Novel dye sensitizers of polymeric metal complexes with benzodithiophene derivatives as donor and their photovoltaic performance

Article abstract of DOI:10.1016/j.saa.2015.09.015

Four novel donor-acceptor (D-A) type conjugated polymeric metal complexes (P1-P4) bearing benzodithiophene or carbazole derivative as donors were synthesized, characterized and applied as dye sensitizers in dye-sensitized solar cells (DSSCs). Salicylaldeh

Full text of DOI:10.1016/j.saa.2015.09.015

Novel dye sensitizers of polymeric metal complexes with benzodithiophene
derivatives as donor and their photovoltaic performance
Yanlong Liao, Jiaomei Hu, Qiufang Xie, Dahai Peng, Ye Liu, Chunxiao
Zhu, Chaofan Zhonga
PII:
DOI:
Reference:
S1386-1425(15)30227-4
doi: 10.1016/j.saa.2015.09.015
SAA 14079
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Accepted date:
12 February 2015
10 September 2015
26 September 2015
Please cite this article as: Yanlong Liao, Jiaomei Hu, Qiufang Xie, Dahai Peng, Ye Liu,
Chunxiao Zhu, Chaofan Zhonga, Novel dye sensitizers of polymeric metal complexes with
benzodithiophene derivatives as donor and their photovoltaic performance, (2015), doi:
10.1016/j.saa.2015.09.015
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ACCEPTED MANUSCRIPT
Novel dye sensitizers of polymeric metal complexes with
benzodithiophene derivatives as donor and their photovoltaic
performance
Yanlong Liaoa,Jiaomei Hua,Qiufang Xiea,Dahai Penga,Ye Liua,Chunxiao
Zhua,Chaofan Zhonga,*
aKey Laboratory of Environmentally Friendly Chemistry and Applications of Ministry of
Education, College of Chemistry, Xiangtan University, Xiangtan, Hunan 411105, China
*Corresponding author: Tel: +86 731 58292202; Fax: +86 731 58292251
Email address: zhongcf798@aliyun.com
Four novel donor–acceptor (D-A) type conjugated polymeric metal
Abstract
complexes ( - ) bearing benzodithiophene or carbazole derivative as donors
P1 P4
were synthesized, characterized and applied as dye sensitizers in dye-sensitized solar
cells (DSSCs). Salicylaldehyde derivative complexes acted as electron acceptors, Zn
(II) or Cd (II) was chosen as the coordinated metal ion, and diaminomaleonitrile was
ancillary ligand in these structures. The thermal, photophysical, electrochemical and
photovoltaic properties of these polymeric metal complexes were investigated by
FT-IR, GPC, TGA, DSC, UV–vis absorption spectroscopy, Elemental analysis, cyclic
voltammetry (CV), J-V curves and IPCE plots. These polymer dyes exhibit good
thermal stability for their application in DSSCs. The DSSC device based on
which
P2
containing benzodithiophene derivative as donor and Cd(II) as coordination ion,
exhibited the highest power conversion efficiency of 2.43% (Jsc= 4.95 mA/cm2,
Voc=0.71 V, FF=69.3%) under AM 1.5G solar irradiation. It indicates a new way to
design dye sensitizers for DSSCs.
Keywords: dye-sensitized solar cell, polymeric metal complex, benzodithiophene
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1. Introduction
Dye-sensitized solar cells are considered as one of the most promising
next-generation photovoltaic cells, which can perform efficient conversion of solar
energy directly into electricity [1]. Since first reported by Grätzel and O’Regan in
1991 with a power conversion efficiency of 7% [2], they have raised a great deal of
attentions for their potential advantages of low cost, easy production, flexibility, and
transparency in comparison with conventional silicon solar cells [3]. Recently, a
high-performance perovskite-sensitized solar cell is reported with the power
conversion efficiency over 15% [4].
As a crucial element of DSSCs, the dye sensitizer which is adsorbed on
semiconducting TiO2 anode, plays an important role in the performance of DSSCs.
