Performance of dye-sensitized solar cells based on novel sensitizers bearing asymmetric double D-π-A chains with arylamines as donors

Article abstract of DOI:10.1016/j.dyepig.2012.02.011

Three novel, metal-free organic sensitizers bearing two asymmetric double donor-π-acceptor (D-π-A) chains (DC1-3), each, and a reference dye containing single D-π-A chain (SC) with cyanoacrylic acid as electron acceptor are synthesized. Their photophysica

Full text of DOI:10.1016/j.dyepig.2012.02.011

Dyes and Pigments 94 (2012) 481e489
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Dyes and Pigments
journal homepage: www.elsevier.com/locate/dyepig
Performance of dye-sensitized solar cells based on novel sensitizers bearing
asymmetric double Dꢀ
p
ꢀA chains with arylamines as donors
**
Yanping Hong a c, Jin-Yun Liao b, Jianlong Fu a, Dai-Bin Kuang b , Herbert Meier , Cheng-Yong Su ,
,
,
d
b
Derong Cao a
,
*
a School of Chemistry and Chemical Engineering, State Key Laboratory of Luminescent Materials and Devices, South China University of Technology,
Guangzhou 510641, China
b MOE Key Laboratory of Bioinorganic and Synthetic Chemistry, KLGHEI of Environment and Energy Chemistry, School of Chemistry and Chemical Engineering,
Sun Yat-sen University, Guangzhou 510275, China
c College of Food Science and Engineering, Laboratory of Plant Resource Exploitation and Utilization, Jiangxi Agricultural University, Nanchang 330045, China
d Institute of Organic Chemistry, University of Mainz, Mainz 55099, Germany
a r t i c l e i n f o
a b s t r a c t
Article history:
Three novel, metal-free organic sensitizers bearing two asymmetric double donor-p-acceptor (D-p-A)
chains (DC1-3), each, and a reference dye containing single D-p-A chain (SC) with cyanoacrylic acid as
electron acceptor are synthesized. Their photophysical, electrochemical properties and the performances
of the corresponding dye-sensitized solar cells (DSSCs) are further investigated. The dyes, DC1, DC2 and
DC3 contain one chain with diphenylamine and another chain with carbazole or phenothiazine as
electron donor, while diphenylamine is only employed as electron donor in SC. Compared to the inferior
Received 10 December 2011
Received in revised form
15 February 2012
Accepted 17 February 2012
Available online 25 February 2012
solar energy to electricity conversion efficiency (h) of 2.82%, 4.66% and 3.80%, respectively, for the DSSCs
Keywords:
based on DC1, DC2 and SC, the DC3 sensitized cell gives
h of 5.19% under standard global AM 1.5 solar
Dye-sensitized solar cell
Organic sensitizer
Organic dye
condition (100 mW cmꢀ2) due to its broader and more intensive absorption in the UVevisible region.
Ó 2012 Elsevier Ltd. All rights reserved.
Donor-p-acceptor
Photovoltaic
1. Introduction
ease of structure tailoring as well as low-cost synthesis process and
compliance with environmental issues [4]. To date, hundreds of
Dye-sensitized solar cells (DSSCs), as a promising photovoltaic
device due to their relatively high efficiency and low-cost fabrica-
tion [1], have been received intense attention since the pioneering
report in 1991 by Grätzel and coworkers [2]. As a critical compo-
nent in DSSCs, the sensitizers play a vital role in providing electron
injection into conduction band of TiO2 upon light irradiation.
Nowadays, the photoelectric conversion efficiencies of DSSCs
organic dyes have been explored to act as sensitizers for DSSCs and
have obtained impressive efficiencies [4e17].
Organic dyes possessing a rod-like configuration with the
electron-donating and electron-accepting groups bridged by a
p-
conjugated unit (Dꢀ ꢀA) are considered as one of the most
p
promising classes of organic sensitizers. It is found that the
photoinduced intramolecular electron transfer takes place in these
dyes easily and the photophysical properties of the dyes can be
easily tuned by varying donor, spacer, and acceptor moieties
[18e20]. The results revealed that the DSSCs based on these
sensitized by Zn-complex dyes have achieved maximal
h over than
12% [3]. However, the limitations concerning these complexes such
as rare sources, heavy-metal toxicity and environmental issues
would limit their application. In recent years, metal-free organic
dyes have been extensively developed as an alternative to noble
metal-complexes due to their high molar extinction coefficients,
Dꢀ
Recently, we reported a novel dye that contained double
symmetric Dꢀ ꢀA chains (DB), and obtained an increased
conversion efficiency of DSSCs compared to the corresponding
single Dꢀ ꢀA dye since one molecule of DB contains two light
pꢀA dyes showed better performances [8,21].
p
p
harvesting units [14]. When asymmetric double Dꢀ ꢀA chains
p
* Corresponding author. Tel./fax: þ86 20 87110245.
