A polymer gel electrolyte to achieve ≥6% power conversion efficiency with a novel organic dye incorporating a low-band-gap chromophore

Article abstract of DOI:10.1039/b809376h

A quasi-solid-state dye-sensitized solar cell with novel organic sensitizers incorporating a benzothiadiazole chromophore showed excellent long-term stability, which exhibited 10% decrease during the 1000 h light soaking; the optimized cell gave a short circuit photocurrent density of 12.03 mA cm^-2, an open circuit voltage of 0.720 V and a fill factor of 0.76, corresponding to an overall conversion efficiency of 6.61% under standard global AM 1.5 solar conditions. The Royal Society of Chemistry 2008.

Full text of DOI:10.1039/b809376h

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PAPER
www.rsc.org/materials | Journal of Materials Chemistry
A polymer gel electrolyte to achieve $6% power conversion efficiency with
a novel organic dye incorporating a low-band-gap chromophore
a
a
b
b
c
a
Jeum-Jong Kim, Hyunbong Choi, Ji-Won Lee, Moon-Sung Kang, Kihyung Song, Sang Ook Kang*
a
and Jaejung Ko*
Received 3rd June 2008, Accepted 16th August 2008
First published as an Advance Article on the web 26th September 2008
DOI: 10.1039/b809376h
A quasi-solid-state dye-sensitized solar cell with novel organic sensitizers incorporating
a benzothiadiazole chromophore showed excellent long-term stability, which exhibited 10% decrease
during the 1000 h light soaking; the optimized cell gave a short circuit photocurrent density of 12.03 mA
ꢀ2
cm , an open circuit voltage of 0.720 V and a fill factor of 0.76, corresponding to an overall conversion
efficiency of 6.61% under standard global AM 1.5 solar conditions.
Introduction
While high conversion efficiency of 7% has been reached with
JK-46 using an ionic liquid under solvent-free conditions, the
long-term stability still remains a major challenge due to the
leakage. Extensive studies have been conducted to substitute
liquid electrolytes with solid-state or quasi-solid-state electro-
Increasing energy demands and depletion of fossil fuels have
1
led to the search for renewable energy sources in recent years.
Dye-sensitized solar cells (DSSCs) have attracted significant
attention as an alternative to the conventional solar cells due
2
to their low-cost of production and high performance. Some
8
lytes. In this article, we report meticulously designed organic
sensitizers containing a low-band-gap chromophore (Fig. 1). We
also investigated the effect of bridged structural modifications on
the power conversion efficiency and long-term-stability with
quasi-solid-state electrolytes.
polypyridyl ruthenium complexes have achieved power conver-
3
sion efficiencies over 10%. Although the ruthenium complexed
dyes exhibited high efficiency and long-term stability, they are
quite expensive and hard to purify. Recently, the solar cell
performance of DSSCs based on organic dye photosensitizers
has been remarkably improved and obtained efficiencies in the
Results and discussion
4
range of 7–9%. One of the main drawbacks of organic sensitizers
The organic sensitizers JK-68 and JK-69 were readily prepared
by the stepwise synthetic protocol illustrated in Scheme 1. The
4,7-dithiophen-2-yl-benzo[1,2,5]thiadiazoles 3 were synthesized
is the sharp and narrow absorption bands in the blue region of
the visible region, impairing their light-harvesting capabilities.
Another disadvantage of organic dyes in DSSCs is the low
stability under thermal stress and light-soaking stress. Therefore,
molecular engineering of organic sensitizers with a high
photovoltaic performance and an enhanced stability is para-
mount. Recently, a successful approach was introduced by
incorporating a nonplanar bis-dimethylfluorenylamino moiety
5
and a bi- or terthiophene unit into the organic framework,
which not only achieves high efficiency but also stabilizes device
performance under long-term light soaking. Using solvent-free
ionic liquid electrolytes, the JK-46 sensitizer thus formed yielded
6
a strikingly high conversion efficiency of 7%. To further improve
the photovoltaic performance of this system, an enhanced
spectral response of the sensitizer in the red region is required.
The introduction of low-band gap chromophores such as the
benzothiadiazole unit in the bridging framework is presumed to
be increased for the spectral response in the red portion of the
7
solar spectrum.
a
Department of New Material Chemistry, Korea University, Jochiwon,
Chungnam, 339-700, Korea. E-mail: jko@korea.ac.kr; Fax: +82 41 867
5
396; Tel: +82 41 860 1337
b
Energy & Environment Lab., Samsung Advanced Institute of Technology
(
SAIT), Yongin, 446-712, Korea
c
Department of Chemistry, Korea National University of Education,
ChongwonChungbuk, 363-791, Korea
Fig. 1 Molecular structure of JK-68 and JK-69.
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Fig. 2 Absorption and emission spectra of JK-68 (solid line) and JK-69
(
dotted line) in THF, and absorption spectra of JK-68 (dashed line) and
JK-69 (dash-dotted line) absorbed on TiO film.
2
Scheme 1 Synthesis of JK-68 and JK-69. Reactants: (a) PdCl
tributyl(2-thienyl)stannane 2a or 2-(3-hexylthiophen-2-yl)-4,4,5,5-tetra-
methyl-[1,3,2]-dioxaborolane 2b, dry THF; (b) NBS, (CH Cl
: AcOH ¼
0 : 50, V/V); (c) 4, Pd(Ph , Na CO , toluene–EtOH–H O; (d) POCl
DMF; (e) cyanoacetic acid, piperidine, CHCl
2 3 2
(PPh ) ,
conjugated system. Similar phenomena were observed in
12
julolidine dyes or conjugated organic dyes. When the JK-69
2
2
sensitizer was absorbed on a TiO electrode, a slight red shift
2
5
3
)
4
2
3
2
3
,
from 468 to 488 nm was found due to the J-aggregation on TiO
electrode. The absorption spectra of the two dyes on TiO elec-
trode are broad. Such a broadening of the absorption spectra is
2
3
.
