Efficient azobenzene co-sensitizer for wide spectral absorption of dye-sensitized solar cells

Article abstract of DOI:10.1039/c7ra12229b

Two azobenzene dyes, [Cu(azobenzene-4,4′-dicarboxylate) diethylenediamine]_n (ADD), [Cd(4,4′-diazenediyldibenzoato)(H₂O)]_n (DDB), have been designed, synthesized, and characterized as efficient co-sensitizers for dye-sensitized solar cells (DSSC). The optical, charge-transfer, electrochemical and photovoltaic properties of ADD and DDB are investigated by UV-visible spectroscopy, transient surface photovoltage measurement, cyclic voltammetry, and photocurrent-photovoltage measurement. The combination of ADD and DDB in DSSC leads to a wide spectral absorption over the whole visible range (350-700 nm). DSSC with ADD and DDB exhibits a short-circuit photocurrent density as high as 16.96 mA cm^-2, open-circuit photovoltage of 0.73 V, a fill factor of 0.57, and overall light conversion efficiency of 7.1% under standard global AM1.5 solar irradiation conditions.

Full text of DOI:10.1039/c7ra12229b

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PAPER
Efficient azobenzene co-sensitizer for wide
spectral absorption of dye-sensitized solar cells†
Cite this: RSC Adv., 2018, 8, 6212
L. Y. Zhang, * S. J. Zou and X. H. Sun
0
0
(ADD), [Cd(4,4 -
Two azobenzene dyes, [Cu(azobenzene-4,4 -dicarboxylate) diethylenediamine]
n
2 n
diazenediyldibenzoato)(H O)] (DDB), have been designed, synthesized, and characterized as efficient
co-sensitizers for dye-sensitized solar cells (DSSC). The optical, charge-transfer, electrochemical and
photovoltaic properties of ADD and DDB are investigated by UV-visible spectroscopy, transient surface
photovoltage measurement, cyclic voltammetry, and photocurrent–photovoltage measurement. The
combination of ADD and DDB in DSSC leads to a wide spectral absorption over the whole visible range
Received 8th November 2017
Accepted 27th January 2018
(
350–700 nm). DSSC with ADD and DDB exhibits a short-circuit photocurrent density as high as 16.96
DOI: 10.1039/c7ra12229b
ꢀ2
mA cm , open-circuit photovoltage of 0.73 V, a fill factor of 0.57, and overall light conversion efficiency
rsc.li/rsc-advances
of 7.1% under standard global AM1.5 solar irradiation conditions.
p* and p–p* transition are located in the ultraviolet and visible
regions, respectively. By introducing different light absorbing
Introduction
In the face of limited fossil fuels and the disastrous environ- groups in the benzene ring, the absorption range and intensity
mental problem, people realize the urgent need to develop of azobenzene complex can be controlled. Azobenzene complex
renewable energy resources for the increasing global energy with above optical property may be a potential sensitizer for
demand. Solar energy is the most hopeful for supplying DSSC.
sustainable energy because it is a type of clean and renewable
energy. Dye-sensitized solar cells (DSSC) have attracted much were designed, synthesized, and co-sensitized TiO
In this paper, two novel azobenzene dyes (ADD and DDB)
2
photo-
attention as a promising technology for the performance/price anode. The properties of ADD and DDB were investigated. The
1
ratio cells. The dye is a key component which determines the combine of ADD and DDB achieved very efficient sensitization
efficiency of DSSC as it absorbs sunlight, excites electrons and over the whole visible range (350–700 nm).
injects electrons into the conductor band of the semiconductor.
In the future, cost-effective organic dyes will play a pivotal role
in the large-scale production and application of DSSC. The
Experimental
development of new dyes is all through the focus of DSSC.
All the starting materials were reagent grade and used as
purchased without further purication. Distilled water was used
throughout. The radical ligand H
ylate, was prepared according to the literature.
2–5
The ideal dye can absorb all the light in solar spectrum. So
far, the most close to the ideal dye are distyryl-substituted
0
2
L, azobenzene-4,4 -dicarbox-
6,7
boradiazaindacene dye (BODIPY) and “black dye”. BODIPY
has panchromatic spectral absorption between 400 and 800 nm
in visible light region. The black dye achieves very efficient
sensitization over the whole visible range extending into the
near-IR region up to 920 nm, yielding an overall conversion
efficiency of 10.4%. Another way to get the full absorption
spectrum is to use a co-sensitization of multi-dyes with different
absorption ranges.
