Thiophene-bridged double D-π-A dye for efficient dye-sensitized solar cell

Article abstract of DOI:10.1021/cm302250y

An organic dye containing two D-π-A branches linked with a thiophene unit has been designed and synthesized for efficient dye-sensitized solar cells (DSSCs). As compared to the rod-shape of the single D-π-A analogue dye, the cross shape of the double D-π-A branched dye is favorable for reducing intermolecular interaction and retarding charge recombination. Controlled intensity modulated photovoltage spectroscopy reveals that electron lifetime for the double D-π-A dye-based DSSC is 14-fold longer than that for the corresponding single D-π-A dye-based DSSC. Linking two D-π-A branches with a thiophene unit increases open-circuit photovoltage by 100 mV and short-circuit photocurrent by 4.10 mA cm^-2. As a consequence, power conversion efficiency is enhanced by about 2-fold. This work presents a new route to designing sensitizers with high suppression ability of charge recombination toward high-performance DSSCs.

Full text of DOI:10.1021/cm302250y

Article
pubs.acs.org/cm
Thiophene-Bridged Double D‑π‑A Dye for Efficient Dye-Sensitized
Solar Cell
Xiaoming Ren, Shenghui Jiang, Mingyang Cha, Gang Zhou, and Zhong-Sheng Wang*
Department of Chemistry & Lab of Advanced Materials, Fudan University, 2205 Songhu Road, Shanghai 200438, P. R. China
S
* Supporting Information
ABSTRACT: An organic dye containing two D-π-A branches linked with a
thiophene unit has been designed and synthesized for efficient dye-sensitized
solar cells (DSSCs). As compared to the rod-shape of the single D-π-A analogue
dye, the cross shape of the double D-π-A branched dye is favorable for reducing
intermolecular interaction and retarding charge recombination. Controlled
intensity modulated photovoltage spectroscopy reveals that electron lifetime
for the double D-π-A dye-based DSSC is 14-fold longer than that for the
corresponding single D-π-A dye-based DSSC. Linking two D-π-A branches with a
thiophene unit increases open-circuit photovoltage by 100 mV and short-circuit photocurrent by 4.10 mA cm−2. As a
consequence, power conversion efficiency is enhanced by about 2-fold. This work presents a new route to designing sensitizers
with high suppression ability of charge recombination toward high-performance DSSCs.
KEYWORDS: double D-π-A organic dye, dye-sensitized solar cells, charge recombination
synthesized for use in DSSCs, and they have demonstrated
better solar cell performance than the single D-π-A analogue
dyes due to the improved photoresponse and photocurrent.17a,d
However, the open-circuit photovoltage for the reported dyes
with two anchor groups is comparable to or lower than that for
the analogue dyes with one anchor group.17b,c For example,
Nazeeruddin et al. and Hagfeldt et al. designed and synthesized
a double branched dye containing one donor (triphenylamine),
two π bridges, and two anchors.17a,b Unfortunately, the dye
with two anchor groups leads to more serious charge
recombination, resulting in lower open-circuit photovoltage
than the dye with one anchor group.17b Thus, the power
conversion efficiency of the reported dyes with two anchors is
limited by the low open-circuit photovoltage. If the double
branched dye is endowed with an ability to suppress charge
recombination, open-circuit photovoltage can be improved, and
hence further improvement of power conversion efficiency can
be anticipated. Therefore, new molecular design of double
branched dyes is still important and interesting to optimize the
dye structures for more efficient DSSCs.
In this study, we designed and synthesized a double D-π-A
dye FNE92 (Figure 1) with a thiophene unit bridging two same
D-π-A chains. The extended π-conjugation due to the
conjugated linking of the two D-π-A branches by a thiophene
unit is expected to enhance molar extinction coefficient, and
also the cross shape of the double D-π-A dye and/or the
crossing part (i.e., the thiophene linker) between the two
branches would block triiodides approaching the TiO2 surface
for charge recombination. Experimental results indicate that the
INTRODUCTION
■
As a promising alternative to silicon-based photovoltaic devices,
dye-sensitized solar cells (DSSCs) have attracted much
attention in both academic1 and industrial fields2 because of
their low cost and easy production. To date, power conversion
efficiencies greater than 11% have been achieved with
ruthenium sensitizers.1a,3 Recently, there has been a surge of
research interest in organic sensitizers, because they have
advantages such as high molar absorption coefficients, facile
molecular tailoring, and cost-effectiveness.4 Furthermore, the
diversity in molecular structures offers infinite possibilities to
tune the photophysical and electrochemical properties, which is
favorable for the optimization of solar cell performance.
