Aqueous electrolyte based dye-sensitized solar cells using organic sensitizers

Article abstract of DOI:10.1039/c2nj40577f

Two novel organic sensitizers containing a 2-(2-methoxyethoxy)ethyl unit are designed and synthesized. Under standard global AM 1.5 solar conditions, the JK-262 sensitized cell in conjunction with an aqueous electrolyte gave a short-circuit photocurrent density (J_sc) of 3.78 mA cm^-2, an open-circuit voltage (V_oc) of 0.68 V, and a fill factor of 0.82, affording an overall conversion efficiency (η) of 2.10%. The η of JK-262 is higher than that of JK-259 due to the larger J_sc. The improved J_sc value is attributable to the broad and red-shifted absorption band as well as the dense packing of JK-262 on the TiO₂ film.

Full text of DOI:10.1039/c2nj40577f

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Aqueous electrolyte based dye-sensitized solar cells
using organic sensitizers†
Hyeju Choi,a Ban-Seok Jeong,a Kwangseok Do,a Myung Jong Ju,a Kihyung Songb
and Jaejung Ko*a
Cite this: NewJ.Chem., 2013,
37, 329
Two novel organic sensitizers containing a 2-(2-methoxyethoxy)ethyl unit are designed and synthesized.
Under standard global AM 1.5 solar conditions, the JK-262 sensitized cell in conjunction with an
aqueous electrolyte gave a short-circuit photocurrent density (Jsc) of 3.78 mA cmꢀ2, an open-circuit
voltage (Voc) of 0.68 V, and a fill factor of 0.82, affording an overall conversion efficiency (Z) of 2.10%.
The Z of JK-262 is higher than that of JK-259 due to the larger Jsc. The improved Jsc value is
attributable to the broad and red-shifted absorption band as well as the dense packing of JK-262 on
the TiO2 film.
Received (in Montpellier, France)
6th July 2012,
Accepted 15th October 2012
DOI: 10.1039/c2nj40577f
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Introduction
The photovoltaic technology has been considered as an effective way
to solve the current energy and environmental crisis.1 Dye-sensitized
solar cells are attracting wide-spread interest for the conversion of
sunlight into electricity because of their low cost and high effi-
ciency.2 A typical DSSC consists of three main parts: dye-sensitized
TiO2 photoanode, electrolyte with Iꢀ/I3ꢀ redox couple, and catalytic
Fig. 1 Structure of the dyes (JK-259 and JK-262).
4ꢀ/3ꢀ
counter electrode. In these cells, the electrolyte is one of the key dye-sensitized solar cell based on the Fe(CN)6
redox couple
components for high power conversion efficiency. The use of using an organic sensitizer, showing a high conversion efficiency of
organic volatile electrolytes and organic dyes as sensitizers in DSSCs 4.1%.9 This finding encouraged us to revisit the water-based DSSCs
is achieved a power conversion efficiency in the range of 8–10%.3 using the organic sensitizers in conjunction with aqueous electro-
However, organic based electrolytes with volatility and flammability lytes. In this work, we report water-based DSSCs using the organic
degrade the durability and safety of the cell.4 The best option for the sensitizers (JK-259 and JK-262) containing 4-(2-(2-methoxyethoxy)-
electrolyte is to use water because water-based DSSCs are less ethoxy)phenylamine as the electron donor and cyanoacrylic acid as
expensive and environmentally benign. Since 1990, it has been the electron acceptor bridged by the 9,9-bis(2-(2-methoxyethoxy)-
generally accepted that the water present in the organic electrolyte ethyl)-9H-fluorenyl linker (Fig. 1). We introduced a 2-(2-methoxy-
of DSSCs is poisonous for efficient solar energy conversion.5 There- ethoxy)ethyl unit on an organic unit to increase water solubility.
fore, water permeation on organic based DSSCs should be pre-
vented by barrier layers.6 Recently, O’Regan and co-workers7 have
shown that high water content in the electrolyte is not inseparably
Result and discussion
linked to poor efficiency and/or instability in DSSCs. So far, most of
work on water-based electrolytes have centered on the ruthenium
dyes.8 Recently, Spiccia and co-workers have described an aqueous
Scheme1illustratesthesyntheticproceduresof organicsensitizers(JK-
259 and JK-262) starting from a 2-bromo-7-iodo-9H-fluorene 1. The
2-bromo-7-iodo-9,9-bis(2-(2-methoxyethoxy)ethyl)-9H-fluorene 2 was
synthesized by alkylation of 1 with 1-iodo-2-(2-methoxyethoxy)-
ethane in the presence of t-BuOK. N-Phenylation of 2 with bis(4-(2-(2-
methoxyethoxy)ethoxy)phenyl)amine was performed under Buchwald
reaction.10 Compound 5 was prepared from 4 by a lithiation with
1.2 equiv. ofn-butyllithium andsubsequentquenchingwithDMF. The
Heck reaction11 of 5 with vinylboronic acid pinacol ester led to 6. The
attachment of 6 to 3 was achievedby theSuzukicoupling reaction.12
a Department of Advanced Material Chemistry, Korea University, 2511 Sejong-ro,
Sejong City 339-700, Korea. E-mail: jko@korea.ac.kr; Fax: +82 44 860 1331;
Tel: +82 44860 1337
b Department of Chemical Education, Korea National University of Education,
Cheongwon, Chungbuk 363-791, Korea
† Electronic supplementary information (ESI) available. See DOI: 10.1039/
c2nj40577f
c
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Electrochemical properties of the sensitizers JK-259 and JK-262
were scrutinized in acetonitrile with 0.1 M tetrabutylammonium
hexafluorophosphate using TiO2 film with absorbed dyes as working
electrodes. The two organic sensitizers adsorbed on a TiO2 film
showed quasi-reversible couples. The oxidation potentials of JK-259
and JK-262 were measured to be 0.90 and 0.94 V vs. NHE, respec-
tively. The high oxidation potential relative to that of the triiodide/
iodide couple (+0.5 V) could lead to fast dye regeneration. The
reduction potentials of two dyes calculated from the oxidation
potentials and the E0–0 determined from the intersection of normal-
ized absorption and emission spectra15 were calculated to be ꢀ1.78
and ꢀ1.46 V vs. NHE. Therefore, the downhill energy offset of the
LUMO in the two dyes ensures an ample driving force for electron
injection.16
The highest-occupied molecular orbitals (HOMOs) and lowest-
unoccupied molecular orbitals (LUMOs) of JK-259 and JK-262 were
performed with the B3LYP/6-21G* (Fig. 3). The calculation reveals
that the HOMO is delocalized over the p-conjugated system via the
diphenylamino group through the fluorenyl unit and the LUMO is
delocalized over the cyanoacrylic unit through fluorenyl and 3,4-
ethyldioxythiophenyl groups. The examination of HOMO–LUMO
illustrates that the photoinduced electron transfer from JK-259 or
JK-262 dyes to TiO2 electrodes can efficiently occur by the
HOMO–LUMO transition as shown in Fig. 3.
