. S. Wang, Y. Cui, Y. Dan-oh, C. Kasada, A. Shinpo, K. Hara, J.
Phys. Chem. C 2007, 111, 7224.
[25] N. Ishimaru, W. Kubo, T. Kitamura, S. Yanagida, Y. Tsukahara,
M. M. Maitani, Y. Wada, Mater. Sci. Eng. B 2011, 176, 996.
[26] G. L. Zhang, Y. Bai, R. Li, D. Shi, S. Wenger, S. M. Zakeeruddin, M.
Grꢀtzel, P. Wang, Energy Environ. Sci. 2009, 2, 92.
[17] Z. J. Ning, Q. Zhang, W. J. Wu, H. C. Pei, B. Liu, H. Tian, J. Org.
Chem. 2008, 73, 3791.
Received: November 28, 2011
Published online: February 10, 2012
Chem. Asian J. 2012, 7, 982 – 991
ꢁ 2012 Wiley-VCH Verlag GmbH & Co. KGaA, Weinheim
www.chemasianj.org
991