2
9 10
by Stille or Suzuki coupling reactions of 4,7-dibromo-2,1,3-
13
due to an interaction between the dyes and TiO
Electrochemical properties of the two sensitizers JK-68 and
JK-69 were evaluated by cyclovoltammetry in CH CN with
0.1 M tetrabutylammonium hexafluorophosphate. TiO films
2
.
7a
benzothiadiazole 1 with stannylthiophene 2a or 2-(3-hexylth-
iophen-2-yl)-4,4,5,5-tetramethyl[1,3,2]dioxaborolane 2b. The
bromothiophenyl derivatives 4 were synthesized by bromination
3
2
of 3 with NBS (N-bromosuccinimide) in CH COOH and
3
stained with the sensitizers were used as working electrodes. The
CH Cl . The Suzuki coupling reaction of 4 with bis(9,9-
2
oxidation potential of the two sensitizers absorbed on TiO film
2
2
dimethyl-9H-fluoren-2-yl)-[4-(4,4,5,5-tetramethyl-[1,3,2]-diox-
aborolan-2-yl)-phenyl]amine 5 yielded 6a–6b. The thiophene
derivatives were converted to their corresponding carbaldehydes
show a quasi-reversible couple at 0.98 V and 1.08 V versus NHE
(normal hydrogen electrode). The reduction potential of the two
dyes calculated from the oxidation potential and the E0–0 deter-
mined from the intersection of absorption and emission spectra is
summarized in Table 1. The excited state oxidation potentials
11
7
a–7b according to the Vilsmeier–Haack reaction. The alde-
hydes 7a and 7b, upon reaction with cyanoacetic acid in the
presence of piperidine in chloroform, produced the sensitizers
JK-68 and JK-69.
(E* ) of the dyes (JK-68: ꢀ0.95 V vs. NHE; JK-69: ꢀ0.99 V vs.
ox
NHE) are much more negative than the conduction band of TiO
2
Fig. 2 shows the absorption and emission spectra of sensitizers
JK-68 and JK-69 measured in THF and the data are listed
in Table 1. The absorption spectrum of JK-68 displays two
at approximately ꢀ0.5 V vs. NHE.
We performed the molecular orbital calculation of JK-68 and
JK-69 to gain insight into the geometrical configuration and
3
ꢀ1
ꢀ1
*
photophysical properties using the B3LYP/3-21G (Fig. 4). The
absorption maxima at 534 nm (3 ¼ 19 700 dm mol cm ) and
3
ꢀ1
ꢀ1
3
74 nm (3 ¼ 36 690 dm mol cm ), which are assigned as the
calculation illustrates that the HOMO of JK-68 and JK-69 is
delocalized over the p-conjugated system through the phenyl
amino unit and the LUMO is delocalized over the cyanoacrylic
unit. Examination of the HOMO and LUMO of both dyes
indicates that HOMO–LUMO excitation moves the electron
distribution from the phenyl amino unit to the cyanoacrylic acid
moiety, and the photo-induced electron transfer from the dyes to
p–p* transitions of the conjugated system. Under the same
conditions the JK-69 that contains the hexyl group on thiophene
3
units exhibits absorption maxima at 468 nm (3 ¼ 19 290 dm
ꢀ1
ꢀ1
3
ꢀ1
ꢀ1
mol cm ) and 370 nm (3 ¼ 72 000 dm mol cm ). The
introduction of a low-band-gap chromophore instead of the
middle thiophene unit in JK-45 caused a red shift to 38–104 nm.
On the other hand, a significant blue shift of JK-69 compared to
JK-68 can be readily interpreted by the molecular modeling
study of the two sensitizers. The ground state structure of JK-68
2
TiO electrode can occur efficiently at the HOMO–LUMO
transition.
The photovoltaic performance of the DSSCs was obtained
using a polymer gel electrolyte comprising 0.6 M 1,2-dimethyl-
ꢁ
possesses a 20.6 twist between N,N-bis(9,9-dimethylfluoren-
2
-yl)aniline and thienyl unit. The dihedral angle of the thienyl
ꢁ
n-propylimidazolium iodide, 0.1 M I , poly(vinylidenefluoride-
2
and benzothiadiazole units in JK-68 is 5.8 (Fig. 3). For JK-69,
ꢁ
co-hexafluoro)propylene (5% PVDF–HFP) and 0.5 M NMBI in
3-methoxypropionitrile (MPN). Fig. 5 shows a photocurrent
density–voltage curve for the DSSCs based on the JK-68 and
JK-69 dyes and the polymer gel electrolyte under standard global
the dihedral angles of the corresponding units are 21.2 and
ꢁ
4
4.4 , respectively. Accordingly, a significant red shift of JK-68
relative to JK-69 derives from more delocalization over an entire
5
224 | J. Mater. Chem., 2008, 18, 5223–5229
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Table 1 Optical, oxidation and DSSC performance parameters of dyes
a
ꢀ1
ꢀ1
b
c
d
ꢀ2
e
h (%)
Dye
l
abs /nm (3/M cm
)
E
ox /V
E
0–0 /V
E
LUMO /V
J
sc/mA cm
9.58
12.03
V
oc/V
FF
JK-68
JK-69
534 (19 740); 374 (36 690)
468 (19 290); 370 (72 000)
0.98
1.08
1.93
2.07
ꢀ0.95
ꢀ0.99
0.643
0.720
75.54
76.19
4.66
6.61
a
b
Absorption spectra were measured in ethanol solution. Oxidation potentials of dyes on TiO
1
with a scan rate of 50 mV s (vs. NHE).
. Performances of DSSCs were measured with 0.18 cm working area. Electrolyte: DMPImI (0.6 M), I (0.1 M), NMBI (0.5 M), PVDF–
2
HFP (5 wt%) in MPN.
