A D-π-A-π-A type dye for highly efficient dye-sensitized solar cells

Article abstract of DOI:10.1039/c5ra05287d

We synthesized a D-π-A-π-A type dye and demonstrated its application in dye-sensitized solar cells (DSSCs). This D-π-A-π-A type dye, named C321, consisted of a triphenylamine as a donor, a 3,4-ethylenedioxythiophene (EDOT) as a π-bridge, and a benzothiazo

Full text of DOI:10.1039/c5ra05287d

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A D–p–A–p–A type dye for highly efficient dye-
sensitized solar cells†
Cite this: RSC Adv., 2015, 5, 37574
b
b
a
b
Chao-Feng Du,‡ab Lei Jiang,‡ Lei Sun, Nian-Yu Huang and Wei-Qiao Deng
*
We synthesized a D–p–A–p–A type dye and demonstrated its application in dye-sensitized solar cells
(DSSCs). This D–p–A–p–A type dye, named C321, consisted of a triphenylamine as a donor, a 3,4-
ethylenedioxythiophene (EDOT) as a p-bridge, and a benzothiazole (BTDA)–phenyl-cyanoacrylic acid as
an A–p–A group. Compared with DSSCs based on a traditional D–p–A type dye C311, the DSSCs based
on C321 exhibited a significant enhancement of cell performance. A power conversion efficiency of 8.2%
was achieved for DSSCs based on C321, which was 9 times higher than that for DSSCs based on C311
(0.9%). The theoretical calculations and electrochemical impedance spectroscopy investigations revealed
the mechanism of the enhancement of cell performance.
Received 25th March 2015
Accepted 16th April 2015
DOI: 10.1039/c5ra05287d
www.rsc.org/advances
in various physical and chemical properties of dye molecules.19
The most common D–p–A type dyes were consisted of a tri-
1. Introduction
phenylamine group as donor, a cyanoacetic acid group as
acceptor, and a thiophene (T) and its derivatives as p-
spacer.15,20–26 For example, the cell based on dye C219 exhibited
a power conversion efficiency (PCE) – 10.3%, which has been
near the created by ruthenium(II) complex dyes.15 To improve
the PCE of metal-free organic dyes, a strategy is to introduce an
electron-accepting unit into the p-spacer group which can be
named as a D–p–A–A type structure.23,27–29 For example, the
introduction of benzothiadiazole (BTDA) unit, an acceptor
group, into the p-spacer group can reduce the gap between
HOMO and LUMO signicantly, which results in an improved
PCE. However, some D–p–A–A type dyes may not be efficient
since the electron recombination between adjacent acceptor
groups and TiO2 substrate can be intensied.30
Dye sensitized solar cells (DSSCs) are regarded as promising
devices for high-efficiency and low-cost solar energy conversion,
1–4
¨
since O'Regan and Gratzel reported the rst DSSC in 1991.
Small cells have recently been achieved with an efficiency of
over 13.0%1–5 and a lifetime of more than 1000 hours.6 The
further development of DSSCs relies on the discovery of new
dyes that provide better photovoltaic properties. Explorations of
new dyes for DSSCs can be divided into two categories: (1) metal
complex dyes with transition metal such as N3,7,8 black dye,9–11
YD2-o-C8 (ref. 12) and SM315;5 (2) metal-free organic dyes such
as C218,13,14 C219 (ref. 15) and D5.16,17 Comparing with the metal
complex dyes, the metal-free organic dyes are much easier to
tune their absorption spectral and electrochemical properties
through tailoring molecules.18
Here, we proposed a D–p–A–p–A type dye by introducing a p
group into a D–p–A–A type dye for DSSCs. As an example, we
synthesized a dye C321 consisted of a triphenylamine as a
donor, a 3,4-ethylenedioxythiophene (EDOT) as a p-bridge, and
a benzothiazole (BTDA)–phenyl-cyanoacrylic acid as a A–p–A
group, as shown in Scheme 1. The PCE of DSSCs based on C321
can reach as high as 8.3%, which is 9 times higher than that of
DSSCs based on a traditional D–p–A type dye C311. Both
theoretical and experimental results indicated that the
enhancement of PCE may origin from the improvement of the
recombination process in DSSCs.
