Engineering of push-pull thiophene dyes to enhance light absorption and modulate charge recombination in mesoscopic solar cells

Article abstract of DOI:10.1002/adfm.201202562

The elaborate selection of diverse π-conjugated segments which bridge the electron donors and acceptors in organic push-pull dyes can not only tune the molecular energy-levels but also impact the interfacial energetics and kinetics of dye-sensitized solar cells (DSCs). In this paper, a series of triphenylamine-cyanoacrylic acid photosensitizers is reported with TT, EDOT-BT, EDOT-CPDT, and CPDT-EDOT (herein TT, EDOT, BT, and CPDT denote terthiophene, ethylenedioxythiophene, bithiophene, and cyclopentadithiophene, respectively) as the π-linkers, and the dye-structure correlated photocurrent and photovoltage features of DSCs based on a cobalt electrolyte are scrutinized via analyzing light absorption and multichannel charge transfer kinetics. Both stepwise incorporation of more electron-rich blocks and rational modulation of connection order of dissimilar segments can result in a negative movement of ground-state redox potential and a red-shift of the absorption peak. While these styles of reducing energy-gap do not exert too much influence on the electron injection from photoexcited dye molecules to titania, the dyestuff employing the EDOT-BT linker presents a faster interfacial charge recombination and a slower dye regeneration, accounting for its inferior cell efficiency of 5.3% compared to that of 9.4% at the AM1.5G conditions achieved by the CPDT-EDOT dye. Four new triphenylamine-cyanoacrylic acid photosensitizers with different thiophene conjugated linkers are synthesized and their important photocurrent and photovoltage features in mesoscopic titania solar cells based on a cobalt electrolyte are detailed via measuring transient photophysical and electrical signals. The best C250 dye presents an excellent power conversion efficiency of 9.4% at the AM1.5G conditions. Copyright

Full text of DOI:10.1002/adfm.201202562

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Engineering of Push-Pull Thiophene Dyes to Enhance
Light Absorption and Modulate Charge Recombination
in Mesoscopic Solar Cells
Ning Cai, Yinglin Wang, Mingfei Xu, Ye Fan, Renzhi Li,* Min Zhang,* and Peng Wang*
injection into titania. To achieve a good
charge collection, photoinjected electrons
in titania must traverse several micro-
meters to the current collector before
tune the molecular energy-levels but also impact the interfacial energetics
being captured by electron acceptors. Con-
The elaborate selection of diverse π -conjugated segments which bridge
the electron donors and acceptors in organic push-pull dyes can not only
and kinetics of dye-sensitized solar cells (DSCs). In this paper, a series
secutive material innovation has impelled
of triphenylamine-cyanoacrylic acid photosensitizers is reported with TT,
EDOT-BT, EDOT-CPDT, and CPDT-EDOT (herein TT, EDOT, BT, and CPDT
denote terthiophene, ethylenedioxythiophene, bithiophene, and cyclopenta-
dithiophene, respectively) as the π-linkers, and the dye-structure correlated
photocurrent and photovoltage features of DSCs based on a cobalt electro-
lyte are scrutinized via analyzing light absorption and multichannel charge
transfer kinetics. Both stepwise incorporation of more electron-rich blocks
and rational modulation of connection order of dissimilar segments can
result in a negative movement of ground-state redox potential and a red-shift
of the absorption peak. While these styles of reducing energy-gap do not exert
too much influence on the electron injection from photoexcited dye mol-
ecules to titania, the dyestuff employing the EDOT-BT linker presents a faster
interfacial charge recombination and a slower dye regeneration, accounting
for its inferior cell efficiency of 5.3% compared to that of 9.4% at the AM1.5G
conditions achieved by the CPDT-EDOT dye.
the advancement of cell performance, and
the highest reported power conversion
efficiency has now reached 12.3% at the
simulated AM 1.5G conditions.[3]
The development of metal-free organic
dyes has been one of the recent research
focuses, on primary account of their
molecular tailoring flexibility and raw
material abundance.[4,5] The design of
capable organic push-pull dyes should at
least consider two aspects of (i) reducing
the molecular energy gap to absorb
more solar photons and (ii) tuning the
electronic as well as steric structures to
regulate the energetics and kinetics at
the titania/dye/electrolyte interface. The
rational option of conjugated π-linkers
is of paramount importance in the cell
performance control, apart from electron
donors and acceptors. In this respect,
thiophene and its numerous derivatives have been actively
exploited as the building blocks of organic chromophores[6–17]
since their initial incorporation in the DSC coumarin dyes.[18]
The various thiophene-based blocks furnish a flexible struc-
tural modification of photosensitizers, which on the other
hand could bring forth complicated dye structure correlated
photovoltaic behaviors.
In this contribution, we synthesize four thiophene dyes
(Figure 1) with TT, EDOT-BT, EDOT-CPDT, and CPDT-EDOT
(TT, EDOT, BT, and CPDT denote terthiophene, ethylen-
edioxythiophene, bithiophene, and cyclopentadithiophene,
respectively) as the conjugated linkers in combination with
the diethylhexyloxy-substituted triphenylamine donor and
cyanoacrylic acid acceptor, to take a close look at the merit of
utilizing more electron-rich conjugated segments in push-pull
sensitizers to extend their spectral response to low energy solar
photons. The dependence of important photovoltaic features
such as external quantum efficiency and photovoltage on the
energy level modulation, is detailed via measuring transient
photophysical and electrical signals to examine multi-channel
charge transfer kinetics.
1. Introduction
The search for viable tactics on transformation of inexhaust-
ible sunlight into sustainable energy reserves such as clean
electricity and solar fuels is presently one of the momentous
global challenges. During the past two decades, a great amount
of research passion has been caught on dye-sensitized solar
cells (DSCs), a promising photovoltaic technology based on the
use of low-cost materials and easy manufacturing processes.[1,2]
In an efficient DSC, light absorption by dye molecules grafted
on a mesoporous titania film is instantly followed by electron
N. Cai, Dr. Y. Wang, Dr. M. Xu, Y. Fan, Dr. R. Li,
Dr. M. Zhang, Prof. P. Wang
State Key Laboratory of Polymer Physics and Chemistry
Changchun Institute of Applied Chemistry
Chinese Academy of Sciences
Changchun, 130022, China
E-mail: renzhi.li@ciac.jl.cn; min.zhang@ciac.jl.cn; peng.wang@ciac.jl.cn
DOI: 10.1002/adfm.201202562
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Figure 2. UV-vis absorption spectra of the triphenylamine-cyanoacrylic
acid photosensitizers in THF.
energies (Eecaxl) at the MPW1K/6-31G∗∗ level listed in Table 1 are
abs
max
in good agreement with the measured red-shifts of
from
λ
C247 to C250. Further analyses on the molecular orbital topolo-
gies (Figure S1, Supporting Information) involving the S0→S1
transitions disclose that the low-energy absorption bands of
C247−C250 are mainly assigned to the intramolecular charge
transfer transitions from the triphenylamine donors and their
adjacent conjugated units to cyanoacrylic acid acceptors and
their adjoining segments.
Apart from the light absorption property of a sensitizer,
the energy-offsets of dye molecules with respect to the titania
nanocrystals and redox electrolytes also play a pivotal role in
determining some subsequent dynamic processes such as
exciton dissociation and long-range charge separation at the
titania/dye/electrolyte interface, which may also have profound
influences on the ultimate power output of a DSC. Thereby we
ꢀ
+
derived the ground-state redox potentials ED/ D of four dyes
dissolved in THF through measuring square-wave voltam-
mograms (Figure 3). As listed in Table 1, the values of ED/D
+
Figure 1. Structures of the triphenylamine-cyanoacrylic acid photosensi-
become low along with the use of more electron-rich units, being
0.22 V for C247, 0.14 V for C248, 0.11 V for C249, and 0.09 V
for C250 against the standard ferrocene/ferrocenium (Fc/Fc+)
redox couple. On the basis of the zero-zero transition energies
(E0−0) estimated from the intersection points of normalized
absorption and photoluminescence (PL) spectra (Figure S2,
Supporting Information), we could calculate the exited state
tizers synthesized.