2
were measured in CH CN with 0.1M (n-C
3
4
H
9
)
4
NPF
6
ꢀ
c
d
E
0–0 was determined from intersection of absorption and emission spectra in ethanol.
2
E
LUMO was calculated
e
by Eox ꢀ E0–0
Fig. 3 The optimized structure calculated with TD-DFT on B3LYP/3-
21G* of a) JK-69 and b) JK-68.
Fig. 5 Spectra of monochromatic incident photon-to-current conver-
sion efficiencies (IPCEs) & J–V curve for DSSC based on spectra of
JK-68 (solid line) and JK-69 (dashed line), Electrolyte: DMPImI (0.6 M),
2
I (0.1 M), NMBI (0.5 M), PVDF–HFP (5 wt%) in MPN.
under the same conditions. A significant increase of Voc in JK-69
is related to the introduction of hexyl groups substituted at the
thiophene units. The alkyl chains are quite effective in increasing
the electron lifetime by preventing the dark current, improving
V
oc of the cell (Fig. 7) and reducing the reorganization energy of
14b
the dye, improving Jsc of the cell. The J–V curve of both
sensitizers is shown in the inset of Fig. 5. The incident photon to
current conversion efficiency (IPCE) of JK-69 exceeds 65% in
a spectral range from 430 to 610 nm, reaching its maximum of
7
3% at 520 nm. For comparison, we measured the photovoltaic
performance by using a volatile electrolyte. The power conver-
sion efficiency of the JK-68, JK-69 and JK-2 based DSSCs can be
increased to 7.51, 8.19 and 8.01% (for JK-68: Jsc ¼ 17.10 mA
Fig. 4 Isodensity surface plots of the HOMO and LUMO of a) JK-68
and b) JK-69.
ꢀ2
ꢀ2
cm ; Voc ¼ 0.61 V; ff ¼ 0.72. for JK-69: Jsc ¼ 14.98 mA cm ;
ꢀ
2
V
oc ¼ 0.77 V; ff ¼ 0.77. for JK-2: Jsc ¼ 14.80 mA cm ; Voc ¼
AM 1.5 solar conditions. The JK-68 and JK-69 sensitized cells
gave the short circuit photocurrent density (Jsc) of 9.58 and
0.74 V; ff ¼ 0.74), respectively, by using an acetonitrile electrolyte
2
comprising 0.6 M DMPImI, 0.05 M I , 0.1 M LiI, and 0.5 M
ꢀ2
1
2.03 mA cm , open circuit voltage (Voc) of 0.643 and 0.720 V
tert-butylpyridine.
and a fill factor of 0.75 and 0.76, corresponding to an overall
conversion efficiency of 4.66 and 6.61%, respectively. To the best
of our knowledge, the efficiency of 6.61% is the highest ever
reported for DSSCs based on organic sensitizer, even higher than
Fig. 6 shows the photovoltaic performance during long-term
accelerated aging of JK-68 and JK-69 sensitized solar cells using
a quasi-solid electrolyte. In particular, the device employing
JK-69 showed an excellent long-term stability, the initial effi-
ciency of 6.61% slightly decreased to 6.0% during the 1000 h
light-soaking test. After 1000 h of light soaking, the Voc of JK-69
decreased by 73 mV, but the loss was compensated by an increase
in the short-circuit current density. The long-term stability of the
6
.1% efficiency obtained by combining an amphiphilic poly-
pyridyl ruthenium sensitizer (Z-907) with a polymer gel electro-
14a
lyte. It is noteworthy that the open circuit voltage (Voc) for
DSSCs based on JK-69 is significantly higher than that for JK-68
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Fig. 6 Evolution of solar cell parameters with JK-68 (blue line, :) and
JK-69 (red line, -) during visible-light soaking (AM 1.5G, 100 mW
ꢀ
2
cm ) at 60 C. A 420 nm cut-off filter was put on the cell surface during
ꢁ
illumination. Electrolyte: DMPImI (0.6 M), I
PVDF–HFP (5 wt%) in MPN.
2
(0.1 M), NMBI (0.5 M),
device is remarkable because only a few ruthenium polypyridyl
sensitizers passed the light-soaking stress for 1000 h while
retaining an efficiency over 6% using a quasi-solid electrolyte.
The enhanced stability of JK-69 compared to JK-68 can be
attributed to the substituted hexyl chains by preventing the
approach of acceptors to the TiO
ing the dark current.
2
surface, resulting in prevent-
To understand the electron-injection property and the change
in Voc of JK-68 and JK-69 more clearly, we measured the electron-
diffusion coefficient and lifetimes of the photoelectrode. Fig. 7
shows the electron-diffusion coefficient (D ) and lifetime (t ) of
Fig. 7 Electron diffusion coefficients (a) and lifetimes (b) in the photo-
electrodes adsorbing different dyes (i.e. JK-68, JK-69, and JK-2).
e
e
the DSSCs employing different dyes (i.e. JK-68, JK-69, and JK-2)
as a function of the Jsc. Note that we considered the similar
structured organic dye (i.e. JK-2) for the comparison. The Jsc
values in the x-axis increased with an increase in the initial laser
intensity controlled by ND filters with different optical densities.
measured under (a) illumination and (b) dark conditions. Under
ꢀ2
the illumination (100 mW cm , open-circuit voltage (OCV)
conditions), the radius of the intermediate frequency semicircle in
the Nyquist plot decreased in the order of JK-69 (75.8 U) > JK-2
(64.9 U) > JK-68 (46.1 U), indicating the improved electron
generation and transport. This result also corresponds well to that
of the short-circuit current shown in Table 1. In the dark under
forward bias (ꢀ0.67 V), the semicircle in intermediate frequency
regime demonstrates the dark reaction impedance caused by the
The D
e e
and t values were determined by the photocurrent and
photovoltage transients induced by a stepwise change in the laser
15–18
light intensity controlled with a function generator.