Generally, metal-free organic dyes are consisted of a donor-
p-acceptor (D–p–A) type structure, of which D is an electron-
donating unit, A is an electron-accepting unit and p is a p-
conjugated spacer unit. The D–p–A dye structure can induce
intramolecular charge transfer (ICT) from donor to acceptor
group which facilitates the high molar extinction coefficient
and redshi the absorption of dye molecules. By changing
donor, acceptor or p-spacer groups, the energy levels of the
highest occupied molecular orbital (HOMO) and the lowest
unoccupied molecular orbital (LUMO) can be shied, resulting
aHubei Key Laboratory of Natural Products Research and Development, College of
Chemistry and Life Sciences, China Three Gorges University, Yichang 443002, China
bState Key Laboratory of Molecular Reaction Dynamics, Dalian National Laboratory
for Clean Energy, Dalian Institute of Chemical Physics, Chinese Academy of
Sciences, Dalian 116023, China. E-mail: dengwq@dicp.ac.cn
2. Results and discussion
2.1. Synthesis
Compound 4 (4-bromo-7-(4-formylphenyl)-2,1,3-benzothiadiazole)
† Electronic supplementary information (ESI) available: See DOI:
10.1039/c5ra05287d
was synthesized via
a Suzuki–Miyaura coupling reaction.
‡ These authors contributed equally to this work.
Compounds 9, 11 and 12 were synthesized via still coupling
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Scheme 1 Synthesis of dyes C311 and C321.
reactions. The synthetic routes of C311 and C321 are shown in a Gaussian09 soware.35 For calculating the absorption spec-
Scheme 1 and the detailed synthesis procedures of 1 to 12 are trum in CH3CN solution, a time-dependent density functional
described in the ESI.†
theoretical (TDDFT) with the MPW1K34 functional was
employed. The optimized geometries of the two dyes, as shown
in Fig. 1, have planar structures in the ground state. The
calculated electron-density diagrams of HOMOs and LUMOs
were shown in Fig. 1 as well. In both dyes, the HOMOs and
LUMOs exhibit p-character. While the HOMO is mainly
2.2. Theoretical calculations
The electronic congurations of the isolated dyes were exam-
ined by using B3LYP33/6-311G** hybrid functional implanted in
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requiring sinj < 10 ps to achieve an injection efficiency of 90% or
even more. If the excited state lifetime is set to 1 ps for C311 and
C321, their hinj equal to 98% and 99%, respectively. The
calculated injection times indicated these dyes exhibit strong
electronic coupling with TiO2 cluster and great quantum yield
for electron injection. The calculated injection efficiencies for
all dyes were very close to 100%. It indicates that the intro-
duction of BTDA, electron-accepting unit, close to cyanoacetic
acid group will not affect the electron injection process from dye
to TiO2 substrate.
To reduce the charge recombination rate between the dye
cation and the injected electron, the positive charge localized
primarily on the donor group should be farther away from the
electrode surface. Based on nonadiabatic electron-transfer
theory, the recombination rate can be analyzed in terms of
Fig. 1 HOMO and LUMO electron density distributions for frontier
orbitals of dyes C311 and C321.
2
the Marcus formula, where HAB is the electronic coupling
between the donor and acceptor groups, DG0 is the reaction
localized over the donor groups, the LUMO is localized on the
accepter and p-spacer groups. The localizations of molecular
orbitals are expected to have an intramolecular charge separa-
tion upon excitation. The calculated dipole-allowed absorptions
were listed in Table 1. The strong absorption peaks for each dye
arise from S0 / S1, which correspond to the promotion of an
electron from the HOMO to LUMO. Therefore, the lowest-lying
absorption transitions were all assigned to p / p* type tran-
sitions from donor to acceptor moieties through a p-spacer.