2. Results and Discussion
The light harvesting capacities of C247−C250 were first evalu-
ated by recording their electronic absorption spectra (Figure 2)
of diluted tetrahydrofuran (THF) solutions, and the detailed
parameters were collected in Table 1. The maximum absorption
∗
+
+
redox potential via the equation ED /D = ED/D − E0−0/e
without considering any entropy change during light excitation,
being −1.95, −1.97, −1.85, and −1.86 V for C247, C248, C249,
and C250, respectively.
λabs
wavelength ( max) of the C247 model dye with the TT π-linker
peaks at 485 nm, which is red-shifted to 522 nm upon replacing
the thiophene unit adjacent to the triphenylamine donor with
EDOT for C248. Further substituting the remaining two thi-
The incident photon-to-collected electron conversion efficien-
cies (IPCEs) of these dyes were further tested in the mesoscopic
titania solar cells based on a tris(2,2′-bipyridine)cobalt(II/III)
electrolyte, the composition of which is described in the experi-
mental section. As depicted in Figure 4, the onset wavelengths
of photocurrent response are stepwise red-shifted from C247 to
C250, which are in general accord with electronic absorptions
of 2.3-μm-thick, dye-coated titania films immersed in the cobalt
ophene units (BT) with CPDT leads to a 34 nm red-shift of
abs
λ
and a remarkably augmented maximum molar absorption
max
coefficient (εmabasx ) from 38 × 103 to 65 × 103 M−1 cm−1 with a
comparison of C248 and C249. Interestingly, moving the CPDT
moiety toward the triphenylamine side for C250 also red-shifts
abs
max
the λ
from 556 to 563 nm. The calculated S0→S1 excitation
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T a b le 1 . Photophysical and electrochemical data of C247, C248, C249, and C250 in THF.
ex
abs
pl
max
abs
Dye
+
ε
E0−
[eV]c)
ED/D
ED
∗
/D
+
E
max
0
cal
λmax
λ
[eV]a)
[V]d)
[V]e)
[nm]b)
[103 M−1 cm−1 b)
]
[nm]b)
C247
C248
C249
C250
2.29
2.22
2.18
2.17
485
41
38
65
63
650
2.17
2.11
1.96
1.95
0.22
0.14
0.11
0.09
−1.95
−1.97
−1.85
−1.86
522
664
556
702
563
702
ex
a)The S0→S1 excitation energy (E ) were calculated at the MPW1K/6-31G∗∗ level with the C-PCM model of THF; b)The maximum absorption wavelength (λambsax), maximum
cal
molar absorption coefficient (εmabasx ), and PL maximum wavelength (λmplax) were derived from the static electronic absorption and emission spectra in THF solutions; c)The
zero-zero transition energy (E0−0) was estimated from the intersection point of normalized absorption and emission spectra; d)The ground-state redox potential (ED /D+) is
reported with Fc/Fc+ as reference; e)The excited-state redox potential (ED + ) was estimated by equation E
change during the light excitation.
=
ED/D + E0 − 0/e without considering any entropy
∗
+
/D
+
∗
D
D
/
electrolyte (Figure S3, Supporting Information). However, it
is noteworthy that the C248 dye possesses a remarkably lower
IPCE summit of 62% at 480 nm in contrast to the other three
counterparts (79% at 490 nm for C247, 76% at 490 nm for
C249, and 81% at 520 nm for C250), albeit the absorptances at
the corresponding wavelengths of even transparent dye-coated
titania films are all over 94%.
could be ascribed to the radiative and nonradiative deactivation
of excited-state dye molecules (D∗). However, the substitution
of alumina with titania brings on significant PL quenching,
indicative of exciton dissociation at the energy-offset titania/dye
interface (lines in Figure 5). By comparing the integral areas of
PL traces of dye-coated titania and alumina films, we estimated
the electron injection yields of the C247, C248, C249, and C250
cells, being 97%, 97%, 94%, and 94%, respectively. Thereby
we conclude that the exciton dissociation yield is not the deter-
minant factor controlling the IPCE summit, notwithstanding
the presence of a similar but minor quantity of non-electron-
injecting dye molecules in our cells.
We further carried out nanosecond transient absorption (TA)
experiments to measure the kinetics of dual-channel charge-
transfer reactions of oxidized dye molecules (D+) with photo-
injected electrons in the titania film and electron-donating spe-
cies in the cobalt electrolyte, which may also affect the IPCE
height. The oxidized states of C247−C250 all exhibit strong
absorptions in the near-infrared region (Figure 6) in contrast
to their neutral counterparts. Thereby in kinetic measurements
we selected the probe light of 765 nm on the other account
of the signal sensitivity of our photomultiplier tube detector,
To understand the origins of IPCE maximum fluctuation, we
utilized the time-correlated single photon counting technique
to examine the possible impact of alternating
∗
+
upon the
ED /D
yield of electron injection from excited-state dye molecules to
titania.[19,20] Employing a C247, C248, C249, or C250-coated
nanoporous alumina film infiltrated with the cobalt electrolyte,
a dummy cell was assembled, which exhibited a strong red light
emission upon exposing to 488 nm laser. On account of the lack
of energy offset for electron injection at the interface between
alumina and dye, the PL decays (dotted curves in Figure 5)
Figure 3. Square-wave voltammograms of dyes in THF with 0.1 M 1-ethyl-
3-methylimidazolium bis(trifluoromethanesulfonyl)imide (EMITFSI)
supporting electrolyte.
Figure 4. Photocurrent action spectra of the triphenylamine-cyanoacrylic
acid dyes in the mesoscopic titania solar cells with a cobalt electrolyte.
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Figure 5. Time-resolved PL decay traces of dye-grafted mesoporous alumina (dotted curves) or titania film (lines) immersed in the cobalt electrolyte
for cell fabrication. Excitation wavelength: 488 nm. The emission intensity (I) was corrected in term of the film absorbance at 488 nm and further
normalized with the PL maximum of the dye-coated alumina film (Imax, alumina).
and also carefully chose the excitation wavelengths in terms
of a ≈0.2 optical density of dye-coated titania films to ensure
an alike exciton distribution profile in our testing cells. The
rate of charge recombination between the photoinjected elec-
trons in titania and oxidized dyes can be derived by recording
the TA decays (traces a−d in Figure 7) of dummy cells, made
from 11.0-μm-thick, dye-coated titania films soaked in the inert
electrolytecomposedof0.5M4-tert-butylpyridine(TBP)and0.1M
lithium bis(trifluoromethanesulfonyl)imide (LiTFSI) in ace-
tonitrile (AN). The absorption traces can be fitted to a stretched
exponential decay function ΔA ∝ A0exp[−(t/τ)α], where A0 is the
pre-exponential factor, α is the stretching parameter, and τ is
the characteristic time. Utilizing the gamma function Γ(x), the
mean times of these charge recombination reactions (<τ>rec
)
were derived through <τ> = (τ/α)Γ(1/α)[21] and compiled in
Table S1 (Supporting Information). In general, substitution of
the thiophene unit conjugated to triphenylamine with EDOT
Figure 7. Transient absorption traces probed at 765 nm of 11.0-μm-thick,
dye-coated titania films soaked with the inert (a–d) and cobalt (e–h) elec-
trolytes. Laser pulse fluence and excitation wavelength: a) 18 μJ cm−2 at
655 nm; b) 17 μJ cm−2 at 719 nm; c) 16 μJ cm−2 at 733 nm; d) 16 μJ cm−2
at 727 nm; e) 18 μJ cm−2 at 661 nm; f) 16 μJ cm−2 at 730 nm; g) 16 μJ cm−2
at 741 nm; and h) 16 μJ cm−2 at 734 nm. Smooth lines are stretched expo-
nential fittings over raw data obtained by averaging 700 laser shots.