Most of efficient organic sensitizers have the donor-π-bridge-
acceptor (D-π-A) structure, containing a donor such as
diphenylamine (DPA),5 carbazole,6 indoline,7 etc., a π
conjugation bridge composed of thiophene,8 methine,9
benzene10 units, etc., and an acceptor such as cyanoacryclic
acid11 or rhodanine-3-acetic acid.12 The single D-π-A sensitizer
has a rod-like configuration, which may cause undesirable dye
aggregation and charge recombination.13 The close π−π
stacking of dye molecules can lead to self-quenching of excited
states and hence inefficient electron injection.14 One effective
strategy for overcoming this problem is the introduction of long
alkyl chains into the dye.15 Employing starburst dyes with bulky
multidonor can also suppress dye aggregation and block the
charge recombination of injected electrons with acceptors in
the electrolyte.16
To enhance optical density and binding strength of dye on
the TiO2, of particular interest is the synthesis of dianchoring
dye,17 which is verified to enhance photocurrent due to the
extended π-conjugated framework and higher molar extinction
coefficient.17a,d Several dianchoring organic dyes have been
Received: July 17, 2012
Revised: August 7, 2012
Published: August 7, 2012
© 2012 American Chemical Society
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tetrabutylammonium hexafluorophosphate (0.1M) in anhydrous
acetonitrile with a scan rate of 50 mV s−1 at room temperature
under argon. Dye-loaded films, platinum, and Ag/Ag+ electrode were
employed as working, counter, and reference electrodes, respectively.
The potential of the reference electrode was calibrated by ferrocene,
and all potentials mentioned in this work are relative to normal
hydrogen electrode (NHE). The film thickness was measured by a
surface profiler (Veeco Dektak 150).
The current density−voltage (J−V) characteristics of DSSCs were
recorded on a Keithley 2400 source meter under illumination of
simulated AM1.5G solar light coming from a solar simulator (Oriel-
94043A) equipped with a Xe lamp and an AM1.5G filter. The light
intensity was calibrated using a standard Si solar cell (Newport 91150).
A black mask with aperture area of 0.2304 cm2 was used to avoid stray
light. Action spectra of incident monochromatic photon-to-electron
conversion efficiency (IPCE) as a function of wavelength were
obtained with an Oriel-74125 system. The intensity of incident
monochromatic light was measured with a Si detector (Oriel-71640).
The electron lifetimes were measured with controlled intensity
modulated photovoltage spectroscopy (IMVS), and charge densities at
open-circuit were measured using charge extraction technique. IMVS
and charge extraction analysis were carried out on an electrochemical
workstation (Zahner XPOT), which includes a green light-emitting
diode (LED, 532 nm) and the corresponding control system. The
intensity-modulated spectra were measured at room temperature with
light intensity ranging from 0.5 to 45 W m−2, in modulation frequency
ranging from 0.1 Hz to 10 kHz, and with modulation amplitude less
than 5% of the light intensity.
Figure 1. Structures of dyes FNE91 and FNE92.
double D-π-A dye FNE92 produced much higher short-circuit
photocurrent and open-circuit photovoltage than the single D-
π-A analogue dye FNE91. Controlled intensity modulated
photovoltage spectroscopy and charge extraction have been
carried out to clarify the factors affecting the open-circuit
photovoltage.
RESULTS AND DISCUSSION
■
Molecular Design and Synthesis. The connection
between two neighbored thiophene units in oligothiophenes
includes αα, αβ, or ββ linkage. Generally, αα linkage
provides a better π-electron conjugation, whereas αβ or β
β linkage has nonplanar structure and therefore reduces the
conjugation.19 In this work, two terthiophene-based D-π-A
chains were connected via a thiophene core with two αβ
linkage. Such αβ linkage not only retains the charge
delocalization in each D-π-A chain, but also provides a rigid
configuration under the assistance of steric effect. As a result,
our designed organic molecules can stand on the TiO2 surface
and therefore the intermolecular π−π interactions can be
reduced significantly, which greatly benefits to photocurrent
generation.
For electron-releasing group (aryl or alkyl) substituted
thiophene unit at 3-position, electrophilic substitution occurs
regioselectively in 2-position of thiophene because of the
inductive effect of 3-substitution.20 Employing this regioselec-
tive strategy, donor and acceptor parts can be sequentially
connected at 2- and 5-positions of the thiophene units. Herein,
the double D-π-A dye FNE92 was synthesized in five steps
using αβ linked terthiophene 1 as the starting core (Scheme
1). After regioselective dibromination, compound 4 was
obtained when two hexyloxy-substituted triphenylamine
donor were attached into the twisted terthiophene backbone
by Stille coupling.21 Further dibromination by N-bromosucci-
nimide (NBS) and subsequent Stille coupling with (5′-(1,3-
dioxolan-2-yl)-[2,2′-bithiophen]-5-yl)tributyl afforded 1, 3-
dioxalane protected intermediate 5. Finally, the tandem
reaction of deprotection and Knoevenagel condensation22
gave the target dye FNE92. For comparison, the reference
dye FNE91 with a single D-π-A chain was prepared similarly
according to literatures.16c
EXPERIMENTAL SECTION
■
Materials and Reagents. The syntheses of dyes FNE91 and
FNE92 are detailed in the Supporting Information. Solvents were
dried by standard procedures. Other chemicals and reagents were
available from commercial sources and used without further
purification. Transparent conductive glass (F-doped SnO2, FTO, 15
Ω/square, transmittance of 85%, Nippon Sheet Glass Co., Japan) was
used as the substrate for the fabrication of TiO2 thin film electrode.