Comparing with C321, C311 exhibited a maximum absorption
at longer wavelength 610 nm and similar oscillator strength of
absorption peak, which probably results in the greater overlap
between its absorption spectrum and the solar spectrum. For
these two dyes, the wavelengths of maximum absorption peaks
decreased with the additional phenyl group about 50 nm. Just
based on the calculated absorption spectral, the D–p–A–p–A
type dye C321 should have a weaker light adsorption than the
D–p–A type dye C311.
The electronic coupling strength governing the photoin-
duced electron transfer is probably determined by the interac-
tion between the LUMO orbital of dye and the conduction band
of TiO2. To investigate this interaction, a detailed investiga-
tion of the partial density of state (PDOS) of the adsorbate's
LUMO has been made. The dye-absorbed geometries were
optimized in the gas phase using the Dmol3 package and the
electronic structure of the combined system was subsequently
calculated at B3LYP/SVP level using the Gaussian09 soware.
The injection times for C311 and C321 are 17 and 12 fs,
respectively. The electron injection efficiency is calculated by:
hinj ¼ 1 ꢀ sinj/slifetime. For organic dyes, the injection process
is in competition with singlet state decay to ground (singlet
excited state lifetime ranging from ꢁ100 ps to a few nanoseconds),
2
free energy, and l is the reorganization energy. The term HAB
can be represented in terms of an exponential function of the
spatial separation
r between the donor and acceptor
groups.31,32 According to the work by Clifford et al.,31 DG0 is
approximately equal to l in the recombination dynamics, and r
is the primary factor affecting the recombination rate. Here, r
is approximated by using the HOMO barycenter (rHOMO) of the
neutral dye. Based on the geometries of dye–TiO2 complexes,
the values of rHOMO of the isolated dye molecule on TiO2
substrate were evaluated as 1.69 and 2.15 nm for C311 and
C321, respectively. The spatial separation between HOMO and
TiO2 substrate increased obviously aer the phenyl group was
introduced. It indicates that the phenyl group can suppress
the electron recombination between dye and TiO2 signi-
cantly, which may result in an enhancement of the photocur-
rent of DSSCs based on C321.
!
2
2
HAB
pffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffi
4plkBT
ðDG0 ꢀ lÞ
4lkBT
kre
¼
exp
ꢀ
(1)
Based on the quantum chemical calculations, we studied the
optical properties, electron injection time and electron recom-
bination for C311 and C321. The results showed that although
C311 has a promising absorption spectral performance, C321
exhibits a weak electron recombination process that may lead to
a high photocurrent.
2.3. Spectroscopic properties
The UV-vis absorption spectra of C311 and C321 measured in
dilute chlorobenzene solution were shown in Fig. 2, exhibiting
two absorption bands over a range of 350–800 nm. The bands
at 378 nm of C311 and 364 nm of C321 corresponded to the
p–p* transition of the conjugated system. The longest wave-
length absorption peak of C321 (lmax ¼ 511 nm) was assigned
to a charge-transfer (CT) transition. The CT band of C311
(lmax ¼ 563 nm) was signicantly red-shied compared to that
of C321. Our calculation results showed that the longest
wavelength absorption peaks of C311 and C321 were 610 and
553 nm, respectively, which were in good agreement with the
Table 1 The calculated dipole-allowed lowest lying transition for C311
and C321 under the TD-MPW1K
Wavelength Oscillator
Transition (nm)
strength
Major contributions
C311 S0 / S1
C321 S0 / S1
610
553
1.3452
1.3824
HOMO / LUMO (88%)
HOMO / LUMO (78%)
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Fig. 2 (a) UV-vis spectra of dyes C311 and C321 in chlorobenzene. (b)
UV-vis spectra of dyes C311 and C321 on transparent TiO2 films (2 mm).