8
Synthesis of ADD
A mixture containing H L (5 mg, 0.019 mmol), CuCl $6H O
2
2
2
0
(
(
60 mg, 0.36 mmol), N,N -dimethylacetamide (DMA 15 mL), H O
2 mL) and ethylenediamine (en 0.01 mL) was stirred at room
2
temperature for 1 h until a clear red solution formed. It was
then transferred into a Parr Teon-lined stainless steel vessel
Azobenzene complex is made up of benzene ring linked by
a nitrogen double bond. Azobenzene complex occurs n–p* and
p–p* transition by irradiation. The absorption bands of the n–
ꢁ
(25 mL) and heated to 120 C for 72 h under autogenous pres-
ꢁ
ꢁ
ꢀ1
sure. Aerwards, it was cooled to 25 C at a rate of 4 C h
.
Brown ake crystals were obtained aer washing with DMA and
drying in air, in about 42% yield (based on Cu). Anal. calcd for
School of Chemical Engineering, Northeast Electric Power University, Jilin 132012, P.
R. China. E-mail: zhanglingyun@vip.sina.com; Fax: +86-432-64806371; Tel: +86-432-
C H N CuO (391.87): C 49.04; H 4.12; N 14.30%; found:
6
†
1
4807273
16 16
4
4
ꢀ
1
4
8.97; H 4.09; N 13.68%. IR data (KBr pellet, cm , Fig. S1†):
Electronic supplementary information (ESI) available. See DOI:
0.1039/c7ra12229b
3316 (s), 1612 (s), 1607 (s), 1554 (s), 1515 (w), 1368 (s), 1293 (w),
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1
7
214 (w), 1153 (w), 1094 (w), 1049 (s), 1008 (m), 870 (m), 783 (s), absorption corrections were performed using SADBAS program.
03 (s).
The structure was solved by direct methods and rened using
2
full-matrix least-squares methods on F with the SHELXS-97
Synthesis of DDB
program. All non-hydrogen atoms were rened anisotropi-
cally. All hydrogen atoms were located geometrically by the
program olex 2. The CCDC number of ADD is 881781. The
detailed crystallographic data and structure renement
parameters for ADD are summarized in Table S1.† Selected
bond lengths and bond angles of ADD are listed in Table S2.†
Hydrogen bond distances and angles for ADD are listed in Table
S3.†
9
The synthesis of DDB is slightly different from the literature. A
mixture containing H L (5 mg, 0.019 mmol), CdCl $2.5H O
2
2
2
(30 mg, 0.15 mmol), H O (12 mL) and triethylamine (0.05 mL)
2
was stirred at room temperature for 1 h until a clear solution
formed. It was then transferred into a Parr Teon-lined stain-
less steel vessel (25 mL) and heated to 150 C for 72 h under
ꢁ
ꢁ
autogenous pressure. Aerwards, it was cooled to 25 C at a rate
ꢁ
ꢀ1
of 4 C h . Brown ake crystals were obtained aer washing
with DMA and drying in air. The synthetic routes of ADD and
DDB are depicted in Scheme 1.
Photoelectrochemical measurements
UV-visible absorption spectra of the samples were measured at
room temperature on U-3010 spectrophotometer (Hitachi,
Japan) with an integrating sphere (model 130-0632). Cyclic
voltammetry experiment was performed with a three-electrode
system, a platinum working electrode, a platinum counter
electrode, and an Ag/AgCl reference electrode. The potentials
Fabrication of DSSC
A colloidal solution of TiO
2
was obtained by being coated on the

uorine-doped tin oxide (FTO) conducting glass by screen
ꢁ
printing and then dried for 6 min at 125 C. The TiO electrodes
2
+
were referenced to the ferrocene/ferrocenium (Fc /Fc) couple.
ꢁ
were gradually heated under an air ow at 325 C for 5 min, at
The photocurrent–photovoltage (J–V) curves of the sealed
ꢁ ꢁ ꢁ
3
75 C for 5 min, at 450 C for 15 min, and at 500 C for 15 min.
ꢀ
2
cells were measured under AM 1.5 illumination (100 mW cm
by using solar simulator. Electrochemical impedance
measurements were carried out by electrochemical work-station
chi660d, Chenhua, China) with three-electrode system in the
)
2
The area of lm was 0.25 cm . The lm electrodes were soaked
a
ꢀ
4
in the DDB solution (concentration: 5 ꢂ 10
M, solvent:
absolute ethanol) for 24 h and the ADD solution (concentration:
(
ꢀ
4
5
ꢂ 10
M, solvent: absolute ethanol) for 24 h at room
dark. Frequency range was 0.05–105 Hz, and the applied
potential was generally between 0–0.700 V. The IPCE spectra
were measured with a Model SR830 DSP Lock-In Amplier and
a Model SR540 Optical Chopper (Stanford Research Corpora-
tion, USA), a 7IL/PX150 renon lamp as light source, and
a 7ISW301 Spectrometer.