Fabrication of DSSCs. TiO2 films (10 μm) consisting of a 6 μm
transparent layer (∼20 nm nanoparticles) and a 4 μm scattering layer
(∼100 nm particles) were prepared using a screen printing
technique,18 followed by sintering at 500 °C under an air flow. After
cooling, the TiO2 films were impregnated in a 0.05 M aqueous TiCl4
solution for 30 min at 70 °C and then rinsed with deionized water.
The TiCl4-treated TiO2 films were annealed at 450 °C for 30 min and
then cooled to 120 °C before immersed into the dye solution (0.3 mM
in chloroform) for 16 h. After adsorption of the dyes, the electrodes
were rinsed with chloroform and acetonitrile, respectively. The
working and Pt-counter electrodes were assembled into a sealed
sandwich solar cell with a thermoplastic frame (Surly 30 μm thick).
Redox electrolyte (0.6 M 1,2-dimethyl-3-n-propylimidazolium iodide,
0.1 M LiI, 0.05 M I2, and 0.5 M 4-tert-butylpyridine in dry acetonitrile)
was introduced through the holes on the back of counter electrode.
Finally, the two holes were sealed using additional hot melt Surlyn film
covered with a thin glass slide under hot pressing.
Characterizations. 1H NMR (400 MHz) and 13C NMR (100
MHz) spectra were measured on a Varian Mercury Plus-400
spectrometer. The chemical shifts were expressed in ppm downfield
from tetramethylsilane (TMS). IR spectra were recorded on a
Shimadzu IRAffinity-1 spectrometer. UV−vis absorption spectra of
dye solutions and dye-loaded films were recorded with a Shimadzu
Model 2550 UV−vis spectrophotometer. Cyclic voltammetry (CV)
measurements were performed with an Autolab analyzer using a
typical three-electrode electrochemical cell in a solution of
Dye Adsorption. To investigate the anchoring properties
of the dyes on the TiO2 films, we carried out IR for the dye
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Scheme 1. Synthetic Routes of Dyes FNE91 and FNE92
powders and dye-loaded TiO2 films, as shown in Figure S1 in
the Supporting Information. Characteristic band at 2216 cm−1
for cyano (CN) was observed for both dye powders and dye-
loaded TiO2 films.17a For dye powders, the carbonyl peaks were
located at 1684 and 1690 cm−1 for FNE91 and FNE92,
respectively. Upon dye adsorption to the TiO2 surface, the
carbonyl peaks disappeared, while instead asymmetric (νas,
1603 cm−1 for FNE91 and 1601 cm−1 for FNE92) and
symmetric stretching (νs, 1371 cm−1 for FNE91 and 1367 cm−1
for FNE92) bands for carboxylate units appeared in the
spectra.23 This observation implies that FNE91 and FNE92
were chemically adsorbed onto the TiO2 surface via single- and
double-anchoring modes, respectively. According to the
Deacon Philips rule24 and previous similar report,17a,b the dye
molecules most likely adsorb on the TiO2 surface via a
bidentate bridging binding mode.
UV−Vis Absorption Properties. Figure 2a shows the
UV−vis absorption spectra of the two dye solutions in
chloroform, and the corresponding data are summarized in
Table 1. Two distinct bands were observed for both dyes. The
band located at shorter wavelength is attributed to the π−π*
electron transition of the chromophore, and the other at longer
wavelength is attributed to the intramolecular charge transfer
(ICT) from the donor to acceptor.25 Owing to the extended π
conjugation from single to double D-π-A structure, molar
extinction coefficient for the π−π* electron transition band
increases from 2.8 × 104 M−1 cm−1 for the single branch to 5.8
× 104 M−1 cm−1 for the double branch. On the contrary, the
ICT band for FNE92 is slightly weaker than that for FNE91.17d
The π−π* electron transition band is less intense than the ICT
band for the single branched dye FNE91, whereas the former is
more intense than the latter for the double branched dye
FNE92 so that the latter appears as a shoulder because of the
peak overlapping. As shown in Figure 3, density functional
calculations at B3LYP/6-31G* level demonstrate that the two
D-π-A branches cross perpendicularly, which interrupts the
coplanarity of the double D-π-A branches, resulting in blue
shifts for both absorption peaks as compared to the single D-π-
A branch (Table 1). The crossing of the two branches at the
thiophene bridge in FNE92 probably weakens the charge
communication so that the ICT band is weaker than the π−π*
electron transition band.
Figure 2b shows the UV−vis absorption spectra for the dye-
loaded films. Upon dye adsorption on the TiO2 surface, the
ICT band for FNE91 blue shifts to 415 nm, because of the
deprotonation of the anchoring group and/or the different
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Figure 3. Front and side views of calculated chemical structure of dye
FNE92.
Figure 2. UV−vis absorption spectra of (a) dye solutions in
chloroform and (b) dye-loaded TiO2 films (1 μm).