Fig. 3 CV spectra of C311 and C321 in dichloromethane (CH2Cl2)
solution (5 ꢂ 10ꢀ4 M) containing 0.1 M TBAHFP.
experimental values. The molar extinction coefficient for the
CT transition of C311 and C321 were 4.11 ꢂ 104 and 4.35 ꢂ 104
Mꢀ1 cmꢀ1, respectively, which are much higher than that of
the well-known dye N719 (<2 ꢂ 104 Mꢀ1 cmꢀ1). The UV-vis
spectra of C311 and C321 adsorbed onto 2 mm transparent
TiO2 lms (Fig. 2b) showed a signicant red-shi of the
CT-band for C321 (lmax shied from 511 nm to 531 nm) and a
slight red-shi for C311 (lmax shied from 563 to 566 nm)
compared to their spectra in solution. All data were listed in
Table 2.
ꢀ
employing a Iꢀ/I3 electrolyte were measured under one sun
solar illumination conditions (AM 1.5G, 100 mW cmꢀ2), as
shown in Fig. 4. The electrolyte solution was consisted of 1.0 M
1,3-dimethylimidazolium iodide, 0.05 M lithium iodide (LiI),
0.03 M iodine, 0.5 M tert-butylpyridine and 0.1 M guanidinium
thiocyanate in an 85 : 15 (v/v) acetonitrile/valeronitrile mixture
(E1). The photovoltaic parameters of DSSCs including short-
circuit photocurrent density (Jsc), open-circuit photovoltage
(Voc), ll factor (FF), and solar-to-electric power conversion
efficiencies (h) were summarized in Table 3. The DSSCs based
on C321 provided an overall solar-to-electric power conversion
efficiency of 8.2% with a high short-circuit photocurrent density
16.78 mA cmꢀ2 and a high open-circuit photovoltage 686 mV
(FF ¼ 71.1%). Under the same conditions, the cells based on
C311 showed a poor performance with an overall h of 0.9% due
to low Jsc and Voc values (Jsc ¼ 2.32 mA cmꢀ2, Voc ¼ 572 mV, FF ¼
70.6%). The incident photon-to-current conversion efficiency
(IPCE) spectra of DSSCs based on C321 and C311 were much
different, as shown in Fig. 5. The IPCE of cells based on C321
exhibited 89% at 560 nm, while cells based on C311 show only
14% at 540 nm. The photovoltaic performances of DSSCs have
2.4. Electrochemical properties
To evaluate the energetics of C311 and C321, cyclic voltammo-
grams (CV) was performed to measure the oxidation potentials
(Eox), which correspond to the HOMO level potentials of the
sensitizers. The oxidation potentials of the dyes were measured
in dichloromethane containing 0.1 M tetrabutylammonium
hexauorophosphate (TBAHFP) as electrolyte, ferrocene/
ferrocenium (Fc/Fc+) as an internal reference (Fig. 3). The
results were summarized in Table 2, the half-wave potentials of
C311 and C321 were 0.5 and 0.45 V, respectively. The HOMO
levels of C311 and C321 can be determined as ꢀ4.89 eV and
ꢀ4.84 eV vs. vacuum, respectively. The LUMO level can be esti-
mated from the values of oxidation potential and the zero-to-zero
transition energy measured at the intersection of absorption
spectra. We estimated that the LUMO energy levels of C311 and
C321 were ꢀ3.24 eV and ꢀ2.99 eV, respectively, which lie above
the conduction band edge of TiO2 (approximately ꢀ4.0 eV vs.
vacuum). This result indicated that the driving force is sufficient
for electron injecting from the dyes into the conduction band of
TiO2. The energies of HOMO and LUMO of the dyes were in good
agreement with the calculation results (list in Table 2).
2.5. Application in DSSCs
The current–voltage (J–V) characteristics of DSSCs based on
C311 and C321 on 6 mm thick TiO2 lms (with 5 mm scattering) Fig. 4 J–V curves of DSSCs sensitized with C311 and C321.
