Effects of structural optimization on the performance of dye-sensitized solar cells: Spirobifluorene as a promising building block to enhance v oc

Article abstract of DOI:10.1039/c6ta03740b

We prepared three new push-pull dyes JA3, JA4 and JA0 through structure optimization, and applied them in DSSCs. Judicious molecular structure optimization of dyes can significantly improve the performance of DSSCs. Spirobifluorene as a building block was introduced onto the phenothiazine donor groups. Compared to JA1, the steric effect of the spirobifluorene building block can effectively reduce charge recombination by preventing the I₃^- of the electrolyte penetrating into the TiO₂ surface, thus the V_oc of JA3 increased from 701 mV to 800 mV. In order to further improve the light-harvesting ability of the DSSC, we introduced a benzothiadiazole unit (BTD) and prepared D-A-π-A dye JA4. As expected, the J_sc of JA4 increased from 12.32 to 14.43 mA cm^-2 compared to that of JA3, and the device reached the highest PCE of 7.0%. Moreover, since extending the π-conjugated system is known to decrease the V_oc of DSSC, the porphyrin unit was removed and dye JA0 was synthesized. Notably, the DSSC based on JA0 reached a very high V_oc of 840 mV and a high PCE of 6.69%: to our knowledge, this is the highest V_oc for DSSCs based on phenothiazine dyes with I^-/I₃^- electrolyte.

Full text of DOI:10.1039/c6ta03740b

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Effects of the structural optimization on the performance of dye-
sensitized solar cells: spirobifluorene as a promising building-
block to enhance Voc
Received 00th January 20xx,
Accepted 00th January 20xx
Hai-Lang Jia,a Ming-Dao Zhang,b Wei Yan,a Xue-Hai Juc and He-Gen Zheng*a
DOI: 10.1039/x0xx00000x
We prepared three new push-pull dyes JA3, JA4 and JA0 through structure optimization, and applied in DSSCs. Obviously,
judicious molecular structure optimization of dyes can significantly improve the performance of DSSCs. Spirobifluorene as
www.rsc.org/
a
building-block was introduced onto the phenothiazine donor groups. Compared to JA1, the steric effect of
-
spirobifluorene building-block can effectively reduce the charge recombination by preventing the I3 of the electrolyte
penetrating into the TiO2 surface, thus the Voc of JA3 increased from 701 mV to 800 mV. In order to further improve the
light-harvesting ability of the DSSC, we introduced benzothiadiazole unit (BTD) and prepared D-A-π-A dye JA4. Just as
expected, the Jsc of JA4 increased from 12.32 to 14.43 mA cm-2 compared to that of JA3, and the device reached the
highest PCE of 7.0%. Moreover, considering extending the π-conjugated system always decreases the Voc of DSSC, we got
rid of the porphyrin unit and synthesized dye JA0. Notably, the DSSC based on JA0 reached a very high Voc of 840 mV and a
-
high PCE of 6.69%, to our knowledge, this is the highest Voc for DSSC based on phenothiazine dyes with I-/I3 electrolyte.
development of novel and efficient sensitizers is one of the most
direct and effective ways to improve the performance of DSSC. D-π-
A (donor-π-acceptor) is the most common framework for efficient
Introduction
dyes.13-15 The framework has outstanding efficient intra-molecular
charge transfer (ICT) properties, moreover, it is very easy to be
modified.16-19 Many groups devote to optimizing the dye molecular
structure, because this strategy can achieve the following purposes:
(i) improve the spectral response of dyes, thereby enhancing the
light-harvesting ability of DSSC; (ii) adjust the energy levels of dyes,
thereby enhancing the electron injection rate and dye regeneration
rate; (iii) suppress dye aggregation and reduce charge
recombination, thereby enhancing the Jsc (short-circuit current
density) and Voc (open-circuit photovoltage) of DSSC; (iv) improve
the photostability and adsorption stability of dyes, thereby
enhancing the long-term stability and durability of DSSC.20-22
Through the continuous efforts and exploration of the researchers,
many new frameworks such as D-D-π-A, D-π-A-π-A, D-π-(A)n and D-
A-π-A have been explored.23-26 Particularly D-A-π-A, the additional
acceptor can adjust the energy levels of dyes, improve the spectral
response, enhance the photovoltaic performances and greatly
improve the photostability of dyes, Zhu et al. have discussed about
this in detail.27,28 Thus, the structure optimization of dyes plays a
very important role in improving the performance of DSSC.