Figure 4. Cyclic voltammograms of FNE91- and FNE92-loaded TiO2
films.
media polarity, whereas the π−π* electron transition band
disappears due to the peak overlapping. By contrast, the π−π*
electron transition band is observable while the ICT band
disappeared because of the peak overlapping for the FNE92
dye-loaded TiO2 film. Although FNE92 has a larger molecular
size than FNE91, the dye amount on the TiO2 (1 μm thick)
surface is similar for both dyes, as seen in Table 1. A more
compact dye layer for FNE92 is formed on the TiO2 surface.
Electrochemical Properties. Energy levels of dye
sensitizers are crucial to judge the possibilities of electron
injection from the excited dye molecules to the conduction
band of TiO2 and dye regeneration by the iodide. The
oxidation potentials were measured by cyclic voltammetry
(Figure 4). The highest occupied molecular orbital (HOMO)
levels for both dyes, taken from the first oxidation potential, are
calculated to be 0.88 V (vs NHE, the same below), which are
force for electron injection from the excited dye molecules to
the conduction band of TiO2.
Solar Cell Performance. Incident photon-to-electron
conversion efficiencies (IPCE) as a function of incident
wavelength for the DSSCs based on the resulting organic
dyes on TiO2 films are plotted in Figure 5. FNE91 shows an
more positive than the redox potential of the I−/I3 redox
−
couple (∼0.4 V), ensuring sufficient driving force for reduction
of oxidized dye molecules. Correspondingly, estimated from the
band gap derived from the absorption onset for the dye-loaded
TiO2 film and HOMO levels,26 the lowest unoccupied
molecular orbital (LUMO) energy levels for both dyes,
approximately taken as the excited oxidation potentials, are
calculated to be −1.07 V. The LUMO levels are more negative
than the conduction band edge of TiO2 (−0.66 V in acetonitrile
containing 0.1 M LiClO4),27 suggesting a sufficient driving
Figure 5. IPCE spectra for DSSCs based on FNE91 or FNE92 in the
absence of deoxycholic acid.
Table 1. Photophysical and Electrochemical Properties of Dyes FNE91 and FNE92
absorption
a
b
c
d
e
dye
λmax (nm)
ε at λmax (104 M−1 cm−1)
dye loading (10−8 mol cm−2
)
HOMO (V vs NHE)
gap (eV)
LUMO (V vs NHE)
FNE91
FNE92
395, 495
380, 480
2.8, 4.1
5.8, 3.6
2.6
2.8
0.88
0.88
1.95
1.95
−1.07
−1.07
a
b
c
Absorption maximum in chloroform solution. The dye loading was determined from a dye-loaded 1 μm thick TiO2 film. The HOMO was taken
d
e
from the first redox potential in CV plot. The gap is estimated from the absorption onset of the dye-loaded TiO2 film. The LUMO was calculated
with the expression of LUMO = HOMO − Gap.
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IPCE maximum of 46%, while FNE92 shows an IPCE
maximum of 80%. As the two dyes have same HOMO and
LUMO energy levels and the latter is sufficiently high for
electron injection, the different IPCE values may result from
the different shape of the two dyes considering that light-
harvesting efficiency is close to 100% for the dye-loaded 10-μm
films. FNE91 has a rod shape and reasonably has strong
intermolecular π−π interaction, which leads to self-quenching
of excited states and hence inefficient electron injection. As a
result, FNE91-based DSSC produces lower IPCE than
expected. By contrast, FNE92 has a cross shape and reasonably
has weak intermolecular π−π interaction. Therefore, FNE92-
based DSSC generates unity maximum IPCE. To verify the
difference of intermolecular π−π interaction, effect of
coadsorption with deoxycholic acid (20 mM in dye solution)
was investigated for both dyes. The experimental result
indicates that coadsorption is effective to improve IPCE
significantly for FNE91 (see Figure S2 in the Supporting
Information) but ineffective for FNE92. This indicates that the
two long hexyloxy groups attached on the donor part in the
single D-π-A structure cannot exhibit the efficient antiaggrega-
tion effect,28 whereas the double D-π-A dye FNE92 with a
cross structure is effective at reducing the intermolecular π−π
interaction and therefore improving IPCE.
Figure 7. Voc as a function of charge density at open circuit for DSSCs
with FNE91 or FNE92. Three identical devices were tested in each
case with standard deviation less than 5%.
molecule contains only one. Upon dye adsorption, the protons
were first dissociated from carboxylic acid groups, but the
dissociated protons mostly stay on the TiO2 surface due to the
interaction of proton and hydroxyl groups on TiO2 though we
cannot determine how much percentage of the protons is
present on the surface.
As a positive shift of CB should lead to a decrease in Voc, the
observed higher Voc for FNE92 should be attributed to retarded
charge recombination, to be discussed next. Figure 8 shows the
The current−voltage characteristics of DSSCs were tested
under simulated AM1.5G illumination (100 mW cm−2). Figure
6 illustrates the J−V curves and the performance parameters are
Figure 8. Electron lifetime against charge density for FNE91- and
FNE92-based DSSCs. Three identical devices were tested in each case
with standard deviation less than 5%.
