A light-resistant organic sensitizer for solar-cell applications

Article abstract of DOI:10.1002/anie.200804719

(Figure Presented) Finely tuned: A stable dye-sensitized solar cell that contains a molecularly engineered organic dye has been prepared. The efficiency of the cell remains at 90% after 1000 h of light soaking at 60 °C. The remarkable stability of the cel

Full text of DOI:10.1002/anie.200804719

Communications
DOI: 10.1002/anie.200804719
Molecular Solar Cells
A Light-Resistant Organic Sensitizer for Solar-Cell
Applications**
Jun-Ho Yum, Daniel P. Hagberg, Soo-Jin Moon, Karl Martin Karlsson,
Tannia Marinado, Licheng Sun,* Anders Hagfeldt, Mohammad K. Nazeeruddin,*
and Michael Grꢀtzel
Angewandte
Chemie
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The conversion of sunlight to electricity by using dye-
sensitized solar cells (DSCs) represents one of the most
promising methods for future large-scale power production
from renewable energy sources.[1] The sensitizer, which
harvests the solar radiation and converts it to electric current,
is one of the key components of these cells. Over the last
17 years, ruthenium complexes have exhibited remarkable
efficiency and stability in DSCs. However, there are several
challenges that limit their development for large-scale
applications. Therefore, several research groups have devel-
oped metal-free organic sensitizers and obtained respectable
efficiencies compared to the ruthenium sensitizers.[2] The
main disadvantage of the organic sensitizers is their stability,
which is generally lower than that of metal complexes,
because of side reactions such as formation of excited triplet
states and unstable radicals. Herein, we report a meticulously
engineered organic sensitizer that exhibits not only an
efficiency that is superior to that of ruthenium sensitizers in
solid DSCs but also remarkable stability under light- and
heat-soaking conditions with liquid electrolyte where the
overall efficiency of the DSC remained at 90% of the initial
value after 1000 hrs.
The organic sensitizer 3-(5-(5-(4-(bis(4-(hexyloxy)phe-
nyl)thiophene-2-yl)thiophene-2-yl)-2-cyanoacrylic acid (D21-
L6) was synthesized by following the procedure reported by
Plater and Jackson, in which aniline was functionalized by the
Ullmann arylation.[3] In our case, a disubstituted triphenyl-
amine 2 was utilized, which was then brominated by N-
bromosuccinimide (NBS) to give the disubstituted triphenyl-
amine bromide 3 (Scheme 1). The first Suzuki coupling
reaction[4] was carried out with 2-thienylboronic acid and
substituted triphenylamine bromide 1 under microwave
irradiation. The thiophene moiety was brominated at the
fifth position with NBS to provide 3. The second Suzuki
coupling reaction was carried out with unprotected 5-formyl-
Scheme 1. Synthesis of the D21L6 sensitizer. Reagents and conditions:
a) 2-thienylboronic acid, [Pd(dppf)Cl2], K2CO3 toluene/MeOH (3:2),
758C, mw, 64%; b) NBS, THF, 08C, 77%; c) 5-formyl-2-thiophenebor-
onic acid, [Pd(dppf)Cl2], K2CO3, toluene/MeOH (3:2), 758C, mw, 45%;
d) cyanoacetic acid, piperidine, MeCN, reflux, D21L6: 70% (step d).
mw=microwave irradiation.
2-thiopheneboronic acid under microwave irradiation to
directly produce the aldehyde 4, which was necessary for
the following reaction.[5] The final reaction was condensation
of the aldehyde with cyanoacetic acid by the Knoevenagel
reaction in presence of piperidine. The bridging thiophene
units are used to provide conjugation between the donor
triphenylamine and the anchoring cyanoacetic acid group.
The hydrophobic hexyloxy groups are attached to the donor
group in order to reduce the aggregation and enhance the
solubility of the sensitizer.