The De
value was obtained by a time constant (t ) determined by fitting
c
ꢀ
a decay of the photocurrent transient with exp(ꢀt/t ) and the TiO
electron transport from the conduction band of TiO to I ions in
2
c
2
3
2
15
19
electrolyte. The increased radius of the semicircle in the inter-
mediate frequency regime means the reduced electron recombi-
film thickness (u) using the equation, D ¼ u /(2.77t ). The t
e
c
e
value was also determined by fitting a decay of photovoltage
1
5
transient with exp(ꢀt/t). The D
e
values of the photoanodes
2
nation rate at the dyed TiO –electrolyte interface. In the dark, the
adsorbing the organic dyes are shown to be very similar to each
other at the identical short-circuit current conditions. This result
radius of the intermediate-frequency semicircle showed the
increasing order of JK-68 (33.4 U) < JK-69 (121.3 U) < JK-2
indicates that the D
molecules, showing the similar trend to those of coumarin dyes.
However, the t values of JK-69 were drastically enhanced,
e
values are hardly affected by the kind of dye
e
(124.8 U), in accord with the trends of the Voc and t values.
In conclusion, we designed and synthesized two highly efficient
organic sensitizers containing a low-band-gap chromophore
(JK-68 and JK-69). The device based on the sensitizer JK-69 and
a polymer gel electrolyte gave an overall conversion efficiency of
6.61%. The efficiency is the highest one reported for DSSCs
based on organic sensitizer. Moreover, the JK-69 sensitized solar
cell with a polymer gel electrolyte showed an excellent stability
e
compared with those of JK-68, with the help of the hydrophobic
aliphatic chains retarding the electron recombination originated
from the direct contact between the electrons on TiO surface and
2
ꢀ
I3 ions in the electrolyte. The results of the electron lifetime are
also consistent with those of the Voc shown in Table 1.
ꢁ
The ac impedances of the cells were measured under dark and
illumination conditions. Fig. 8 shows the ac impedance spectra
under light soaking at 60 C for 1000 h. We believe that the
development of highly efficient organic sensitizers with excellent
5
226 | J. Mater. Chem., 2008, 18, 5223–5229
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Photoelectrochemical data were measured using a 1000 W
xenon light source (Oriel, 91193) that was focused to give 1000 W
ꢀ2
m , the equivalent of one sun at Air Mass(AM) 1.5, at the
surface of the test cell. The light intensity was adjusted with a Si
solar cell that was double-checked with an NREL-calibrated Si
solar cell (PV Measurement Inc.). The applied potential and
measured cell current were measured using a Keithley model
2
400 digital source meter. The current–voltage characteristics of
the cell under these conditions were determined by biasing the
cell externally and measuring the generated photocurrent. This
process was fully automated using Wavemetrics software.
Fluorine-doped tin oxide (FTO) glass plates (Pilkington TEC
Glass-TEC 8, solar 2.3 mm thickness) were cleaned in a detergent
solution using an ultrasonic bath for 30 min and then rinsed with
water and ethanol. Then, the plates were immersed in 40 mM
ꢁ
TiCl
4
(aqueous) at 70 C for 30 min and washed with water and
ethanol. A transparent nanocrystalline layer was prepared on the
FTO glass plates by using a doctor blade printing TiO paste
Solaronix, Ti-Nanoxide T/SP), which was then dried for 2 h at
2
(
ꢁ
2
5 C. The TiO
ꢁ
2
electrodes were gradually heated under an air
ꢁ
ꢁ
flow at 325 C for 5 min, at 375 C for 5 min, at 450 C for
ꢁ
1
5 min, and at 500 C for 15 min. The thickness of the trans-
parent layer was measured by using an Alpha-step 250 surface
profilometer (Tencor Instruments, San Jose, CA). A paste
containing 400 nm sized anatase particles (CCIC. PST-400C)
was deposited by means of doctor blade printing to obtain the
ꢁ
scattering layer, and then dried for 2 h at 25 C. The TiO
2
elec-
ꢁ
trodes were gradually heated under an air flow at 325 C for
ꢁ
ꢁ
ꢁ
5
min, at 375 C for 5 min, at 450 C for 15 min, and at 500 C for
15 min. The resulting film was composed of a 10 mm thick
transparent layer and a 4 mm thick scattering layer. The TiO
Fig. 8 Electrochemical impedance spectra measured under the illumi-
ꢀ
2
nation (100 mW cm ) and at the dark for the cells employing different
2
ꢁ
dyes (i.e. JK-68, JK-69, and JK-2).
electrodes were treated again with TiCl
at 70 C for 30 min and
4
ꢁ
sintered at 500 C for 30 min. Then, they were immersed in JK-68
(0.3 mM in tetrahydrofuran and 10 mM CDCA) and JK-69
(0.3 mM in tetrahydrofuran) solutions and kept at room
temperature for 24 h. FTO plates for the counter electrodes were
stability is possible through sophisticated structural modifica-
tions, and work on these is now in progress.
cleaned in an ultrasonic bath in H
2
O, acetone, and 0.1M aqueous
Experimental
HCl, subsequently. The counter electrodes were prepared by
Electron diffusion coefficients and lifetimes were measured by the
stepped light-induced transient measurements of photocurrent
placing a drop of an H
2
PtCl
6
solution (2 mg Pt in 1 mL ethanol)
ꢁ
on an FTO plate and heating (at 400 C) for 15 min. The dye
15–17
and voltages (SLIM-PCV).
The transients were induced by
adsorbed TiO
2
electrodes and the Pt counter electrodes were
ꢁ
a stepwise change in the laser intensity. A diode laser (l ¼ 635 nm)
as a continuous light source was modulated using a function
generator (UDP-303, PNCYS Co. Ltd, Korea). The initial laser
assembled into a sealed sandwich-type cell by heating at 80 C
using a hot-melt ionomer film (Surlyn) as a spacer between the
electrodes. A drop of the electrolyte solution was placed in the
drilled hole of the counter electrode and was driven into the cell
via vacuum backfilling. Finally, the hole was sealed using addi-
tional Surlyn and a cover glass (0.1 mm thickness).