** Corresponding author. Tel.: þ86 20 84113015.
E-mail addresses: kuangdb@mail.sysu.edu.cn (D.-B. Kuang), drcao@scut.edu.cn
(D. Cao).
with diphenylamine and phenoxazine as donors were introduced
into one dye molecule, the dye showed broad absorption range and
better performance of its sensitized solar cells [15]. In order to get
0143-7208/$ e see front matter Ó 2012 Elsevier Ltd. All rights reserved.
doi:10.1016/j.dyepig.2012.02.011

482
Y. Hong et al. / Dyes and Pigments 94 (2012) 481e489
more insight into the impact on the performance of the solar cells
under the conditions of introducing different donors or extending
conjugated system into the sensitizers which bear asymmetric
2. Experimental section
2.1. Instrumentation and materials
double Dꢀ ꢀA chains, here we designed a series of organic
p
sensitizers with different arylamines as donors, such as diphenyl-
1H NMR and 13C NMR spectra were recorded on a Bruker
400 MHz spectrometer in CDCl3 or DMSO-d6 with tetrame-
thylsilane as inner reference. MS data were recorded on an
Esquire HCT PLUS mass spectrometer. Elementary analyses were
performed using a Vario ELIII Analyzer. The melting point was
taken on Tektronix X4 microscopic melting point apparatus and
uncorrected. The absorption and emission spectra of the dyes in
CH2Cl2/MeOH solution (2 ꢁ 10ꢀ5 M) were measured at room
temperature by Shimadzu UV-2450 UVeVis spectrophotometer
and Fluorolog III photoluminescence spectrometer, respectively.
Electrochemical redox potentials were obtained by cyclic vol-
tammetry (CV) using a three-electrode cell and an electrochem-
istry workstation (e-corder (ED 401) potentiostat). The dyes
sensitized TiO2 films used as the working electrodes. The Ag/AgCl
in saturated KCl solution and Pt wire were utilized as reference
and counter electrodes with a scan rate of 50 mV/s. Tetrabuty-
lammonium hexafluorophosphate (TBAPF6) 0.1 M was used as
amine, carbazole and phenothiazine (DC1-3). Moreover, a sensi-
tizer with a single Dꢀ
p
ꢀA chain was synthesized as reference (SC).
As shown in Scheme 1, DC1, DC2 and DC3 were designed with the
following characteristics: (i) the asymmetric Dꢀ ꢀA chains linked
p
by non-conjugated n-hexane chain resulting two separate light
harvesting systems would enhance the absorption intensity and
broaden the absorption range due to the absorption overlap and
complement of both the donors and p-spaces; at the same time, the
linker of alkyl chain might be expected to depress aggregation of
the dye on the TiO2 surface [10,22], to increase the electron lifetime
since the better surface protection, which would enhance the
overall performance of the DSSCs [23]. (ii) in the Dꢀ ꢀA chains,
p
different electron-donating capability donors of carbazole and
phenothiazine were adopted to tune the HOMO and LUMO energy
levels of the dyes to change the absorption range and intensity,
which would affect the conversion efficiencies of the DSSCs.
COOH
CN
CHO
N
N
2
N
(iii)
(iv)
2
2
N
N
N
5
(ii)
CN
COOH
CHO
CHO
3
DC1
N
COOH
CN
(i)
(ii)
N
N
H
N
N
(iv)
(iii)
2
2
2
2
Br
N
N
N
1
CN
COOH
S
4
S
6
CHO
S
DC2
CN
COOH
CHO
S
S
S
CN
CN
CN
N
N
N
(v)
(iv)
(iii)
6
2
2
2
N
S
N
S
N
CN
CN
CN
S
S
S
CHO
COOH
S
NC
10
8
DC3
CHO
(i)
(iii)
(v)
S
CN
N
C6H13
7
N
H
N
C6H13
2
N
C6H13
9
CN
COOH
(iii)
CHO
S
S
(iv)
CN
CN
N
C6H13
N
C6H13
SC
11
Scheme 1. Synthesis of the dyes DC1, DC2, DC3 and SC. (i) 1,6-Dibromohexane or 1-bromohexane, NaH, MeO(CH2)2OMe, 85 ꢂC, Ar, 2 h. (ii) Carbazole or phenothiazine, DMSO, KOH,
N2, rt, 3 h. (iii) POCl3, DMF, ClC2H4Cl, 90 ꢂC, N2, 4 h. (iv) Cyanoacetic acid, CHCl3, piperidine, reflux, 3 h. (v) 2-Thiopheneacetonitrile, t-BuOK, THF, reflux, 2 h.