[*] D. P. Hagberg, K. M. Karlsson, Prof. L. Sun
Center of Molecular Devices, Organic Chemistry
Royal Institute of Technology
Teknikringen 30, 10044 Stockholm (Sweden)
Fax: (+46)8-791-2333
E-mail: lichengs@kth.se
The D21L6 sensitizer shows an absorption maximum in
the visible region at 458 nm, with a high molar extinction
coefficient (e = 37000mÀ1 cmÀ1), which arises from p–p*
charge transfer (CT) transitions (Figure 1). The cyclic vol-
tammogram of the D21L6 sensitizer measured with a 0.1 VsÀ1
scan rate in acetonitrile containing tetrabutylammonium
tetrafluoroborate (0.1m) shows a reversible couple that
arises from oxidation of the substituted triphenylamine–
bithiophene groups at 0.98 V versus the normal hydrogen
electrode (NHE). The excited-state oxidation potential of the
sensitizer, which is À1.35 V versus NHE, as obtained from the
absorption and emission spectra of D21L6, plays an important
role in the electron injection process. The excited state
oxidation potential is notably more negative than the TiO2
conduction band. On the other hand, the oxidation potential
Dr. J.-H. Yum, S.-J. Moon, Dr. M. K. Nazeeruddin, Prof. M. Grꢀtzel
LPI, Institut des Sciences et Ingꢁnierie Chimiques
Facultꢁ des Sciences de Base
ꢂcole Polytechnique Fꢁdꢁrale de Lausanne
1015 Lausanne (Switzerland)
Fax: (+41)21-693-4111
E-mail: mdkhaja.nazeeruddin@epfl.ch
T. Marinado, Prof. A. Hagfeldt
Center of Molecular Devices, Physical Chemistry
Royal Institute of Technology, Stockholm (Sweden)
[**] We acknowledge financial support of this work by the Swiss Federal
Office for Energy (OFEN), the Korea Foundation for International
Cooperation of Science & Technology through the Global Research
Lab, the Swedish Energy Agency, the Swedish Research Council, and
the Knut and Alice Wallenberg foundation. (G.R.L.) Program funded
by the Ministry of Science and Technology. We thank Lien-Hoa Tran
(Stockholm University) for the HRMS measurements and Dr. Robin
Humphry-Baker, Dr. S. M. Zakeeruddin, Dr. Peter Pꢁchy, Pascal
Comte, and Dr. Paul Liska for their kind assistance.
À
of D21L6 is more positive than the IÀ/I3 redox couple
(ca. 0.4 V versus NHE), which ensures that there is a
sufficient driving force for electron injection, and for the
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lyte. The IPCE data of D21L6 plotted as a function of
excitation wavelength exhibit a high plateau value of 90%.
Strikingly, the IPCE is still close to 90% at 600 nm where the
light absorption of the sensitizer in solution is negligibly small.
This important red shift in the photocurrent response is
attributed to lateral interaction in the adsorbed monolayer of
the sensitizer and warrants further analysis. Under standard
global AM 1.5 solar conditions, the D21L6-sensitized cell
gave a short-circuit photocurrent density value (Jsc) of
14.10 mAcmÀ2, an open-circuit voltage value (Voc) of
728 mV and a fill factor (ff) of 0.71, which correspond to an
overall conversion efficiency h, derived from the equation h =
Jsc ꢀ Voc ꢀ ff/light intensity, of 7.25%. The DSC demonstrated
an almost-linear behavior under different light intensities
(Table 1). The integrated current of IPCE is 14.2 mAcmÀ2
which is consistent with Jsc of 14.1 mAcmÀ2 under standard
global AM1.5 solar conditions.
Figure 1. Normalized UV/Vis absorption (solid line) and emission
(dashed line) spectra of D21L6 in ethanol.
dye regeneration reaction to compete efficiently with recap-
ture of the injected electrons by the dye cation radical.