Scheme 1 Schematic diagram for the synthesis of dyes.
Table 1 demonstrates the device performance of two cells
constructed with the addition of up to 100% water to the electrolyte.
The electrolyte used in both cells consists of 2 M 1-propyl-3-
methylimidazolium iodide (PMMI), 0.05 M iodine, 0.1 M guanidi-
nium thiocyanate (GuSCN), and 0.5 M tert-butylpyridine (TBP) in
methoxypropionitrile (MPN). In order to prevent phase separation in
the 100% water electrolyte, 1% Triton X-100 was added to the
electrolytic solution.17 At water containing electrolyte in both dyes,
Fig. 2 Absorption and emission spectra of JK-259 (black solid lines) and JK-262
(red solid lines) in THF.
The Knoevenagel condensation13 of the aldehydes 7 and 9 with
cyanoacetic acid in the presence of piperidine yielded the sensi-
tizers JK-259 and JK-262.
Fig. 2 shows the electronic absorption and emission spectra
of the JK-259 and JK-262 sensitizers measured in THF. The
absorption spectrum of JK-259 exhibits an intense absorption
peak at 418 nm (e = 83 400 dm3 molꢀ1 cmꢀ1), which is due to
the p–p* transition of the conjugate molecule. Obviously, the
absorption coefficient is enhanced with the increase of the
conjugation length. Under the same conditions, the JK-262
sensitizer with a 3,4-ethyldioxythiophenyl unit on the spacer
framework exhibits a strong absorption band at 449 nm, which
is 31 nm red-shifted relative to that of JK-259. The red-shift
derives from the presence of an electron-rich 3,4-ethylenedioxy-
thiophenyl unit14 and a small distortion angle with respect
to the fluorenyl unit (24.41). When the JK-259 and JK-262
sensitizers are excited within their p–p* band in an air-
equilibrated solution at 298 K, the photoluminescence spectra
of JK-259 and JK-262 exhibit strong luminescence maxima of
542 and 598 nm, respectively.
Fig. 3 Isodensity surface plots of the HOMO ꢀ 1, HOMO, LUMO, LUMO + 1 of
(a) JK-259 and (b) JK-262.
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Table 1 Photovoltaic performance of DSSCs with three dyes and electrolytes
with different water contents
Dye
Water content (%) Jsc (mA cmꢀ2
)
Voc (V) FF
Z (%)
JK-259
0
20
40
60
80
100
0
20
40
60
80
100
0
5.60
4.54
3.34
2.73
2.31
2.28
8.10
6.29
5.54
4.90
4.37
3.78
9.60
6.62
4.30
3.31
0.70
0.65
0.62
0.65
0.66
0.66
0.74
0.66
0.66
0.67
0.67
0.68
0.75
0.74
0.75
0.74
0.77 3.00
0.72 2.12
0.72 1.48
0.77 1.38
0.81 1.24
0.79 1.16
0.73 4.39
0.71 2.93
0.73 2.65
0.76 2.51
0.77 2.21
0.82 2.10
0.76 5.46
0.82 4.02
0.77 2.48
0.82 2.01
JK-262
JK-2
20
60
100
TBP treatment on the TiO2 films improved the photovoltaic perfor-
mance and stability. The sensitizers without any addition of TBP
were easily decomposed. A large increase in Voc and Jsc occurred for
both dyes when 0.5 M TBP was added into the electrolyte. A similar
phenomenon was observed in organic electrolyte-based DSSCs.18 As
shown in Table 1, the fill factor (ff) and open-circuit voltage in
the water-containing electrolyte gradually increased with the incre-
mental addition of water, but the short-circuit photocurrent (Jsc)
sharply decreased under the same conditions. The decrease of
photocurrent may be contributable to the dye detachment,19 for-
mation of iodates20 as well as decrease in electron lifetime.17
The incident monochromatic photon-to-current conversion effi-
ciency (IPCE) with a sandwich type cell based on JK-259 and JK-262
is shown in Fig. 4. IPCE values higher than 20% were observed in
the range of 370–470 nm with a maximum value of 26% at 455 nm
for the device based on JK-259 in 100% water based electrolyte.