Y. Hong et al. / Dyes and Pigments 94 (2012) 481e489
483
supporting electrolyte in CH3CN. The measurements were cali-
brated using ferrocene as standard. The redox potential of ferro-
cene internal reference is taken as 0.63 V versus normal hydrogen
electrode (NHE). The currentevoltage measurements were
carried out by adopting a Keithley 2400 source meter under
simulated AM 1.5 G illumination (100 mW cmꢀ2) provided by
solar simulator (91192, Oriel). A 1 kW Xenon arc lamp (6271,
Oriel) was served as a light source. The incident light intensity-
was calibrated with a NREL standard Si solar cell. The IPCE spectra
were measured as a function of wavelength from 350 to 800 nm
on the basis of a Spectral Products DK240 monochromator. The
electrochemical impedance spectroscopy (EIS) measurements
were held on the Zahner Zennium electrochemical workstation in
dark condition, with an applied bias of ꢀ0.7 V. A 10 mV AC
sinusoidal signal was employed over the constant bias with the
(6-Phenothiazin-10-yl-hexyl)diphenyl-amine (4). It was
prepared as a colorless liquid in 94.7% yield from phenothiazine by
the same procedure established for 3. 1H NMR (CDCl3, 400 MHz,
ppm):
d 1.31e1.39 (m, 2H), 1.40e1.47 (m, 2H), 1.61e1.68 (m, 2H),
1.74e1.82 (m, 2H), 3.65 (t, J ¼ 7.6 Hz, 2H), 3.82 (t, J ¼ 7.2 Hz, 2H),
6.82e6.84 (m, 2H), 6.88e6.96 (m, 8H), 7.11e7.15 (m, 4H), 7.22e7.24
(m, 4H). 13C NMR (CDCl3, 100 MHz, ppm):
d 26.6, 26.7, 26.8, 27.4,
47.1, 52.1, 115.3, 120.8, 121.0, 122.3, 124.9, 127.1, 127.4, 129.2, 145.2,
148.0. ESI MS: m/z 450.2. Found: 451.2 [M þ H]þ. Anal. calcd. for
C30H30N2S: C, 79.96; H, 6.71; N, 6.22; S 7.12. Found: C, 79.71; H,
6.73; N, 6.24; S, 7.09.
9-{6-[(4-Formyl-phenyl)-phenyl-amino]-hexyl}-9H-carba-
zol-3-carbaldehyde (5). To a solution of 3 (1.67 g, 4.0 mmol) and
dry DMF (1.76 g, 24 mmol) in ClC2H4Cl (15 mL), POCl3 (3.69 g,
24 mmol) was added slowly at 0 ꢂC. Then the bath was heated to
90 ꢂC and maintained for 4 h. Dilute aqueous solution of NaOH was
added and the mixture extracted with CH2Cl2. The organic fractions
were washed with brine and dried over anhydrous sodium sulfate.
The solvent was removed under reduced pressure and the residue
was urified by chromatography on silica gel (dichloromethane:
petroleum ¼ 2: 1) to give 5 (1.61 g, 84.8%) as a pale-yellow liquid. 1H
frequency ranging between
1 MHz and 10 mHz. Intensity-
modulated photovoltage spectroscopy (IMVS) measurements
were carried out on an electrochemical workstation (Zahner,
Zennium) with a frequency response analyzer under a modulated
green light emitting diodes (457 nm) driven by a source supply
(Zahner, PP211), which provided both dc and ac components of
the illumination. The modulated light intensity was 10% or less
than the base light intensity. The frequency range was set from
100 kHz to 0.1 Hz.
NMR (CDCl3, 400 MHz, ppm):
d 1.15e1.25 (m, 4H), 1.43e1.53 (m,
2H), 1.64e1.75 (m, 2H), 3.49 (t, J ¼ 7.2 Hz, 2H), 4.09 (t, J ¼ 6.4 Hz,
2H), 6.49e6.51 (m, 2H), 6.68e6.69 (m, 2H), 6.99e7.00 (m, 2H),
7.11e7.24 (m, 4H), 7.35e7.39 (m, 1H), 7.47e7.49 (m, 2H), 7.80e7.82
(m 1H), 7.95e7.97 (m,1H), 8.38e8.40 (m, 1H), 9.58(s, 1H), 9.90(s,
2.2. Syntheses
1H). 13C NMR (CDCl3, 100 MHz, ppm):
d 26.3, 26.7, 26.8, 28.5, 42.8,
(6-Bromo-hexyl)-diphenyl-amine (1). A solution of diphenyl-
amine (6.76 g, 40 mmol), NaH (2.40 g, 60 mmol) in MeO(CH2)2OMe
(40 mL) was stirred at room temperature for 0.5 h under argon.