Figure 6. J−V curves for DSSCs based on FNE91 or FNE92 in the
absence of deoxycholic acid.
electron lifetime against charge density for FNE91- and
FNE92-based DSSCs. At the same charge density, the electron
lifetime of FNE92-based DSSC is longer than that of FNE91-
based DSSC by 14-fold. This indicates that charge recombina-
tion between electrons in TiO2 film and electron acceptors in
the electrolyte is significantly retarded by the double D-π-A
branched dye as compared to the single D-π-A branched dye.
At 45 W m−2 LED light (532 nm), the extracted charge
densities are 16.1 and 34.6 μC cm−2 for FNE91 and FNE92-
based DSSCs, respectively. The higher charge density for
FNE92 is attributed to the longer electron lifetime and higher
Jsc as well. According to the Q−Voc plot, the Voc gain arising
solely from the increased charge density or retarded charge
recombination is 113 mV. Thus, the collective effect of CB shift
and retarded charge recombination rate is 83 mV (= 113 mV −
30 mV) increase in Voc, in good agreement with the
experimentally observed Voc increase (90 mV) under 45 W
m−2 LED light (532 nm). Therefore, it is concluded that the
observed enhancement of Voc from single- to double-branched
dye is attributed to the collective effect of retarded charge
recombination and positive shift of CB.
listed in Table 1. The FNE91-based DSSC produced a Jsc of
7.13 mA cm−2, a Voc of 0.67 V, and an FF of 0.71,
corresponding to an η of 3.4%. Under the same condition,
the DSSC based on FNE92 offered a Jsc of 11.25 mA cm−2, a
Voc of 0.77 V, and an FF of 0.76, corresponding to an η of 6.6%.
The Jsc is improved by 4.10 mA cm−2, Voc is lifted by 0.10 V,
and the η is enhanced by 94% from FNE91 to FNE92. The
difference in Jsc is consistent with the IPCE trend as shown in
Figure 5. The increase in Voc by 0.10 V from the single to
double D-π-A branched dye can be explained by the analyses of
conduction band (CB) position and charge recombination rate.
Figure 7 shows the relation between Voc and extracted charge
density (Q) at open circuit. At a fixed Q, an increased Voc
indicates a negative shift of CB, and a decreased Voc means a
positive shift of CB.29 As compared to FNE91-based DSSC,
FNE92-based DSSC showed a downward CB shift by 30 mV.
The positive shift of CB is likely caused by more protons
present on TiO2 surface for FNE92,27 because both dyes have
similar adsorbed amount on the TiO2 surface but one FNE92
molecule contains two carboxylic acids while one FNE91
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Based on the optimized geometrical structure of the two
dyes, FNE91 has a rod shape, whereas FNE92 has a cross
shape (Figure 3). When the dye molecules were adsorbed on
the TiO2 surface, the cross structure for FNE92 can block
triiodides approaching the TiO2 surface for charge recombina-
tion, while the rod shape for FNE91 may remain some larger
gaps between molecules so that triiodides can approach the
TiO2 surface easier for charge recombination. As a
consequence, much longer electron lifetime and higher Voc
are observed for FNE92 with a cross structure than those for
FNE91. By comparison with some reported dyes (NKX-
2677,26 MK-2,6 and the standard N719 dye,3b see Figure S3 in
the Supporting Information), the double D-π-A dye FNE92
also exhibits advantage in the generation of high Voc. We have
prepared DSSCs with the above-mentioned reported dyes for
direct comparison with the DSSCs based on FNE91 and
FNE92 under the same conditions, and the results are
summarized in Table 2. NKX-2677 having no alkyl chains
Figure 9. Evolutions of photovoltaic performance parameters for
FNE92-based quasi-solid-state DSSC under one sun soaking.
Table 2. Photovoltaic Performance Parameters for DSSCs
with Various Dye Sensitizers
cross structure also blocks triiodides approaching the TiO2
surface, and therefore electron lifetime is enhanced remarkably
at the same charge density compared to the rod-shaped
monobranched analogue dye. In addition, the double-branched
dye causes a downward displacement of CB compared to the
single-branched dye. The collective effect of the CB shift and
retarded charge recombination rate can account for the
observed Voc enhancement from mono- to dibranched dye.
This finding presents a new route to designing sensitizers
toward weak intermolecular π−π interaction and slow charge
recombination.
Jsc
Voc
(V)
η
(%)
ε(104 M−1 cm−1) (λmax
/
(mA cm−2
)
FF
nm)
NKX-
2677
9.63
0.60
0.75
4.3
6.4 (511)
MK-2
11.96
7.13
0.71
0.67
0.77
0.74
0.72
0.71
0.76
0.75
6.1
3.4
6.6
6.2
3.8 (480)
4.1 (495)
3.6 (480)
1.3 (535)
FNE91
FNE92
N719
11.25
11.22
suffers from serious dye aggregation and thus produces low Voc
and η. When alkyl chains are linked to the thiophene bridge for
MK-2 or to the donor part for FNE91, higher Voc is produced.