Figure 6. Absorption change as a function of wavelength upon applying
a small positive potential to a 2.4-um-thick, dye-coated titania film dipped
in EMITFSI.
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brings forth evident accelerations of charge recombination,
suggesting that there may be a hydrogen-bonding interaction
of the ethylenedioxyl group with the active hydroxyls on the
surface of titania, which will shorten the tunneling distance
between electrons trapped in the titania nanocrystals and holes
localized on the oxidized dye molecules.[22,23] The adverse inter-
action seems to be more or less attenuated via the introduction
of two hydrophobic hexyl groups attached on CPDT in the cases
of C249 and C250.
However, replacing the inert electrolyte with the cobalt
electrolyte induced noticeably accelerated absorption decays
(traces e−h in Figure 7), indicating the arising of rapid electron
transfer from the tris(2,2′-bipyridine)cobalt(II) cations in the
electrolyte to the oxidized dye molecules. Based on the same
protocol presented above, the mean reaction times (<τ>reg) of
dye regeneration were also calculated and listed in Table S1
(Supporting Information). It is observed that the replacement
of thiophene with electron-richer EDOT from C247 to C248
evidently slows down the dye regeneration rate, on probable
+
account of a negative shift of ED/D which reduces the absolute
value of the Gibbs free energy for this charge transfer reaction.
+
E
However, the positive correlation between
eration rate is broken down along with the stepwise negative
and dye regen-
D/D
+
E
shift of
from C248 to C250 induced by the incorporation
D/D
of electron-richer CPDT instead of BT as well as the modulation
of the connection sequence of EDOT and CPDT. This finding
may suggest the dominant roles of reorganization energy and
electronic coupling factor[24] in the charge transfer reactions
discussed here, both of which could be considerably affected by
the microstructures of dye assemblies on titania. The speedy
recombination and sluggish regeneration of C248 relative to
other three dyes jointly lead to an evident decline of the long-
range charge separation yield (ϕlcs) of 83%, compared to those
of 100%, 95%, and 96% for C247, C249, and C250, respectively,
explaining the aforementioned IPCE summits. It is noted that
there is not a satisfactory linear correlation between the IPCE
summit and ϕlcs, which could be ascribed to the influences of
light absorption, charge collection yield, and the laser intensity
dependent long-range charge separation yield.
The photocurrent density−voltage (j−V) characteris-
tics (Figure 8A) of cells made from titania films coated by
C247−C250 in conjunction with the cobalt electrolyte were
recorded under the irradiance of 100 mW cm−2 , simulated
AM1.5 sunlight and the detailed photovoltaic parameters were
listed in Table 2. Among these four dyes, the C250 sensitizer
presents the highest open-circuit photovoltage (Voc) of 0.78 V
and the largest short-circuit photocurrent density (jsc) of
16.2 mA cm−2 , affording a power conversion efficiency of 9.4%.
We also measured the current density−voltage (j−V) curves of
these four cells at various light intensities and plotted Voc as a
function of jsc in Figure 8B. Assuming that jsc is proportional
to photocarrier generation flux, we can compare the difference
of Voc at the same photocarrier generation flux. It is noted that
at a given jsc, the C250 dye possesses the highest photovoltage
among these dyes whereas C248 presents the lowest one.
The comparison on these two dyes is the focus of our further
electrical analyses.
Figure 8. A ) j–V characteristics measured under irradiation of
100 mW cm−2 , simulated AM1.5 sunlight. B) Plots of open-circuit photo-
voltage (Voc) versus short-circuit photocurrent density (jsc). An antireflec-
tion film was adhered to a testing cell during measurements. Aperture
area of the employed metal mask: 0.158 cm2.
(EF,n) in titania, which could be associated with a movement of
titania conduction band edge (Ec) and/or a variation of electron
density.[25–28] At a certain flux of photocarrier generation, the
electron density is dominated by the interfacial recombination
of titania electrons with electron-accepting species in electro-
lytes and/or dye cations. Thus, we performed transient photo-
voltage decay and charge extraction experiments to understand
the physical origin of Voc variation. It is noted that there is
≈25 mV downward shift of the conduction-band edge of titania
T a b le 2 . Photovoltaic parameters obtained at the simulated AM1.5G
conditions.a)
Dye
jsc
Voc
[V]
FF
η
[%]
[mA cm−2
]
C247
C248
C249
C250
11.6
10.5
14.9
16.2
0.75
0.69
0.76
0.78
0.76
0.73
0.75
0.74
6.6
5.3
8.5
9.4
a)The validity of our photovoltaic data is confirmed by comparing the calculated
jsc via wavelength integration of the product of the standard AM1.5 emission
spectrum (ASTM G173-03) and measured IPCE spectra with the experimental jsc,
showing a less than 5% error. Also note that all our cells show a linear dependence
of photocurrent on light intensity as shown in Figure S4 (Supporting Information).
For a given redox electrolyte, we can ascribe the observed rise
or fall of Voc of DSCs to the shift of electron quasi-Fermi-level
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4. Experimental Section
Materials: AN and THF were distilled before use and other reagents
were purchased from commercial sources and used without further
purification. 4,4,5,5-Tetramethyl-2-{4-[N,N-bis(4-(2-ethylhexyloxy)phenyl)
amino]phenyl}-1,3,2-dioxaborolane,[29]
4-(3,4-ethylenedioxythiophene-
5-yl)-N,N-bis(4-(2-ethylhexyloxy)phenyl)aniline,[30] 6-bromo-4,4-dihexyl-
4H-cyclopenta[2,1-b:3,4-b′]dithiophene-2-carbaldehyde,[31]
6-{4-[N,N-bis(4-(2-ethylhexyloxy)phenyl)-amino]phenyl}-4,4-dihexyl-
4H-cyclopenta[2,1-b:3,4-b′]dithiophene,[29] 5-bromo-5′′-formyl-2,2′:5′′,2′′-
terthiophene,[32]
5′-bromo-2,2′-bithiophene-5-carbaldehyde,[33]
and
5-bromo-3,4-ethylenedioxy-2-formylthiophene[34] were synthesized acco-
rding to the corresponding literature methods. The Suzuki–Miyaura or
Stille cross-coupling of bromine substituted aldehydes with a pinacol
triaryl boronate or an aromatic stannane produced the dye precursors,
which were further converted to the title cyanoacrylic acids by the
classical Knoevenagel condensation reaction. The synthetic details are
described as follows.
5-{4-[N,N-Bis(4-(2-ethylhexyloxy)phenyl)amino]phenyl}-
Figure 9. A) Extracted electron density in titania against open-circuit
photovoltage and B) electron lifetime as a function of extracted electron
density for cells made with titania films coated by C248 and C250.
2,2′:5′,2′′-terthiophene-5′′-carbaldehyde: To
a
stirred solution of
5-bromo-5′′-formyl-2,2′:5′,2′′-terthiophene (0.707 g, 1.991 mmol),
4,4,5,5-tetramethyl-2-{4-[N,N-bis(4-(2-ethylhexyloxy)phenyl)amino]
phenyl}-1,3,2-dioxaborolane (1.500 g, 2.389 mmol), and K3PO4
(2.113 g, 9.955 mmol) in dioxane/H2O (v/v, 5/1, 55 mL) was added
2-dicyclohexylphosphino-2′,6′-dimethoxybiphenyl (16 mg, 0.040 mmol)
and palladium acetate (8 mg, 0.040 mmol). The reaction was carried
out at 45 °C under argon for 5 h and then cooled to room temperature.