Then, 1,6-dibromohexane (11.7 g, 48 mmol) was poured into the
mixture and heated at 85 ꢂC for 2 h. After cooling, the reaction
mixture was filtered and the solvent was evaporated. The residue
was purified by chromatography on a silica gel (petroleum) to give
1 (5.52 g, 41.7%) as a colorless liquid. 1H NMR (CDCl3, 400 MHz,
52.0, 108.6, 109.1, 113.0, 114.3, 120.0, 120.4, 122.6, 123.6, 126.1, 126.2,
126.4, 126.7, 128.2, 129.8, 131.4, 140.7, 143.6, 145.2, 152.9, 153.4,
189.8, 191.3. ESI MS: m/z 474.2. Found: 475.2 [M þ H]þ. Anal. Calcd.
for C32H30N2O2: C, 80.98; H, 6.37; N, 5.90. Found: C, 81.14; H, 6.40;
N, 5.87.
10-{6-[(4-Formyl-phenyl)-phenyl-amino]-hexyl}-10H-phe-
nothiazin-3-carbaldehyde (6). It was prepared as a yellow liquid in
72.7% yield from 4 by the same procedure established for 5. 1H NMR
ppm):
1.79e1.86 (m, 2H), 3.37 (t, J ¼ 6.4 Hz, 2H), 3.68 (t, J ¼ 7.6 Hz, 2H),
6.95 (m, 6H), 7.25 (m, 4H). 13C NMR (CDCl3, 100 MHz, ppm):
26.2,
27.3, 27.9, 32.6, 33.7, 52.1, 120.8, 121.1, 129.2, 148.0. ESI MS: m/z
331.1. Found: 330.3 [MꢀH]þ. Anal. Calcd. for C18H22BrN: C, 65.06; H,
6.67; N, 4.22. Found: C, 65.12; H, 6.69; N, 4.21.
d
1.32e1.39 (m, 2H), 1.40e1.48 (m, 2H), 1.63e1.71 (m, 2H),
(CDCl3, 400 MHz, ppm): d 1.32e1.39 (m, 2H), 1.42e1.49 (m, 2H),
1.64e1.68 (m, 2H), 1.76e1.83 (m, 2H), 3.68 (t, J ¼ 7.6 Hz, 2H), 3.88 (t,
J ¼ 6.8 Hz, 2H), 6.64e6.67 (m, 2H), 6.84e6.88 (m, 2H), 6.95e6.97
(m, 1H), 7.10e7.17 (m, 4H), 7.28e7.30 (m, 1H), 7.40e7.44 (m, 2H),
7.58e7.65 (m, 4H), 9.72 (s, 1H), 9.78 (s, 1H). 13C NMR (CDCl3,
d
100 MHz, ppm): d 26.3, 26.4, 26.5, 27.1, 47.5, 52.3, 113.2, 114.5, 114.8,
Hexyl-diphenyl-amine (2). It was prepared as a colorless liquid
in 74.2% yield from diphenylamine and 1-bromohexane by the
same procedure established for 1. 1H NMR (CDCl3, 400 MHz, ppm):
115.9, 123.6, 123.9, 125.2, 126.3, 127.4, 127.5, 128.3, 129.9, 130.0,
131.0, 131.6, 143.3, 145.5, 150.6, 153.2, 153.7, 189.9, 190.1. ESI MS: m/z
506.2. Found: 529.1 [M þ Na]þ. Anal. Calcd. for C32H30N2O2S: C,
75.86; H, 5.97; N, 5.53; S, 6.33. Found: C, 75.67; H, 6.00; N, 5.55; S,
6.30.
d
0.87 (t, J ¼ 6.4 Hz, 3H), 1.28e1.36 (m, 6H), 1.61e1.69 (m, 2H), 3.67
(t, J ¼ 7.6 Hz, 2H), 6.90e6.94 (m, 2H), 6.96e6.98 (m, 4H), 7.21e7.26
(m, 4H). 13C NMR (CDCl3, 100 MHz, ppm):
31.7, 52.4, 120.9, 121.1, 129.3, 148.2.