ꢀ
2
intensity was a constant 90 mW cm and was attenuated up to
ꢀ2
approximately 10 mW cm using a ND filter, which was posi-
2
tioned at the front side of the fabricated samples (0.04 cm ). The
laser was operated at a voltage of 3.0 V and stepped down to 2.9 V
for 5 s. Then the single shot of the time profiles of the photocurrent
and photovoltage was obtained from an oscilloscope (TDS
4
,7-Di-thiophen-2-yl-benzo[1,2,5]thiadiazole (3a)
3
052B, Tektronix) through a current amplifier (SR570, Stanford
To a stirred solution of 4,7-dibromo-2,1,3-benzothiadiazole 1
(2 g, 6.8 mmol) and tributyl(2-thienyl)stannane 2a (5.2 mL,
16.4 mmol) in dry THF (50 mL) was added PdCl (PPh ) (97 mg,
Research Systems) and a voltage amplifier (5307, NF electronic
Instruments), respectively. For the measurement of SLIM-PCV,
the TiO2 thickness of the photoelectrode was controlled at
approximately 3.3 mm. The measurements were carried out at
ambient temperature and atmosphere and low relative humidity
2
3 2
2 mol%). The mixture was refluxed under a nitrogen atmosphere
for 3 h. After removal of the solvent under reduced pressure, the
residue was purified by column chromatography on silica gel
(
<10%) conditions. We have checked the cell temperature using
(CH
2
Cl
2
: hexane ¼ 1 : 2, R ¼ 0.32). Recrystallization from
f
a thermocouple and were not aware of significant changes in the
temperature during the measurements.
ethanol gave the title compound 3a (1.8 g) as red–orange needles.
1
Yield: 88%. mp 124–125 C. H NMR (CDCl
ꢁ
3
): d 8.10 (d, 2H, J
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¼
2.4 Hz), 7.84 (s, 2H), 7.45 (d, 2H, J ¼ 4.5 Hz), 7.21 (dd, 2H, J ¼
phenyl]amine 5 (272 mg, 0.45 mmol), Pd(PPh3)4 (56 mg),
1
3
3
.9 and 5.1 Hz). C NMR (CDCl ): d 153.0, 139.8, 128.4, 127.9,
3
Na CO (50 mg) was dissolved in toluene (20 ml)–EtOH (20 ml)–
2
3
1
27.2, 126.4, 126.2. Anal. calcd for C H N S : C, 55.97; H, 2.68.
1
H O (20 ml) and the mixture was refluxed for 12 h. After evap-
2
4
8
2
3
Found: C, 55.78; H, 2.71.
orating the solvent under reduced pressure, H
methylene chloride (50 ml) were added. The organic layer was
separated and dried in MgSO . The solvent was removed under
reduced pressure. The pure product 6a was obtained by column
chromatography on silica gel using CH Cl as an eluent (R
.63). Yield: 68%. mp 137 C. H NMR (CDCl
): 8.13 (d, 2H, J ¼
.3 Hz), 7.88 (s, 2H), 7.68–7.13 (m, 6H), 7.46–7.13 (m, 15H), 1.44
2
O (50 ml) and
4
,7-Bis-(3-hexylthiophen-2-yl)benzo[1,2,5]thiadiazole (3b)
,7-Dibromo-2,1,3-benzothiadiazole 1 (673 mg, 2.3 mmol) and 2-
4
4
2
2
f
¼
(
3-hexylthiophen-2-yl)-4,4,5,5-tetramethyl-[1,3,2]-dioxaborolane
b (1.35 g, 4.59 mmol), Pd(PPh (266 mg, 5 mol%), and
Na CO (488 mg, 4.6 mmol) were dissolved in toluene (30 ml)–
EtOH (20 ml)–H O (20 ml) and the mixture was refluxed for 20 h.
After evaporating the solvent under reduced pressure, H O
ꢁ
1
0
3
3
2
3 4
)
13
2
3
(
s, 12H). C NMR (CDCl ): 155.3, 153.7, 152.8, 152.6, 147.9,
3
2
1
47.1, 145.7, 139.6, 139.1, 139.0, 137.8, 134.6, 134.2, 128.9, 128.2,
127.5, 127.2, 126.9, 126.7, 126.1, 126.0, 125.7, 125.2, 123.8, 123.5,
23.3, 122.7, 120.8, 119.6, 119.0, 47.0, 29.8. Anal. calcd for
C H N S : C, 77.38; H, 4.81. Found: C, 77.98; H, 4.84.
2
(
50 ml) and methylene chloride (50 ml) were added. The organic
1
layer was separated and dried in MgSO . The solvent was
4
5
0
37
3 3
removed under reduced pressure. The pure product 3b was
obtained by column chromatography on silica gel (CH
2
Cl
): 7.64
s, 2H), 7.44 (d, 2H, J ¼ 5.7 Hz), 7.10 (d, 2H, J ¼ 5.1 Hz), 2.66
2
:
Bis(9,9-dimethyl-9H-fluoren-2-yl)-(4-{4-hexyl-5-[7-(3-
hexylthiophen-2-yl)benzo[1,2,5-]thiadiazol-4-yl]-thiophen-2-
yl}phenyl)amine (6b)
1
hexane ¼ 1 : 2, R
f
¼ 0.41). Yield: 70%. H NMR (CDCl
3
(
(
t, 4H, J ¼ 7.8 Hz), 1.62 (m, 2H), 1.20 (m, 12H), 0.80 (t, 6H, J ¼
1
3
6
.9 Hz). C NMR (CDCl
27.6, 126.0, 31.7, 30.8, 29.5, 29.2, 22.7, 14.2. Anal. calcd for
: C, 66.62; H, 6.88. Found: C, 66.76; H, 6.43.