Under the same conditions, the action spectrum of JK-262 is red-
shifted by 100 nm compared to that of JK-259 due to an apparent
red-shift in the absorption spectrum. Under standard global air
mass 1.5 solar conditions, the JK-259 sensitized cell in 100% water
containing electrolyte gave a short circuit photocurrent density (Jsc)
of 2.28 mA cmꢀ2, an open circuit voltage (Voc) of 0.66 V, and a fill
factor (ff) of 0.79, corresponding to an overall conversion efficiency
(Z) of 1.16%. Under the same conditions, the JK-262 sensitized cell
gave a Jsc of 3.78 mA cmꢀ2, a Voc of 0.68 V, and a ff of 0.82,
corresponding to an Z value of 2.1ꢀ0%, which is the highest one in
the water based DSSCs with Iꢀ/I3 electrolytes. The increased fill
factor upon the incremental addition of water may be attributable to
the fast catalytic characteristic, resulting in the reduced resistance. Fig. 4 (a) J–V curve and (b) IPCE spectra of JK-259 and (c) J–V curve and (d) IPCE
spectra of JK-262.
For comparison, we fabricated the cell using the sensitizer with
hydrophobic nature (JK-2). Upon the incremental addition of water,
the efficiency was sharply dropped from 5.46% in no water electro-
lyte to 2.10% in 100% water electrolyte. Therefore, the molecular originates from a broad and red-shifted absorption band (Fig. 2) and
engineering of organic sensitizers with hydrophilic terminals the dense packing of JK-262 on the TiO2 films. To check the effect of
demonstrates some advantage for aqueous electrolyte based DSSCs. packing on both sensitizers, we measured the amount of dyes
From these results, we have observed that the Z value of the JK-262 adsorbed on the TiO2 films by desorbing the dyes from the TiO2
based cell is higher than that of the JK-259 based cell due to a large surface with KOH. The amount of two dyes adsorbed on the TiO2
photocurrent. The large photocurrent in JK-262 relative to JK-259 film were measured to be 7.01 ꢁ 10ꢀ6 and 8.84 ꢁ 10ꢀ6 mmol cmꢀ2
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for JK-259 and JK-262, respectively. The low adsorption of JK-259 may
be attributable to the presence of two bulky (2-methoxy-ethoxy)ethyl
units. The bulky sensitizer requires more space on the TiO2 surface
and penetrates less easily in the small cavities of the TiO2 than the
less hindered sensitizer. Therefore, the electron recombination can
be facilitated along with the insufficient coverage on the TiO2
surface, resulting in the decrease in the te value.21
Fig. 5 shows the lifetimes (te) of the DSSCs employing W00 (no
water) and W100 (100% water) for JK-259 and W00 and W100 for
JK-262 displayed with a function of Jsc and Voc. The te values show a
big gap among the dyes, giving W00 of JK-262 4 W00 of JK-259 4
W100 of JK-262 4 W100 of JK-259. The different te values might be
derived from the different dye structures. The te values of JK-262
were longer than those of JK-259 due to the relatively poor dye
adsorption on the TiO2 film. The electron recombination can be
facilitated along with the insufficient coverage on the TiO2 surface
for JK-259 dye, resulting in the decrease in the te values.21 The
result of the electron lifetime in both dyes is consistent with that of
Voc shown in Table 1.
The electrocatalytic activity of CE in DSSCs can be conveniently
evaluated by using symmetrical dummy cells, in which a thin
layer of electrolyte solution is sandwiched between two identical
electrodes.22–25 Fig. 6a shows the Nyquist plots of the symmetrical
dummy cells consisting of two Pt-coated FTO electrodes with
different amounts of water in the electrolyte. The experimental data
could be fitted into the equivalent circuit shown in the inset of
Fig. 6a, which is well known as a Randles-type circuit, where RS is
ohmic serial resistance, RCT is charge transport resistance at the
interface between electrode surface and electrolyte, ZD is the Nernst
diffusion impedance in the bulk electrolyte solution between the
two identical electrodes, and CPE is a constant phase element
describing deviation from the ideal capacitance due to the surface
roughness of the electrodes.26,27
Fig. 6 (a) Nyquist plots of electrochemical impedance spectra (EIS) measured at 0 V
from 106 Hz to 0.1 Hz on dummy cells with two identical Pt-coated FTO electrodes
with an AC amplitude of 10 mV. The inset is equivalent circuit diagram for fitting the
EIS data. Solid lines are fitted curves to the equivalent circuit. (b) Electrochemical
impedance spectra measured under the illumination (100 mW cmꢀ2) for JK-262
employing different dyes (’ W00, K W20, . W60, % W100).
Table 2 Electrochemical parameters obtained by fitting the EIS data of the
The corresponding electrochemical parameters, obtained by
fitting the plots with ZView software based on the equivalent
circuit, are listed in Table 2. The resulted RCT values imply that
reference and water-added dummy cells, using an equivalent circuit
Electrolyte
RS (O cm2)
RCT (O cm2)
CPE:b
the charge transfer resistance of the water-added dummy cells W00
2.47
2.59
1.98
2.34
2.21
0.14
0.08
0.81
0.96
0.96
0.96
0.94
W20
is decreased compared to that of the reference dummy cell,
which is in agreement with the report by Sakaguchi et al. on
W60
W100
quasi-solid state DSSCs with chemically cross-linked gelators.28
The RCT is an important parameter to evaluate the catalytic
performance of counter electrode (CE) in DSSCs. It is because
the exchange current density, J0 (i.e., the equal cathodic and
anodic currents normalized to the projected electrode area at
equilibrium), should be akin to photocurrent density on the
TiO2 photoanode working under full sun illumination on a CE.