The solution was extracted with ethyl acetate before the organic phase
was washed with water and dried over anhydrous sodium sulfate.
After evaporation of the solvent under reduced pressure, the crude
product was purified by column chromatography over silica gel with
dichloromethane/petroleum ether (v/v, 2/1) as the eluent to afford
an orange solid as the desired product (1.392 g, 90% yield). 1H NMR
(400 MHz, DMSO-d6, δ): 9.88 (s, 1H), 8.00 (d, J = 4.0 Hz, 1H), 7.58 (d, J
= 3.6 Hz, 1H), 7.55 (d, J = 4.0 Hz, 1H), 7.48 (d, J = 8.8 Hz, 2H), 7.40 (d,
J = 4.0 Hz, 1H), 7.36 (d, J = 4.0 Hz, 1H), 7.34 (d, J = 3.6 Hz, 1H), 7.04
(d, J = 8.8 Hz, 4H), 6.92 (d, J = 8.8 Hz, 4H), 6.77 (d, J = 8.8 Hz, 2H),
3.84 (d, J = 5.6 Hz, 4H), 1.67 (m, 2H), 1.44 (m, 8H), 1.31 (m, 8H), 0.89
(m, 12H). 13C NMR (100 MHz, DMSO-d6, δ): 183.74, 155.70, 148.37,
145.07, 143.81, 141.16, 139.45, 139.24, 138.32, 133.27, 133.00, 128.15,
126.98, 126.29, 126.22, 125.14, 124.92, 124.43, 123.18, 118.94, 115.55,
70.12, 38.72, 29.93, 28.44, 23.32, 22.50, 13.93, 10.92. MS (ESI) m/z
calcd. for (C47H53NO3S3): 775.3. Found: 776.5 ([M+H]+). Anal. calcd.
for C47H53NO3S3: C, 72.73; H, 6.88; N, 1.80. Found: C, 72.61; H, 7.01;
N, 1.77.
when the sensitizer is changed from C248 to C250, which can
be deduced from Figure 9A by comparing the extracted elec-
tron density (dn) at the same potential bias. However, for the
C250 cell there is an over one order of magnitude longer charge
recombination lifetime (τn) at a given dn (Figure 9B), which
outreaches the adverse effect of a lower conduction-band edge,
explaining its superior photovoltage at a given jsc (Figure 8B).
We also note that the charge recombination attenuation along
with the sensitizer alternation form C248 to C250 is not caused
by the dye load amount variation (C248, 2.4 × 10−8 mol cm−2 μm−1 ;
C250, 1.7 × 10−8 mol cm−2 μm−1 ) but likely induced by the lat-
eral molecular diameter augmentation.
3. Conclusions
We have synthesized four new organic sensitizers featuring
stepwise shifts of both low-energy absorption peak and ground-
state redox potential, and the C250 dye displays an excellent
power conversion efficiency of 9.4% measured under the
100 mW cm−2 , simulated AM1.5 sunlight in conjunction with
a tris(2,2′-bipyridine)cobalt(II/III) redox couple. The employ-
ment of electron-rich conjugated blocks has been demonstrated
as a viable strategy to narrow down the energy gap of organic
DSC dyes for efficient solar photon capture, without impacting
the exciton dissociation efficiency at the titania/dye interface.
We have also observed the breakdown of positive correlation
between dye regeneration rate and ground-state redox poten-
tial of sensitizers, suggesting the vital role of the dye assembly
microstructure on titania in charge transfer kinetics. This
finding could be reasonably exploited in the future dye design,
albeit the necessity for an appropriate energy-offset between dye
and redox couple for swift dye regeneration. Our work has also
shown that the dye-structure related interfacial charge recombi-
nation of titania electrons with electrolytes and/or oxidized dye
molecules is one of the key determinant of cell photovoltage,
which needs to be paid much attention in the development of
new sensitizers.
5′-(7-(4-(Bis(4-(2-ethylhexyloxy)phenyl)amino)phenyl)-2,3-
dihydrothieno[3,4-b][1,4]dioxin-5-yl)-2,2′-bithiophene-5-carbaldehyde:
To
a stirred solution of 4-(3,4-ethylenedioxythiophene-5-yl)-N,N-bis(4-(2-
ethylhexyloxy)phenyl)aniline (3.102 g, 4.832 mmol) in anhydrous THF
(50 mL) was added dropwise n-butyllithium (1.6 M in hexane, 3.322 mL,
5.315 mmol) at −78 °C. The resulting mixture was stirred at –78 °C for
1 h before tributylstannyl chloride (1.697 mL, 6.282 mmol) was added
in one portion. The cold bath was then removed and the solution was
stirred at room temperature for 6 h. Water (50 mL) was added to quench
the reaction and the solution was extracted with ethyl ether before the
organic phase was washed with water and dried over anhydrous sodium
sulfate. The solvent was evaporated under reduced pressure to afford
a viscous yellow liquid, the main component of which was identified
by 1H NMR as 4-(2-tributylstannyl-3,4-ethylenedioxythiophene-5-yl)-
N,N-bis(4-(2-ethylhexyloxy)phenyl)aniline with 70% yield and used
for next reactions without further purification. To a stirred solution of
5′-bromo-2,2′-bithiophene-5-carbaldehyde (0.301 g, 1.103 mmol) and
4-(2-tributylstannyl-3,4-ethylenedioxythiophene-5-yl)-N,N-bis(4-(2-
ethylhexyloxy)phenyl)aniline (1.078 g, 1.158 mmol) in toluene (15 mL)
was added Pd(PPh3)2Cl2 (0.077 g, 0.110 mmol). The resulting mixture
was refluxed for 15 h and then cooled to room temperature. After
evaporation of the solvent under reduced pressure, the crude product
was purified by column chromatography over silica gel with ethyl acetate/
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1851

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petroleum ether (v/v, 1/10) as the eluent to obtain a reddish orange
solid as the desired product (0.644 g, 70% yield). 1H NMR (400 MHz,
DMSO-d6, δ): 9.87 (s, 1H), 7.98 (d, J = 4.0 Hz, 1H), 7.56 (d, J = 4.0 Hz,
1H), 7.53 (d, J = 4.0 Hz, 1H), 7.49 (d, J = 8.8 Hz, 2H), 7.23 (d, J = 3.6 Hz,
1H), 7.01 (d, J = 8.8 Hz, 4H), 6.91 (d, J = 8.0 Hz, 4H), 6.80 (d, J =
9.2 Hz, 2H), 4.47 (s, 2H), 4.39 (s, 2H), 3.83 (d, J = 5.6 Hz, 4H), 1.67 (m,
2H), 1.35 (m, 16H), 0.90 (m, 12H). 13C NMR (150 MHz, DMSO-d6, δ):
182.63, 155.37, 147.22, 145.57, 145.43, 140.55, 139.50, 139.13, 138.96,
138.70, 137.22, 136.01, 133.21, 132.20, 126.35, 126.25, 123.49, 119.14,
115.39, 114.69, 107.83, 70.31, 64.81, 64.33, 38.57, 29.73, 28.15, 22.05,
21.50, 13.30, 10.54. MS (ESI) m/z calcd. for (C49H55NO5S3): 833.32.
Found: 834.32 ([M+H]+). Anal. calcd. for (C49H55NO5S3): C, 70.55; H,
6.65; N, 1.68. Found: C, 70.50; H, 6.74; N, 1.65.