3
): 154.4, 141.8, 132.3, 130.0, 129.4,
The product 6b was prepared using the same procedure for 6a
ꢁ
1
1
except that 4b was used instead of 4a. Yield: 71%. mp 100 C. H
NMR (CDCl ): 7.74–7.64 (m, 8H), 7.50–7.16 (m, 15H), 2.76 (m,
H), 1.74 (m, 4H), 1.51 (s, 12H), 1.29 (m, 12H), 0.90 (m, 6H).
NMR (CDCl ): 155.2, 154.4, 154.2, 153.6, 147.6, 147.1, 144.5,
42.9, 141.7, 139.0, 134.4, 132.3, 131.1, 130.0, 129.6, 129.3, 128.5,
C
26
H
32
N
2
S
3
3
13
4
C
3
4
-(5-Bromothiophen-2-yl)-7-(thiophen-2-
1
1
1
yl)benzo[1,2,5]thiadiazole (4a)
27.5, 127.3, 127.1, 126.6, 126.0, 124.7, 123.9, 123.4, 122.6, 120.8,
19.5, 118.8, 46.9, 31.7, 30.8, 29.8, 29.5, 29.2, 29.1, 27.1, 22.7,
A solution of 4,7-di-2-thienyl-2,1,3-benzothiadiazole 3a (350 mg,
1
.17 mmol) in acetic acid (50 ml) and CH Cl (50 ml) was stirred
2 2
62 61 3 3
22.6, 14.2, 14.1. Anal. calcd for C H N S : C, 78.85; H, 6.51.
at room temperature. Then NBS (229 mg, 1.28 mmol) was added
in small portions over 30 min. The solution was stirred overnight,
The mixture was poured into water (100 ml) and the separated
organic layer was dried over magnesium sulfate, and the solvent
was evaporated. The crude product was separated by flash
Found: C,78.69; H, 6.88.
5
-[7-(5-{4-[Bis(9,9-dimethyl-9H-fluoren-2-yl)-
amino]phenyl}thiophen-2-yl)benzo[1,2,-5]thiadiazol-4-
yl]thiophene-2-carbaldehyde (7a)
column chromatography on silica gel (CH
2
Cl
2
: hexane ¼ 1 : 4,
Phosphorus oxychloride was added to 6a in N,N-dime-
ꢁ
R
f
¼ 0.46). Compound 4a was obtained as a orange powder.
ꢁ
1
Yield: 70%. mp 126 C. H NMR (CDCl
thylformamide (DMF, 5 ml) at 0 C. The solution was stirred for
ꢁ
3
): 8.12 (d, 1H, J ¼
2
4hat 80 C. Afterremoval of DMF in vacuo, the reaction mixture
3
3
1
1
4
.3 Hz), 7.82 (m, 3H), 7.47 (d, 1H, J ¼ 5.1 Hz), 7.21 (dd, 1H, J ¼
13
was neutralized with sodium acetate and extracted with methylene
chloride. The crude product was purified by column chromatog-
.9 and 4.5 Hz), 7.15 (d, 1H, J ¼ 3.9 Hz). C NMR (CDCl ):
3
52.6, 152.3, 140.8, 139.3, 130.8, 128.2, 127.8, 127.2, 127.1, 126.4,
25.7, 125.2, 125.0, 114.6. Anal. calcd for C H BrN S : C,
raphy using methylene chloride as an eluent (R
f
¼ 0.34). Yield:
): 9.97 (s, 1H), 8.20 (m, 2H),
.01 (d, 1H, J ¼ 7.9 Hz), 7.91 (d, 1H, J ¼ 8.1 Hz), 7.84 (d, 1H, J ¼
.9 Hz), 7.68–7.59 (m, 6H), 7.42–7.12 (m, 13H), 1.43 (s, 12H).
1
4
7
2 3
ꢁ
1
6
8
3
5%. mp 145 C. H NMR (CDCl
3
4.33; H, 1.86. Found: C, 44.46; H, 2.00.
13
C
4
-(5-Bromo-3-hexylthiophen-2-yl)-7-(3-hexylthiophen-2-yl)-
NMR (CDCl ): 182.4, 155.7, 155.1, 155.8, 153.8, 147.4, 146.9,
3
benzo[1,2,5]thiadiazole(4b)
1
45.1, 143.5, 143.1, 143.3, 142.7, 139.8, 138.2, 134.4, 130.2, 130.0,
The product 4b was prepared using the same procedure for 4a
1
except that 3b was used instead of 3a. Yield: 56%. H NMR
129.1, 129.0, 128.2, 127.0, 126.7, 126.4, 125.7, 124.8, 123.6, 123.4,
122.4, 120.8, 119.5, 118.3, 46.7, 29.6. Anal. calcd for
C H N OS : C, 76.18; H, 4.64. Found: C, 76.02; H, 4.50.
(
CDCl
.5 Hz), 7.07 (d, 1H, J ¼ 1.2 Hz), 2.65 (m, 4H), 1.61 (m, 4H), 1.21
m, 12H), 0.81 (m, 6H). C NMR (CDCl ): 154.2, 153.9, 142.3,
41.8, 133.8, 132.0, 131.9, 129.8, 129.2, 127.9, 126.1, 126.0, 113.0,
1.6, 31.5, 30.7, 30.5, 29.4, 29.1, 29.0, 22.5, 14.1. Anal. calcd for
3
): 7.63 (m, 2H), 7.44 (d, 1H, J ¼ 5.1 Hz), 7.11 (d, 1H, J ¼
5
1
37
3
3
4
13
(
3
5
-[7-(5-{4-[Bis(9,9-dimethyl-9H-fluoren-2-yl)-amino]phenyl}-3-
hexylthiophen-2-yl)b-enzo[1,2,5]thiadiazol-4-yl]-4-
hexylthiophene-2-carbaldehyde (7b)
1
3
C H BrN S : C, 57.02; H, 5.71. Found: C, 56.90; H, 5.53.