There are mainly two types of dyes, metal-organic dyes and metal-free organic dyes
[5]. Ruthenium complex dyes are the typical metal-organic dyes, such as N719 [6],
N3 [7], and black dye [8]. To date, a DSSC exhibits an excellent conversion efficiency
of 11.5% by using Ru-based dye CYC-B11 [9]. However, the limited resource and
high cost impede their development as dye sensitizers. Extensive research has been
focused on organic dyes as promising candidates to Ru-based complexes dyes due to
the advantage of inexpensive, high molar extinction coefficient and tunable absorption
and electrochemical properties [10]. But organic dyes are less stable than metal
complexes dyes, which can probably cause the formation of excited triplet states and
unstable radicals under light irradiation. Hence, the idea of polymeric metal
complexes dyes as metal–organic hybrid polymer materials used for DSSCs has great
appeal. The strong interaction between organic and inorganic components creates
unique electrochemical, photophysical and photochemical properties, which make
these conjugated polymers potential materials for applications in solar energy
conversion [11].
Sensitizers for DSSCs often feature push-pull molecular structures [12].
Benzodithiophene derivatives attracted some interest as a common unit in conjugated
polymers, they are excellent electron donor materials for the preparation of highly
efficient D-A type polymers for photovoltaic devices [13]. Because they have large
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planar conjugated structure and form π-π stacking easily, which improves mobility,
and the steric hindrance between adjacent units is very small [14]. Carbazole
derivatives are also usually used as electron donor in dye molecular due to the
electron-rich nitrogen heteroatom [15]. The salicylaldehyde derivatives of aromatic
imine-based ligands prepared by condensation reaction between aldehyde and primary
amine have been widely used in the synthesis of new coordination complexes [16].
But there are few reports about their use as dye sensitizers for DSSCs.
Accordingly, we report four D-A type polymeric metal complexes dyes for
DSSCs. The benzodithiophene or carbazole derivatives are used as electron donor,
salicylaldehyde derivatives complex as electron acceptor. Diaminomaleonitrile acts as
ancillary ligand. Introduction of CN groups aims to enhance the electron-withdrawing
ability of electron acceptor part, and to facilitate the electron injection between the
dyes and TiO2 surface [17]. Zn (II) or Cd (II) is chosen as the coordinated metal ion
for their low cost and easy to get. To increase the solubility of these dyes, long
aliphatic side chains are incorporated into the dye structures. Moreover, the optical
properties, thermal properties, and photovoltaic properties of these polymeric metal
complexes are also investigated in this paper.
2. Experimental section
2.1. Materials
All starting materials were obtained from Shanghai Chemical Reagent Co. Ltd
(Shanghai China) and were used without further purification. DMF and were dried by
distillation over CaH2. All other reagents and solvents were commercially purchased
and
were
used
as
received.
3,5-dibromosalicylaldehyde
( )
1
[18],
3,6-dibromo-N-otylcarbazole ( ) [20] was prepared according to the literature
4
methods.
2.2. Instruments and measurements
1H NMR spectra were obtained in CDCl3 and recorded with a Bruker ARX400
(400 MHz) Germany, and the spectra were referenced against tetramethylsilane
(δ=0.00 ppm) as the internal standard. FT-IR spectra were recorded using KBr pellets
with a Perkin-Elmer Spectrum One FT-IR spectrometer over the range 400–4000 cm-1.
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The UV-vis absorption spectra were measured with Lamada 25H spectrometer.
Samples were dissolved in DMF and diluted to a concentration of 10-5- 10-4mol L-1.
Gel Permeation Chromatography (GPC) analyses were measured by WATER 2414
system equipped with a set of HT3, HT4 and HT5, l-styrayel columns with DMF as
eluent, and polystyrene was used as standard. Elemental analysis for C, H, N was
performed on Perkin-Elmer 2400 II instrument under nitrogen atmosphere.