d
14.1, 22.7, 26.8, 27.5,
4-(Hexyl-phenyl-amino)-benzaldehyde (7). It was prepared as
a light yellow liquid in 77.8% yield from 2 by using the method
(6-Carbazol-9-yl-hexyl)diphenyl-amine (3) Carbazole (0.836 g,
5.0 mmol) was added to a suspension of KOH (0.336 g, 6.0 mmol) in
DMSO (15 mL) under nitrogen. The mixture was stirred for 10 min
after which time 1 (1.83 g, 5.5 mmol) was added. The reaction was
stirred for 4 h at room temperature. Water was added and extracted
with dichloromethane (3 ꢁ 30 mL), the organic phases were then
washed with brine, dried with anhydrous sodium sulfate and
evaporated. The residue was purified by chromatography on silica
gel (dichloromethane: petroleum ¼ 1: 20) to give 3 (1.84 g, 88.3%) as
established for 5. 1H NMR (CDCl3, 400 MHz, ppm):
d 0.87 (t,
J ¼ 6.8 Hz, 3H), 1.28e1.37 (m, 6H), 1.65e1.72 (m, 2H), 3.71 (t,
J ¼ 8.0 Hz, 2H), 6.68e6.70 (m, 2H), 7.19e7.21 (m, 2H), 7.25e7.29 (m,
1H), 7.40e7.44 (m, 2H), 7.63e7.66 (m, 2H), 9.72 (s, 1H). 13C NMR
(CDCl3, 100 MHz, ppm):
d 13.9, 22.5, 26.4, 27.22, 31.4, 52.5, 113.1,
126.2, 126.3, 127.4, 130.0, 131.6, 145.6, 153.2, 190.0. ESI MS: m/z
281.2. Found: 282.1 [M þ H]þ. Anal. Calcd. for C19H23NO: C, 81.10; H,
8.24; N, 4.98. Found: C, 80.93; H, 8.27; N, 4.99.
(E)-3-[4-({6-[3-((E)-2-Cyano-2-thiophen-2-yl-vinyl)pheno-
thiazin-10-yl]hexyl}phenyamino)phenyl]-2-thiophen-2-yl-
acrylonitrile (8). To a stirred solution of t-BuOK (0.0224 g,
0.20 mmol) and 2-thiopheneacetonitrile (0.985 g, 8.0 mmol) in THF
(20 mL), 6 (1.01 g, 2.0 mmol) was added at room temperature under
nitrogen. The reaction mixture was refluxed for 2 h then cooled to
room temperature then the mixture was concentrated under
reduced pressure. The resulting residue was purified by chroma-
tography on silica gel (ethyl acetate: petroleum ¼ 1: 15) to give 8
a colorless liquid. 1H NMR (CDCl3, 400 MHz, ppm):
d 1.37e1.38 (m,
4H), 1.59e1.66 (m, 2H), 1.82e1.89 (m, 2H), 3.64 (t, J ¼ 7.6 Hz, 2H),
4.27 (t, J ¼ 7.2 Hz, 2H), 6.91e6.96 (m, 6H), 7.21e7.25 (m, 6H),
7.36e7.38 (m, 2H), 7.43e7.47 (m, 2H), 8.09e8.11 (m, 2H). 13C NMR
(CDCl3, 100 MHz, ppm): d 26.8, 27.1, 27.3, 28.9, 42.8, 52.1, 108.6,118.7,
120.3,120.8,121.0,122.8,125.5,129.2,140.3,148.0. ESI MS: m/z 418.2.
Found: 419.3 [M þ H]þ. Anal. Calcd. for C30H30N2: C, 86.08; H, 7.22;
N, 6.69. Found: C, 85.89; H, 7.24; N, 6.72.

484
Y. Hong et al. / Dyes and Pigments 94 (2012) 481e489
(1.18 g, 82.5%) as a scarlet liquid. 1H NMR (CDCl3, 400 MHz, ppm):
1.34e1.40 (m, 2H), 1.43e1.47 (m, 2H), 1.64e1.71 (m, 2H), 1.75e1.82
acetic acid ¼ 100: 5: 1) to give DC1 as a yellow solid (0.366 g, 75.3%).