Table 2 Calculated and experimental parameters for dyes C311 and C321
lmax,exp
3max,exp
(Mꢀ1 cmꢀ1
Eox
(V)
Ered
(V)
HOMOexp
(eV)
LUMOexp
(eV)
HOMOcal
(eV)
LUMOcal
(eV)
Eogpt
(eV)
Ecgal
(eV)
Dye
(nm)
)
C311
C321
563
511
4.11 ꢂ 104
4.35 ꢂ 104
0.7
0.65
ꢀ0.95
ꢀ1.2
ꢀ4.89
ꢀ4.84
ꢀ3.24
ꢀ2.99
ꢀ4.95
ꢀ4.82
ꢀ3.12
ꢀ2.94
1.65
1.85
1.83
1.92
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Table 3 Photovoltaic parameters of DSSCs sensitized by C311 and
C321
Dye
Jsc (mA cmꢀ2
)
Voc (mV)
FF (%)
h (%)
C311
C321
2.32
16.78
572
686
70.6
71.1
0.9
8.2
Fig. 6 (a) Nyquist and (b) Bode phase plots of dye-sensitized solar
cells sensitized by C311 and C321 dyes. The cells were measured at 0.7
V bias voltage in the dark.
recombination rate (kr) at the TiO2/dye/electrolyte interface of
DSSCs. Through the recombination rate and Rct equation,38
where A is the cell area, T is the temperature, kB is Boltzmann's
constant, L is the thickness of the lm, q is elementary charge
and nc is the density of electrons in the conduction band, the
charge-transfer resistance is inversely proportional to the
recombination rate.
Fig. 5 IPCE spectra for DSSCs sensitized with C311 and C321.
kBT
RctALq2nc
kr ¼
(2)
been optimized by using different TiO2 lm thickness (Fig. S1,†
Table 4). A TiO2 layer (6 mm transparent +5 mm scattering)
showed the best photocurrent density and solar-to-electric
power conversion efficiencies.
The nc values can be calculated by the by tting the curves of
Nyquist phase (eqn (S1)†). The nc values of the cells sensitized by
C311 and C321 are 3.72 ꢂ 1017 and 1.28 ꢂ 1019 cmꢀ3, respec-
tively. Through the above equation, the kr of DSSCs sensitized by
C311 and C321 are 142.6 and 4.2 sꢀ1. The recombination rate of
C311 is 34 times higher than that of C321, demonstrating that
the charge recombination of the device sensitized by C321 is
efficiently suppressed, leading to the improvement of the
photocurrent and photovoltaic. The electron lifetime (tn) can be
estimated according to the equation: tn ¼ 1/(2pfmax), where fmax
is the maximum frequency of the mid-frequency peak.39 The fmax
values were determined as 2511 and 39.8 Hz for the DSSCs based
on C311 and C321, respectively. Correspondingly, the calculated
electron lifetimes were 0.13 and 4.0 ms for the DSSCs based on
C311 and C321. This result suggests that the tn of the DSSCs
based on C321 exhibited a 123 times higher than that of DSSCs
based on C311, leading to the improvement of the photocurrent.
This experimental result was in consistent with the calculation
result that C321 has a much weaker recombination process than
C311. The EIS results explained the signicant enhancement of
cell performance by replacing a D–p–A type dye (C311) with a D–
p–A–p–A type dye (C321).
The difference between C311 and C321 is only a p-conju-
gated spacer unit (phenyl ring) between the benzothiadiazole
unit and the anchoring group. However, this small modication
changed the D–p–A type dye C311 as the D–p–A–p–A type dye
C321, which results in a signicant enhancement of the
photovoltaic performances. In order to explain this phenom-
enon, the electrochemical impedance spectroscopy (EIS) of as-
prepared DSSCs based on C311 and C321 were measured.