Impressively, the PCE of YD2-o-C8 was 12.3% in 2011, later, SM315
was prepared after further optimization in 2014, and the PCE of
SM315 reached 13%.29,30
With the energy crisis and environment pollution becoming more
and more serious, the development and utilization of new energy
has become one of the immediate tasks for human. Solar energy
has great potential for exploitation, the characteristics of rich
resources, convenient collection and clean pollution-free
completely meets the requirements of sustainable development of
human society.1,2 In 1991, Grätzel and co-workers first reported the
dye-sensitized solar cells (DSSC), they obtained 7.1% of power
conversion efficiency (PCE) with low cost.3 Over the next 20 years,
DSSC got rapid development with the continuous efforts of many
researchers, a large number of excellent dyes and the related
materials have been developed.4-8 Recently, Kakiage prepared the
silyl-anchor dye ADEKA-1, which exhibited a high PCE of 14.3% with
cobalt-based redox electrolyte. To our knowledge, this is the
highest PCE by far for DSSC.9
A
complete DSSC is made of photoanode, sensitizer,
electrolyte and counter electrode.10-12 The core of DSSC is to use
sensitizer to absorb photons and generate electrons, thus, the
Phenothiazine is often used as a donor in DSSC for its efficient
π-conjugated system and unique hole-transporting ability.31-35 In
our previous work, we used phenothiazine unit containing a long
alkyl to modify the porphyrin dye JA1. The DSSC based on JA1
exhibited a PCE of 5.76%, with the Voc of 701 mV, Jsc of 12.10 mA
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cm-2, and FF of 67.8%.36 Herein, we further modified the molecular (FTO) glass plates (15 Ω / square). For preparation of the DSSCs,
structure of JA1 and prepared JA3, JA4 and JA0 (Fig. 1). FTO glass plates were cleaned in a detergent solution using an
Spirobifluorene as
a building-block was introduced onto the ultrasonic bath for 30 min for two times and then rinsed with
phenothiazine donor groups, we deduced that the steric effect of water and ethanol. Then, the plates were immersed into 40
-
spirobifluorene can effectively prevent the I3 of the electrolyte mM TiCl4 (aqueous) at 70
℃ for 30 min and washed with water
penetrating into the TiO2 surface, thereby reducing the charge and ethanol. The TiO2 paste consisted of 12 μm thick films
recombination, thus the Voc of JA3 has increased to 800 mV. In (particle size, 20 nm, pore size 32 nm). The TiO2 films were
order to improve the light-harvesting ability of the DSSC, performed with a programmed procedure: (1) 80
benzothiadiazole (BTD) was added in D-A-π-A dye JA4. BTD has (2) 135 for 10 min; (3) 325 for 30 min; (4) 375
been widely used in the design of D-A-π-A dyes.37 Herein, the (5) 450
for 15 min, and (6) 500 for 15 min. Then the films
additional strong electron-withdrawing unit exhibits significant were treated again with TiCl4 at 70 for 30 min and sintered
broadening of Soret and Q-band absorbance features compared to at 500 for 30 min. Then the electrode was immersed into
JA3, yielding improved light-harvesting and efficiency. Because the dye solution (0.3 mM of JA0, 0.2 mM of JA3 and JA4,
absorption property of JA4 has been good improvement THF/EtOH=1/4) for 18 h at room temperature. The working
℃
for 15 min;
℃
℃
℃ for 5 min;
℃
℃
℃
℃
a
compared to JA3, so the Jsc of JA4 increased from 12.32 to 14.43 mA electrode and the Pt counter electrode were then sealed with
cm-2. In addition, Incorporation of BTD into JA4 as an electron trap a Surlyn film (25 μm) by heating the sandwich-type cell at
is in favour of electron distribution, and facilitating the electron 110
℃. The electrolyte was introduced through pre-drilled
migration direction to the acceptor. Moreover, considering holes in the counter electrode and was driven into the cell via
porphyrin units can cause dye aggregation and π-π stacking, so we vacuum backfilling, and the hole was sealed with a Surlyn film
got rid of the porphyrin unit and synthesized dye JA0. Notably, the and a thin glass (0.1 mm thickness) cover by heating. The
DSSC based on JA0 reached a very high Voc of 840 mV and a high electrolyte was composed of 0.6
M
1-butyl-3-
PCE of 6.69%, to our knowledge, this is the highest Voc for DSSC methylimidazolium iodide (BMII), 50 mM I2, 50 mM LiI, 0.5 M
-
based on phenothiazine dyes with I-/I3 electrolyte. Because the tert-butylpyridine and 0.1 M guanidiniumthiocyanate (GuNCS)
-
theoretical Voc is about 900 mV with I-/I3 electrolyte, thus, this in acetonitrile.