6-{2-{4-[N,N-Bis(4-(2-ethylhexyloxy)phenyl)amino]phenyl}-3,4-
(ethylenedioxy)thiophen-5-yl}-4,4-dihexyl-4H-cyclopenta[2,1-b:3,4-b′]
dithiophene-2-carbaldehyde: To a stirred solution of 6-bromo-4,4-dihexyl-
4H-cyclopenta[2,1-b:3,4-b′]dithiophene-2-carbaldehyde (0.500 g, 1.103
mmol) and 4-(2-tributylstannyl-3,4-ethylenedioxythiophene-5-yl)-N,N-
bis(4-(2-ethylhexyloxy)phenyl)aniline (1.078 g, 1.158 mmol) in toluene
(15 mL) was added Pd(PPh3)2Cl2 (0.077 g, 0.110 mmol). The resulting
mixture was refluxed for 15 h and then cooled to room temperature.
After evaporation of the solvent under reduced pressure, the crude
product was purified by column chromatography over silica gel with
ethyl acetate/petroleum ether (v/v, 1/30) as the eluent to obtain a red
solid as the desired product (0.825 g, 74% yield). 1H NMR (400 MHz,
DMSO-d6, δ): 9.81 (s, 1H), 7.95 (s, 1H), 7.49 (d, J = 9.0 Hz, 2H), 7.25
(s, 1H), 7.02 (d, J = 9.0 Hz, 4H), 6.91 (d, J = 9.0 Hz, 4H), 6.80 (d, J =
9.0 Hz, 2H), 4.45 (s, 2H), 4.38 (s, 2H), 3.83 (d, J = 5.4 Hz, 4H), 1.88
(m, 4H), 1.67 (m, 2H), 1.40 (m, 8H), 1.30 (m, 8H), 1.12 (m, 12H), 0.89
(m, 16H), 0.77 (t, J = 6.4 Hz, 6H). 13C NMR (150 MHz, DMSO-d6, δ):
182.66, 162.28, 157.16, 155.37, 147.19, 146.17, 142.43, 139.50, 138.95,
138.69, 137.21, 132.88, 130.82, 126.35, 126.25, 123.49, 119.14, 116.32,
115.39, 114.72, 107.66, 70.32, 64.81, 64.33, 53.35, 38.58, 36.47, 30.52,
29.74, 28.48, 28.16, 23.64, 23.16, 22.06, 21.50, 13.41, 13.31, 10.55. MS
(ESI) m/z calcd. for (C62H79NO5S3): 1013.5. Found: 1014.8 ([M+H]+).
Anal. calcd. for C62H79NO5S3: C, 73.40; H, 7.85; N, 1.38. Found: C, 73.31;
H, 7.79; N, 1.35.
178.43, 160.24, 157.48, 155.51, 149.22, 147.85, 145.92, 139.64, 138.80,
136.49, 133.05, 132.33, 126.65, 126.05, 125.76, 122.77, 120.26, 119.57,
116.83, 115.51, 112.71, 70.13, 65.20, 64.81, 53.62, 38.71, 36.47, 30.93,
29.92, 28.88, 28.43, 23.64, 23.31, 22.48, 21.95, 13.91, 13.79, 10.91. MS
(ESI) m/z calcd. for (C62H79NO5S3): 1013.5. Found: 1014.2 ([M+H]+).
Anal. calcd. for C62H79NO5S3: C, 73.40; H, 7.85; N, 1.38. Found: C, 73.27;
H, 7.77; N, 1.34.
2-Cyano-3-{5-{4-[N,N-bis(4-(2-ethylhexyloxy)phenyl)amino]phenyl}-
2,2′:5′,2′′-terthienyl-5′′-yl}acrylic Acid ( C247): To a stirred solution of
5-{4-[N,N-bis(4-(2-ethylhexyloxy)phenyl)amino]phenyl}-2,2′:5′,2′′-
terthiophene-5′’-carbaldehyde (1.290 g, 1.664 mmol) and 2-cyanoacetic
acid (0.424 g, 4.992 mmol) in chloroform (50 mL) was added piperidine
(0.990 g, 11.648 mmol). The resulting mixture was refluxed for 12
h and then cooled to room temperature before being acidified with 2
M hydrochloric acid aqueous solution. The solution was extracted
with chloroform before the organic phase was washed with water and
dried over anhydrous sodium sulfate. After evaporation of the solvent
under reduced pressure, the crude product was purified by column
chromatography over silica gel with methanol/chloroform (v/v, 1/50) as
eluent to yield a purple powder (1.233 g, 88% yield). 1H NMR (400 MHz,
DMSO-d6, δ): 13.68 (s, 1H), 8.35 (s, 1H), 7.88 (d, J = 4.0 Hz, 1H), 7.55
(d, J = 4.0 Hz, 2H), 7.48 (d, J = 8.8 Hz, 2H), 7.40 (d, J = 3.6 Hz, 1H),
7.36 (d, J = 4.0 Hz, 1H), 7.34 (d, J = 3.6 Hz, 1H), 7.04 (d, J = 8.8 Hz,
4H), 6.93 (d, J = 8.8 Hz, 4H), 6.77 (d, J = 8.8 Hz, 2H), 3.83 (d, J = 5.6
Hz, 4H), 1.68 (m, 2H), 1.44 (m, 8H), 1.21 (m, 8H), 0.89 (m, 12H). 13C
NMR (100 MHz, DMSO-d6, δ): 163.71, 155.66, 148.33, 145.07, 144.42,
143.82, 140.53, 139.42, 138.33, 134.20, 133.19, 133.04, 127.92, 126.92,
126.27, 126.17, 124.98, 124.84, 124.43, 123.16, 118.94, 117.02, 115.50,
98.51, 70.10, 38.71, 29.92, 28.43, 23.31, 22.48, 13.90, 10.90. HR-MS (ESI)
m/z calcd. for (C50H54N2O4S3): 842.32457. Found: 865.31314 ([M+Na]+).
Anal. calcd. for C50H54N2O4S3: C, 71.22; H, 6.46; N, 3.32. Found: C,
71.14; H, 6.55; N, 3.28. IR (KBr): 1686 cm−1 (COOH), 2217−1 cm (CN).
2-Cyano-3-{5′-{2-{4-[N,N-bis(4-(2-ethylhexyloxy)phenyl)amino]phenyl}-
3,4-(ethylenedioxy)thiophen-5-yl}-2,2′- bithienyl-5-yl}acrylic Acid ( C248):
To a stirred solution of 5′-(7-(4-(bis(4-(2-ethylhexyloxy)phenyl)amino)
phenyl)-2,3-dihydrothieno[3,4-b][1,4]dioxin-5-yl)-2,2′-bithiophene-5-
carbaldehyde (0.580 g, 0.695 mmol) and 2-cyanoacetic acid (0.177 g,
2.086 mmol) in chloroform (21 mL) was added piperidine (0.413 g,
4.865 mmol). The resulting mixture was refluxed for 12 h and then cooled
to room temperature before being acidified with 2 M hydrochloric acid
aqueous solution. The solution was extracted with chloroform before the
organic phase was washed with water and dried over anhydrous sodium
sulfate. After evaporation of the solvent under reduced pressure, the
crude product was purified by column chromatography over silica gel
with methanol/chloroform (v/v, 1/50) as eluent to yield a purple-black
powder (0.551 g, 88% yield). 1H NMR (600 MHz, DMSO-d6, δ): 13.64 (s,
1H), 8.46 (s, 1H), 7.96 (d, J = 3.6 Hz, 1H), 7.57 (m, 2H), 7.48 (d, J = 8.4
Hz, 2H), 7.23 (d, J = 3.6 Hz, 1H), 7.01 (d, J = 8.4 Hz, 4H), 6.91 (d, J =
9.0 Hz, 4H), 6.78 (d, J = 8.4 Hz, 2H), 4.47 (s, 2H), 4.37 (s, 2H), 3.82 (d,
J = 5.4 Hz, 4H), 1.65 (m, 2H), 1.36 (m, 16H), 0.89 (m, 12H). 13C NMR
(150 MHz, DMSO-d6, δ): 163.13, 155.38, 147.27, 145.60, 145.46, 140.59,
139.46, 139.16, 137.14, 136.03, 133.24, 132.14, 127.04, 126.33, 124.15,
123.33, 123.24, 119.06, 116.08, 115.37, 106.53, 97.50, 70.34, 64.85,
64.28, 38.58, 29.72, 28.14, 23.15, 22.03, 13.38, 10.53. HR-MS (ESI) m/z
calcd. for (C52H56N2O6S3): 900.33005. Found: 923.31867 ([M+Na]+).