temperature, respectively. Then, the co-sensitized lms were
dried in air. The counter electrodes were thermally platinized
conducting glass (5 mM H
2
PtCl
6
in dry isopropanol, heated at
ꢁ
4
00 C for 10 min). The electrolyte was consisted of 0.5 M LiI,
2
0.05 M I , 0.1 M 4-tert-butylpyridine in 1 : 1 (volume ratio)
acetonitrile–propylene carbonate.
Results and discussion
Crystal structure
Characterization
X-ray structure determination
Single crystal X-ray diffraction analysis reveals that ADD crys-
tallizes in the orthorhombic space group P2 2 2 . The asym-
metric unit of ADD contains one Cu(II) atom, one L ligand and
one en molecule. ADD is coordinated into a distorted rectan-
gular pyramid geometry by two nitrogen atoms (N(1) and N(2))
A suitable crystal with dimensions of 0.24 mm ꢂ 0.12 mm ꢂ
1
1 1
0
.05 mm was selected for single-crystal X-ray diffraction and the
2
ꢀ
data were collected at 296(2) K on Bruker Apex II CCD area-
detector diffractometer (Mo Ka, 0.071073 nm). A total of
1
0 123 reections were collected by a 4–u scan mode at room
ꢁ
temperature in the range of 1.65< q < 28.46 including 4016
independent ones with Rint ¼ 0.0199. Data reductions and
Fig. 1 The coordination environments of Cu1 in ADD (symmetry code:
A, ꢀ0.5 ꢀ x, ꢀy, 0.5 + z).
Scheme 1 Synthetic routes to ADD and DDB.
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from one en, one oxygen atom (O(2)) from carboxylic acid group
2
ꢀ
of one L ligand and two oxygen atoms (O(3) and O(4)) from
2
ꢀ
carboxylic acid group of another L
ligand (Fig. 1). The
distances of Cu–N/O [0.193(13)–0.270(16) nm] and the angle of
ꢁ
O/N–Cu–O/N [53.61(5)–92.55(6) ] are in the normal range of
1
0
those observed in reported Cu(II) compounds.
2
ꢀ
In ADD, L ligand exhibits a m2-terdentate bridging coor-
dination mode, in which the carboxylic acid oxygen atom (O(2))
coordinate one Cu(II) cations, and the oxygen atoms (O(3)A and
O(4)A) of another carboxylic acid group adopt chelating coor-
dination model to link another Cu(II) cations. As shown in
Fig. 2, Cu(II) cations are linked into an innite 1D zig-zag chain
Fig. 3 1D chains are connected into 2D supramolecular layer struc-
tures through hydrogen bonding interactions in ADD (symmetry code:
2
ꢀ
along c axis by the carboxylic oxygen groups of L ligands with B, 1 + x, y, z).
the adjacent sinusoidal ruffling motif Cu/Cu distance of ca.
2.474 nm. While en molecules chelate to Cu(II) cations from
both sides of the chain.
electrolyte. Fig. 4 shows the cyclic voltammetry of ADD and DDB
in CH Cl solution. ADD and DDB exhibit a reversible oxida-
tion–reduction behavior. The ground-state oxidation potential
There exist N–H/O [N(1)/O(1)B ¼ 0.294(3) nm, N(1)–
2
2
ꢁ
H(1B)/O(1)B ¼ 135 ; N(2)/O(3)B ¼ 0.289(2) nm, N(2)–H(2A)/
ꢁ
O(3)B ¼ 168 ] hydrogen bonds between adjacent zig-zag chains,
(
(
E ) corresponding to the high occupied molecular orbital
ox
HOMO) level is determined by the peak potential of CV. Eox of
11
linking the 1D chains into a two-dimensional (2D) layer struc-
ture (Fig. 3).