The photovoltaic performance characteristics of D21L6-
sensitized solar cells with liquid and solid-state electrolyte are
shown in Figure 2a,b. The incident monochromatic photon-
to-current conversion efficiency (IPCE) and current–voltage
(J/V) characteristics were obtained with a sandwich cell
comprising N-methyl-N-butyl imidazolium iodide (0.6m),
iodine (0.04m), LiI (0.02m), guanidinium thiocyanate
(GuNCS, 0.05m), and tert-butylpyridine (0.28m) in a valero-
nitrile/acetonitrile mixture (15:85 v/v) as the liquid electro-
Table 1: J/V characteristics of D21L6-sensitized solar cells with either
volatile or solid-state electrolytes under different light intensities.
Intensity [% sun]
J
sc [mAcmÀ2
]
Voc [mV]
ff
h [%]
9.30
51.62
100.19
9.32
51.26
99.52
1.39
7.50
14.10
0.78
4.83
9.64
666
712
728
740
791
798
0.77
0.74
0.71
0.73
0.62
0.57
7.49
7.45
7.25
4.51
4.64
4.44
liquid
solid
For the solid-state dye-sensitized solar cells (SSDSCs), a
2,2’,7,7,’-tetrakis(N,N-dimethoxyphenylamine)-9,9’-spirobi-
fluorene (spiro-MeOTAD) hole conductor was used as a
redox couple.[6] The SSDSC exhibited Jsc = 9.64 mAcmÀ2,
Voc = 798 mV, and ff = 0.57, which led to an overall conversion
efficiency, h, of 4.44% under standard global AM 1.5 solar
conditions, which is a high value for a SSDSC based on
organic[6a] and ruthenium sensitizers reported to date.[7] After
submission of this manuscript a D-p-A sensitizer employing a
fused thiophene dimer unit as a p bridge was reported that
reached 4.8% conversion efficiency in a SSDSC.[2h] The IPCE
value of the SSDSCs was 54% at 460 nm (Figure 2a), which is
somewhat lower than the IPCE over 500–620 nm of liquid
DSCs; this arises from a lower light-harvesting yield because
of the use of a thinner TiO2 film. When the film thickness
(1.7 mm) of TiO2 is considered, the results from D21L6 are
promising with regards to applications in solid-state cells. A
further advantage of the solid-state devices is the Voc value
obtained (798 mV), which is higher than that of the liquid-
electrolyte cells (728 mV). This is not only due to the redox
level of the hole conductor, which is more positive than the
respective IÀ/I3À couple used in the latter but also because of
the thinner TiO2 film which helps to decrease the dark
current.
Figure 3 shows the photovoltaic performance during a
long-term accelerated aging of a D21L6-sensitized solar cell
using an ionic liquid electrolyte in a solar simulator at full
intensity (100 mWcmÀ2) and 608C. The Jsc, Voc, ff, and h
values were recorded over a period of 1000 h (Table 2). The
overall efficiency remained at 90% of the initial value after
1000 h of light soaking at 608C. This 10% decrease is caused
Figure 2. a) Photocurrent action spectrum and b) current–voltage char-
acteristics of D21L6-sensitized solar cells with volatile (solid lines) and
solid-state electrolyte (dashed lines).
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Chemie
recorded on Bruker 500 and 400 MHz instruments by using the
residual signals d = 7.26 ppm and 77.0 ppm from CDCl3, d = 2.50 and
39.4 ppm from [D6]DMSO and d = 2.05, 29.84, and 206.26 ppm from
[D6]acetone, as internal references for 1H and 13C respectively. HRMS
were performed using a Q-Tof Micro (Micromass Inc., Manchester,
England) mass spectrometer equipped with a Z-spray ionization
source.