Thermogravimetric analyses (TGA) and Differential Scanning Calorimetry (DSC)
were performed on Shimadzu TGA-7 Instrument and Perkin-Elmer DSC-7 thermal
analyzer at a heating rate of 20 ºC min-1 from 25 to 600 ºC in nitrogen atmosphere,
respectively. Electrochemical redox potentials were obtained by cyclic voltammetry
(CV), and conducted on a CHI630C electrochemistry workstation in a [Bu4N]BF4 (0.1
mol L-1) CH3CN solution at a scan rate of 100 mV s-1 at room temperature. The
working electrode was a glassy carbon electrode, the auxiliary electrode was a
platinum wire electrode and a saturated calomel electrode (SCE) was used as
reference electrode.
2.3. Fabrication of DSSCs
The DSSCs devices with sandwich structure in this paper are based on TiO2
semiconductors. Titania paste was prepared following a procedure: fluorine-doped
SnO2 conducting glass (FTO) were cleaned and immersed in aqueous 40 mmol L-1
TiCl4 solution at 70 ºC for 30 min. The 20–30 nm particles sized TiO2 colloid was
coated onto the above FTO glass by the sliding glass rod method and following
sintered at 450 ºC for 30 min which has been repeated for three times to obtain a TiO2
film of 10-15 μm thickness. After cool to 100 ºC, the TiO2 films were soaked in 0.5
mmol L-1 dye samples in DMF solution and maintained under dark for 24 h at room
temperature. Then the film were cleaned by anhydrous ethanol. After drying,
electrolyte containing LiI (0.5 mol L-1), I2 (0.05 mol L-1) and 4-tert-butylpyridine (0.5
mol L-1) was dripped on the surface of TiO2 electrodes. A Pt foil was used as counter
electrode was clipped onto the top of the TiO2. The dye-coated semiconductor film
was illuminated through a conducting glass support without a mask. The
photoelectron chemical performance of the solar cell was measured using a Keithley
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2602 Source meter controlled by a computer. The cell parameters were obtained under
an incident light with intensity 100 mW cm-2, which was generated by a 500-W Xe
lamp passing through an AM 1.5 G filter with an effective area of 0.2 cm2.
2.4. Synthesis
2.4.1. Synthesis of 2,4-dibromo-6-((p-tolylimino)methyl)phenol (2) [19]
A ethanol solution of p-toluidine (1.63g, 15mmol) was added in a ethanol
solution of (1) (4.22g, 15mmol) while stirring at room temperature. The mixed
solution was continue stirred at room temperature for 3h. The formed solid was
separated by filtration under reduced pressure, washed with ethanol and dried under
vacuum. The crude product was recrystallized from ethanol, resulting in orange
crystal solid (4.71g, 85%). FTIR (KBr, cm-1): 3443, 3082, 2968, 1621, 1591, 688.
1HNMR (CDCl3, δ, ppm): 14.63 (s, 1H), 8.54 (s, 1H), 7.74 (s, 1H), 7.48 (s, 1H),
7.21-7.24 (m, 4H), 2.40 (s, 3H).
2.4.2. Synthesis of C1 [21]
A ethanol solution (30ml) of Zn(CH3COO)2·2H2O (0.35g, 1.5mmol) was slowly
dropped into a mixture of (2) (0.55g, 1.5mmol) and diaminomaleonitrile (0.16g,
1.5mmol) in ethanol (45ml) with stirring and refluxing. After the solutiom was
refluxed for 10h, the reaction system was then allowed to cool to room temperature.
The precipitate was collected by filtration, washed with ethanol several times and then
dried in vacuum. A brick-red solid was collected (0.57g, 63%). FTIR (KBr, cm-1):
3435(N-H), 3062(=C-H), 2975(C-H), 2221(C≡N), 1619(C=N), 1054(C=N-M),
567(N-M). Anal. Calcd. for [C20H17Br2N5O3Zn]: C, 40.01; H, 2.83; N, 11.67. Found:
C, 40.78; H, 2.95; N, 11.32%.
2.4.3. Synthesis of C2
With the similar synthetic method for C1 With Cd(CH3COO)2·2H2O (0.41g,
1.5mmol) afforded reddish brown solid (0.66g, 68%). FTIR (KBr, cm-1): 3434(N-H）,
3063(=C-H), 2978(C-H), 2226(C≡N),1626(C=N), 1051(C=N-M), 548(N-M). Anal.