ADD and DDB are 0.84 and 0.79 V (vs. NHE) respectively, which
ꢀ
ꢀ
We examined the structural homogeneity of bulk powder
sample of ADD through comparison of experimental and
simulated PXRD patterns. The peak positions of the experi-
mental patterns are nearly in agreement with those of the
simulated one generated from single-crystal X-ray diffraction
data (Fig. S2†), suggesting that the product of ADD is pure single
phase.
are more positive than the redox potential of I
3
/I couple (0.4 V
vs. NHE). It suggests that the oxidized ADD and DDB formed
aer electron injection into the conductor band of TiO should
/I in the electrolyte. The
absorption threshold of ADD is 550 nm, which corresponds to
12
2
ꢀ
3
ꢀ
be thermodynamically reduced by I
13
the band gap energy of 2.25 eV according to eqn (1).
To estimate the stability of ADD and DDB, the thermal
E
g
(eV) ¼ 1240/l (nm)
(1)
behavior was carried out by TGA under N
temperature range from 20 to 800 C at a rate of 10 C min
2
atmosphere in the
ꢁ
ꢁ
ꢀ1
.
ꢁ
The excited-state redox potential (Ered) of ADD correspond-
ing to the low unoccupied molecular orbital (LUMO) level is
calculated to be ꢀ1.41 V according to eqn (2).
For ADD, the weight loss of 80.56% from 295 to 382 C corre-
sponds to the loss of the ligand and en for ADD (calculated value
is 79.67%) (Fig. S3†). For DDB, the rst mass loss of 5.32%
14
ꢁ
occurs between 150 to 226 C, corresponding to the release of its
Ered ¼ Eox + E
g
(2)
one coordinated water molecule (calcd 4.63%) (Fig. S4†). The
ꢁ
solid then continues to lose mass from 387 to 725 C, corre-
2
ꢀ
sponding to the decomposition of one L ligand (obsd 62.34%,
ꢁ
calcd 62.23%). Finally, a plateau occurs from 740 to 800 C. The
residue equals 32.34%, which is attributed to CdO (calcd
32.21%).
Cyclic voltammetry is used to study the electrochemical
properties of ADD and DDB, the mechanism of electron injec-
tion from the ADD and DDB to conductor band of TiO , the
2
oxidation and reduction regeneration of ADD and DDB in the
Fig. 4 Cyclic voltammograms of the ADD and DDB in CH
taining 0.1 M TBAPF solution.
2
Cl
2
con-
6
Fig. 2 1D chain structure in ADD.
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The absorption threshold of DDB is 700 nm. Ered of DDB is
0.98 V. Ered of ADD and DDB is more negative than the bottom
ꢀ
of conductor band of TiO (ꢀ0.5 V vs. NHE), which conrms
2
that the electron injection from excited state is thermodynam-
ically favorable. Fig. 5 shows the schematic energy levels of ADD
and DDB based on the absorption and the electrochemical data.
The exciting, electron injecting and redox regenerating of ADD
and DDB are exhibited in Fig. 5, indicating ADD and DDB can
2
efficiently sensitize TiO photoanode of DSSC.
Transient surface photovoltage (TPV) measurement was
performed to study the mechanisms of charge separation,
diffusion and recombination processes. Fig. 6 shows the posi-
tive TPV response for ADD and DDB. The layer thickness of
materials is much greater than the diffusion distance of excess
electrons. Therefore, the TPV shape depends not on the layer
thickness of materials but the carrier changes with the time.
The positive TPV response implies that negative charges
transfer towards the bottom and positive charges accumulate at
the surface area. The electrons and holes diffuse from surface to
bottom due to the concentration gradient. The diffusion coef-
Fig. 6 The transient surface photovoltage spectra of ADD and DDB.
absorbed on the TiO
00 nm. The new absorption peak central at 370 nm is attrib-
uted to the absorption of TiO . It is known that the dyes have the
2
lm exhibits absorption response in 350–
7
2
strong attractive forces among the molecules at the solid–liquid
interface. The attractive forces can lead the shi of absorption
peak. The attractive forces have two forms: red-shi J-
aggregation and blue-shi H-aggregation. The maximum
absorption peak of ADD attached to TiO lm has obviously
2
blue-shied by 20 nm from 480 to 460 nm compared to that in
absolute ethanol solution, owing to dye anchoring and H-
2
aggregation on TiO semiconductor surface. As a whole, the
combination of ADD and DDB broadens and intensies the
absorption of DSSC, which should be protable for light har-
vesting and photocurrent generation in DSSC.

cient of electrons is larger than that of holes. The TPV
response of DDB is stronger than that of ADD. The enhanced
TPV of DDB indicates that the separation of photo-generated
electrons and holes is much more pronounced than that of
15
ADD. Charge separation increased progressively from the
ꢀ
7
instant at 10 s until it attained a saturation value. The TPV
apexes on the time scale for ADD is smaller than that of DDB.