Fig. 6 shows the Nyquist and Bode plots for DSSCs based on
C311 and C321. The responses in the frequency regions around
103 to 105, 10 to 102, and 0.05 to 1 Hz were contributed to
charge-transfer processes occurring at the Pt electrode/
electrolyte interface, the TiO2 electrode/dye/electrolyte inter-
face, and the Nernst diffusion within the electrolyte, respec-
tively.36 The larger semicircle in the Nyquist plots was attributed
to the charge-transfer resistance (Rct) at the TiO2 electrode/dye/
electrolyte interface. The Rct values can be calculated by tting
the curves using an equivalent model,37 the equivalent circuit
shown in Fig. S2.† The tted Rct of the cells sensitized by C311
and C321 are 9.7 and 42.6 U. It corresponds to the charge
3. Conclusion
Table 4 Photovoltaic parameters of DSSCs sensitized by C321 dye
absorbed on TiO2 films of different thicknesses
In summary, we report a new D–p–A–p–A type dye C321. Due to
the introduction of a p-conjugated spacer unit (phenyl ring)
between the benzothiadiazole (BTDA) unit and the anchoring
group, C321 exhibited a great enhancement on the photovoltaic
performance compared with the traditional D–p–A type dye
C311. The cell efficiency of DSSCs based on C321 can reach as
high as 8.2%, which was superior to that of DSSCs based on
C311 (0.9%) under one sun illumination. The EIS results
TiO2 lm
thickness (mm)
Jsc
Voc
(mV)
FF
(%)
h
Entry
(mA cmꢀ2
)
(%)
1
2
3
4 + 5
6 + 5
8 + 5
12.91
16.44
14.46
678
688
684
71.7
71.2
74.2
6.3
8.1
7.3
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revealed that C321 has a higher charge-transfer resistance (Rct)
and a higher electron lifetime than C311 in DSSCs, which was in
consistent with the calculation results. These results suggested
that the D–p–A–p–A type dye would be a novel class of dyes for
efficient DSSCs.
2-Cyano-3-{7-{4-[N,N-bis(4-hexyloxyphenyl)-4-aminophenyl]-
3,4-ethylenedioxythiophene-2-yl}benzo[1,2,5]thiadiazole-4-yl}-
acrylic acid (C311). Compound 11 (150 mg, 0.21 mmol),
ammonium acetate (16 mg, 0.21 mmol) and cyanoacetic acid
(179 mg, 2.2 mmol) were dissolved in a mixture of DCM/MeCN
(60 mL, 2 : 1 v/v). The mixture was reuxed under argon atmo-
sphere for 10 h. Aer cooling to room temperature, the reaction
mixture was dissolved in dichloromethane (3 ꢂ 50 mL), washed
with water (2 ꢂ 20 mL) and dried over MgSO4. The solvent was
4. Experimental section
4.1. Device fabrication
The photoelectrodes were prepared by screen-printing double removed in vacuo. The crude product was puried by column
layers of nanocrystalline TiO2 particles, for transparent lms a 6 chromatography (dichloromethane/methanol) to obtain dye
mm thick layer of 20 nm-sized TiO2 particles was printed on the C311 as a dark blue solid (111 mg, 65%). H NMR (400 MHz,
1
uorine doped tin oxide (FTO, TCO-15, 14 ohm/square, NSG, CDCl3) d: 9.26 (s, 1H), 8.92 (d, J ¼ 7.6 Hz, 1H), 8.59 (d, J ¼ 7.6 Hz,
1H), 7.69 (d, J ¼ 8.4 Hz, 2H), 7.08 (d, J ¼ 8.4 Hz, 4H), 6.95 (d, J ¼
Japan) conducting glass by successive screen printing using a
TiO2 paste (DSL 18-NR, Dyesol, Australia). Where applicable, a 5
8.4 Hz, 2H), 6.85 (d, J ¼ 8.8 Hz, 4H), 4.52 (m, 2H), 4.42 (m, 2H),
3.96 (t, J ¼ 6.0 Hz, 4H), 1.82 (m, 4H), 1.51 (m, 4H), 1.37 (m, 8H),
mm thick scattering layer of 400 nm sized TiO2 particles (WER-2,
Dyesol, Australia) was then covered on top of the transparent 0.94 (m, 6H). 13C NMR (400 MHz, DMSO-d6) d: 155.4, 153.9,
ꢃ
layer. The electrodes were dried at 150 C for 5 min and then 150.7, 147.7, 142.8, 139.8, 139.5, 137.3, 128.1, 127.2, 126.8,
heated at 500 ꢃC for 45 min, aer cooling to room temperature 126.7, 124.4, 123.8, 122.7, 121.0, 119.1, 115.5, 108.9, 67.6, 65.1,
the electrodes were soaked in a 40 mM TiCl4 aqueous solution 64.2, 30.9, 28.7, 25.2, 22.0, 13.8. MALDI-TOF (m/z): 814.6 [M+].
