Synthesis and characterization of cross-linkable ruthenium complex dye and its application on dye-sensitized solar cells

Article abstract of DOI:10.1002/pola.23793

A new crosslinkable light sensitizer, Ru(2,2′-bipyridine- 4,40-bicarboxylic acid)(4,4′-bis(11-dodecenyl)-2,2′-bipyridine)( NCS)₂, denoted as Ru-C for titanium oxide nanocrystallinebased solar cells was synthesized with its crosslinking properties invesitigated by Fourier-transform infrared and UV-vis absorption spectroscopies. After crosslinking by itself or copolymerizing with methyacrylic acid, their sensitized solar cells with poly(methylacrylate)-gelled electrolyte system not only attained more than 5% of power conversion efficiency at AM 1.5 illumination (100 mW/cm²), but also gave rise to long storage life. To the best our knowledge, this is the first crosslinkable dye ever applied to the DSSC in the literature.

Full text of DOI:10.1002/pola.23793

Synthesis and Characterization of Cross-Linkable Ruthenium Complex
Dye and Its Application on Dye-Sensitized Solar Cells
KEN-YEN LIU,1 CHIAO-LING HSU,2 SHUN-HSING CHANG,1 JIAN-GING CHEN,3 KUO-CHUAN HO,2,3 KING-FU LIN1,2
1Department of Materials Science and Engineering, National Taiwan University, Taipei 106, Taiwan
2Institute of Polymer Science and Engineering, National Taiwan University, Taipei 106, Taiwan
3Department of Chemical Engineering, National Taiwan University, Taipei 106, Taiwan
Received 29 August 2009; accepted 17 October 2009
DOI: 10.1002/pola.23793
Published online in Wiley InterScience (www.interscience.wiley.com).
ABSTRACT: A new crosslinkable light sensitizer, Ru(2,20-bipyri-
dine-4,40-bicarboxylic acid)(4,40-bis(11-dodecenyl)-2,20-bipyri-
AM 1.5 illumination (100 mW/cm2), but also gave rise to long
storage life. To the best our knowledge, this is the first crosslink-
C
V
dine)(NCS)2, denoted as Ru-C for titanium oxide nanocrystalline-
based solar cells was synthesized with its crosslinking proper-
ties invesitigated by Fourier-transform infrared and UV-vis
absorption spectroscopies. After crosslinking by itself or
copolymerizing with methyacrylic acid, their sensitized solar
cells with poly(methylacrylate)-gelled electrolyte system not
only attained more than 5% of power conversion efficiency at
able dye ever applied to the DSSC in the literature. 2009 Wiley
Periodicals, Inc. J Polym Sci Part A: Polym Chem 48: 366–372,
2010
KEYWORDS: crosslinking; curing of polymer; dye-sensitized
solar cells; irradiation; polymer-gelled electrolyte; synthesis;
ruthenium dye
INTRODUCTION Solar energy is generally perceived as one of
the cleanest and unlimited energy resources for the mankind.
Although the tranditional silicon-based solar cell has high
light-to-electric power conversion efficiency, its high material
cost has limited its use. With the advancement of nanotech-
nology and organic optoelectronic materials, researchers have
endeavored to explore the low cost photovoltaic cells by tak-
ing the advantge of these cutting age technologies.1–7 Since
the ruthenium dye-sensitized solar cell (DSSC) was reported
to achieve power conversion efficiency of 11%,8,9 it has
attracted great attentions from both academic and industrial
reserachers.10–23 To pursue better photovoltaic performance,
various structural modifications to the ruthenium dye have
been attempted, such as tethering additional conjugate moi-
eties on bipyridyl ligand for increasing the light absorp-
tion,12–17 tethering hydrophobic aliphatic long chains on
bipyridyl ligand to prolong the service life,18 and tethering tri-
ethylene oxide methyl ether groups on bipyridyl ligand for
enhancing the photocurrent and service stability.19,20
system leads to better performance of the DSSCs.29 The DSSC
with the electrolyte system gelled by poly(methylacrylate)
(PMA, Tg ¼ 6 ꢀC) had a power efficiency of 7.17%, close to
that with liquid electroyte system. The second is that the typi-
cal ruthenium dyes contain carboxylate groups which were
designed to adsorb onto the nano-porous TiO2 layer render-
ing the excited electrons straightforwardly injected into the
conduction band of the TiO2.8 However, during service those
ruthenium dyes are prone to desorb from TiO2 surface owing
to the fact that they are surrounded by the electrolytes.