strategy is very beneficial to improve the performance of DSSC. We
Characterizations of DSSCs
mainly investigated the optical properties and photovoltaic
The photocurrent-voltage (I-V) curves of the DSSCs were
performance of the three dyes, and analyzed these differences
measured on a Keithley 2400 source meter under standard
caused by the different structures.
global AM 1.5G solar irradiation supplied by a xenon light
source (Oriel). The incident photo-to-electron conversion
efficiency (IPCE) spectra of the DSSCs were measured by a DC
method. The light source was a 300 W xenon lamp (Oriel 6258)
C8H17
O
OC8H17
C8H17
O
OC8H17
S
coupled with a flux controller to improve the stability of the
irradiance. The single wavelength was selected by
S
O
O
N
Zn
N
Zn
a
OH
OH
monochromator (Cornerstone 260 Oriel74125). Light intensity
was measured by a NREL traceable Si detector (Oriel 71030NS)
and the short circuit currents of the DSSCs were measured by
an optical power meter (Oriel 70310).
C8H17
O
OC8H17
C8H17
O
OC8H17
JA1
JA3
S
C8H17
O
OC8H17
S
S
N
N
N
N
S
O
O
Theoretical calculations
N
Zn
N
OH
OH
Density function theory (DFT) calculations were performed at
the DFT-B3LYP/LanL2DZ level with Gaussian 09 suite of
programs.
C8H17
O
OC8H17
JA0
JA4
UV-Vis spectra, photoluminescence, electrochemical properties
and measurement of the amounts of dye adsorption
Fig. 1 Chemical structures of JA1, JA3, JA4 and JA0.
The UV-Vis absorption spectra were recorded on a Shimadzu
UV-3600 spectrometer. Fluorescence spectra were recorded
on a Perkin Elmer LS55 spectrophotometer. The fluorescence
lifetimes of the dyes were measured on a FLS920 spectrometer.
The cyclic voltammograms of the dyes were recorded by
Experimental
Synthesis of dyes
The chemical structures of JA1, JA3, JA4 and JA0 were shown
in Fig. 1, and the synthetic route was depicted in Scheme S1.
The synthesis details and characterization data were shown in
supporting information.
IM6EX
Electrochemical
Workstation.
Electrochemical
Chenhua
Impedance Spectroscopy was studied using
a
CHI660D model Electrochemical Workstation (Shanghai).
The amounts of dye adsorption on the TiO2 films were
measured by a Shimadzu UV-3600 spectrometer. The sensitized
electrodes were immersed into a 0.1 M NaOH solution in a mixed
solvent (H2O/THF=1/1), which resulted in desorption of each dye.
Fabrication of DSSCs
The working electrode (active area is 0.196 cm2) was prepared
by screen printing the TiO2 paste on Fluorine-doped tin oxide
2 | J. Name., 2012, 00, 1-3
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Table 1 Optical and electrochemical properties of dyes
Results and discussion
Dye aλmax/nm (ε×105 M-1 bλmax/nm cEOX/V dE0-0/eV
eE*OX/V
(NHE)
-1.43
Optical properties
cm-1)
452(0.082)
(NHE)
0.98
1.11
The UV-Vis absorption spectra of JA0, JA3 and JA4 in THF are shown
JA0
in Fig. 2, and the corresponding data are collected in Table 1. D-π-A JA3
567
638
2.41
2.07
447(3.66),574(0.15)
627(0.29)
-0.96
dye JA3 exhibited typical porphyrin absorption characteristics at the
JA4
435(1.52),459(0.92)
576(0.12),648(0.47)
685
1.04
1.90
-0.86
Soret and Q bands. The absorption below 400 nm can be attributed
to electronic transitions from π-π*, and the 400-700 nm range can
be attributed to intramolecular charge transfer (ICT). At the Soret
bands, dye JA3 showed a high molar extinction coefficient (3.66×105
M-1 cm-1) at 447 nm. When the benzothiadiazole unit was added in
aAbsorption maximum in THF solution (1×10-6 M), bemission maximum in
d
THF solution (1×10-6 M), cthe ground state oxidation potentials, E0-0 was
estimated from the intercept of the normalized absorption and emission
spectra, eE*OX was calculated by the formula: E*OX = EOX-E0-0
.