d
mp 168ꢀ169 ꢂC. 1H NMR (DMSO-d6, 400 MHz, ppm):
d 1.15w1.27
(m, 2H), 3.68 (t, J ¼ 7.2 Hz, 2H), 3.84 (t, J ¼ 6.8 Hz, 2H), 6.69e6.72 (m,
2H), 6.81e6.84 (m, 2H), 6.91e6.95 (m, 1H), 7.01e7.04 (m, 2H),
7.09e7.12 (m, 2H), 7.15e7.19 (m, 4H), 7.20e7.22 (m, 2H), 7.23e7.25
(m, 2H), 7.30e7.31 (m, 1H), 7.36e7.40 (m, 2H), 7.50 (s, 1H),
(m, 4H), 1.45 (br. s, 2H), 1.70 (br. s, 2H), 3.62 (br. s, 2H), 4.36 (br. s,
2H), 6.62e7.64 (m, 2H), 7.17e7.27 (m, 4H); 7.41e7.61 (m, 4H),
7.69e7.71 (m,1H), 7.80e7.82 (m, 2H), 8.01 (s,1H), 8.10e8.11 (m,1H),
8.21e8.23 (m, 1H), 8.40 (s, 1H), 8.78 (s, 1H). 13C NMR (DMSO-d6,
7.68e7.74 (m, 3H). 13C NMR (CDCl3, 100 MHz, ppm):
d
26.5, 26.6,
100 MHz, ppm): d 25.8, 26.1, 26.6, 28.3, 42.5, 51.6, 95.8, 99.4, 110.1,
27.3, 29.7, 47.4, 52.2, 100.2, 103.2, 114.6, 115.2, 115.6, 117.2, 118.0,
122.8, 123.1, 123.9, 124.7, 125.0, 125.4, 125.5, 125.6, 126.5, 126.6,
127.4, 127.5, 127.6, 127.9, 128.0, 128.2, 128.3, 129.9, 130.8, 138.3,
139.5, 139.9, 140.3, 143.8, 146.0, 147.0, 150.1. ESI MS: m/z 716.2.
Found: 739.3 [M þ Na]þ. Anal. Calcd. for C44H36N4S3: C, 73.71; H,
5.06; N, 7.81; S, 13.42. Found: C, 73.59; H, 5.09; N, 7.85; S, 13.37.
(E)-3-[4-(Hexyl-phenyl-amino)-phenyl]-2-thiophen-2-yl-
113.5, 117.6, 117.6, 117.7, 120.1, 120.3, 120.5, 122.0, 122.5, 125.3, 126.5,
126.8, 126.9, 127.1, 127.7, 130.1, 133.2, 140.7, 142.5, 144.7, 151.9, 153.2,
154.6, 164.3, 164.6. ESI MS: m/z 608.2. Found: 606.9 [MꢀH]ꢀ. Anal.
Calcd. for C38H32N4O4: C, 74.98; H, 5.30; N, 9.20. Found: C, 74.79; H,
5.27; N, 9.17.
(E)-3-[4-({6-[3-((E)-2-Carboxy-2-cyanovinyl)phenothiazin-
10-yl]-hexyl}-phenylamino)phenyl]-2-cyanoacrylic acid (DC2). It
was prepared as a black solid in 62.1% yield from 6 by the same
procedure established for DC1, mp 230ꢀ231 ꢂC. 1H NMR (DMSO-d6,
acrylonitrile (9). It was prepared as a yellow liquid in 87.8% yield
from 7 by using the method established for 8. 1H NMR (CDCl3,
400 MHz, ppm):
d
0.79 (t, J ¼ 6.4 Hz, 3H), 1.17e1.26 (m, 6H),
400 MHz, ppm): d 1.28e1.40 (m, 4H), 1.50e1.58 (m, 2H), 1.61e1.68
1.55e1.62 (m, 2H), 3.61 (t, J ¼ 8.0 Hz, 2H), 6.64e6.66 (m, 2H),
6.91e6.93 (m, 1H), 7.09e7.14 (m, 5H), 7.16e7.17 (m, 1H), 7.29e7.32
(m, 2H), 7.61e7.63 (m, 2H). 13C NMR (CDCl3, 100 MHz, ppm):
(m, 2H), 3.70 (t, J ¼ 6.8 Hz, 2H), 3.90 (t, J ¼ 6.0 Hz, 2H), 6.68e6.70
(m, 2H), 6.96e6.99 (m, 1H), 7.03e7.05 (m, 1H), 7.10e7.14 (m, 2H),
7.11e7.19 (m, 1H), 7.21e7.23 (m, 2H), 7.28e7.31 (m, 1H), 7.43e7.47
(m, 2H), 7.76 (s, 1H), 7.83e7.85 (m, 3H), 8.03 (s, 1H), 8.06 (s, 1H).
d
14.1, 22.7, 26.8, 27.4, 31.7, 52.6, 100.3, 114.7, 118.1, 122.8, 124.8,
125.5, 125.6, 126.8, 128.0, 130.0, 130.9, 140.1, 140.5, 146.3, 150.3. ESI
MS: m/z 386.2. Found: 387.1 [M þ H]þ. Anal. Calcd. for C25H26N2S: C,
77.68; H, 6.78; N, 7.25; S, 8.30. Found: C, 77.58; H, 6.80; N, 7.26; S,
8.29.