To overcome this potential problem, we designed a crosslink-
able ruthenium dye by tethering aliphitic side chains carry-
ing allyl groups on one of the bipyridyl ligands so that they
can be crosslinked after applying onto the TiO2 layer. We
expect that the dissolution of the dye by electrolyte system
during service can be alleviated. Accordingly, in this contri-
bution Ru(2,20-bipyridine-4,40-bicarboxylic acid)(4,40-bis(11-
dodecenyl)-2,20-bipyridine)(NCS)2, denoted as Ru-C was syn-
thesized with 4,40-bis(p-dodec-11-enyl)-2,20-bipyridine as a
ligand that carries allyl groups for crosslinking. After its
crosslinking properties were investigated by ultraviolet-visi-
ble (UV-vis) absorption and Fourier-transform infrared spec-
troscopies, its was applied to the DSSC with the PMA-gelled
electrolyte system. Methylacrylic acid (MAA) monomers were
also employed to participate in the crosslinking reactions of
Ru-C being adsorbed on the TiO2 layer. The photovoltaic per-
formance of resulting DSSCs shows that they could not only
However, the original designed DSSC has two potential prob-
lems that are detrimental to its long-term survice life. The
first is the leakage and evaporation problems of liquid elec-
trolyte used in the DSSC. Varieties of polymers and their
nanocomposites have been attemped to gel the electrolye sys-
tem so that the leakage preblem can be prevented.21,24–28
Recently, we have reported that utilizing the polymer with
lower glass transition temperature (Tg) to gel the electrolyte
Correspondence to: K.-F. Lin (E-mail: kflin@ccms.ntu.edu.tw)
C
V
Journal of Polymer Science: Part A: Polymer Chemistry, Vol. 48, 366–372 (2010) 2009 Wiley Periodicals, Inc.
366
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ARTICLE
attain more than 5% of power conversion efficiency at AM
1.5 illumination (100 mW/cm2), but also possess a good
long-term stability.
EXPERIMENTAL
Materials
All solvents and chemicals were obtained from Acores and
Aldrich. Cis-di(thiocyanato)bis(2,20-bipyridyl-4,40-dicarboxy-
late)-ruthenium(II) dye was a commercial product by the
trade name N3 obtained from Solaronix S. A., Ambones, Swit-
zerland. Ru-C was synthesized by the typical one-pot syn-
thetic method developed for heteroleptic polypyridyl ruthe-
nium complexes10 as illustrated in Figure 1.
Synthesis of 11-Iodoundec-1-ene (1)
Triphenylphosphine (Acros, 78 mmol), imidazole (Acros, 78
mmol), and iodine (Acros, 78 mmol) were successively
added to 10-undecen-1-ol (Aldrich, 39 mmol) in a mixture of
diethylether/acetonitrile (225 mL/75 mL) with stirring. After
reaction for 20 min, ꢁ500 mL of diethylether was added,
and the mixture was filtered on celite. The yellow solution
recovered was washed with a saturated sodium bicarbonate
solution and brine, dried over magnesium sulfate, filtered,
and concentrated by rotary evaporation. The crude oil was
purified by flash chromatography on silica gel using hexane
1
to yield 11-iodoundec-1-ene (10.8 g, 98%) as an oil. H NMR
(500 MHz, CDCl3,): d 1.28–1.37 (m, 12H), 1.78–1.85 (m, 2
H), 2.01–2.06 (m, 2 H), 3.17–3.20 (t, 2H), 4.92–5.01 (m, 2H),
5.76–5.84 (m, 1H).
FIGURE 1 Synthesis scheme of Ru-C.