29
The J0 varies inversely with the RCT
.
A lower RCꢀT implies a
more facile electron transfer from the CE to the I3 ions and,
therefore, the Jsc of the DSSC increases relative to that of the
reference DSSC. In fact, there is one report that Jsc increases
with increasing water content, as a result of the decreased
charge transfer resistance,30 in contrast to the decrease in Jsc
noted in other reports.31,32 Fig. 6b shows the Nyquist plots of
the DSSCs at open circuit condition under 1 sun illumination.
In typical EIS analysis, the RS of DSSCs is generally composed of
at least three internal resistances. The semicircles in the
Fig. 5 Lifetimes in the photoelectrodes different dyes (n W00 of JK-262;
J W00 of JK-259; & W100 of JK-262;B W100 of JK-259).
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different frequency regimes indicate the Nernst diffusion limited ferrocenium/ferrocene redox couple was used as an internal
impedance of the redox species in the electrolyte, impedance by reference.
transport and recombination competition at the TiO2/dye/electrolyte
interface (RTR), and electrochemical charge transfer resistance at the
Electron transport measurements
CE/electrolyte interface (RCT). The semicircle at the highest fre- The electron lifetimes (te) in the TiO2 photoelectrode were mea-
quency regime in Fig. 6b is related to the CE/electrolyte event, sured by the stepped light-induced transient measurements of
and the RCT at the CE/electrolyte interface can be obtained from the photocurrent and voltage (SLIM-PCV).36–39 The transients were
real component values. As shown in Fig. 6b, RCT of the DSSCs with induced by a stepwise change in the laser intensity. A diode laser
W60 and W100 is so active that cannot be fitted, but RCT of the (l = 635 nm) as a light source was modulated using a function
DSSCs with W20 and W00 exhibits 6.8 and 6.1, respectively. The generator. The initial laser intensity was constant 90 mW cmꢀ2 and
presence of water in the electrolyte solution increases its hydro- was attenuated up to approximately 10 mW cmꢀ2 using a ND filter
philicity and thus would facilitate the charge transfer at the which was positioned at the front side of the fabricated samples
electrode/electrolyte interface due to the enhanced movement of (TiO2 film thickness = ca. 6 mm; active area = 0.04 cm2). The
the ionic species. The increased fill factor of the water added DSSCs photocurrent and photovoltage transients were monitored using a
except for the DSSC with W20 compared to that of the reference digital oscilloscope through an amplifier. The te value was deter-
DSSC in Table 1 also supports this observation. It is known that the mined by fitting a decay of photovoltage transient with exp(ꢀt/te).36
fill factor depends on the resistances of the photoanode, electrolyte All experiments were conducted at room temperature.
and CE. The increase in the fill factor in the case of the cell with
Fabrication of cell
W60 and W100 is attributed to its lower charge transfer resistance,
relative to that of the cell without water additives.
FTO glass plates (Pilkington TEC Glass-TEC 8, Solar 2.3 mm thick-
In contrast to the expectation based on the decrease in RCT as ness) were cleaned in a detergent solution using an ultrasonic bath
shown in Fig. 6a, however, the Jsc values of the water-added for 30 min, rinsed with water and ethanol. The FTO glass plates
DSSCs were decreased compared to that of the DSSC with W00, were immersed in 40 mM TiCl4 (aqueous) at 70 1C for 30 min and
as shown in Table 1. RTR of the intermediate frequency semi- washed with water and ethanol. A transparent nanocrystalline layer
circles in the Nyquist plots for JK-262 decreased in the order of on the FTO glass plate was prepared by doctor blade printing TiO2
W100 (50.5 O) 4 W60 (46.2 O) 4 W20 (33.6 O) 4 W00 (22.1 O), paste (Solaronix, Ti-Nanoxide T/SP) and then dried for 2 h at 25 1C.
indicating the improved charge generation and transport. This The TiO2 electrodes were gradually heated under an air flow at
result is consistent with that of short circuit photocurrent shown 325 1C for 5 min, at 375 1C for 5 min, at 450 1C for 15 min, and at
in Table 1. In summary, we can conclude that the decrease in the 500 1C for 15 min. The thickness of the transparent layer was
Jsc values of the water-containing DSSCs in the electrolyte could measured by using an Alpha-step 250 surface profilometer (Tencor
be explained by the detachment of the adsorbed dye through the Instruments, San Jose, CA), a paste for the scattering layer contain-
hydrolysis of the TiO2–water surface linkage.
ing 400 nm sized anatase particles (CCIC, PST-400C) was deposited
by doctor blade printing and then dried for 2 h at 25 1C. The TiO2
electrodes were gradually heated under an air flow at 325 1C for
5 min, at 375 1C for 5 min, at 450 1C for 15 min, and at 500 1C for
Experimental
2-Bromo-7-iodo-9H-fluorene (1),33 1-iodo-2-(2-methoxyethoxy)- 15 min. The resulting layer was composed of 20 mm thickness of
ethane,34 and 7-bromo-2,3-dihydrothieno[3,4-b][1,4]dioxine-5- transparent layer and 4 mm thickness of scattering layer. The TiO2
carbaldehyde35 were synthesized according to the procedures electrodes were treated again by TiCl4 at 70 1C for 30 min and
in the literatures.