13C NMR (DMSO-d6, 100 MHz, ppm):
d 25.8, 25.8, 26.0, 26.9, 46.8,
51.7, 99.2, 105.2, 113.8, 115.8, 116.5, 118.3, 118.6, 120.7, 122.4, 123.5,
123.6,126.4,127.1,127.4,128.1,128.4,130.3,130.9,132.8,143.2,145.1,
148.0, 149.8, 151.6, 151.9, 154.22, 165.1, 165.7. ESI MS: m/z 640.2.
Found: 639.3 [MꢀH]ꢀ. Anal. Calcd. for C38H32N4O4S: C, 71.23; H,
5.03; N, 8.74; S, 5.00. Found: C, 71.17; H, 5.01; N, 8.73; S, 4.98.
(E)-3-{5-[(E)-2-(4-{[6-(3-{(E)-2-[5-((E)-2-Carboxy-2-
(E)-3-{4-[(6-{3-[(E)-2-Cyano-2-(5-formylthiophen-2-yl)
vinyl]phenothiazin-10-yl}
hexyl)phenylamino]phenyl}-2-(5-
formylthiophen-2-yl)acrylonitrile (10). It was prepared as a red-
black solid in 66.7% yield from 8 by the same procedure estab-
lished for 5, mp 90ꢀ91 ꢂC. 1H NMR (CDCl3, 400 MHz, ppm):
cyanovinyl)thiophen-2-yl]-2-cyanovinyl}phenothiazin-10-yl)-
hexyl]phenylamino}phenyl)-1-cyanovinyl]thiophen-2-yl}-2-
cyanoacrylic acid (DC3). It was prepared as a black solid in 64.6%
yield from 10 by the same procedure established for DC1, mp
d
1.37e1.43 (m, 2H), 1.44e1.52 (m, 2H), 1.67e1.74 (m, 2H), 1.76e1.83
(m, 2H), 3.79 (t, J ¼ 7.2 Hz, 2H), 3.89 (t, J ¼ 6.4 Hz, 2H), 6.84e6.86 (m,
2H), 6.95e6.97 (m, 2H), 7.05e7.14 (m, 3H), 7.17e7.19 (m, 2H),
7.29e7.32 (m, 2H), 7.36e7.40 (m, 3H), 7.58 (s, 1H), 7.69e7.70 (m,
1H), 7.72e7.74 (m, 2H), 7.78e7.80 (m, 1H), 7.83e7.86 (m, 2H),
126ꢀ128 ꢂC. 1H NMR (DMSO-d6, 400 MHz, ppm):
d 1.36 (br. s, 4H),
1.55 (br. s, 2H), 1.65 (br. s, 2H), 3.79 (br. s, 2H), 3.88 (br. s, 2H),
6.94e7.08 (m, 5H), 7.11e7.22 (m, 5H), 7.37 (br. s, 1H), 7.44 (br. s, 1H),
7.62e7.80 (m, 6H), 7.82e7.96 (m, 4H), 8.01 (s, 1H), 8.17 (s, 1H). 13C
9.81(s, 1H), 9.86 (s, 1H). 13C NMR (CDCl3, 100 MHz, ppm):
d 26.4,
26.5, 26.6, 27.4, 47.4, 52.1, 101.9, 104.6, 115.2, 115.8, 116.5, 117.1, 117.3,
123.5, 123.7, 124.0, 125.2, 126.0, 126.7, 126.8, 126.9, 127.5, 127.6,
128.1, 128.6, 128.7, 129.0, 129.4, 130.7, 131.6, 136.9, 138.5, 139.3,
141.6, 142.5, 143.4, 147.8, 148.1, 148.7, 152.2, 182.4, 190.3. ESI MS: m/z
772.2. Found: 773.1 [M þ H]þ. Anal. Calcd. for C46H36N4O2S3: C,
71.47; H, 4.69; N, 7.25; S, 12.44. Found: C, 71.68; H, 4.71; N, 7.24; S,
12.42.
(E)-2-(5-Formyl-thiophen-2-yl)-3-[4-(hexyl-phenyl-amino)-
phenyl]acrylonitrile (11). It was prepared as a red liquid in 79.4%
yield from 9 by using the method established for 5. 1H NMR (CDCl3,
NMR (DMSO-d6, 100 MHz, ppm): d 25.6, 25.6, 25.8, 26.9, 46.6, 51.3,
100.9, 102.2, 115.7, 116.3, 117.0, 117.4, 118.3, 118.4, 118.7, 122.2, 122.4,
123.3, 124.3, 126.1, 126.3, 127.1, 127.3, 127.7, 127.9, 128.4, 129.8, 130.7,
131.3, 131.3, 132.1, 132.2, 136.7, 136.9, 138.8, 139.4, 141.0, 141.5, 141.6,
141.6,143.0, 144.4, 147.2, 147.7, 149.8, 150.5, 163.2, 164.4. ESI MS: m/z
906.2. Found: 905.0 [MꢀH]ꢀ. Anal. Calcd. for C52H38N6O4S3: C,
68.85; H, 4.22; N, 9.26; S, 10.60. Found: C, 68.72; H, 4.19; N, 9.26;
10.30.