Synthesis of 4,40-Di(11-dodecenyl)-2,20-bipyridine (2)
A solution (45.6 mL) of 1.6 M n-butyllithium in hexane
(Acros) was added, via a syringe, to a solution of diisopro-
pylamine (72.9 mmol) in 24 mL of tetrahydrofuran at 0 ꢀC
1H-NMR (500 MHz, d6-DMSO): d 7.90(d, 1H), 8.84(s, 1H),
8.90(d, 1H).
with stirring.31 After
1
h, 4,40-dimethyl-2,20-bipyridine
Synthesis of Ru-C (4)
(Aldrich, 27.5 mmo1) in 150 mL of tetrahydrofuran was
added dropwise and the resulting dark red-orange mixture
was kept stirring at 0 ꢀC for 3 h. Then, 11-iodoundec-1-ene
(55 mmol) in 40 mL of tetrahydrofuran was added slowly
To a solution of 0.176 mmol [RuCl2(p-cymene)]2 (Aldrich) in
30 mL dry DMF was added ꢀ0.352 mmol compound 2 with
stirring. After reaction at 80 C under argon for 4 h at dark,
0.352 mmol of compound 3 was added. After refluxed at
ꢀ
via a syringe at 0 C. After reaction for 3 h at the same tem-
ꢀ
160 C for another 4 h, excess NH4NCS (Acros) was added to
perature, it was quenched with 10 mL of methanol. The
obtained clear yellow-brown solution was poured into cold
water and then extracted by diethylether. After removal of
diethylether, the product was recrystallized from hexane.
(7.0 g, 59%) 1H NMR (500 MHz, CDCl3): d 1.25–1.33 (m,
24H), 1.63–1.73 (m, 4H), 1.99–2.06 (m, 4H), 2.67 (t, 4H),
4.90–5.01 (m, 4H), 5.74–5.85 (m, 2H), 7.13 (d, 2H), 8.25 (s,
2H), 8.55 (d, 2H).
ꢀ
the reaction mixture. The reaction proceeded at 130 C for 5
h and then the solvent was removed using a rotary-evapora-
tor under vacuum. Water was added to the resulting mixture
to remove excess NH4NCS. The water-insoluble product was
collected on a sintered glass crucible by suction filtration
and washed with distilled water, followed by diethylether
and dried in air. The crude product was dissolved in metha-
nol and then passed through the Sephadex LH-20 column
using methanol as the eluent. The main band was collected
and concentrated. A few drops of 0.01 M HNO3 aqueous so-
lution were added to precipitate the product. 1H-NMR (500
MHz, d6-DMSO): d 1.20–1.33 (m, 24H), 1.53–1.80 (m, 4H),
1.97–2.00 (m, 4H), 2.62 (t, 2H), 2.91 (t, 2H), 4.90–4.98 (m,
4H), 5.73–5.80 (m, 2H), 7.08 (d, 1H), 7.32 (d, 1H), 7.63 (d,
1H), 7.82 (d, 1H), 7.85 (d, 1H), 8.30 (d, 1H), 8.54 (s, 1H),
8.70 (s, 1H), 8.95 (s, 1H), 9.07 (d, 1H), 9.10 (s, 1H), 9.46 (d,
1H). Anal for C48H60N6O4RuS2 calcd.: C, 60.67, H, 6.36, N,
8.84%, found: C, 59.89, H, 6.53, N, 8.37%.
Synthesis of 4,40-Dicarboxy-2,20-bipyridine (3)
To a solution of 16.3 mmol Na2Cr2O7 (Acros) in 25 mL con-
centrated sulfuric acid was slowly added 4 mmol of 4,40-di-
methyl-2,20-bipyridine with stirring. After 30 min, the reac-
tion mixture was poured into 200 mL of cold water forming
a light yellow precipitate. After filtration and drying, the
obtained solid was dissolved in 10% NaOH aqueous solution
followed by slow acidification (pH ¼ 2) with 10% HCl aque-
ous solution. After a second filtration the compound was
dried under vacuum to afford a white solid. (1.06 g, 80%)
CROSS-LINKABLE RUTHENIUM COMPLEX DYE, LIU ET AL.