sintered at 500 1C for 30 min. The TiO2 electrodes were immersed
1H and 13C NMR spectra were recorded using a Varian Mercury into the JK-259 and JK-262 (0.3 mM in acetonitrile : tert-butanol :
300 spectrometer. MALDI-TOF Mass spectrometry was performed ethanol = 2 : 1 : 1) and kept at room temperature for 16 h. The FTO
using Voyagert DE-STR, 4700 Proteomics. Optimized structures plate (Pilkington TEC Glass-TEC 8, Solar 2.3 mm thickness) for
were calculated by TD-DFT using the B3LYP functional and the counter electrodes cleaned with an ultrasonic bath in H2O, acetone
6-21G* basis set. The highest occupied molecular orbital (HOMO) and 0.1 M HCl aq., subsequently. Counter electrodes were prepared
and lowest unoccupied molecular orbital (LUMO) energies were by coating with a drop of H2PtCl6 solution (2 mg of Pt in 1 mL of
determined using minimized singlet geometries to approximate the ethanol) on a FTO plate and heating at 400 1C for 15 min. The dye
ground state. UV-vis data were measured using a Perkin-Elmer adsorbed TiO2 electrode and Pt-counter electrode were assembled
Lambda 2S UV-visible spectrometer. Photoluminescence spectra into a sealed sandwich-type cell by heating at 80 1C with a hot-melt
were recorded on a Perkin LS fluorescence spectrometer. Cyclic ionomer film (Surlyn SX 1170-25, Solaronix) as a spacer between the
voltammetry (CV) was performed using VersaSTAT 3 (Princeton electrodes. A drop of electrolyte solution (2 M 1-propyl-3-methylimi-
Applied Research). Anhydrous acetonitrile was used as the solvent dazolium iodide (PMMI), 0.05 M iodine, 0.1 M guanidinium
and 0.1 M of tetrabutylammonium hexafluorophosphate was used thiocyanate (GuSCN), 0.5 M tert-butylpyridine (TBP) in methoxypro-
as the supporting electrolyte. TiO2 films stained with the sensitizers pionitrile (MPN) and water) was placed on the drilled hole in the
were used as working electrodes, a platinum wire as the counter counter electrode of the assembled cell and was driven into the cell
electrode, and a Ag/Ag+ electrode as the reference electrode. The via vacuum backfilling. Finally, the hole was sealed using additional
measurements were done using a scan rate of 50 mV sꢀ1 and Surlyn and a cover glass (0.1 mm thickness).
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2-Bromo-7-iodo-9,9-bis(2-(2-methoxyethoxy)ethyl)-9H-fluorene (2)
(1H, d, J = 8.1 Hz), 7.89 (1H, dd, J = 8.1 Hz, J = 1.5 Hz), 7.93 (1H, s),
10.05 (1H, s). 13C NMR (CDCl3, 75 MHz, ppm): d 39.25, 51.80, 58.84,
66.71, 69.79, 71.55, 120.12, 122.15, 123.00, 124.09, 126.95, 130.07,
130.73, 135.58, 137.80, 145.40, 149.46, 152.47, 191.57.
Compound 1 (1.5 g, 4.04 mmol) was dissolved in anhydrous THF
(20 mL) and cooled to 0 1C under a nitrogen atmosphere. To this
solution, tert-BuOK (1.36 g, 12.12 mmol) was added in several
portions. After stirring for 30 min, 1-iodo-2-(2-methoxyethoxy)ethane
(5.43 g, 16.16 mmol) was added to the solution and stirred at RT for
overnight. The resulting mixture was extracted with ethyl acetate,
dried over Na2SO4, filtered and concentrated under reduced pres-
sure. The residue was purified with silica column chromatography
using ethyl acetate/CH2Cl2 (3 : 7) as eluent to obtain as viscous oil in
60% yield. 1H NMR (CDCl3, 300 MHz, ppm): d 2.36 (6H, t, J =
7.5 Hz), 2.75 (6H, t, J = 7.5 Hz), 3.18 (4H, m), 3.30 (10H, m), 7.39 (1H,
d, J = 8.4 Hz), 5.31 (1H, br s), 6.82 (4H, d, J = 9.3 Hz), 6.91 (4H, d, J =
4.8 Hz). 7.46 (1H, dd, J = 8.1 Hz, J = 1.5 Hz), 7.51 (1H, d, J = 8.1 Hz),
7.53 (1H, d, J = 1.2 Hz), 7.67 (1H, dd, J = 7.8 Hz, J = 1.5 Hz), 7.74 (1H,
d, J = 1.2 Hz). 13C NMR (CDCl3, 75 MHz, ppm): d 39.45, 51.82, 59.02,
66.78, 69.93, 71.71, 93.07, 121.16, 121.19, 121.75, 126.64, 130.58,
132.55, 136.47, 138.36, 138.97, 150.61, 150.94.
(E)-9,9-Bis(2-(2-methoxyethoxy)ethyl)-7-(2-(4,4,5,5-tetra-methyl-
1,3,2-dioxaborol-an-2-yl)vinyl)-9H-fluorene-2-carbaldehyde (6)
Compound 5 (0.87 g, 1.82 mmol), vinylboronic acid pinacol ester
(0.31 mL, 1.82 mmol), diisopropylamine (1.04 mL, 7.37 mmol) and
bis(tri-tert-butylphosphine)palladium(0) (47.5 mg, 0.092 mmol) were
dissolved in dry toluene (10 mL) and stirred at 80 1C for 24 h. After
cooling, the resulting mixture was extracted with ethyl acetate, dried
over Na2SO4, filtered and concentrated under reduced pressure. The
product 6 was obtained by silica gel column chromatography using
EA as eluent in 60% yield. 1H NMR (CDCl3, 300 MHz, ppm): d 1.33
(12H, s), 2.41–2.50 (4H, m), 2.70–2.80 (4H, m), 2.14 (4H, m), 3.25
(10H, m), 6.26 (1H, d, J = 18.6 Hz), 7.44–7.57 (3H, m), 7.70–7.81
(2H, m), 7.88 (1H, d, J = 8.4 Hz), 7.94 (1H, s), 10.05 (1H, s). Anal.
calcd for C32H43BO7: C, 69.82; H, 7.87. Found: C, 69.58; H, 7.72%.