D-A-π-A dye JA4, the spectrum was changed obviously, most
evident by the splitting of the Soret band, resulting in a shoulder at
459 nm on the maximum at 435 nm. The whole spectrum became
broader compared to JA3, especially at the Q bands, the band at
574 nm had a little change compared to that of JA3, but the lowest-
energy Q-band absorption of JA4 was significantly redshifted to 648
nm. For JA0, there was no porphyrin unit in the molecular structure,
thus, dye JA0 displayed a narrow absorption. The maximum
absorption peak of JA0 lay at 452 nm with the molar extinction
coefficient of 8.2×103 M-1 cm-1. The major emission bands of JA3,
JA4 and JA0 lay at 638 nm, 685 nm and 567 nm, respectively, it is
consistent with the trend of the absorption spectra of the three
dyes (Fig. S1). The absorption spectra of the three dyes sensitized
12 µm thick TiO2 substrate were further investigated (Fig. S2). All
the spectra showed a broader and higher absorption compared to
the spectra in THF. After anchored on TiO2 surface, the ICT bands of
dye JA3 and JA4 displayed a slight blue-shift (H-aggregation), which
can be ascribed to deprotonation of the carboxylic acid. Obviously,
the ICT bands of dye JA0 displayed red-shift (J-aggregation), we
thought that the amounts of dye adsorption will increase sharply
due to lack of porphyrin units, the result will cause J-aggregation.38
This speculation can be supported by the absorption spectra of the
dyes on TiO2 films with 10 mM chenodeoxycholic acid (CDCA). We
found that the ICT bands of JA3 and JA4 displayed a slight red-shift
and the ICT band of JA0 displayed blue-shift. Though dye
aggregation may quench the excited state and hamper electron
injection, the J-aggregation also can enhance the performance of
the DSSC due to the enhanced light-harvesting at longer
wavelengths.39,40
Electrochemical studies
We measured the cyclic voltammetry curves of the three dyes to
evaluate the possibility of electron transfer from the excited dyes to
the conduction band of TiO2. The cyclic voltammetry curves were
shown in Fig. S3, and the corresponding data were collected in
Table 1. We knew that the ground state oxidation potentials (EOX) of
JA0, JA3 and JA4 were 0.98 V, 1.11 V and 1.04 V (versus NHE),
respectively. Because the redox potential of the I-/I3- couple is about
0.4 V (versus NHE), and the EOX of the three dyes are all positive
than 0.4 V, thus, the three oxidized dye molecules can be
regenerated by the reducing species in the iodine electrolyte. As
shown in Fig. S4, the zero-zero excitation energy (E0-0) was
estimated from the intercept of the normalized absorption and
emission spectra. The values of JA0, JA3 and JA4 are 2.41 eV, 2.07
eV and 1.90 eV, respectively. Hence, the corresponding excited
oxidation potentials (E*OX) of JA0, JA3 and JA4 are -1.43 V, -0.96 V
and -0.86 V, respectively. The values are all more negative than the
CB level of the TiO2 (-0.5 V versus NHE), which implies an efficient
electron injection process from the excited dye into the conduction
band of TiO2. Especially for JA0, such high electron injection driving
force suggests that the DSSC based on JA0 will has a good electron
injection rate.
Fig. 3 The HOMO and LUMO frontier molecular orbitals of JA0, JA3 and JA4
calculated at the DFT-B3LYP/LanL2DZ level with the Gaussian 09 suite of
programs.
Theoretical Calculations
Density function theory (DFT) calculations at the DFT-
B3LYP/LanL2DZ level with Gaussian 09 suite of programs were
utilized to insight into the electron-density distributions of the three
Fig. 2 UV-Vis absorption spectra of JA0, JA3 and JA4 in THF.