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JOURNAL OF POLYMER SCIENCE: PART A: POLYMER CHEMISTRY DOI 10.1002/POLA
Fabrication of DSSCs
vents. Elemental analysis was conducted by HERAEUS
VarioEL EA, NCH elemental analysis instrument. UV-vis
absorption spectra were recorded on a Jasco model 555
spectrometer. FT-IR spectra were recorded on a Jasco model
480 Fourier-transform infrared spectrometer. Cyclic voltam-
Dye-sensitized solar cells were fabricated using fluorine-
doped tin oxide (FTO) glass (20–25 X/cm2) as a substrate
for photoelectrode. To prepare a mesoporous anatase TiO2
layer coated on the FTO glass by sol-gel process, 72 mL tita-
nium isopropoxide (TTIP, Aldrich) was added to 430 mL of
0.1 M HNO3. After vigorously stirring for 30 min, the solu-
tion was heated to 85–90 ꢀC and kept stirring for 8 h for
peptization. After filtering to remove the large particles, the
solution was placed in the autoclave for reaction at 240 ꢀC
for 12 h. After cooling, it was concentrated to 13 wt % of
TiO2. Poly(ethylene glycol) was then added to the solution in
30 wt % of TiO2 weight. After further stirring for 5 h to
obtain the TiO2 paste, it was spread on the FTO glass sub-
tract using a glass rod and an adhesive tape was used as a
spacer to control the thickness to ꢁ120 lm. The photoelec-
trode was obtained by heating the TiO2 on the FTO glass in
mogram was recorded on
a
potentiostat/galvanostat
(PGSTAT 302N, Autolab, Eco-Chemie, the Netherlands) using
the platinum as counter electrode and Ag/AgCl as reference
electrode in acetonitrile with 0.1 M tetra-butylammonium
tetrafluoroborate at a scan rate of 100 mV/s. Photovoltaic
characterization of the DSSCs was carried out by illuminating
the cell with a 1000 W ozone-free Xenon lamp equipped
with a water-based IR filter and AM 1.5 filter (Sciencetech).
The open circuit voltage (Voc) and photocurrent-voltage char-
acterization plots were recorded with a potentiostat/galvano-
stat (PGSTAT 302N, Autolab, Eco-Chemie, the Netherlands).
ꢀ
an oven at 450 C for 30 min and repeating the coating and
RESULTS AND DISCUSSION
heating process two more times to complete the sintering
process. An active area of 0.25 cm2 TiO2 was selected from
sintered electrode, immersed in a solution of acetonitrile and
Characteracation and Crosslinking Properties of
Ru-C Dye
Figure 2 shows the 1H NMR spectrum of Ru-C with the
asigned aromatic and vinyl protons. Notably, all of the pyridyl
rings in two different ligands are electronically in different
environment. Any two symmetrical pyridyl ring protons in a
bipyridine ligand have two different reasonance peaks, indi-
cating that the ligands are coordinated to ruthenium center in
cis-heteroleptic complex form.36 Besides, the vinyl protons in
the aliphatic side chains can be clearly seen at d ¼ 4.90–4.98
ppm and d ¼ 5.73–5.80 ppm. Figure 3 shows the 13C NMR
spectrum of Ru-C with the asigned carbons for the aromatic,
carboxlic acid, NCS, and vinyl groups. Twenty resonance
peaks in the aromatic region from two bipyridine ligands, two
peaks from two carboxylic acids, and two peaks from two
NCS groups also supported that the ligands are coordinated
to ruthenium center in cis form. The resonance peaks at d ¼
114 and 138 were contribued by the vinyl carbons.
tertiary butanol (volume ratio of 1:1) containing 3 ꢂ 10ꢃ4
M
of Ru-C for 24 h, rinsed with acetone, and dried. After that,
two drops of 1 ꢂ 10ꢃ5 M azobisisobutyronitrile (AIBN,
Acros) initiator in hexane (or acetonitrile) was applied on
top of the Ru-C layer, which was immediately polymerized
under UV exposure at 300 W/m2 for 1 min and followed by
ꢀ
heating under 50 C for 20 min to remove the remaining sol-
vent. To copolymerize with methylacrlylic acid (MAA) mono-
mers, the AIBN solution was combined with 1 ꢂ 10ꢃ3
M
MAA (Acros). Besides, for comparison, N3 dye coating on
mesoporous anatase TiO2 thin film was also prepared in the
same method but without treatment of AIBN and UV expo-
sure. The counter electrode was fabricated by sputtering a
thin Pt layer with a thickness of ꢁ100 nm on indium tin ox-
ide (ITO, with a sheet resistivity of 8–10 X/square) glass
plate. The electrolyte solution containing proper amounts of
LiI, I2, and 4-tert-butylpyridine (TBP, Acros) in acetonitrile
was prepared in dry box first. Then, the dried polymethylac-
rylate (PMA) powder prepared by soap-free emulsion poly-
merization32–35 was added to the electrolyte solutions at an
amount of 25 vol % of acetonitrile, which were then heated
FT-IR spectrum of Ru-C in KBr pallet is shown in Figure 4.