7-Bromo-N,N-bis(4-(2-(2-methoxyethoxy)ethoxy)phenyl)-9,9-
bis(2-(2-methoxy-ethoxy)ethyl)-9H-fluorene-2-amine (3)
(E)-7-(2-(7-(Bis(4-(2-(2-methoxyethoxy)ethoxy)phenyl)-amino)-
9,9-bis(2-(2-methoxyethoxy)ethyl)-9H-fluoren-2-yl)vinyl)-9,9-
Bis(4-(2-(2-methoxyethoxy)ethoxy)phenyl)-amine (0.33 g, 0.814 mmol), bis(2-(2-methoxyethoxy)ethyl)-9H-fluorene-2-carbaldehyde (7)
compound 2 (0.56 g, 0.974 mmol), tris(dibenzylidene-acetone)dipall-
Compound 3 (0.85 g, 0.997 mmol), compound 6 (0.55 g,
adium(0) (1.85 mg, 0.00202 mmol), 2,20-bis(diphenylphosphino)-
0.999 mmol), potassium carbonate (0.55 g, 3.98 mmol) in distilled
1,10-binaphthyl (3.80 mg, 0.0061 mmol) and sodium tertiary
water (2.0 mL) and tetrakis(tri-phenylphosphine)palladium(0)
butoxide (0.11 g, 1.15 mmol) in anhydrous toluene (10 mL) were
(58 mg, 0.050 mmol) in anhydrous THF (10 mL) were refluxed at
refluxed overnight. After cooling, a crude product was extracted with
80 1C for 24 h. After cooling, THF was evaporated under reduced
pressure. A crude product was extracted with ethyl acetate, dried over
ethyl acetate, dried over Na2SO4, filtered by a glass filter and
concentrated under reduced pressure. The residue was purified with
Na2SO4, filtered and concentrated under reduced pressure. The
silica column chromatography using ethyl acetate/CH2Cl2 (3 : 7) as
product 7 was obtained by silica gel column chromatography using
eluent to obtain as a brown oil in 50% yield. 1H NMR (CDCl3,
EA as eluent as an yellow oil in 32% yield. 1H NMR (CDCl3, 300 MHz,
300 MHz, ppm): d 2.20–2.24 (4H, m), 2.75–2.86 (4H, m), 3.21–3.26
ppm): d 2.18–2.41 (4H, m), 2.50 (4H, m), 2.73–2.91 (8H, m), 3.16–3.36
(4H, m), 3.30 (6H, s), 3.34 (4H, t, J = 4.5 Hz), 3.40 (6H, s), 5.42 (1H, s),
(28H, m), 3.40 (6H, s), 3.59 (4H, m), 3.74 (4H, m), 3.87 (4H, t, J =
7.46 (1H, dd, J = 8.1 Hz, J = 1.8 Hz), 7.50–7.56 (4H, m), 7.65 (1H, d, J =
4.8 Hz), 4.14 (4H, t, J = 4.8 Hz), 6.85 (4H, d, J = 9.0 Hz), 6.90 (1H, dd,
8.7 Hz). 13C NMR (CDCl3, 75 MHz, ppm): d 31.12, 39.53, 51.44, 59.19,
J = 8.1 Hz, J = 2.1 Hz), 7.00 (1H, d, J = 2.1 Hz), 7.04 (4H, d, J = 9.0 Hz),
7.24 (1H, d, J = 8.1 Hz), 7.46 (3H, t, J = 8.1 Hz), 7.54–7.57 (3H, m), 7.64
(1H, s), 7.76 (1H, d, J = 7.8 Hz), 7.81 (1H, d, J = 7.8 Hz), 7.89 (1H, dd,
59.27, 67.27, 67.84, 69.98, 70.08, 70.92, 71.94, 72.14, 115.61, 119.77,
120.50, 126.40, 126.50, 130.40, 132.19, 139.67, 141.23, 149.01, 149.91,
150.90, 155.10, 156.92. MALDI-TOF, m/z: calcd, 851.32; found,
J = 7.8 Hz, J = 1.2 Hz), 7.95 (1H, s), 10.05 (1H, s). 13C NMR (CDCl3, 75
851.36 (M+).
MHz, ppm): d 39.76, 51.05, 51.52, 59.13, 59.25, 67.10, 67.43, 67.83,
69.97, 70.06, 70.89, 71.83, 71.93, 72.13, 115.58, 115.81, 119.22,
120.12, 120.61, 121.05, 121.48, 124.31, 126.34, 126.64, 127.48,
130.06, 130.31, 132.99, 135.14, 135.37, 138.37, 138.74, 140.74,
7-Bromo-9,9-bis(2-(2-methoxyethoxy)ethyl)-9H-fluorene-2-
carbaldehyde (5)
2,7-Dibromo-9,9-bis(2-(2-methoxyethoxy)ethyl)-9H-fluorene (1.55 g, 141.32, 146.59, 148.76, 149.22, 150.14, 150.52, 151.08, 155.04.