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dyes. As shown in Fig 3, the HOMO levels of porphyrin dyes JA3 and
JA4 are delocalized throughout the phenothiazine donors and the
porphyrin rings, and the HOMO levels of JA0 are delocalized in the
phenothiazine donor. When the benzothiadiazole unit was added in
D-A-π-A dyes JA0 and JA4, the electron-density distributions are
significantly different from D-π-A dye JA3. For JA3, the LUMO a JA4
orbitals are mainly delocalized in porphyrin ring and acceptor. For
Table 2 Photovoltaic parameters of the DSSCs obtained from the J-V curves
Dye
Jsc (mA cm-2)
12.32
12.10
12.33
Voc (V)
0.840
0.701
0.800
0.772
FF (%)
64.63
67.80
63.52
62.77
η (%)
6.69
5.76
6.27
7.00
a JA0
b JA1
a JA3
14.44
a The size of the active area for each cell is 0.196 cm2, the DSSCs were all
measured under standard global AM 1.5G solar irradiation, b the DSSC based
on JA1 was reported in ref. 36.
JA0 and JA4, the LUMO orbitals are mainly delocalized in the BTD
units and acceptors. The electronic properties of the three dyes
indicate that such a well-separated orbital distribution is conducive
to the electron transfer from HOMO to LUMO and can induce the
photoinduced charge injection from the LUMO to the conduction
band of TiO2.
We performed the time-resolved luminescence in THF and on
TiO2 surface to insight into the electron injection dynamics of the
three dyes (Fig. S5).29,30 The fluorescence lifetimes of JA0, JA3 and
JA4 in THF are 6.42 ns, 2.51 ns and 4.83 ns, respectively. When the
three dyes anchored on TiO2 surface, the emission of the three dyes
are all strongly quenched. The lifetimes of JA0, JA3 and JA4 on TiO2
are about 600 ps, 610 ps and 570 ps, respectively. The results
suggest that the three dyes all have high electron injection
efficiency, as a result of efficient photoinduced charge injection
from the LUMO of the dyes to the conduction band of TiO2.
Photovoltaic performance of DSSCs
The DSSCs based on the three dyes were fabricated under the same
conditions. The photocurrent-density-photovoltage (J–V) curves of
were shown in Fig. 4, and the photovoltaic parameters were
collected in Table 2. In our previous work, the DSSC based on JA1
exhibited a PCE of 5.76%, with the Voc of 701 mV, Jsc of 12.10 mA
cm-2, and FF of 67.8%. When the spirobifluorene unit was added in
phenothiazine donor, the DSSC based on JA3 exhibited a PCE of
6.27%, with the Voc of 800 mV, Jsc of 12.33 mA cm-2, and FF of
63.52%. It is clear that the Jsc has a little change, in contrast, the Voc
increased 99 mV. We deduced that the steric effect of
-
spirobifluorene can effectively prevent the I3 of the electrolyte
penetrating into the TiO2 surface, thereby reducing the charge
recombination, thus the Voc of JA3 increased 99 mV compared to
that of JA1. When BTD unit was added in JA4, the PCE of the device
reached the highest value of 7.0%, and the Jsc increased from 12.33
to 14.44 mA cm-2. But the Voc decreased 28 mV, the reason was that
the conjugation extension may cause dye aggregation and π-π
stacking, thereby resulting in a decreased Voc. Interestingly, if we
get rid of porphyrin unit, the DSSC based on JA0 still exhibited a
high PCE of 6.69%, although there was a decrease in the Jsc, but the
Voc reached the highest value of 840 mV. To our knowledge, this is
Fig. 4 (a) The J–V curves of DSSCs based on JA0, JA1, JA3 and JA4; (b) The
IPCE curves of DSSCs based on JA0, JA1, JA3 and JA4.
of spirobifluorene can effectively retard charge recombination, thus
the Voc of JA0 is very high.
As shown in Fig. 4b, the incident photon-to-current conversion
efficiency (IPCE) spectra of the devices were also measured. The
IPCE curves of JA1 and JA3 all exhibited photocurrent generation up
to about 680 nm, but the values of JA3 were higher that of JA1 in
the range of 450-680 nm. JA4 displayed impressively high IPCE
values in the whole visible range, with photocurrent generation up
to about 750 nm, demonstrating the utility of the BTD unit for
improvements in visible and infrared light-harvesting properties.