Notably, the major absorption band at 2100 cmꢃ1 was con-
tributed by the stretching of ꢃNSC groups, that at 1723
cmꢃ1 was contributed by carboxylic acid groups, and those
at around 2800 and 2900 cmꢃ1 were contributed by the ali-
phatic chains tethering to the bipyridine ligand. The absorp-
tion bands contributed by the vinyl groups of Ru-C dye can
be clearly seen at 907 and 3070 cm-1. To investigate the
reactivity of the vinyl groups, a drop of the Ru-C solution
with AIBN (1 mol % of Ru-C) in acetonitrile was dripped on
the glass slide, which was immediately polymerized under
UV exposure at 300 W/m2 for 1 min and followed by heating
under 50 ꢀC for 20 min to remove the remaining solvent.
The crosslinked Ru-C which could not be dissolved in any
solvent was collected for FT-IR measurement in KBr pallet.
Compared with the untreated Ru-C by normalizing the spec-
trum to the major absorption band at 2100 cmꢃ1 (Fig. 4),
the vinyl peaks at 907 and 3070 cmꢃ1 were significantly
reduced, indicating that the vinyl groups were able to per-
form the crosslinking reactions. Although diallyl monomers
have long been used to produce a range of thermoset
ꢀ
to 50 C with sonication until the solutions were homogene-
ously gelled. The final concentrations of the PMA-gelled elec-
trolytes were 0.5 M LiI, 0.05 M I2, and 0.5 M TBP. To seal
the DSSCs, a hot melt sealing foil SX1170–60 (SOLARONIX)
was center-cut and placed on top of the counter electrode to
form a frame for enclosing the coated dye, and then the pho-
toelectrode was placed on top of the frame. Both electrodes
were assembled by melting the sealing foil with heat. The
gelled electrolytes after heating to fluid was injected from a
small filling hole which was predrilled on the counter elec-
trode. At last, the filling hole was sealed with hot melt foil.
Analytical Methods
Nuclear magnetic resonance spectra were recorded on a
ꢀ
Bruker AVANCE 500 spectrometer at 25 C by utilizing deu-
terated chloroform or dimethyl sulphoxide (d6-DMSO) as sol-
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ARTICLE
FIGURE 2 1H-NMR spectrum of Ru-C.
products,37 it should be noted that the reactivity of allyl
groups depends on their reaction conditions and containing
compounds.
DSSC specimens except that the glass plate was used instead
of the FTO glass. The 66% of crosslinked Ru-C dye still
remained on the TiO2 mesoporous layer after immersed as
estimated by the absorption peak at 520 nm wavelength,
whereas the non-crosslinked N3 dye has been completely
removed. Interestingly, as MAA monomers were combined
with AIBN initiator to crosslink with Ru-C, the remained
Ru-C on the mesoporous layer increased to 77% (Fig. 5). It
suggested that copolymerization of MAA with Ru-C during
crosslinking reaction to form crosslinked Ru-C-co-MAA would
increase the extent of crosslinking reactions for Ru-C.
Because the ruthenium dyes anchored to the mesoporous
TiO2 surface using two carboxylic groups,38 the allyl groups
in the end of aliphatic side chains should be away from the
The crosslinked Ru-C dye was able to resist its desorption
from the TiO2 mesoporous layer by 0.1 N NaOH in EtOH/ter-
tiary butanol/H2O (volumn ratio 1:1:1) solution, which was
usually employed to remove the ruthelium dye for measure-
ment of the dye content adsorbing on TiO2 mesoporous
layer.8 Figure 5 shows the UV-vis absorption spectra of
crosslinked Ru-C, crosslinked Ru-C-co-MAA, and N3 dyes,
respectively adsorbing on the TiO2 mesoporous layer before
and after immersed in the aforementioned solution for 1
min and then fully rinsed with water. The samples were pre-
pared by the same method as that for preparation of the
FIGURE 3 13C-NMR spectrum of Ru-C.