2
6
31
2 3
The product 7b was prepared using the same procedure for 7a
except that 6b was used instead of 6a and excess phosphorus
Bis(9,9-dimethyl-9H-fluoren-2-yl)-{4-[5-(7-thiophen-2-
ylbenzo[1,2,5]thiadiazol-4-yl)-thiophen-2-yl]-phenyl}amine (6a)
ꢁ
1
oxychloride (10 equiv.). Yield: 60%. mp 93 C. H NMR
CDCl ): 9.96 (s, 1H), 7.79–7.13 (m, 22H), 2.70 (m, 4H), 1.66 (m,
4H), 1.44 (s, 12H), 1.25 (m, 12H), 0.87 (m, 6H). C NMR
(
3
13
A mixture of 4a (170 mg, 0.45 mmol), bis(9,9-dimethyl-9H-
fluoren-2-yl)-[4-(4,4,5,5-tetramethyl-[1,3,2]-dioxaborolan-2-yl)-
(CDCl
3
): 183.1, 155.2, 154.1, 153.8, 153.7, 147.8, 147.1, 145.1,
5
228 | J. Mater. Chem., 2008, 18, 5223–5229
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1
1
1
2
7
43.4, 143.2, 143.0, 142.7, 139.0, 138.0, 134.5, 130.6, 130.5, 129.2,
29.1, 128.3, 127.2, 126.7, 126.6, 125.7, 124.9, 123.8, 123.5, 122.6,
20.8, 119.6, 118.9, 47.0, 31.7, 31.6, 30.8, 30.5, 29.9, 29.5, 29.3,
4 (a) T. Horiuchi, H. Miura and S. Uchida, Chem. Commun., 2003,
3
036; (b) T. Horiuchi, H. Miura, K. Sumioka and S. Uchida,
J. Am. Chem. Soc., 2004, 126, 12218; (c) L. Schmidt-Mende,
U. Bach, R. Humphry-Baker, T. Horiuchi, H. Miura, S. Ito,
S. Uchida and M. Gr a¨ tzel, Adv. Mater., 2005, 17, 813; (d) S. Ito,
S. M. Zakeeruddin, R. Humphry-Baker, P. Liska, R. Charvet,
P. Comte, M. K. Nazeeruddin, P. P e´ chy, M. Takada, H. Miura,
S. Uchida and M. Gr a¨ tzel, Adv. Mater., 2006, 18, 1202; (e)
T. Kitamura, M. Ikeda, K. Shigaki, T. Inoue, N. A. Anderson,
X. Ai, T. Lian and S. Yanagida, Chem. Mater., 2004, 16, 1806; (f)
K. Hara, T. Sato, R. Katoh, A. Furube, T. Yoshihara, M. Murai,
M. Kurashige, S. Ito, A. Shinpo, S. Suga and H. Arakawa, Adv.
Funct. Mater., 2005, 15, 246; (g) N. Koumura, Z.-S. Wang, S. Mori,
M. Miyashita, E. Suzuki and K. Hara, J. Am. Chem. Soc., 2006,
128, 14256.
5 (a) S. Kim, J. K. Lee, S. O. Kang, J. Ko, J.-H. Yum, S. Fantacci, F. De
Angelis, D. Di Censo, M. K. Nazeeruddin and M. Gr a¨ tzel, J. Am.
Chem. Soc., 2006, 128, 16701; (b) I. Jung, J. K. Lee, K. H. Song,
K. Song, S. O. Kang and J. Ko, J. Org. Chem., 2007, 72, 3652; (c)
S. Kim, H. Choi, D. Kim, K. Song, S. O. Kang and J. Ko,
Tetrahedron, 2007, 63, 3115.
9.1, 27.2, 22.7, 22.6, 14.2, 14.1. Anal. calcd for C63
7.82; H, 6.32. Found: C, 77.87; H, 6.43.
61 3 3
H N OS : C,
3
-{5-[7-(5-{4-[Bis(9,9-dimethyl-9H-fluoren-2-yl)-
amino]phenyl}thiophen-2-yl)benzo-[1,2,5]thiadiazol-4-
yl]thiophen-2-yl}-2-cyanoacrylic acid (8a)
A mixture of 7a (48 mg, 0.06 mmol) and cyanoacetic acid (10 mg,
.12 mmol) was vacuum-dried and CHCl and piperidine were
added. The solution was refluxed for 15 h. Then H O (50 ml) was
added. The organic layer was separated and dried over MgSO
0
3
2
4
.
The solvent was removed under reduced pressure. The pure
product 8a was obtained by column chromatography on silica gel
1
ꢁ
(
CH
2
Cl
2
: MeOH ¼ 6 : 1, R
f
¼ 0.27). Yield: 58%. mp 290 C. H
6
H. Choi, C. Baik, S. O. Kang, J. Ko, M.-S. Kang, M. K. Nazeeruddin
and M. Gr a¨ tzel, Angew. Chem., Int. Ed., 2008, 47, 327.