The Voc obtained from FNE92 is the highest for the dyes
tested, and it is even higher than that obtained from N719
under the same conditions.
ASSOCIATED CONTENT
■
S
* Supporting Information
Syntheses and characterizations of the sensitizers FNE91 and
1
FNE92 by H NMR, 13C NMR, and HRMS. This material is
available free of charge via the Internet at http://pubs.acs.org.
Long-term stability is one of the critical parameters for
practical applications. Sealed DSSCs with a quasi-solid-state gel
electrolyte (0.1 M LiI, 0.1 M I2, 0.1 M 4-tert-butylpyridine and
0.6 M 1,2-dimethyl-3-propylimidazolium iodide in 3-methox-
ypropionitrile gelated with 5 wt % poly(vinylidenefluoride-co-
hexafluoropropylene) at open-circuit equipped with a 400 nm
cutoff filter were subjected to continuous light soaking (100
mW cm−2, device surface temperature was ∼50 °C). Figure 9
displays the evolution of photovoltaic performance parameters
of FNE92-based quasi-solid-state DSSC under one sun soaking
over a period of 1000 h. Voc and FF experienced small
fluctuations, whereas Jsc remained almost constant up to 370 h
followed by a slight decrease (<4%) with time. As a result, the
performance of the quasi-solid-state DSSC reached the best
(Voc = 0.67 V, Jsc = 13.58 mA cm−2, FF = 0.63, η = 5.7%) at 170
h and then decreased a little (<5%). FNE92-based quasi-solid-
state DSSCs demonstrated good long-term stability during
visible light soaking.
AUTHOR INFORMATION
Corresponding Author
*E-mail: zs.wang@fudan.edu.cn..
Notes
■
The authors declare no competing financial interest.
ACKNOWLEDGMENTS
■
This work was financially supported by the National Basic
Research Program (No. 2011CB933302) of China, National
Natural Science Foundation of China (20971025, 90922004,
and 50903020), Shanghai Pujiang Program (11PJ1401700),
Jiangsu Major Program (BY2010147), Shanghai Leading
Academic Discipline Project(B108), and the Project sponsored
by SRF for ROCS, SEM.
REFERENCES
■
(1) (a) Yella, A.; Lee, H. W.; Tsao, H. N.; Yi, C.; Chandiran, A. K.;
Nazeeruddin, M. K.; Diau, E. W. -G.; Yeh, C. -Y.; Zakeeruddin, M. K.;
Gratzel, M. Science 2011, 334, 629−634. (b) Hagfeldt, A.; Boschloo,
̈
CONCLUSIONS
■
G.; Sun, L.; Kloo, L.; Pettersson, H. Chem. Rev. 2010, 110, 6595−
In summary, we have designed and synthesized a thiophene
bridged double D-π-A dye FNE92, which has much stronger
π−π* electron transition band than its monobranched analogue
dye FNE91. The cross structure of FNE92 reduces
intermolecular π−π interaction and is thus favorable for
electron injection and hence photocurrent generation. The
6663. (c) Cai, N.; Moon, S. J.; Cevey-Ha, L.; Moehl, T.; Humphry-
Baker, R.; Wang, P.; Zakeeruddin, S. M.; Gratzel, M. Nano Lett. 2011,
̈
11, 1452−1456. (d) Bai, Y.; Zhang, J.; Zhou, D.; Wang, Y.; Zhang, M.;
Wang, P. J. Am. Chem. Soc. 2011, 133, 11442−11445. (e) Chen, T.;
Wang, S.; Yang, Z.; Feng, Q.; Sun, X.; Li, L.; Wang, Z.-S.; Peng, H.
Angew. Chem., Int. Ed. 2011, 50, 1815−1819. (f) Huang, Q.; Zhou, G.;
3498
dx.doi.org/10.1021/cm302250y | Chem. Mater. 2012, 24, 3493−3499

Chemistry of Materials
Article
Fang, L.; Hu., L.; Wang, Z.-S. Energy Environ. Sci. 2011, 4, 2145−2151.
(g) Wang, H.; Zhang, X.; Gong, F.; Zhou, G.; Wang, Z.-S. Adv. Mater.
B.; Tian, H. J. Org. Chem. 2008, 73, 3791−3797. (c) Thomas, K. R. J.;
Hsu, Y. C.; Lin, J. T.; Lee, K. M.; Ho, K. C.; Lai, C. H.; Cheng, Y. M.;
Chou, P. T. Chem. Mater. 2008, 20, 1830−1840.
2012, 24, 121−124. (h) O’Regan, B.; Gratzel, M. Nature 1991, 353,
̈
(17) (a) Abbotto, A.; Manfredi, N.; Marinzi, C.; Angelis, F. D.;
737−740. (i) Choi, H.; Lee, J. K.; Song, K. H.; Song, K.; Kang, S. O.;
Ko, J. Tetrahedron 2007, 63, 1553−1559.
Mosconi, E.; Yum, J. -H.; Zhang, X.; Zakeeruddin, S. M.; Gratzel, M.