4-Bromo-N,N-bis(4-hexoxylphenyl)aniline (1): Aniline (1.02 g,
10.4 mmol), copper powder (0.919 g, 10 mmol), K2CO3 (16.36 g,
118 mmol), 18-crown-6 (50 mg), and 1-(hexyloxy)-4-iodobenzene
(18.0 g, 303.9 mmol) was heated to reflux at 1908C with stirring
under a nitrogen atmosphere for 48 h. The reaction mixture was
allowed to cool to ambient temperature and was dissolved in CH2Cl2.
The solution was washed with distilled water the organic phase was
dried with MgSO4 and concentrated by evaporation. Column
chromatography using petroleum ether/DCM 9:1 gave N,N-bis-(4-
hexoxylphenyl)aniline as a pale yellow oil (2.05 g, 46%). A solution
of N,N-bis(4-hexoxylphenyl)aniline (1.485 g, 3.34 mmol) in THF
(20 mL) was cooled to 08C. NBS (562 mg, 3.34 mmol) was added in
one portion. The reaction mixture was stirred at 08C for 3 h. The
reaction was quenched by addition of water and extracted with DCM.
The combined organic extract was dried over anhydrous MgSO4 and
filtered. Solvent removal by rotary evaporation followed by column
chromatography over silica gel using petroleum ether/DCM 8:1
yielded 1 as a pale yellow oil (1.7 g, 96%). 1H NMR (500 MHz,
CDCl3): d = 7.22 (d, J = 8.6 Hz, 2H), 7.00 (d, J = 8.0 Hz, 4H), 6.81 (d,
J = 8.8 Hz, 4H), 6.78 (d, J = 9.4 Hz, 2H), 3.92 (t, J = 6.4 Hz, 4H), 1.77
(m, 4H), 1.45 (m, 4H), 1.34 (m, 8H), 0.91 ppm (t, J = 7.0 Hz, 6H).
13C NMR (125 MHz, [D6]acetone): d = 157.5, 150.9, 142.7, 130.7,
128.3, 122.3, 122.2, 117.1, 69.7, 33.3, 31.1, 27.5, 24.3, 15.3 ppm.
4-(hexyloxy)-N-(4-(hexyloxy)phenyl)-N-(4-(thiophene-2-yl)phe-
nyl)benzenamine (2): A solution of 2-thienylboronic acid (122 mg,
0.95 mmol) and K2CO3 (329 mg, 2.36 mmol) in dry methanol (2 mL)
was added to a solution of 1 (250 mg 0.48 mmol) and [Pd(dppf)Cl2]
(39 mg 0.048 mmol) in dry toluene (3 mL). The mixture was heated by
microwave irradiation at 758C for 20 min. The reaction was quenched
by the addition of water (30 mL) and extracted with CH2Cl2 (3 ꢀ
30 mL). The combined organic extracts were dried over anhydrous
MgSO4 and filtered. Solvent removal by rotary evaporation followed
by column chromatography over silica gel using petroleum ether gave
Figure 3. Variations of photovoltaic parameters (Jsc, Voc, ff, and h) with
aging time for the device based on (7+5) mm film sensitized with
D21L6 and ionic liquid electrolyte during successive 1 sun visible-light
soaking at 608C.
Table 2: J/V characteristics of the D21L6-sensitized solar cell with ionic-
liquid electrolyte during continuous 1 sun visible-light soaking at 608C.
Aging time [h]
J
sc [mAcmÀ2
]
Voc [mV]
ff
h [%]
0
500
1008
13.44
12.91
12.63
686
659
644
0.65
0.68
0.67
5.98
5.75
5.44
by the slight drop of 42 mV in the Voc and 0.8 mAcmÀ2 in the
Jsc values. An average of Jsc = 13.04 mAcmÀ2 during 1000 h of
light soaking means that the total charge passed through a
surface area of 1 cm2 is equal to 46944 coulombs. When a
surface concentration of 10À7 molescmÀ2 for the sensitizer is
used, a turnover number of 4.69 million can be derived, which
the D21L6 dye sustains without any noticeable decline in
performance. This demonstrates that the amount of dye on
the TiO2 surface remained intact after light soaking at 608C.