CROSS-LINKABLE RUTHENIUM COMPLEX DYE, LIU ET AL.
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JOURNAL OF POLYMER SCIENCE: PART A: POLYMER CHEMISTRY DOI 10.1002/POLA
FIGURE 6 Cyclic voltammograms of crosslinked Ru-C and Ru-
C-co-MAA.
FIGURE 4 FT-IR spectra of Ru-C (a) before and (b) after
crosslinked.
Fcþ/Fc redox couple determined by the same voltammetric
cell was found to be 0.36 V. Since the ionic potential of Fc is
4.8 eV,41 the highest occupied molecular orbital (HOMO)
energy levels of crosslinked Ru-C and Ru-C-co-MAA dyes
would be ꢃ5.37 and ꢃ5.35 eV, respectively. On the other
hand, the band gaps of both crosslinked Ru-C and Ru-C-co-
MAA dyes estimated from the absorption edge of their UV-vis
absorption spectra shown in Figure 4 are 1.8 eV. Thus, the
LUMO of crosslinked Ru-C and Ru-C-co-MAA would be ꢃ3.57
and ꢃ3.55 eV, respectively, which are both higher than the
conduction band edge of TiO2 (ꢃ4.0 eV).9 The excited elec-
trons by light absorption would be thermodynamically favored
to inject into the conduction band of the TiO2. Moreover, the
TiO2 surface due to the hydrophobic effect. Notably, our lab
recently verified that only single layer of Ru-C molecules
with the thickness of 2.6 nm was able to adsorb onto the
sintered anatase TiO2 surface.39 The deposition of MAA
monomers on top of the Ru-C layer would directly involve
the crosslinking reaction of Ru-C.
Photovoltaic Properties of Crosslinked Ru-C Dye
Crosslinkable optoelectronic polymers have been frequently
employed as an active emitting material for polymeric light
emitting diode and exhibit excellent thermal stability, me-
chanical strength, and device performace.40 However, to our
knowledge, this is the first report of the crosslinkable ruthe-
nium dye ever applying to the DSSC. The cyclic voltammo-
grams of crosslinked Ru-C and Ru-C-co-MAA dyes, respec-
tively adsorbing on TiO2 mesoporous layer were shown in
HOMO of the dye is lower than the oxidation potential of I-/I3
-
redox couple (ꢃ4.6 eV vs. vacuum),42 leading to fast dye
regeneration.
The DSSCs with PMA-gelled electrolyte system were then fab-
ricated to investigate the photovoltaic performance of cross-
linked Ru-C and Ru-C-co-MAA dyes, respectively. The concen-
trations of the PMA-gelled electrolytes were 0.5 M LiI, 0.05 M
Figure 6, by which their estimated half-wave potentials (E1/2
)
of RuII/III couple are 0.93 and 0.91 V. Notably, the E1/2 of
FIGURE 7 Photocurrent-voltage plots of the DSSCs with cross-
linked Ru-C and Ru-C-co-MAA, respectively under AM 1.5 radi-
ation (100 mW/cm2).
FIGURE 5 Absorption spectra of crosslinked Ru-C, Ru-C-co-
MAA, and N3 dyes before and after rinsed with 0.1N NaOH in
EtOH/tertiary butanol/H2O (volume ratio 1:1:1).
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ARTICLE
with crosslinked Ru-C-co-MAA increased 5% and that with
crosslinked Ru-C increased 1%. On the other hand, the DSSC
with N3 dye decreased to 55% of its original value. Notably,
although many ruthenium dyes have been reported possess-
ing excellent service stability,20,43–45 few of them have stayed
in higher power efficiency than their initial value after long-
term test. The increase of power efficiencey for the DSSCs
with crosslinked dyes was due to the increase of photocur-
rent. Voc barely changed. Gra¨tzel and coworker43 have
reported for the aging of DSSCs with K-19 and Z-907 dyes at
ꢀ
80 C that both power efficiency and short-circuit photocur-
rent increased in the initial stage of aging. It was demos-
trated to be due to the faster dye regeneration after aging by
using transit absorbance decay kinetics of the oxidized state
of the dyes adsorbed on nanocrystalline TiO2 films and
attributed to the excess penetration of electrolytes into the
pores of mesoporous TiO2 layer. Similar to their assessment,
the increase of power efficiency during the initial storage of
our DSSCs might be due to the excess penetration of gelled
electrolytes into the pores of mesoporous TiO2 layer contain-
ing crosslinked dyes. Notably, our DSSCs with both cross-
linked dyes remained in higher power efficiencies than their
initial values after 30 days of storage test. In contrast, the
power efficiencey of the DSSC with N3 dye was rapidly
decreased after 2 weeks. The results strongly suggested that
the DSSCs with crosslinked Ru-C and Ru-C-co-MAA dyes,
respectively had longer service life compared with that with
traditional N3 dye.