̈
Energy Environ. Sci. 2009, 2, 1094−1101. (b) Jiang, X.; Karlsson, K. M.;
Gabrielsson, E.; Johansson, E. M. J.; Quintana, M.; Karlsson, M.; Sun,
L.; Boschloo, G.; Hagfeldt, A. Adv. Funct. Mater. 2011, 21, 2944−2952.
(c) Liu, J.; Zhang, J.; Xu, M.; Zhou, D.; Jing, X.; Wang, P. Energy
Environ. Sci. 2011, 4, 3021−3029. (d) Cao, D.; Peng, J.; Hong, Y.;
Fang, X.; Wang, L.; Meier, H. Org. Lett. 2011, 13, 1610−1613.
(e) Heredia, D.; Natera, J.; Gervaldo, M.; Otero, L.; Fungo, F.; Lin, C.
-Y.; Wong, K. -T. Org. Lett. 2010, 12, 12−15. (f) Hong, Y.; Liao, J.-Y.;
Cao, D.; Zang, X.; Kuang, D.-B.; Wang, L.; Meier, H.; Su, C.-Y. J. Org.
Chem. 2011, 76, 8015−8021.
(2) (a) Han, L.; Fukui, A.; Chiba, Y.; Islam, A.; Komiya, R.; Fuke, N.;
Koide, N.; Yamanaka, R.; Shimizu, M. Appl. Phys. Lett. 2009, 94,
013305/1−013305/3. (b) Gaudiana, R. J. Phys. Chem. Lett. 2010, 1,
1288−1289. (c) Spath, M.; Sommeling, P. M.; vanRoosmalen, J. A. M.;
̈
Smit, H. J. P.; vanderBurg, N. P. G.; Mahieu, D. R.; Bakker, N. J.;
Kroon, J. M. Prog. Photovolt. 2003, 11, 207−220. (d) Wu, J.; Xiao, Y.;
Tang, Q.; Yue, G.; Lin, J.; Huang, M.; Huang, Y.; Fan, L.; Lan, Z.; Yin,
S.; Sato, T. Adv. Mater. 2012, 24, 1884−1888.
(3) (a) Nazeeruddin, M. K.; Kay, A.; Rodicio, I.; Humphry-Baker, R.;
Mueller, E.; Liska, P.; Vlachopoulos, N.; Gratzel, M. J. Am. Chem. Soc.
̈
(18) Wang, Z.-S.; Kawauchi, H.; Kashima, T.; Arakawa, H. Coord.
Chem. Rev. 2004, 248, 1381−1389.
(19) Xia, C.; Fan, X.; Locklin, J.; Advincula, R. C.; Gies, A.; Nonidez,
W. J. Am. Chem. Soc. 2004, 126, 8735−8743.
1993, 115, 6382−6390. (b) Nazeeruddin, M. K.; De Angelis, F.;
Fantacci, S.; Selloni, A.; Viscardi, G.; Liska, P.; Ito, S.; Takeru, B.;
Gratzel, M. G. J. Am. Chem. Soc. 2005, 127, 16835−16847. (c) Chen,
̈
C.; Wang, M.; Li, J.; Pootrakulchote, N.; Alibabaei, L.; Ngoc-le, C.;
(20) (a) Clementi, S.; Marino, G. Tetrahedron 1969, 25, 4599−4603.
(b) Clark, D. T. Tetrahedron 1968, 24, 2567−2573.
(21) Milstein, D.; Stille, J. K. J. Am. Chem. Soc. 1978, 100, 3636−
3638.
(22) Knoevenagel, E. Ber. Deutsch. Chem. Gesell. 1898, 31, 2596−
2619.
Decoppet, J.; Tsai, J.; Gratzel, C.; Wu, C.; Zakeeruddin, S. M.; Gratzel.,
̈
̈
M. ACS Nano 2009, 3, 3103−3109.
(4) Mishra, A.; Fischer, M. K. R.; Bauerle, P. Angew. Chem., Int. Ed.
2009, 48, 2474−2499.
(5) (a) Yum, J. H.; Hagberg, D. P.; Moon, S. J.; Karlsson, K. M.;
Marinado, T.; Sun, L. C.; Hagfeldt, A.; Nazeeruddin, M. K.; Gratzel,
̈
(23) Tian, H.; Yang, X.; Chen, R.; Zhang, R.; Hagfeldt, A.; Sun, L. J.
Phys. Chem. C 2008, 112, 11023−11033.
M. Angew. Chem., Int. Ed. 2009, 48, 1576−1580. (b) Zhang, G.; Bala,
H.; Cheng, Y.; Shi, D.; Lv, X.; Yu, Q.; Wang, P. Chem. Commun. 2009,
2198−2200. (c) Choi, H.; Baik, C.; Kang, S. O.; Ko, J.; Kang, M. S.;
(24) Deacon, G. B.; Phillips, R. J. Coord. Chem. Rev. 1980, 33, 227−
250.
Nazeeruddin, M. K.; Gratzel, M. Angew. Chem., Int. Ed. 2008, 47, 327−
̈
(25) Roquet, S.; Cravino, A.; Leriche, P.; Alev
Roncali, J. J. Am. Chem. Soc. 2006, 128, 3459−3466.