ꢃ
ꢃ
at 70 C for 40ꢃmin. Aer sintering at 500 C for 15 min and
cooling to 100 C, the sintered electrodes were immersed into
sensitizer solution (0.3 mM of the dye with 2 mM of cheno-
deoxycholic acid, in chlorobenzene) for 6 h, and then assembled
3-{4-{7-{4-[N,N-Bis(4-hexyloxyphenyl)-4-aminophenyl]-3,4-ethyl-
enedioxythiophene-2-yl}benzo[1,2,5]thiadiazole-4-yl}phenyl}-
2-cyanoacrylic acid (C321). Dye C321 was synthesized by the
same method as dye C311 by using compound 12 (85 mg, 0.10
using a thermally platinized FTO counter electrode through a 50 mmol) instead of compound 11. Dye C321 was obtained as a
1
mm thick hot melt ring (Bynel, Dupont) by heating. The elec- dark blue solid (41 mg, 45%). H NMR (400 MHz, DMSO-d6) d:
trolyte solution was 1.0 M 1,3-dimethylimidazolium iodide, 0.05 8.51 (d, J ¼ 8.0 Hz, 1H), 8.18 (d, J ¼ 8.4 Hz, 2H), 8.05 (m, 4H),
M lithium iodide (LiI), 0.03 M iodine, 0.5 M tert-butylpyridine 7.61 (d, J ¼ 8.8 Hz, 2H), 7.03 (d, J ¼ 8.8 Hz, 4H), 6.92 (d, J ¼ 8.8
and 0.1
M
guanidinium thiocyanate in an 85 : 15 (v/v) Hz, 4H), 6.84 (d, J ¼ 8.8 Hz, 2H), 4.52 (m, 2H), 4.42 (m, 2H), 3.95
(t, J ¼ 6.4 Hz, 4H), 1.74 (m, 4H), 1.45 (m, 4H), 1.33 (m, 8H), 0.90
acetonitrile/valeronitrile mixture. The electrolyte was lled in
the cell's internal space by using a vacuum pump.
(m, 6H). 13C NMR (400 MHz, DMSO-d6) d: 155.8, 153.3, 152.3,
147.9, 142.4, 140.1, 137.8, 129.9, 129.7, 127.3, 127.2, 125.8,
124.6, 120.2, 119.9, 115.9, 99.9, 68.1, 31.5, 29.2, 25.7, 22.5, 14.4.
4.2. Device characterization
+
MALDI-TOF (m/z): 890.7 [M ].
The UV-Vis absorption spectrum was recorded on a Persee TU-
1810 UV-Vis spectrometer. Sun 2000 solar simulator (Abet-
technologies, USA) was used to give an irradiance of 100 mW
cmꢀ2 (AM 1.5G) of the cell and light intensity was measured by
using a silicon reference cell. The photocurrent density–voltage
(J–V) characteristics under simulated AM 1.5G illumination
were measured by using a Keithley 2400 Source meter. Incident
photon-to-current conversion efficiency (IPCE) were measured
by a QE/IPCE Measurement Kit (Oriel, USA, M66901), and the
incident-photon ux was obtained by using a calibrated silicon
reference photodiode. The devices were masked to a working
area of 0.160 cm2. Electrochemical data was obtained by a Versa
STAT 3 (METEK, USA) electrochemical workstation.
Acknowledgements
This work was supported by NSFC 9133316, 21403211, and
“Chutian” project of China Three Gorges University. The
authors thank the National Supercomputing Center in Shenz-
hen for providing computing resources.
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