FIGURE 8 Time-course changes of power efficiencies for various
DSSCs with the indicated dyes. [Color figure can be viewed
in the online issue, which is available at www.interscience.
wiley.com.]
I2, and 0.5 M TBP. Their typical photocurrent-voltage charac-
teristics were shown in Figure 7. The average short-circuit cur-
rent density (Jsc) and open circuit voltage (Voc) of DSSCs with
crosslinked Ru-C were 11.1 6 1.42 mA/cm2 and 0.68 6 0.03 V
with a fill factor (ff) of 0.67 6 0.03. The average power effi-
ciency (g) was 5.1 6 0.37%. Whereas, the DSSCs with cross-
linked Ru-C-co-MAA have Jsc ¼ 12.52 6 0.72 mA/cm2, Voc
¼
0.67 6 0.01 V, ff ¼ 0.63 6 0.01 and g ¼ 5.18 6 0.19%. The
incorporation of MAA to crosslink with Ru-C has brought
higher current density but slightly lower Voc and fill factor,
leading to a barely increased power efficiency. Because the
polymerized MAA units that contain carboxylic acid were able
CONCLUSIONS
The synthesized Ru-C dye can be crosslinked by itself or
with MAA monomers through its allyl groups. By using the
PMA-gelled electrolyte system, the DSSC with crosslinked
Ru-C attained Jsc ¼ 11.1 6 1.42 mA/cm2, Voc ¼ 0.68 6 0.03
V, ff ¼ 0.67 6 0.03, and g ¼ 5.1 6 0.37% under AM 1.5 and
100 mW/cm2 illumination, whereas that with crosslinked
to attract I3 /I- redox couples in the gelled electrolyte system,
-
it enhanced the dye regeneration so as to increase the photo-
current. However, it also implies that the dark current would
be increased so that both the open circuit voltage and fill fac-
tor were decreased. On the other hand, it is noteworthy here
that we may choose other monomers with certain functional
groups to crosslink with Ru-C to fabricate the DSSC with the
desired properties. The application of this novel technique is
conceivably versatile.
Ru-C-co-MAA acquired Jsc ¼ 12.52 6 0.72 mA/cm2, Voc
¼
0.67 6 0.01 V, ff ¼ 0.63 6 0.01 and g ¼ 5.18 6 0.19%. For
the time-course change test of power efficiency in storage,
both DSSSCs showed an initial increase of power efficiencies
and then stayed almost unchanged for a month, whereas
that with N3 dye showed a rapid decrease of efficiency in 2
weeks. This extraordinary stability of the DSSCs with cross-
linked Ru-C and Ru-C-co-MAA, respectively has shed a light
on their potential application for outdoor use.
The crosslinked Ru-C and Ru-C-co-MAA dye-sensitized DSSCs,
respectively with PMA-gelled electrolyte sysetem were then
subjected to measure the long-term stability along with the
N3 dye for comparison. All the samples were sealed with hot
melt foil and stored at ambient environment. At chosen time
intervals, the samples were taken to measure the power effi-
ciency at room temperature under AM 1.5 and 100 mW/cm2
illumination. The power efficiencies of three samples at dif-
ferent storage time shown in Figure 8 were normalized to
their intial measured values. The results show that the effi-
ciences of all three cells in the initial storge stage fluctuated
with time. Notably, those with crosslinked Ru-C and Ru-C-co-
MAA dyes slightly increased whereas that with N3 dye
decreased. After 720 h of storage time, the efficiency of DSSC
The authors thank for the financial support of the National Sci-
ence Council in Taiwan, Republic of China, through Grantes
NSC95-2221-E-002-206 and NSC 96-2120-M-002-016.
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