Anal. calcd. for (C52H56N2O6S3): C, 69.30; H, 6.26; N, 3.11. Found: C,
69.21; H, 6.30; N, 3.09. IR (KBr): 1686 cm−1 (COOH), 2217 cm−1 (CN).
2-Cyano-3-{6-{2-{4-[N,N-bis(4-(2-ethylhexyloxy)phenyl)amino]phenyl}-
3,4-(ethylenedioxy)thiophen-5-yl}-4,4-dihexyl-4H-cyclopenta[2,1-b:3,4-b′]
dithiophene-2-yl}Acrylic Acid (C249): To a stirred solution of 6-{2-{4-[N,N-
bis(4-(2-ethylhexyloxy)phenyl)amino]phenyl}-3,4-(ethylenedioxy)
thiophen-5-yl}-4,4-dihexyl-4H-cyclopenta[2,1-b:3,4-b′]dithiophene-2-
carbaldehyde (0.271 g, 0.270 mmol) and 2-cyanoacetic acid (0.068 g,
0.810 mmol) in chloroform (15 mL) was added piperidine (0.160 g,
1.880 mmol). The resulting mixture was refluxed for 12 h and then cooled
to room temperature before being acidified with 2 M hydrochloric acid
aqueous solution. The solution was extracted with chloroform before the
organic phase was washed with water and dried over anhydrous sodium
5-{6-{4-[N,N-Bis(4-(2-ethylhexyloxy)phenyl)amino]phenyl}-4,4-dihexyl-
4H-cyclopenta[2,1-b:3,4-b′]dithiophene-2-yl}-3,4-ethylenedioxythiophen-2-
carbaldehyde: To a stirred solution of 6-{4-[N,N-bis(4-(2-ethylhexyloxy)
phenyl)-amino]phenyl}-4,4-dihexyl-4H-cyclopenta[2,1-b:3,4-b′]
dithiophene (0.900 g, 1.063 mmol) in anhydrous THF (10 mL) was
added dropwise n-butyllithium (1.6 M in hexane, 0.730 mL, 1.170 mmol)
at −78 °C. The resulting mixture was stirred at –78 °C for 3 h before
tributylstannyl chloride (0.375 mL, 1.382 mmol) was added in one
portion. The cold bath was then removed and the solution was stirred
at room temperature overnight. Water (10 mL) was added to quench
the reaction and the solution was extracted with ethyl ether before the
organic phase was washed with water and dried over anhydrous sodium
sulfate. The solvent was evaporated under reduced pressure to afford a
viscous yellow liquid, the main component of which was identified by
1H NMR as 4-(2-tributylstannyl-4,4-dihexyl-4H-cyclopenta[2,1-b:3,4-b′]
dithiophene-6-yl)-N,N-bis(4-(2-ethylhexyloxy)phenyl)aniline with 90%
yield and used for next reactions without further purification. To a stirred
solution of 5-bromo-3,4-ethylenedioxy-2-formylthiophene (0.204 g, 0.818
mmol) and 4-(2-tributylstannyl-4,4-dihexyl-4H-cyclopenta[2,1-b:3,4-b′]
dithiophene-6-yl)-N,N-bis(4-(2-ethylhexyloxy)phenyl)aniline (1.085 g,
0.957 mmol) in toluene (10 mL) was added Pd(PPh3)2Cl2 (0.058 g, 0.082
mmol). The resulting mixture was refluxed for 6 h and then cooled to
room temperature. After evaporation of the solvent under reduced
pressure, the crude product was purified by column chromatography
over silica gel with ethyl acetate/petroleum ether (v/v, 1/5) as eluent to
1
obtain a red solid as the desired product (0.763 g, 92% yield). H NMR
(600 MHz, DMSO-d6, δ): 9.82 (s, 1H), 7.50 (s, 1H), 7.47 (d, J = 9.0 Hz,
2H), 7.38 (s, 1H), 7.01 (d, J = 9.0 Hz, 4H), 6.92 (d, J = 9.0 Hz, 4H),
6.78 (d, J = 9.0 Hz, 2H), 4.50 (s, 4H), 3.83 (d, J = 6.0 Hz, 4H), 1.89
(m, 4H), 1.68 (m, 2H), 1.40 (m, 8H), 1.29 (m, 8H), 0.91 (m, 12H), 0.89
(m, 16H), 0.76 (t, J = 7.2 Hz, 6H). 13C NMR (150 MHz, DMSO-d6, δ):
©
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Adv. Funct. Mater. 2013, 23, 1846–1854

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sulfate. After evaporation of the solvent under reduced pressure, the
crude product was purified by column chromatography over silica gel
with methanol/chloroform (v/v, 1/50) as eluent to yield a black powder
(0.255 g, 89% yield) 1H NMR (400 MHz, DMSO-d6, δ): 13.35 (s, 1H),
8.40 (s, 1H), 7.91 (s, 1H), 7.50 (d, J = 8.8 Hz, 2H), 7.27 (s, 1H), 7.01
(d, J = 8.8 Hz, 4H), 6.91 (d, J = 8.8 Hz, 4H), 6.79 (d, J = 8.8 Hz, 2H),
4.45 (s, 2H), 4.38 (s, 2H), 3.83 (d, J = 5.6 Hz, 4H), 1.90 (m, 4H), 1.67
(m, 2H), 1.40 (m, 8H), 1.30 (m, 8H), 1.12 (m, 12H), 0.89 (m, 16H),
0.77 (t, J = 6.4 Hz, 6H). 13C NMR (150 MHz, DMSO-d6, δ): 163.79,
163.05, 157.26, 155.40, 148.32, 147.25, 146.45, 140.13, 139.47, 138.98,
137.24, 135.29, 133.04, 132.23, 126.38, 126.27, 123.42, 119.09, 116.91,
116.30, 115.39, 115.15, 107.71, 93.35, 70.33, 64.86, 64.33, 53.16, 38.59,
37.21, 30.51, 29.74, 28.46, 28.17, 23.17, 23.65, 22.07, 21.50, 13.42, 13.31,
10.56. HR-MS (ESI) m/z calcd. for (C65H80N2O6S3): 1080.51785. Found:
1080.51246 ([M]+). Anal. calcd. for C65H80N2O6S3: C, 72.18; H, 7.46; N,
2.59. Found: C, 72.09; H, 7.54; N, 2.51. IR (KBr): 1678 cm−1 (COOH),
2210 cm−1 (CN).
was deployed as the negative electrode of DSCs presented in this paper.
A 2.3-μm-thick translucent layer of 25 nm sized titania particles was first
deposited on a FTO glass and further covered with a 4.5-μm-thick light-
scattering layer of 350−450 nm sized titania particles (WER4-O, Dyesol).