To the best of our knowledge, this is the most remarkable
stability for organic sensitizer.
In summary, we have demonstrated that meticulous
engineering of organic sensitizer, D21L6, yielded very high
incident monochromatic photon-to-current conversion effi-
ciency and remarkable stability, which we believe is a
breakthrough in the field of organic sensitizers useful for
photovoltaic applications. We conclude that the organic
sensitizer D21L6 is indeed a promising low-cost material for
dye-sensitized solar cells.
2
as a
pale yellow oil (168 mg, 64%). 1H NMR (500 MHz,
[D6]acetone): d = 7.45 (d, J = 8.7 Hz, 2H), 7.31 (d, J = 4.5 Hz, 1H),
7.27 (d, J = 4.5 Hz, 1H), 7.04 (d, J = 8.9 Hz, 4H), 6.90 (d, J = 8.9 Hz,
4H), 6.86 (d, J = 8.7 Hz, 2H), 3.9 (t, J = 6.4 Hz, 4H), 1.76 (m, 4H),
1.47 (m, 4H), 1.36 (m, 8H), 0.91 ppm (t, J = 7.0 Hz, 6H); 13C NMR
(125 MHz, [D6]acetone): d = 157.8, 150.4, 142.2, 129.9, 128.7, 128.2,
128.1, 125.4, 123.6, 121.8, 117.2, 69.8, 33.6, 31.0, 27.8, 24.3, 15.3. HRMS
(TOF-MS-ESI) m/z: 527.2847 [M+]; calcd for C34H41NO2S [M+]:
527.2858.
N-(4-(5-bromothiophen-2-yl)phenyl)-4-(hexyloxy)-N-(4-(hexy-
loxy)phenyl)benzenamine (3): NBS (144 mg, 0.81 mmol) was added
in one portion to a solution of 2 (426 mg, 0.81 mmol) in THF (10 mL)
at 08C. The reaction mixture was stirred at 08C for 3 h. The reaction
was quenched by the addition of water and extracted with DCM. The
combined organic extract was dried over anhydrous MgSO4 and
filtered. Solvent removal by rotary evaporation followed by column
chromatography over silica gel using petroleum ether/DCM 8:1 gave
3
as a
pale yellow oil (375 mg, 77%). 1H NMR (500 MHz,
[D6]acetone): d = 7.39 (d, J = 8.7 Hz, 2H), 7.09 (m, 1H), 7.06 (d, J =
8.9 Hz, 4H), 6.90 (d, J = 8.9 Hz, 4H), 6.83 (d, J = 8.7 Hz, 2H), 3.97 (t,
J = 6.4 Hz, 4H), 1.76 (m, 4H), 1.48 (m, 4H), 1.36 (m, 8H), 0.91 ppm
(t, J = 7.0 Hz, 6H); 13C NMR (125 MHz, [D6]acetone): d = 158.0,
150.9, 148.2, 141.9, 133.2, 128.9, 128.0, 126.9, 123.9, 121.4, 117.3, 110.6,
69.8, 33.3, 31.1, 27.5, 24.3, 15.3 ppm; HRMS (TOF-MS-ESI) m/z:
605.2006 [M+]; calcd for C34H40BrNO2S [M+]: 605.1958.
Experimental Section
Dichloromethane, dimethylformamide (DMF), hexane, and tetrahy-
drofuran (THF) were dried by passing through a solvent column
composed of activated alumina. 1H and 13C NMR spectra were
5-(5-(4-(bis(4-(hexyloxy)phenyl)amino)phenyl)thiophene-2-
yl)thiophene-2-carbaldehyde (4): Compound 3 (375 mg, 0.62 mmol),
Angew. Chem. Int. Ed. 2009, 48, 1576 –1580
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Communications
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(dppf)Cl2] (50 mg, 0.06 mmol), and K2CO3 (427 mg, 3.09 mmol)
were dissolved in a mixture of toluene (3 mL) and methanol
(2 mL). The mixture was heated by microwave irradiation at 758C
for 15 min. The reaction was quenched by the addition of water
(30 mL) and extracted with CH2Cl2 (3 ꢀ 30 mL). The combined
organic extracts were dried over anhydrous MgSO4 and filtered.