Interestingly, we found JA0 had an excellent IPCE spectrum, the
DSSC based on JA0 not only exhibited photocurrent generation up
to about 680 nm, but also had a higher value in the whole visible
range. It is consistent with the Jsc of the DSSCs. We measured the
-
the highest Voc for DSSC based on phenothiazine dyes with I-/I3
electrolyte. As we all known, with the same electrode materials and
the same electrolyte for DSSCs, the key to improving the Voc is to
improve the electron density of the TiO2 conduction band. We can
improve the electron injection rate or reduce the electron
recombination to achieve this purpose. Wang et al. designed a
series of double D-π-A dyes, this strategy was favorable for reducing
intermolecular interaction and retarding charge recombination,
thus the Voc was greatly improved.41-44 Herein, the LUMO of JA0 is
sufficiently high for electron injection, in addition, the steric effect
4 | J. Name., 2012, 00, 1-3
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amounts of dye adsorption of the three dyes anchored on TiO2 electron lifetime value of JA0, JA3 and JA4 is 41.9, 22.7 and 11.8 ms,
surface. The values of JA0, JA3 and JA4 are 6.95, 1.25 and 1.56×10-7 respectively. The longer electron lifetime corresponds to lower dark
mol cm-2, respectively. This may be another reason for the current. Thus, the DSSC based on JA0 has the highest Voc.
differences between the Jsc of the DSSCs.
Conclusions
In summary, we prepared three new push–pull dyes JA0, JA3 and
JA4, and applied in DSSCs. Compared to JA1, the steric effect of
spirobifluorene building-block can effectively reduce the charge
recombination, thus the Voc of JA3 increased from 701 mV to 800
mV. The BTD unit added in dye JA4 can further optimize the
molecular structure. The additional acceptor of the BTD unit
adjacent to donors can improve the distribution of donor electrons
and enhance the light-harvesting ability, thus the Jsc of JA4
increased from 12.32 to 14.43 mA cm-2 and the device reached the
highest PCE of 7.0%. Moreover, considering extending the π-
conjugated system always decreases the Voc of DSSCs, we get rid of
the porphyrin unit and synthesized dye JA0. Notably, the DSSC
based on JA0 reached a very high Voc of 840 mV and a high PCE of
6.69%, to our knowledge, this is the highest Voc for DSSC based on
-
phenothiazine dyes with I-/I3 electrolyte. Thus, judicious molecular
structure optimization of push-pull dyes can significantly improve
the performance of DSSCs.
Acknowledgements
This work was supported by grants from the National Natural
Science Foundation of China (Nos. 21371092; 21401107),
National Basic Research Program of China (2010CB923303),
Natural Science Foundation of Jiangsu Province, China (No.
BK20140986).
Fig. 5 (a) Nyquist plots of DSSCs based on JA0, JA3 and JA4; (b) Bode phase
plots of DSSCs based on JA0, JA3 and JA4.
Notes and references
Electrochemical impedance spectroscopy analysis
1
2
3
4
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With the same electrode materials and the same electrolyte for
DSSCs, the fluctuation of electron density (charge recombination
rate in DSSCs) has an important influence on the Voc. At a given
photocarrier generation flux, the electron density is mainly
determined by the interfacial recombination rate of TiO2 electrons.
We investigated the electrochemical impedance spectroscopy (EIS)
under dark to study the charge recombination dynamics of the
DSSCs.45-47 The applied voltage was -0.7 V and scanned from 105 to
1 Hz.48,49 As shown in Fig. 5, the large semicircle represents the
charge recombination resistance (Rrec) at the TiO2/dye/electrolyte
interface. Obviously, the radius of the large semicircle decreased in
the order: JA0 > JA3 > JA4, this suggested that the JA0 based-device
had the largest Rrec. The results suggested that JA0 can efficiently
reduce the charge recombination. In generally, extending the π-
conjugated system always decreases the Voc of DSSCs. It is in
agreement with the Voc of the DSSCs based on the three dyes.
Moreover, the peak frequency (f) at lower frequency region from
the Bode phase plots of the DSSCs can be obtained (Fig. 5b). The
electron lifetime (τ) can be calculated by τ=1/(2πf).50-52 The f of JA0,
JA3 and JA4 is 3.8, 7.0 and 13.5 Hz, respectively. The corresponding
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Table of contents entry
Judicious structure optimization of push-pull dyes can significantly improve the performance of
DSSCs. Obviously, the Voc, Jsc and PCE of the DSSC based on JA4 were all improved after
optimization compared to that of JA1.