Preparation procedures of titania nanocrystals, screen-printing pastes,
and nanostructured titania films were very similar to those described in a
previous paper.[41] A circular titania electrode (≈0.28 cm2) was dye-loaded
by immersing it into a 100 μM dye solution in the mixed solvent of AN
and THF. The dye-coated titania electrode was assembled with a thermally
platinized FTO electrode by use of a 25-μm-thick Surlyn ring to produce
a thin-layer electrochemical cell. The infiltrated electrolyte is composed
of 0.25 M tris(2,2′-bipyridine)cobalt(II) di[bis(trifluoromethanesulfonyl)-
imide], 0.05 M tris(2,2′-bipyridine)cobalt(III) tris[bis(trifluoromethanesul-
fonyl)imide], 0.5 M TBP, and 0.1 M LiTFSI in AN. Details on photovoltaic
characterizations can be found in our previous publication.[42]
Charge Extraction and Transient Photovoltage Decay Measurements:
Transient photoelectrical experiments[43] were performed on an
Autolab-PGSTAT302N electrochemical workstation with the ADC10M
high-speed module, which can satisfy 100-ns time-resolved current
and voltage tests. The static and perturbing lights were supplied with
home-made white and red light-emitting diode arrays. We employed
a red light to generate a photovoltage perturbation near the open-
circuit photovoltage of a testing cell under the irradiation of a certain
white light and measured the voltage decay thereafter. The modulated
photovoltage by the red pulse of a testing cell is below 5 mV and the
transient signals follow a mono-exponential decay. Fitting an exponential
function to the photovoltage decay can produce the electron lifetime.
The electron density was estimated by the charge extraction method.
We first maintained a testing cell at open circuit under a white light and
then changed it to short circuit upon switching off the light to record the
concomitant current transients. Further calculation with integral of the
current trace can generate the electron density.
2-Cyano-3-{5-{6-{4-[N,N-bis(4-(2-ethylhexyloxy)phenyl)amino]
phenyl}-4,4-dihexyl-4H-cyclopenta[2,1-b:3,4-b′]dithiophene-2-yl}-3,4-
ethylenedioxythiophen-2-yl}acrylic acid (C250): To a stirred solution of
5-{6-{4-[N,N-bis(4-(2-ethylhexyloxy)phenyl)amino]phenyl}-4,4-dihexyl-
4H-cyclopenta[2,1-b:3,4-b′]dithiophene-2-yl}-3,4-ethylenedioxythiophen-
2-carbaldehyde (0.530 g, 0.521 mmol) and 2-cyanoacetic acid (0.133 g,
1.564 mmol) in chloroform (20 mL) was added piperidine (0.310 g,
3.647 mmol). The resulting mixture was refluxed for 12 h and then cooled
to room temperature before being acidified with 2 M hydrochloric acid
aqueous solution. The solution was extracted with chloroform before the
organic phase was washed with water and dried over anhydrous sodium
sulfate. After evaporation of the solvent under reduced pressure, the
crude product was purified by column chromatography over silica gel
with methanol/chloroform (v/v, 1/50) as eluent to yield a black powder
1
(0.503 g, 89% yield) H NMR (600 MHz, THF-d8, δ): 8.46 (s, 1H), 7.62
(m, 3H), 7.42 (s, 1H), 7.19 (d, J = 9.0 Hz, 4H), 7.06 (d, J = 9.0 Hz,
2H), 7.03 (d, J = 9.0 Hz, 4H), 4.64 (s, 4H), 4.03 (d, J = 5.4 Hz, 4H),
2.13 (m, 4H), 1.89 (m, 2H), 1.65 (m, 8H), 1.53 (m, 8H), 1.34 (m, 12H),
1.11 (m, 16H), 0.97 (t, J = 5.4 Hz, 6H). 13C NMR (150 MHz, THF-d8, δ):
165.27, 161.90, 159.14, 157.50, 149.90, 148.48, 142.50, 141.93, 140.91,
137.87, 135.39, 134.48, 128.48, 127.88, 127.14, 125.47, 121.87, 121.40,
117.98, 117.77, 116.52, 109.93, 94.67, 71.65, 67.34, 66.59, 55.59, 41.13,
39.37, 33.05, 32.05, 31.13, 30.56, 26.08, 25.30, 24.44, 23.99, 14.91, 14.85,
12.00. HR-MS (ESI) m/z calcd. for (C65H80N2O6S3): 1080.51785. Found:
1080.51554 ([M]+). Anal. calcd. for C65H80N2O6S3: C, 72.18; H, 7.46; N,
2.59. Found: C, 72.06; H, 7.52; N, 2.49. IR (KBr): 1675 cm−1 (COOH),
2210 cm−1 (CN).
UV-Vis Absorption and Photoluminescence (PL) Measurements: Steady
UV-vis absorption and PL spectra were measured with an Agilent G1103A
spectrometer and a PerkinElmer LS55 luminescence spectrometer,
respectively. The emitted light was tested with a Hamamatsu R928
red-sensitive photomultiplier. Transient absorption decay traces were
recorded with a LP920 laser flash spectrometer with a tunable OPOLett
355II laser to supply the nanosecond excitation pulse. The PL decays
were measured with a LifeSpec-II fluorescence spectrometer equipped
with an EPL488 laser diode.
Supporting Information
Supporting Information is available from the Wiley Online Library or
from the author.
Acknowledgements
N.C., Y.W., and M.X. contributed equally to this work. The National
Science Foundation of China (Nos. 50973105, 51125015, 51103146,
and 21203175), the National 973 Program (No. 2011CBA00702), the
National 863 Program (No. 2011AA050521), and the Key Scientific
and Technological Program of Jilin Province (No. 10ZDGG012) are
acknowledged for financial support. We are grateful to Dyesol for
supplying the WER4-O scattering paste and to DuPont Packaging and
Industrial Polymers for supplying the Surlyn and Bynel films.
Received: September 6, 2012
Published online: November 1, 2012
Computational Details: The ground state geometries were optimized
employing the hybrid B3LYP[35] function and
a 6-31G∗∗ basis
set. Vertical excitation energies were calculated by TD-DFT at the
MPW1K[36–38]/6-31G∗∗ levels. The effect of THF on the geometries and
absorption spectra has been simulated by the C-PCM method.[39] All
calculations were carried out with the Gaussian 09 program package.[40]
Redox Potential Measurements: Square-wave voltammograms of
these four new dyes dissolved in THF were recorded on an Autolab-
PGSTAT302N electrochemical workstation by use of a three-electrode
electrolytic cell, consisting of a platinum gauze counter electrode, a
silver wire auxiliary electrode, and a platinum ultramicroelectrode. All
potentials were reported relative to the Fc/Fc+ reference.
[1] B. O’Regan, M. Grätzel, Nature 1991, 353, 737.
[2] M. Grätzel, Acc. Chem. Res. 2009, 42, 1788.
[3] A. Yella, H.-W. Lee, H. N. Tsao, C. Yi, A. K. Chandiran, M. K. Nazeeruddin,
E. W.-G. Diau, C. Y. Yeh, S. M. Zakeeruddin, M. Grätzel, Science
2011, 334, 629.
[4] A. Mishra, M. K. R. Fischer, P. Bäuerle, Angew. Chem. Int. Ed. 2009,
48, 2474.
[5] J. N. Clifford, E. Martínez-Ferrero, A. Viterisi, E. Palomares, Chem.
Soc. Rev. 2011, 40, 1635.
Cell Fabrication and Photovoltaic Characterization: A double layer
titania film made via screen-printing on a precleaned fluorine-doped tin
oxide (FTO) conducting glass (Nippon Sheet Glass, Solar, 4 mm thick)
[6] D. P. Hagberg, T. Edvinsson, T. Marinado, G. Boschloo, A. Hagfeldt,
L. Sun, Chem. Commun. 2006, 2245.
©
wileyonlinelibrary.com
Adv. Funct. Mater. 2013, 23, 1846–1854
2013 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim
1853

www.afm-journal.de
www.MaterialsViews.com
[7] N. Koumura, Z.-S. Wang, S. Mori, M. Miyashita, E. Suzuki, K. Hara,
J. Am. Chem. Soc. 2006, 128, 14256.
[27] J. N. Clifford, E. Martínez-Ferrero, E. Polomares, J. Mater. Chem.
2012, 22, 12415.
[8] S. Kim, J. K. Lee, S. O. Kang, J. Ko, J.-H. Yum, S. Fantacci,
F. De Anglis, D. Di Censo, M. K. Nazeeruddin, M. Grätzel, J. Am.
Chem. Soc. 2006, 128, 16701.