Solvent removal by rotary evaporation followed by column chroma-
tography over silica gel using petroleum ether/CH2Cl2 4:1 gave 4 as an
1
orange solid (178 mg, 45%). H NMR (500 MHz, [D6]acetone): d =
9.90 (s, 1H), 7.90 (d, J = 4.0 Hz, 1H), 7.50 (d, J = 8.7 Hz, 2H), 7.47 (d,
J = 3.9 Hz, 1H), 7.42 (d, J = 3.90 Hz, 1H), 7.32 (d, J = 3.9 Hz, 1H),
7.08 (d, J = 8.9 Hz, 4H), 6.85 (d, J = 8.9 Hz, 4H), 6.75 (d, J = 8.7 Hz,
2H), 3.99 (t, J = 6.5 Hz, 4H), 1.77 (m, 4H), 1.48 (m, 4H), 1.36 (m,
8H), 0.91 ppm (t, J = 6.9 Hz, 6H); 13C NMR (125 MHz, [D6]acetone):
d = 184.4, 158.1, 151.2, 148.3, 148.2, 143.5, 141.8, 140.1, 135.1, 129.5,
129.1, 128.3, 126.6, 125.9, 124.9, 121.1, 117.3, 69.8, 33.3, 31.1, 27.5, 24.3,
15.3 ppm; HRMS (TOF-MS-ESI) m/z: 637.2688 [M+]; calcd for
C39H43NO3S2 [M+]: 637.2679.
3-(5-(5-(4-(bis(4-(hexyloxy)phenyl)thiophene-2-yl)thiophene-2-
yl)-2-cyanoacrylic acid (D21L6). Compound 4 (178 mg, 0.28 mmol),
cyanoacetic acid (35 mg, 0.42 mmol), and piperidine (5 mg,
6.06 mmol) were dissolved in acetonitrile (10 mL) and heated under
reflux for 3 h. The solvent was removed by rotary evaporation.
Purification by extraction (petroleum ether and aqueous HCl (1%)
gave the final compound D21L6 (137 mg, 70%) as a dark red solid.
m.p. 144.7–145.28C. 1H NMR (500 MHz, [D6]DMSO): d = 8.25 (s,
1H), 7.78 (d, J = 4.0 Hz, 1H), 7.49 (m, 3H), 7.46 (d, J = 3.9 Hz, 1H),
7.36 (d, J = 3.8 Hz, 1H), 7.02 (d, J = 8.8 Hz, 4H), 6.90 (d, J = 8.8 Hz,
4H), 6.73 (d, J = 8.6 Hz, 2H), 3.92 (t, J = 6.4 Hz, 4H), 1.68 (m, 4H),
1.41 (m, 4H), 1.29 (m, 8H), 0.86 ppm (t, J = 6.9 Hz, 6H); 13C NMR
(125 MHz, [D6]DMSO): d = 163.4, 155.5, 148.5, 145.2, 143.6, 139.3,
138.9, 134.4, 132.7, 128.8, 128.1, 127.5, 127.0, 126.3, 125.2, 124.1, 123.3,
118.6, 117.9, 115.5, 67.6, 30.9, 28.6, 25.1, 22.0, 13.8 ppm; HRMS (TOF-
MS-ESI) m/z: 704.2707 [M+]; calcd. for C42H44N2O4S2 [M+]: 704.2737.