Calcd. for [C20H17Br2N5O3Cd]: C, 37.07; H, 2.63; N, 10.81. Found: C, 37.85; H, 2.26;
N, 11.27%.
2.4.4. Synthesis of P1
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The polymeric metal complex was synthesized by Yamamoto coupling method
according to the literature [22]. Under nitrogen atmosphere, metal complex
(0.24g,
C1
0.4mmol), bis(triphenylphosphine) nickel(II) chloride (0.26g, 0.4mmol),
2,6-dibromo-4,8-bis(2’-ethhylhexyl)oxy)benzodithiophene ( ) (0.24g, 0.4mmol), zinc
3
(0.13g, 2mmol), triphenylphosphine (0.21g,0.8mmol), and a little bipyridine (0.006g,
0.038mmol) were dissolved in DMF(15 mL) under nitrogen. Then the mixture was
stirring at 90 ℃ for 48 h. After that, it was filtered after cooled to room temperature
and the filtrate was poured into a large excess of ethanol. The precipitate was filtered
and washed with cold ethanol, then dried in vacuum for one day to afford brown solid
(0.21g, 58%). FTIR (KBr, cm-1): 3431(N-H), 3036(=C-H), 2961, 2925, 2857(C-H),
2194(C≡N), 1606(C=N), 1045(C=N-M), 485(N-M). Anal. Calcd. for
[C46H53N5O5S2Zn]: C, 62.44; H, 5.60; N,7.92. Found: C, 61.87; H, 5.73; N, 8.56%.
Mn=8.24 Kg/mol, PDI=1.55.
2.4.5. Synthesis of P2
With the similar synthetic method as described for
. A mixture of metal
P1
complex
, bis(triphenylphosphine) nickel(II) chloride, monomer , zinc,
C2
3
triphenylphosphine, and a little bipyridine and DMF afforded brown solid (0.19g,
51%). FTIR (KBr, cm-1): 3419(N-H), 3039(=C-H), 2973, 2921, 2862(C-H),
2153(C≡N), 1619(C=N), 1047(C=N-M), 488 (N-M). Anal. Calcd. for
[C46H53N5O5S2Cd]: C, 59.29; H, 5.69; N,7.52. Found: C, 59.84; H, 6.21; N, 7.15%.
Mn=9.37 Kg/mol, PDI=1.47.
2.4.6. Synthesis of P3
With the similar synthetic method as described for
. A mixture of metal
P1
complex
, bis(triphenylphosphine) nickel(II) chloride, monomer , zinc,
C1
4
triphenylphosphine, and a little bipyridine and DMF afforded brown solid (0.18g,
63%). FTIR (KBr, cm-1): 3406(N-H), 3059(=C-H), 2961, 2921, 2851(C-H),
2187(C≡N), 1612(C=N), 1025(C=N-M), 482(N-M). Anal. Calcd. for [C40H40N6O3Zn]:
C, 66.95; H, 5.58; N, 11.72. Found: C, 67.73; H, 5.86; N, 11.17%. Mn=6.74 Kg/mol,
PDI=1.65.
2.4.7. Synthesis of P4
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With the similar synthetic method as described for
. A mixture of metal
P1
complex
, bis(triphenylphosphine) nickel(II) chloride, monomer , zinc,
C2
4
triphenylphosphine, and a little bipyridine and DMF afforded brown solid (0.17g,
55%). FTIR (KBr, cm-1): 3421 (N-H), 3053(=C-H), 2962, 2926, 2856(C-H),
2193(C≡N), 1618(C=N), 1041(C=N-M), 495(N-M). Anal. Calcd. for [C40H40N6O3Cd]:
C, 62.83; H, 5.24; N, 10.99. Found: C, 63.64; H, 5.59; N, 11.28%. Mn=6.48 Kg/mol,
PDI=1.52.
3. Results and discussion
3.1. Synthesis and characterization
The detailed synthetic routes of the monomers and the four polymeric metal
complexes are depicted in Scheme. 1. The intermediate (2) was prepared by the
condensation of 3,5-dibromosalicylaldehyde with p-toluidine in ethanol solution. The
target four polymers were obtained by the Yamamoto coupling [22], the reactions
were carried out in N2 atmosphere. The four as-synthesized polymers showed good
solubility in DMF and DMSO solvent at room temperature. But they can not be
dissolved well in chloroform or other solvents.