[9] Z.-S. Wang, Y. Cui, K. Hara, Y. Dan-oh, C. Kasada, A. Shinpo, Adv.
Mater. 2007, 19, 1138.
[28] T. Stergiopoulos, P. Falaras, Adv. Energy Mater. 2012, 2, 616.
[29] J. Liu, D. Zhou, F. Wang, F. Fabregat-Santiago, S. G. Miralles,
X. Jing, J. Bisquert, P. Wang, J. Phys. Chem. C 2011, 115, 14425.
[30] W. Zeng, Y. Cao, Y. Bai, Y. Wang, Y. Shi, M. Zhang, F. Wang, C. Pan,
P. Wang, Chem. Mater. 2010, 22, 1915.
[10] K. R. J. Thomas, Y.-C. Lin, K.-M. Lee, K.-C. Ho, C.-H. Lai, Y.-M. Chen,
P.-T. Chou, Chem. Mater. 2008, 20, 1830.
[31] R. Li, J. Liu, N. Cai, M. Zhang, P. Wang, J. Phys. Chem. B 2010, 114,
4461.
[11] H. Qin, S. Wenger, M. Xu, F. Gao, X. Jing, P. Wang,
S. M. Zakeeruddin, M. Grätzel, J. Am. Chem. Soc. 2008, 130, 9202.
[12] D.-Y. Chen, Y.-Y. Hsu, H.-C. Hsu, B.-S. Chen, Y.-T. Lee, H. Fu,
M.-W. Chung, S.-H. Liu, H.-C. Chen, Y. Chi, P.-T. Chou, Chem.
Commun. 2010, 46, 5256.
[32] T. Nishizawa, K. Tajima, K. Hashimoto, J. Mater. Chem. 2007, 17, 2440.
[33] S. P. G. Costa, R. M. F. Batista, M. M. M. Raposo, Tetrahedron 2008,
64, 9733.
[34] M. Jessing, M. Brandt, K. J. Jensen, J. B. Christensen, U. Boas,
J. Org. Chem. 2006, 71, 6734.
[13] Y. Bai, J. Zhang, D. Zhou, Y. Wang, M. Zhang, P. Wang, J. Am. Chem.
Soc. 2011, 133, 11442.
[14] Y. Cui, Y. Wu, X. Lu, X. Zhang, G. Zhou, F. B. Miapeh, W. Zhu,
Z.-S. Wang, Chem. Mater. 2011, 23, 4394.
[15] M. Xu, M. Zhang, M. Pastore, R. Li, F. De Angelis, P. Wang, Chem.
Sci. 2012, 3, 976.
[35] A. D. Becke, J. Chem. Phys. 1993, 98, 1372.
[36] B. J. Lynch, P. L. Fast, M. Harris, D. G. Truhlar, J. Phys. Chem. A
2000, 104, 4811.
[37] M. Cossi, V. Barone, J. Chem. Phys. 2001, 115, 4708.
[38] M. Pastore, E. Mosconi, F. De Angelis, M. Grätzel, J. Phys. Chem. C
2010, 114, 7205.
[16] Y.-C. Chen, H.-H. Chou, M. C. Tsai, S.-Y. Chen, J. T. Lin, C.-F. Yao,
K. Chen, Chem. Eur. J. 2012, 18, 5430.
[39] M. Cossi, N. Rega, G. Scalmani, V. Barone, J. Comput. Chem. 2003,
24, 669.
[17] S. Haid, M. Marszalek, A. Mishra, M. Wielopolski, J. Teuscher,
J.-E. Moser, R. Humphry-Baker, S. M. Zakeeruddin, M. Grätzel,
P. Bäuerle, Adv. Funct. Mater. 2012, 22, 1291.
[18] K. Hara, M. Kurashige, Y. Dan-oh, C. Kasada, A. Shinpo, S. Suga,
K. Sayama, H. Arakawa, New J. Chem. 2003, 27, 783.
[19] S. E. Koops, P. R. F. Barnes, B. O’Regan, J. R. Durrant, J. Phys.
Chem. C 2010, 114, 8054.
[20] T. D. Santos, A. Morandeira, S. Koops, A. J. Mozer, G. Tsekouras,
Y. Dong, P. Wagner, G. Wallace, J. C. Earles, K. C. Gordon, D. Officer,
J. R. Durrant, J. Phys. Chem. C 2010, 114, 3276.
[21] A. Y. Anderson, P. R. F. Barnes, J. R. Durrant, B. O’Regan, J. Phys.
Chem. C 2011, 115, 2439.
[22] H. Imahori, S. Kang, H. Hayashi, M. Haruta, H. Kurata, S. Isoda,
S. E. Canton, Y. Infahsaeng, A. Kathiravan, T. Pascher, P. Chábera,
A. P. Yartsev, V. Sundström, J. Phys. Chem. A 2011, 115, 3679.
[23] S. Mathew, H. Iijima, Y. Toude, T. Umeyama, Y. Matano, S. Ito,
N. V. Tkachenko, H. Lemmetyinen, H. Imahori, J. Phys. Chem. C
2011, 115, 14415.
[40] M. J. Frisch, G. W. Trucks, H. B. Schlegel, G. E. Scuseria,
M. A. Robb, J. R. Cheeseman, G. Scalmani, V. Barone, B. Mennucci,
G. A. Petersson, H. Nakatsuji, M. Caricato, X. Li, H. P. Hratchian,
A. F. Izmaylov, J. Bloino, G. Zheng, J. L. Sonnenberg, M. Hada,
M. Ehara, K. Toyota, R. Fukuda, J. Hasegawa, M. Ishida, T. Nakajima,
Y. Honda, O. Kitao, H. Nakai, T. Vreven, J. A. Montgomery, J. E. Peralta,
F. Ogliaro, M. Bearpark, J. J. Heyd, E. Brothers, K. N. Kudin,
V. N. Staroverov, R. Kobayashi, J. Normand, K. Raghavachari,
A. Rendell, J. C. Burant, S. S. Iyengar, J. Tomasi, M. Cossi,
N. Rega, N. J. Millam, M. Klene, J. E. Knox, J. B. Cross, V. Bakken,
C. Adamo, J. Jaramillo, R. Gomperts, R. E. Stratmann, O. Yazyev,
A. J. Austin, R. Cammi, C. Pomelli, J. W. Ochterski, R. L. Martin,
K. Morokuma, V. G. Zakrzewski, G. A. Voth, P. Salvador,
J. J. Dannenberg, S. Dapprich, A. D. Daniels, Ö. Farkas,
J. B. Foresman, J. V. Ortiz, J. Cioslowski, D. J. Fox, Gaussian 09,
Revision A.1, Gaussian, Inc., Wallingford, CT 2009.
[41] P. Wang, S. M. Zakeeruddin, P. Comte, R. Charvet, R. Humphry-Baker,
M. Grätzel, J. Phys. Chem. B 2003, 107, 14336.
[24] R. A. Marcus, J. Chem. Phys. 1965, 43, 679.
[42] J. Liu, R. Li, X. Si, D. Zhou, Y. Shi, Y. Wang, X. Jing, P. Wang, Energy
Environ. Sci. 2010, 3, 1924.
[43] B. C. O’Regan, K. Bakker, J. Kroeze, H. Smit, P. Sommeling,
J. R. Durrant, J. Phys. Chem. B 2006, 110, 17155.
[25] B. O’Regan, J. R. Durrant, Acc. Chem. Res. 2009, 42, 1799.
[26] F. Fabregat-Santiago, G. Garcia-Belmonte, I. Mora-Séro, J. Bisquert,
Phys. Chem. Chem. Phys. 2011, 13, 9083.
©
1854 wileyonlinelibrary.com
2013 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim
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