Solar-cell fabrication and characterization: The photoanodes
composed of nanocrystalline TiO2 were prepared according to a
previously reported procedure.[8] The TiO2 electrodes were immersed
in a solution of D21L6 (0.3 mm in ethanol) and kept at room
temperature for 15 h. An electrolyte solution (N-methyl-N-butyl
imidiazolium iodide (0.6m), iodine (0.04m), LiI (0.025m), GuNCS
(0.05m), and tert-butylpyridine (0.28m) in a mixture of valeronitrile
and acetonitrile (15:85 v/v) was used for the redox couple. For
stability tests, the binary ionic-liquid electrolyte consisted of iodine
(0.2m), N-butyl benzimidazole (NBB, 0.5m), and GuNCS (0.1m) in a
mixture of 1-propyl-3-methylimidazolium iodide (PMII) and 1-ethyl-
3-methyl-imidazolium tetracyanoborate (EMIB(CN)4 , Merck; 65:35
v/v).[9a] NBB was synthesized according to a published procedure.[9b]
The J/V characteristics and IPCE of the DSCs were measured by
using previously reported techniques.[8] The measurement delay time
of photo J/V characteristics of DSCs was fixed to 40 ms for volatile
electrolyte and 200 ms for ionic-liquid electrolyte, respectively. The
detailed procedure for solid-state solar cell fabrication was described
previously.[6] A nanoporous layer (ca. 1.7 mm) of TiO2 (20 nm) was
prepared for photoanode and the hole-transporting materials used
was Spiro-MeOTAD, which was dissolved in chlorobenzene. tert-
Butylpyridine and Li(CF3SO2)2N were added as additives. The device
fabrication was completed by evaporating a 50 nm gold electrode
over the top of the cell.
[4] A. Suzuki, J. Organomet. Chem. 1999, 576, 147.
[5] M. Melucci, G. Barbarella, M. Zambianchi, P. Di Pietro, A.
Bongini, J. Org. Chem. 2004, 69, 4821.
[6] a) L. Schmidt-Mende, U. Bach, R. Humphry-Baker, T. Horiuchi,
H. Miura, S. Ito, S. Uchida, M. Grꢂtzel, Adv. Mater. 2005, 17, 813;
b) H. J. Snaith, L. Schmidt-Mende, M. Grꢂtzel, M. Chiesa, Phys.
Rev. B 2006, 74, 045306.
[7] a) L. Schmidt-Mende, S. M. Zakeeruddin, M. Grꢂtzel, Appl. Phys.
Lett. 2005, 86, 013504; b) H. J. Snaith, A. J. Moule, C. Klein, K.
Meerholz, R. H. Friend, M. Grꢂtzel, Nano Lett. 2007, 7, 3372;
c) D. Kuang, C. Klein, H. J. Snaith, R. Humphry-Baker, S. M.
Zakeeruddin, M. Grꢂtzel, Inorg. Chim. Acta 2008, 361, 699; d) J.-
H. Yum, P. Chen, M. Grꢂtzel, ChemSusChem 2008, 1, 699.
[8] M. K. Nazeeruddin, P. Pꢅchy, T. Renouard, S. M. Zakeeruddin, R.
Humphry-Baker, P. Comte, P. Liska, C. Le, E. Costa, V. Shklover,
L. Spiccia, G. B. Deacon, C. A. Bignozzi, M. Grꢂtzel, J. Am.
Chem. Soc. 2001, 123, 1613.
Received: September 26, 2008
Revised: November 13, 2008
Published online: December 29, 2008
[9] a) D. Kuang, P. Wang, S. Ito, S. M. Zakeeruddin, M. Grꢂtzel, J.
Am. Chem. Soc. 2006, 128, 7732; b) D. Kuang, C. Klein, S. Ito, J. E.
Moser, R. Humphry-Baker, N. Evans, F. Duriaux, C. Grꢂtzel,
S. M. Zakeeruddin, M. Grꢂtzel, Adv. Mater. 2007, 19, 1133.
Keywords: dyes/pigments · electrochemistry ·
.
long-term stability · sensitizers · solar cells
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