́ ̂ ̀
eque, O.; Frere, P.;
330. (d) Qu, S.; Hua, J.; Tian, H. Science China Chem. 2012, 55, 677−
697. (e) Ning, Z.; Fu, Y.; Tian, H. Energy Environ. Sci. 2010, 3, 1170−
1181. (f) Ning, Z.; Zhang, Q.; Pei, H.; Luan, J.; Lu, C.; Cui, Y.; Tian,
H. J. Phys. Chem. C 2009, 113, 10307−10313.
(26) Hara, K.; Wang, Z.-S.; Sato, T.; Furube, A.; Katoh, R.; Sugihara,
H.; Dan-oh, Y.; Kasada, C.; Shinpo, A.; Suga, S. J. Phys. Chem. B 2005,
109, 15476−15482.
(6) Koumura, N.; Wang, Z.-S.; Mori, S.; Miyashita, M.; Suzuki, E.;
Hara, K. J. Am. Chem. Soc. 2006, 128, 14256−14257.
(7) (a) Kuang, D.; Uchida, S.; Humphry-Baker, R.; Zakeeruddin, S.
(27) Redmond, G.; Fitzmaurice, D. J. Phys. Chem. 1993, 97, 1426−
1430.
(28) Liu, B.; Liu, Q. L.; You, D. Y.; Li, X.; Naruta, Y.; Zhu, W. J.
Mater. Chem. 2012, 22, 13348−13356.
(29) Kopidakis, N.; Neale, N. R.; Frank, A. J. J. Phys. Chem. B 2006,
110, 12485−12489.
M.; Gratzel, M. Angew. Chem., Int. Ed. 2008, 47, 1923−1927.
̈
(b) Howie, W. H.; Claeyssens, F.; Miura, H.; Peter, L. M. J. Am.
Chem. Soc. 2008, 130, 1367−1375. (c) Zhu, W.; Wu, Y.; Wang, S.; Li,
W.; Li, X.; Chen, J.; Wang, Z.-S.; Tian, H. Adv. Funct. Mater. 2011, 21,
756−763. (d) Wu, Y.; Marszalek, M.; Zakeeruddin, S. M.; Zhang, Q.;
Tian, H.; Gratzel, M.; Zhu, W. Energy Environ. Sci. 2012, 5, 8261−
̈
8272.
(8) Choi, H.; Baik, C.; Kang, S. O.; Ko, J.; Kang, M. S.; Nazeeruddin,
M. K.; Gratzel, M. Angew. Chem., Int. Ed. 2008, 47, 327−330.
̈
(9) Hara, K.; Sato, T.; Katoh, R.; Furube, A.; Yoshihara, T.; Murai,
M.; Kurashige, M.; Ito, S.; Shinpo, A.; Suga, S.; Arakawa, H. Adv. Funct.
Mater. 2005, 15, 246−252.
(10) (a) Hagberg, D. P.; Edvinsson, T.; Marinado, T.; Boschloo, G.;
Hagfeldt, A.; Sun, L. C. Chem. Commun. 2006, 2245−2247. (b) Haid,
S.; Marszalek, M.; Mishra, A.; Wielopolski, M.; Teuscher, J.; Moser, J.
-E.; Humphry-Baker, R.; Zakeeruddin, S. M.; Gratzel, M.; Bauerle, P.
̈
̈
Adv. Funct. Mater. 2012, 22, 1291−1302.
(11) Hara, K.; Kurashige, M.; Ito, S.; Shinpo, A.; Suga, S.; Sayama, K.;
Arakawa, H. Chem. Commun. 2003, 252−253.
(12) Horiuchi, T.; Miura, H.; Uchida, S. Chem.Commun. 2003,
3036−3037.
(13) Hagberg, D. P.; Marinado, T.; Karlsson, K. M.; Nonomura, K.;
Qin, P.; Boschloo, G.; Brinck, T.; Hagfeldt, A.; Sun, L. J. Org. Chem.
2007, 72, 9550−9556.
(14) Liu, D.; Fessenden, R. W.; Hug, G. L.; Kamat, P. V. J. Phys.
Chem. B 1997, 101, 2583−2590.
(15) Wang, Z.-S.; Koumura, N.; Cui, Y.; Takahashi, M.; Sekiguchi,
H.; Mori, A.; Kubo, T.; Furube, A.; Hara, K. Chem. Mater. 2008, 20,
3993−4003.
(16) (a) Hagberg, D. P.; Yum, J. H.; Lee, H.; DeAngelis, F.;
Marinado, T.; Karlsson, K. M.; Humphry-Baker, R.; Sun, L. C.;
Hagfeldt, A.; Gratzel, M.; Nazeeruddin, M. K. J. Am. Chem. Soc. 2008,
̈
130, 6259−6266. (b) Ning, Z. J.; Zhang, Q.; Wu, W. J.; Pei, H. C.; Liu,
3499
dx.doi.org/10.1021/cm302250y | Chem. Mater. 2012, 24, 3493−3499