1
Fig. 1 shows the H NMR spectrum of monomer . Signals at 8.54, 2.40 ppm are
2
attributed to proton of H-C=N and methyl, respectively. There is no proton signal of
H-C=O that further prove the success of the synthesis of .
2
The IR spectra of the metal complex (
,
) and the target polymers ( - are
P1 P4)
C1 C2
shown in Fig. 2. As for
, the absorption peaks at 1054cm-1 and 1051 cm-1 are
C1, C2
assigned to their C=N-M stretching vibration, respectively [23]. And their N-M
stretching vibration peak appeared at 567 cm-1 and 548 cm-1, respectively. While the
C=N-M stretching vibration signals of
-
appear at 1045 cm-1, 1047 cm-1, 1025
P1 P4
cm-1 and 1041cm-1, respectively, and their corresponding N-M stretching vibration
peaks appeared at 485 cm-1, 488 cm-1, 482 cm-1 and 495 cm-1, respectively. It is
obvious that these kinds of peaks of the polymeric metal complexes show red-shift
comparing with the corresponding metal complexes. This is due to the extending of
conjugation system after polymerization.
The number average molecular weight and the weight average molecular weight
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of the four target polymers dyes (P1-P4) are measured by gel permeation
chromatography (GPC) and the corresponding data are shown in Table 1. The four
polymer dyes have number average molecular weights (Mn) of 8.24, 9.37, 6.74 and
6.48 kg mol-1, respectively, with a PDI in the range of 1.55, 1.47, 1.65, and 1.52,
respectively. Changes in the molecular weight further proved an evidence for the
successful synthesis of the four target polymers.
3.2. Optical properties
Fig. 3 shows the absorption spectra of C1, C2 and P1-P4 in DMF solution, and
the corresponding data are summarized in Table 2. The light absorption of 356nm and
367nm for metal complexes C1, C2 is mainly due to metal-to-ligand charge transfer.
We observe that the maximum absorption peak of P1–P4 are at 455, 471, 414, and
425 nm, respectively. These strong absorption bands result from intramolecular
charge transfer between the electron-donating unit and the electron-accepting moiety.
It can be easily found that the maximum absorptions of the polymeric metal
complexes (P1–P4) are obviously red shifted comparing with corresponding metal
complex C1, C2 due to the introduction of the benzodithiophene or carbazole
derivatives, and the increase of an effective conjugated chain length.
The normalized photoluminescent (PL) spectra of P1–P4 in DMF solution are
shown in Fig. 4, the exciation wavelengths were set according to the maximal
absorption peak of UV–vis spectrum. It can be seen in table 2 that the PL peaks of
P1–P4 are at 526, 551, 502, and 511 nm, respectively, which can be attributed to the
π– π* transition of intra-ligand.
3.3. Thermal stability
The thermal properties of these four polymeric metal complexes were studied by
TGA and DSC. The results are shown in Fig. 5 and the corresponding data was
recorded in Table 1. The results of TGA show the excellent stability of polymers
P1–P4 with 5 % weight loss temperatures (Td) of 337, 328, 356, and 344 ℃ under
nitrogen, respectively. This is important for the thermal stability of DSSCs. And their
glass transition temperature (Tg) are 157, 150, 168, and 162 ℃, respectively. There is
no fixed melting point which is due to our synthetic method and purification means
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that we only obtained the amorphous products. Their high glass transition temperature
shows that these polymeric metal complexes will be a valuable material for
application in DSSCs.