2.93 mmol) was dissolved in anhydrous THF (30 mL) and cooled
3-(7-((E)-2-(7-(Bis(4-(2-(2-methoxyethoxy)ethoxy)phenyl)-
amino)-9,9-bis(2-(2-methoxyethoxy)ethyl)-9H-fluoren-2-
to ꢀ78 1C under a nitrogen atmosphere. A solution of n-butyllithium
(1.83 mL of a 1.6 M solution in hexane, 2.93 mmol) was added
yl)vinyl)-9,9-bis(2-(2-methoxyethoxy)ethyl)-9H-fluoren-2-yl)-2-
dropwise. After stirring at ꢀ78 1C for 1 h, DMF (0.49 mL, 6.33 mmol)
cyanoacrylic acid (JK-259)
was added to the solution and allowed to warm to room tempera-
ture for 2 h. The reaction was quenched by the addition of water, Compound 7 (100 mg, 0.084 mmol) and cyanoacetic acid (28.4 mg,
extracted with ethyl acetate, dried over Na2SO4, filtered and con- 0.334 mmol) were dissolved in dry CH3CN (40 mL) and THF (40 mL).
centrated under reduced pressure. The residue was used for the To this mixture, piperidine (0.1 mL) was added under a nitrogen
following reaction without further purification as viscous oil in 90% atmosphere and the solution was refluxed at 80 1C for 24 h. After
yield. 1H NMR (CDCl3, 300 MHz, ppm): d 2.38–2.52 (4H, m), cooling, 1 M HCl solution (10 mL) was added and the solution was
2.74–2.80 (4H, m), 3.15 (4H, m), 3.27 (10H, m), 7.52 (1H, dd, stirred at RT for 3 h. The resulting mixture was extracted with ethyl
J = 8.1 Hz, J = 1.5 Hz), 7.62 (1H, s), 7.63 (1H, d, J = 8.1 Hz), 7.80 acetate, dried over Na2SO4, filtered and concentrated under reduced
c
334 New J. Chem., 2013, 37, 329--336
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pressure. The product JK-259 was obtained by silica gel column 51.21, 59.13, 59.22, 64.74, 65.29, 67.37, 67.81, 69.94, 70.03, 70.87,
chromatography using ethyl acetate/methanol (9 : 1) as eluent. Red 71.89, 72.10, 115.24, 115.44, 115.59, 119.16, 120.32, 120.72, 121.50,
1
solid in 44% yield. H NMR (CD3OD, 300 MHz, ppm): d 2.15–2.36 125.85, 126.22, 126.47, 129.48, 129.85, 132.36, 137.53, 141.12, 141.41,
(4H, m), 2.45 (4H, m), 2.88 (8H, m), 3.12–3.28 (28H, m), 3.36 (6H, s), 149.13, 149.21, 150.74, 155.15, 179.51.
3.56 (4H, m), 3.68 (4H, m), 3.82 (4H, t, J = 4.5 Hz), 4.09 (4H, t, J =
(E)-3-(7-(7-(Bis(4-(2-(2-methoxyethoxy)ethoxy)phenyl)-amino)-9,9-
bis(2-(2-methoxyethoxy)ethyl)-9H-fluoren-2-yl)-2,3-dihydrothieno-
[3,4-b][1,4]dioxin-5-yl)-2-cyanoacrylic acid (JK-262)
4.5 Hz), 6.83 (1H, d, J = 2.4 Hz), 6.87 (4H, d, J = 9.0 Hz), 7.01 (4H, d,
J = 9.0 Hz), 7.19 (1H, d, J = 2.1 Hz), 7.34 (1H, d, J = 6.3 Hz), 7.43–7.56
(4H, m), 7.70–7.74 (2H, m), 7.79–7.81 (2H, m), 7.92 (1H, d, J = 8.1 Hz),
8.15 (1H, s), 8.22 (1H, s). 13C NMR (CD3OD, 75 MHz, ppm): d 40.37,
52.31, 52.82, 59.10, 68.21, 68.43, 68.89, 70.72, 70.83, 71.49, 72.74,
72.94, 110.52, 116.57, 119.54, 121.17, 121.56, 122.05, 125.74, 127.37,
131.38, 133.00, 134.36, 136.86, 139.59, 140.06, 141.64, 142.43, 145.07,
149.97, 150.56, 151.32, 151.77, 152.05, 156.41, 168.56. MALDI-TOF,
m/z: calcd, 1262.63; found, 1262.63 (M+). Anal. calcd for
C74H90N2O16: C, 70.34; H, 7.18. Found: C, 70.08; H, 7.11%.
Compound 9 (70 mg, 0.074 mmol) and cyanoacetic acid (25.0 mg,
0.29 mmol) were dissolved in dry CH3CN (20 mL) and THF (20 mL).