NMR (DMSO-d
6
): 8.49 (s, 1H), 8.24–8.04 (m, 5H), 7.74–7.49
13
(
m, 9H), 7.31 (m, 6H), 7.10 (m, 4H), 1.37(s, 12H). C NMR
DMSO-d ): 169.9, 163.1, 154.9, 153.2, 151.7, 151.5, 147.3, 146.4,
7
(a) M. Velusamy, K. R. Justin Thomas, J. T. Lin, Y.-C. Hsu and
K.-C. Ho, Org. Lett., 2005, 10, 1899; (b) Q. M. Zhou, Q. Hou,
L. P. Zheng, X. Y. Deng, G. Yu and Y. Cao, Appl. Phys. Lett.,
(
6
1
1
1
45.7, 143.5, 140.9, 138.4, 138.2, 136.6, 135.6, 134.2, 129.6, 129.4,
27.8, 127.1, 127.0, 126.8, 126.5, 126.0, 125.0, 124.1, 123.7, 123.3,
23.2, 122.7, 121.3, 119.7, 119.1, 118.7, 46.5, 26.7. Anal. calcd for
2
004, 84, 1653; (c) C. J. Brabec, C. Winder, N. S. Sariciftci,
J. C. Hummelen, A. Dhanabalan, P. A. Van Hal and
R. A. Janssen, Adv. Funct. Mater., 2002, 12, 709; (d) C. Winder
and N. S. Sariciftci, J. Mater. Chem., 2004, 12, 1077; (e)
E. Bundgaard and F. C. Krebs, Sol. Energy Mater. Sol. Cells,
54 38 4 2 3
C H N O S : C, 74.46; H, 4.40. Found: C, 74.11; H, 4.30.
2
2006, 39, 2823.
007, 91, 954; (f) E. Bundgaard and F. C. Krebs, Macromolecules,
3
-{5-[7-(5-{4-[Bis(9,9-dimethyl-9H-fluoren-2-yl)-amino]phenyl}-
3-hexylthiophen-2-yl)benzo[1,2-,5]thiadiazol-4-yl]-4-
8
(a) U. Bach, D. Lupo, P. Comte, J. E. Moser, F. Weiss o¨ rtel,
J. Salbeck, H. Spreizer and M. Gr a¨ tzel, Nature, 1998, 395, 583; (b)
G. R. A. Kumara, A. Konno, K. Shiratsuchi, J. Tsukahara and
K. Tennakone, Chem. Mater., 2002, 14, 954; (c) J. H. Kim,
M.-S. Kang, Y. J. Kim, J. Won, N.-G. Park and Y. S. Kang, Chem.
Commun., 2004, 1662; (d) M. Biancardo, K. West and F. C. Krebs,
Sol. Energy Mater. Sol. Cells, 2006, 90, 2575; (e) S. Lu, R. Koeppe,
S. Gunes and N. S. Sariciftci, Sol. Energy Mater. Sol. Cells, 2007,
(
hexylthiophen-2-yl}-2-cyanoacrylic acid (8b)
The product 8b was prepared using the same procedure for 8a
ꢁ
1
except that 7b was used instead of 7a. Yield: 64%. mp 224 C. H
NMR (DMSO-d ): 8.32 (s, 1H), 7.75–7.11 (m, 22H), 3.42 (m, 4H),
.45 (m, 4H), 1.36 (s, 12h), 1.10 (m, 12H), 0.71 (m, 6H). C NMR
DMSO-d ): 168.5, 162.7, 155.1, 153.5, 151.6, 151.3, 147.7, 146.4,
6
13
2
9
1, 1081; (f) T. C. Wei, C. C. Wan and Y. Y. Wang, Sol. Energy
(
6
Mater. Sol. Cells, 2007, 91, 1892; (g) J. N. Freitas, C. Longo,
A. F. Nogueira and M.-A. Paoli, Sol. Energy Mater. Sol. Cells,
1
1
1
3
45.5, 143.3, 140.6, 138.0, 137.7, 136.5, 135.8, 134.1, 129.6, 129.3,
27.3, 127.1, 126.9, 126.8, 126.3, 126.0, 124.9, 124.0, 123.6, 123.1,
23.0, 122.7, 121.8, 120.0, 118.9, 117.7, 47.5, 33.7, 32.6, 30.7, 30.5,
0.0, 29.6, 29.2, 29.1, 27.0, 22.0, 21.6, 13.9, 13.8. Anal. calcd for
2
008, 92, 1110.
M. M. M. Raposo, A. M. C. Fonseca and G. Kirsch, Tetrahedron,
004, 60, 4071.
9
2
10 X. Zhang, H. Gorohmaru, M. Kadowaki, T. Kobayashi, T. Ishi-i,
T. Thiemann and S. Mataka, J. Mater. Chem., 2004, 14, 1901.
C H N O S : C, 76.26; H, 6.01. Found: C, 76.61; H, 6.31.
2 3
6
6
62
4
1
1
1
1 (a) V. J. Majo and P. T. Perumal, J. Org. Chem., 1996, 61, 6523;
b) O. Meth-Cohn and M. Ashton, Tetrahedron Lett., 2000, 41,
2749.
2 (a) S. Kim, H. Choi, C. Baik, K. Song, S. O. Kang and J. Ko,
Tetrahedron, 2007, 63, 11436; (b) H. Choi, J. K. Lee, K. H. Song,
K. Song, S. O. Kang and J. Ko, Tetrahedron, 2007, 63, 1553.
3 K. Hara, M. Kurashige, Y. Dan-oh, C. Kasada, A. Shinpo, S. Suga,
K. Sayama and H. Arakawa, New J. Chem., 2003, 27, 783.
(
Acknowledgements
We are grateful to the KOSEF through National Research
Laboratory (No. R0A-2005-000-10034-0) program, the MKE
(
(
The Ministry of Knowledge and Economy) under the ITRC
Information Technology Research Center) program (IITA-
14 (a) P. Wang, S. M. Zakeeruddin, J. E. Moser, M. K. Nazeeruddin,
T. Sekiguchi and M. Gr a¨ tzel, Nat. Mater., 2003, 402; (b)
N. Koumura, Z. S. Wang, S. Mori, M. Miyashita, E. Suzuki and
K. Hara, J. Am. Chem. Soc., 2006, 128, 14256.
2
008-C1090-0804-0013) and BK21 (2006).
1
5 S. Nakade, T. Kanzaki, Y. Wada and S. Yanagida, Langmuir, 2005,
1, 10803.
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This journal is ª The Royal Society of Chemistry 2008
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