3.4. Electrochemical properties
The electrochemical behaviors of the polymers were investigated by cyclic
voltammetry. The highest occupied molecular orbital (HOMO) and the lowest
unoccupied molecular orbital (LUMO) energy levels of the polymers are important
for evaluating the possibility of electron transfer from the excited dyes to the
conductive band of TiO2 and the regeneration of dyes. They can be calculated
conveniently by the following equations as well as energy gap (Eg) [24]:
HOMO=－e(Eox + 4.40) (eV)
LUMO=－e(Ered + 4.40) (eV)
Eg= HOMO － LUMO
(1)
(2)
(3)
Fig. 6 shows the cyclic voltammetry curves of P1-P4, and the data are
summarized in Table 2. The oxidation potential values (Eox) of P1-P4 are 1.15, 1.06,
1.26, and 1.21V, respectively, which can be attributed to the benzodithiophene or
carbazole derivatives donor segment. The reduction potential values (Ered) of P1-P4
are -0.96, -0.98, -1.02, and -0.99V, respectively, which can be attributed to the
metal-ligand complex acceptor segment. Accordingly, the HOMO energy values of
P1-P4 are -5.55, -5.46, -5.66, and -5.61 eV, respectively, which are are lower than the
-
standard potential of I-/I3 redox couple (-4.83 eV) [25]. The LUMO energy values are
-3.44, -3.42, -3.38, and -3.41 eV, respectively, which are higher than the conduction
band of TiO2 (-4.26 eV). The details are shown in Fig. 7. It indicates that electrons can
transfer from the excited dye to the TiO2 efficiently and can facilitate dyes’
regeneration. The electrochemical band gaps (Eg) of P1-P4 are estimated to be 2.11,
2.04, 2.28 and 2.20 eV, respectively, which are consistent with the optical band gaps,
so they are suitable for fabrication of optoelectronic devices.
3.5. Photovoltaic properties
The photocurrent density-voltage (J–V) curves of the DSSCs devices based on
the four polymeric metal complexes are reported in Fig. 8. The corresponding datas
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are listed in Table 3. It can be seen that the open-circuit voltage (Voc) of P1-P4 are
0.69, 0.71, 0.64 and 0.67 V, respectively. The corresponding fill factor (FF) are 68.2,
69.3, 64.8, and 64.5. And the short-circuit current density (Jsc) follow the order of P2
(4.95 mA/cm2) > P1 (4.77 mA/cm2) > P4 (4.51 mA/cm2) > P3 (4.43 mA/cm2). This is
in accordance with the order of the power conversion efficiency (η) of the four dyes
that P2 (2.43%) > P1 (2.24%) > P4 (1.95%) > P3 (1.84%). We found that polymers
containing benzodithiophene derivatives as electron donor show higher Jsc values than
polymers containing carbazole derivatives, this is due to the stronger
electron-donating capability of benzodithiophene than carbazole, which is more
conducive to the generation of photocurrent. Besides, the electron transport properties
of Cd complexes are better than Zn complexes. Since the radius of Cd(II) is bigger
that of Zn(II), the coordination bond between ligands and cadmium is stronger
relative to zinc , which lead to the stronger electronic withdrawing ability of the
former and facilitate the electron transport in the dye molecules, thus the polymers
with Cd ion exhibited better photovoltaic properties than the polymers with Zn ion.
However, Jsc values of these materials are still low. This is related to many
factors, such as the low charge separation and transportation efficiency, and the
narrow absorption spectra of the polymers. It can also be seen from the input photon
to converted current efficiency (IPCE) curves as shown in Fig. 9. The IPCE values of
the four polymers are relatively low with only 30-40% at 400-450nm. This is not as
good as Si which as photovoltaic material with a broader spectral response ranges
400~1100 nm, and the IPCE value can reach to over 80% in the visible spectrum
region [26]. But it shows a new way to design dye sensitizers.
4. Conclusions
Four novel D-A polymeric metal complexes dyes containing benzodithiophene
or carbazole derivatives as electron donors were designed, synthesized and applied for
DSSCs. These dyes exhibit good thermal stability for their application in DSSCs. The
strength of the electron-donating group as well as different metal ion greatly
influenced the performance of the photovoltaic device. DSSC based on P2 shows the
best power conversion efficiency of 2.43% with a better light absorption and higher
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Jsc value among the four dyes studied. The results show that this type of functional
materials would be a potential material for DSSCs.