This indicates that separation and diffusion of electrons and
holes in ADD is faster than that in DDB. The recombination of
electrons and holes is also faster than that in DDB. The lifetime
of electrons in ADD is shorter than that in DDB.
Fig. 8 shows the current density versus voltage curves of DSSC
based on the lms of ADD/TiO
2
, DDB/TiO
under 100 mW cm illumination. The photovoltaic perfor-
mances of ADD/TiO -based DSSC, e.g. the short photocurrent
density (Jsc), the open circuit voltage (Voc), the ll factor (FF),
2 2
and ADD + DDB/TiO
Fig. 7 shows normalized absorption spectra of ADD and of
ꢀ
2
ꢀ
5
ꢀ1
DDB in absolute ethanol solution (10 mol L ). ADD shows
absorbing response in the blue light region (400–550 nm) with
maximum absorption peak at 480 nm. DDB shows wide and
intense visible light absorption between 500 and 700 nm. The
absorption bands of ADD and DDB are attributed to the p–p*
2
ꢀ2
and overall energy conversion efficiency (h) are 8.83 mA cm
,
0
.77 V, 0.50, 3.4%, respectively. J , V , FF, and h of DDB/TiO -
sc oc
2
ꢀ
2
16,17
based DSSC are 13.33 mA cm , 0.71 V, 0.55, 5.3%, respectively.
Jsc of DDB/TiO -based DSSC is bigger than that of ADD/TiO -
transitions.
Obviously, the combination of ADD and DDB
can effectively broaden the absorption response of DSSC. As
shown in Fig. 8, the absorption spectrum of ADD and DDB
2
2
based DSSC. This is attributed to broaden absorption range of
DDB in visible light region. Voc is the difference potential
Fig. 5 LUMO and HOMO energy levels of ADD and DDB with respect
to the conductor band (CB) edge and the valence band (VB) edge
ꢀ
ꢀ
energies of TiO
2
and the I
3
/I redox potential.
Fig. 7 The UV-visible absorption spectra of ADD and DDB.
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Fig. 8 The current density versus voltage curves of DSSC based on
ꢀ
2
ADD and DDB under 100 mW cm illumination.
between the electrochemical potential of the redox couple in the
18
electrolyte and the conduction band edge of TiO photoanode.
2
LUMO level of ADD is higher than that of DDB. The upward shi
of the conduction band edge of TiO caused by ADD is much
intense than that of DDB, so Voc of ADD is higher than that of
DDB. The photovoltaic performances of ADD + DDB/TiO -based
DSSC are obviously increased compared with that of single ADD
2
2
ꢀ
2
Fig. 9 Impedance spectra of DSSC based on AAD, DDB and ADD +
DDB in dark. (a) Nyquist plots; (b) Bode phase plots.
or DDB. Jsc of ADD + DDB/TiO -based DSSC (16.96 mA cm ) has
2
a remarkably increase compared relative to that of single ADD
or DDB. This increase of Jsc indicates that ADD and DDB
effectively co-sensitized TiO
2
photoanode and resulted in
a higher light harvesting. ADD and DDB complement each other respectively; O, which depends on the parameters Yo,1 and B,
in solar spectrum. This co-sensitization of ADD and DDB is an accounts for a nite-length Warburg diffusion (ZDif), and Q is
efficient method of improving efficiency. The overall solar the symbol for the constant phase element, CPE (its parameters
19
conversion efficiency of DSSC based on ADD + DDB/TiO
2
are Yo,2 and n).
Yo,1 and Yo,2 are Warburg coefficients at the
tremendously increases to 7.1%.
photoanode/dye/electrolyte interface and the Pt/electrolyte
Electrochemical impedance spectroscopy (EIS) has been interface, respectively, corresponding to the module 1 and 2
widely used to correlate device structure with a suitable model in the equivalent circuit. RDif ¼ B/Yo,1, B is parameter. Table 1
for the study of kinetics of electrochemical and photo- lists parameters obtained by tting the impedance spectra of
electrochemical processes occurring in DSSC. Fig. 9 shows composite solar cells using the equivalent circuit. The series
s
electrochemical impedance spectroscopy of ADD, DDB and resistance of the system (R ), can account for the resistance of
ADD + DDB based on DSSC in the dark. In Fig. 9, experimental polymer electrolyte, the resistance within the photoelectrode
data are represented by symbols while the solid lines corre- lm and the FTO electrode, as well as contacts. A semicircle
spond to the t obtained by Zsimpwin soware using the observed at high frequency is associated to the capacitance and
19,20
19,21
equivalent circuit R (C (R O ))(R Q ).