To this mixture, piperidine (0.1 mL) was added under a nitrogen
atmosphere and the solution was refluxed at 80 1C for 24 h. After
cooling, 1 M HCl solution (10 mL) was added and the solution was
stirred at RT for 3 h. The resulting mixture was extracted with ethyl
acetate, dried over Na2SO4, filtered and concentrated under
reduced pressure. The product JK-262 was obtained by silica gel
column chromatography using ethyl acetate/methanol (9 : 1) as
eluent in 34% yield. 1H NMR (CD3OD, 300 MHz, ppm): d
2.15–2.32 (4H, m), 2.88 (4H, m), 3.20–3.30 (14H, m), 3.37 (6H, s),
3.57 (4H, m), 3.70 (4H, m), 3.83 (4H, t, J = 4.5 Hz), 4.11 (4H, t, J =
4.2 Hz), 4.44 (4H, s), 6.84 (1H, d, J = 2.4 Hz), 6.89 (4H, d, J = 9.0 Hz),
7.00 (1H, d, J = 1.5 Hz), 7.03 (4H, d, J = 9.0 Hz), 7.50 (1H, d, J =
8.1 Hz), 7.57 (1H, d, J = 8.1 Hz), 7.72 (1H, d, J = 8.7 Hz), 7.83 (1H, s),
8.30 (1H, s). 13C NMR (CD3OD, 75 MHz, ppm): d 30.73, 40.27, 52.54,
59.07, 59.13, 66.08, 66.67, 68.40, 68.89, 70.71, 70.82, 71.48, 72.72,
72.92, 110.98, 116.57, 119.96, 120.22, 121.32, 121.75, 122.16, 126.75,
127.48, 131.00, 133.84, 139.06, 142.14, 142.34, 148.65, 150.32,
150.51, 151.95, 156.51. MALDI-TOF, m/z: calcd, 1008.41; found,
1008.48 (M+). Anal. calcd for C55H64N2O14S: C, 65.46; H, 6.39.
Found: C, 65.27; H, 6.24.
N,N-Bis(4-(2-(2-methoxyethoxy)ethoxy)phenyl)-9,9-bis-
(2-(2-methoxyethoxy)ethyl)-7-(4,4,5,5-tetramethyl-1,3,2-di-
oxaborolan-2-yl)-9H-fluorene-2-amine (8)
Compound 3 (0.16 g, 0.188 mmol) was dissolved in anhydrous
THF (20 mL) and cooled to ꢀ78 1C under a nitrogen atmosphere.
A solution of n-butyllithium (0.14 mL of a 1.6 M solution in
hexane, 0.23 mmol) was added dropwise. After stirring at ꢀ78 1C
for 30 min, 2-iso-propoxy-4,4,5,5-tetramethyl-1,3,2-dioxaborolane
(0.058 mL, 0.282 mmol) was added to the solution and allowed
to warm to room temperature for 2 h. The reaction was
quenched by the addition of water, extracted with ethyl acetate,
dried over Na2SO4, filtered and concentrated under reduced
pressure. The residue was used for the following reaction with-
out further purification. 1H NMR (CDCl3, 300 MHz, ppm): d 1.36
(12H, s), 2.16–2.38 (4H, m), 2.73–2.80 (4H, m), 3.21 (4H, m), 3.28
(6H, s), 3.33 (4H, t, J = 4.5 Hz), 3.39 (6H, s), 3.58 (4H, m) 3.73 (4H,
m), 3.85 (4H, t, J = 4.5 Hz), 4.12 (4H, t, J = 5.1 Hz), 6.83 (4H, dt, J =
8.7 Hz, J = 1.8 Hz), 6.87 (1H, dd, J = 8.4 Hz, J = 1.8 Hz), 6.98 (1H, d,
J = 2.1 Hz), 7.02 (4H, dt, J = 9.0 Hz, J = 2.1 Hz), 7.45 (1H, d, J = 8.1
Hz), 7.52 (1H, d, J = 7.2 Hz), 7.74 (2H, d, J = 9.6 Hz).
Conclusions
We have meticulously designed and synthesized a new class of
fluorenyl-bridged organic sensitizers for aqueous electrolytes. A
solar-cell device based on the organic sensitizer JK-262 in
conjunction with an aqueous electrolyte gave an overall con-
version efficiency of 2.10%. The power conversion efficiency of
the DSSCs based on the two sensitizers was shown to be
sensitive to the bridged units. Using a water-based electrolyte,
a greener process for DSSCs fabrication can be developed for
the realization of environmentally benign dye solar cells.
7-(7-(Bis(4-(2-(2-methoxyethoxy)ethoxy)phenyl)amino)-9,9-
bis(2-(2-methoxy-ethoxy)ethyl)-9H-fluoren-2-yl)-2,3-
dihydrothieno[3,4-b][1,4]dioxine-5-carbaldehyde (9)
Compound 8 (0.27 g, 0.300 mmol), 7-bromo-2,3-dihydrothieno[3,4-b]-
[1,4]dioxine-5-carbaldehyde (0.11 g, 0.441 mmol), 2 M solution of
potassium carbonate (0.17 g, 1.23 mmol) in distilled water (0.6 mL)
and tetrakis(triphenyl-phosphine)palladium(0) (17 mg, 0.015 mmol)
in anhydrous THF (30 mL) were refluxed at 80 1C for 24 h. After
cooling, THFwas evaporatedunder reduced pressure. A crude product
was extracted with ethyl acetate, dried over Na2SO4, filtered and
concentrated under reduced pressure. The product 9 was obtained
by silica gel column chromatography using ethyl acetate/CH2Cl2 as
Acknowledgements
We are grateful to the grant of Korea University research
program (2012).
1
eluent in 25% yield. H NMR (CDCl3, 300 MHz, ppm): d 2.18–2.37
Notes and references
(4H, m), 2.79–2.90 (4H, m), 3.23–3.26 (4H, m), 3.28 (6H, s), 3.29–3.35
(4H, m), 3.40 (6H, s), 3.59 (4H, m), 3.74 (4H, m), 3.87 (4H, t, J = 4.5 Hz),
4.14 (4H, t, J= 4.5 Hz), 4.43 (4H, s), 6.85 (4H, d, J= 8.7 Hz), 6.89 (1H, dd,
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(1H, s), 7.93 (1H, s). 13C NMR (CDCl3, 75 MHz, ppm): d 31.08, 39.48,
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