In our next work, we will design new conjugated polymeric metal complexes dyes
with much stronger electron-donating units so as to make the maximum absorption
red-shift, and further improving Jsc value. Besides, more suitable metal ions should be
found to tune the molecule structure and broaden absorption spectra, and thus to
obtain outstanding energy conversion efficiency.
Acknowledgments
We appreciate the financial support of the Open Project Program of Key
Laboratory of Environmentally Friendly Chemistry and Applications of Ministry of
Education, China ( No.09HJYH10).
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Fig. 1
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Fig. 2
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Fig. 3
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Fig. 4
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Fig. 5
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Fig. 6
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Fig. 7
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Fig. 8
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Fig. 9
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Scheme 1
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Table 1
Molecular weights and thermal properties of the polymeric metal complexes.
b
c o
Polymer
PDI
1.47
N
9
Tg [oC]
Td [ C]
a [×103]
a[×103]
M n
M w
12.15
8.24
157
337
328
P1
9.37
13.07
1.39
10
150
P2
6.74
6.48
11.13
9.86
1.65
1.52
9
8
168
162
356
344
P3
P4
a Determined by gel permeation chromatography using polystyrene as standard.
b Determined by DSC with a heating rate of 20 oC/min under nitrogen.
c The temperature at 5% weight loss under nitrogen.
Table 2
Optical and electrochemical properties of the polymeric metal complexes.
PL
(nm)b
λa,max
(nm)a
HOMO
(eV)
LUMO
(eV)
Polymer
Eox (V)c
Ered (V)c
Eg,EC/eV d
526
551
502
511
P1
P2
P3
P4
455
471
414
425
1.15
1.06
1.26
1.21
-0.96
-0.98
-1.02
-0.99
-5.55
-5.46
-5.66
-5.61
-3.44
-3.42
-3.38
-3.41
2.11
2.04
2.28
2.20
a The maxima absorption from the UV–vis spectra in DMF solution.
b The PL maxima in DMF solution.
c Values determined by cyclic voltammetry.
d Electrochemical band gap estimated from HOMO and LUMO.
Table 3
Photovoltaic parameters of devices with sensitizers P1-P4 in DSSCs at full sunlight
(AM 1.5 G, 100 wM cm-2).
Polymer Solvent Jsc (mA / cm2)
Voc (V)
0.69
FF (%)
68.2
 (%)
2.24
2.43
1.84
1.95
DMF
DMF
DMF
DMF
4.77
4.95
4.43
4.51
P1
P2
P3
P4
0.71
69.3
0.64
64.8
0.67
64.5
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Figure Legends:
Scheme. 1. Synthesis of the monomers and polymeric metal complexes P1-P4.
Fig. 1. 1H NMR spectra of 2 in CDCl3 solution.
Fig. 2. FT-IR spectra of C1, C2, P1-P4.
Fig. 3. UV-vis absorption spectra of C1, C2 and polymeric metal complexes P1-P4
in DMF solution.
Fig. 4. PL spectra of polymeric metal complexes P1–P4 in DMF solution.
o
Fig. 5. TGA curves of P1-P4 with a heating rate of 20 C/min under nitrogen
atmosphere.
Fig. 6. Cyclic voltammograms for P1-P4 in CH3CN/0.1 M [Bu4N]BF4 at 100 mV/s.
Fig. 7. HOMO and LUMO energy levels of the polymers.
Fig. 8. J-V curves of DSSCs based on dyes (P1-P4) under the illumination of AM
1.5, 100 mW cm-2.
Fig. 9. Spectra of incident photon-to-current conversion efficiencies (IPCE) for
DSSCs based on dyes (P1-P4).
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Graphical abstract
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Highlights
·Four novel polymeric metal complexes are designed and synthesized for being used
as dyes of dye-sensitized solar cells (DSSCs). The results show that they exhibit
some photovoltaic performance, and pave a potential way for researching and
developing dyes.
·The dyes with benzodithiophene derivatives as donor (P1, P2) show better
photovoltaic performance than that with carbazole derivatives as donor (P3,P4).
This show a new way to design and synthesize polymeric metal complexes for
being used as dyes.
·The four polymers were investigated by UV–vis absorption spectroscopy and PL
spectroscopy, which lays a foundation for further photochemical research.
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