The spectra show two resistance at Pt/electrolyte interface (CPE and R
2
elements).
s
1
1
1
2 2
semicircles at medium frequency region and high frequency For the elements related with Pt/electrolyte interface, R
2
of ADD,
region. The equivalent circuit is a useful tool for understanding DDB, and ADD + DDB is 38.51 U, 26.72 U, and 18.92 U,
ꢀ
the output performance of solar cells and for further compre- respectively. The decrease of R
2
means that much more I
3
at
hension of the electrical behavior of DSSC. In equivalent circuit, the Pt electrode surface to take place redox reaction and hence
the symbols R and C describe resistance and capacitance, the FF of the DSSC. The large semicircle at the medium
Table 1 Parameters obtained by fitting the impedance spectra of composite solar cells using the equivalent circuit
ꢀ1
ꢀ1
ꢀ1
ꢀ1/2
1/2
1/2
o,2/S
DSSC
R
s
U
C
1
F
R
1
U
Y
o,1
S
B/U S
R
2
/U
Y
n
ꢀ5
ꢀ5
ꢀ5
ꢀ3
ꢀ3
ꢀ2
ꢀ5
ꢀ5
ꢀ5
ADD
DDB
ADD + DDB
19.89
18.46
22.60
29.51 ꢂ 10
32.97 ꢂ 10
47.91 ꢂ 10
138.4
55.72
33.66
45.25 ꢂ 10
91.35 ꢂ 10
15.18 ꢂ 10
1.24
1.58
0.95
38.51
26.72
18.92
12.64 ꢂ 10
17.39 ꢂ 10
18.07 ꢂ 10
0.8
0.8
0.8
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frequency is attributed to the electron transfer process at the
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dye/TiO /electrolyte interface (capacitance, C ; charge transfer
2
1
2
0,22
resistance, R ).
C of ADD, DDB, and ADD + DDB is 29.51 ꢂ
1
1
ꢀ
5
, 32.97 ꢂ 10ꢀ5, and 47.91 ꢂ 10 , respectively. The
ꢀ5
10
increasing lm capacitance means more electrons at the inter-
face of dye/TiO
DSSC. The decreasing value of R
low at the interface of dye/TiO
electron transmission.
2
/electrolyte as the light absorption is hence for
means that the resistance is
/electrolyte. This is favorable for
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1
2
The high lm capacitance and the low resistance are favor-
able for improving the performances of DSSC. Meanwhile, the
recombination characteristic peak of DSSC based on ADD, DDB,
and ADD + DDB is 9.8, 8.1, and 3.7 Hz. This indicates electron
lifetime in ADD + DDB DSSC is longest. The high lm capaci-
tance and low resistance, low recombination characteristic
frequency makes the highest h possible. Therefore, h of DSSC
based ADD + DDB is highest.
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In summary, we have designed and synthesized two new azo- 11 F. Daniele, C. Massimo, R. Gianna, Z. Lorenzo, P. Maurizio,
benzene dyes, ADD and DDB as the sensitizer for DSSC appli-
cation. The combination of ADD and DDB broadens the spectral
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T. Maurizio, d. B. Fabrizia Fabrizi, B. Riccardo, S. Adalgisa,
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solar conversion efficiency of 7.1%. This result suggests azo-
Lin, D. Song-Yuan and S. Qin-Hua, Org. Electron., 2014, 15,
benzene dyes are potential high efficient organic sensitizers.
2079.
More work should be processed in aspect of optimizing the 13 G. Min, D. Peng, R. Yan-Jie, M. Fanshun, T. He and C. Sheng-
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14 L. Liyen, T. Chihung, L. Francis, H. Tsungwei, C. Shuhua,
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7
509.
Conflicts of interest
1
5 Z. Yu, W. Lingling, L. Bingkun, Z. Jiali, F. Haimei, W. Dejun,
There are no conicts to declare.
L. Yanhong and X. Tengfeng, Electrochim. Acta, 2011, 56,
6517.
Acknowledgements
16 G. Song, F. Ruiqing, Q. Liangsheng, W. Ping, C. Shuo,
W. Xinming and Y. YuLin, CrystEngComm, 2014, 16, 1113.
This work was supported by the Jilin Provincial Science &
Technology Department (20170204016GX), The Education
Department of Jilin Province, Science and Technology Project
1
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