(E)-2-Cyano-3-(5-{(E)-1-cyano-2-[4-(hexyl-phenyl-amino)-
phenyl]vinyl}-thiophen-2-yl)-acrylic acid (SC). It was prepared as
a black solid in 79.2% yield from 11 by using the method established
400 MHz, ppm):
d
0.80 (t, J ¼ 6.4 Hz, 3H), 1.18 (br. s, 6H), 1.59e1.64
(m, 2H), 3.65 (t, J ¼ 8.0 Hz, 2H), 6.63e6.65 (m, 2H), 7.13e7.15 (m,
2H), 7.19e7.25 (m, 2H), 7.32 (s, 1H); 7.35e7.38 (m, 2H), 7.60e7.61
(m, 1H), 7.69e7.71 (m, 2H), 9.77 (s, 1H). 13C NMR (CDCl3,
for DC1, mp 73ꢀ74 ꢂC 1H NMR (DMSO-d6, 400 MHz, ppm):
d 0.82 (t,
J ¼ 6.4 Hz, 3H), 1.21e1.24 (m, 4H), 1.28e1.32 (m, 2H), 1.54e1.62 (m,
2H), 3.75 (t, J ¼ 7.8 Hz, 2H), 6.75e6.78 (m, 2H), 7.26e7.28 (m, 2H),
7.29e7.31 (m, 1H), 7.45e7.7.51 (m, 3H), 7.79 (s, 1H), 7.83e7.85 (m,
2H), 7.93e7.94 (m, 1H), 8.42 (s, 1H). 13C NMR (DMSO-d6, 100 MHz,
100 MHz, ppm):
d 14.0, 22.6, 26.7, 27.3, 31.6, 52.7, 98.4, 114.1, 117.4,
121.7, 125.6, 126.4, 127.3, 130.1, 131.9, 137.2, 141.6, 143.3, 145.7, 150.3,
151.3, 182.4. ESI MS: m/z 414.2. Found: 415.2 [M þ H]þ. Anal. Calcd.
for C26H26N2OS: C, 75.33; H, 6.32; N, 6.76; S, 7.73. Found: C, 75.31;
H, 6.34; N, 6.77; S, 7.74.
ppm): d 13.9, 22.1, 25.9, 26.9, 31.1, 51.8, 96.8, 99.1, 114.0, 116.7, 117.7,
121.6, 125.2, 126.3, 127.0, 130.2, 132.0, 134.4, 140.9, 143.6, 145.2,
145.9, 148.9, 151.1, 163.6. ESI MS: m/z 481.1. Found, 435.7
[MꢀCOOH]ꢀ. Anal. Calcd. for C29H27N3O2S: C, 72.32; H, 5.65; N,
8.72; S, 6.66. Found: C, 72.39; H, 5.67; N, 8.73; S, 6.65.
(E)-3-[4-({6-[3-((E)-2-Carboxy-2-cyanovinyl)carbazol-9-yl]-
hexyl}phenylaminophenyl]-2-cyanoacrylic
acid
(DC1).
5
(0.379 g, 0.80 mmol) dissolved in CHCl3 (15 mL) was condensed
with 2-cyanoacetic acid (0.680 g, 8.0 mmol) in the presence of
piperidine (0.32 mL, 3.2 mmol). The mixture was refluxed for 3 h
under nitrogen. After cooling, the mixture was poured into
a mixture of CH2Cl2 and 2 M aqueous HCl. The organic layer was
separated and dried over anhydrous sodium sulfate. After removal
of the solvent at reduced pressure, the crude product was purified
by chromatography on silica gel (methylene chloride: methanol:
2.3. Fabrication of DSSCs
The paste fabrication process of the TiO2 (20 nm particle size)
screen-printed FTO coated glass (15
Glass, Japan) was carried out according to the previous paper
[24]. Briefly, TiO2 powder (20 nm) (1.0 g) was ground for 40 min
in the mixture of ethanol (8.0 mL), acetic acid (0.2 mL), terpineol
U/square, Nippon Sheet

Y. Hong et al. / Dyes and Pigments 94 (2012) 481e489
485
Fig. 1. (a) Absorption spectra and (b) Normalized absorption and emission spectra of the dyes in CH2Cl2/MeOH.
(3.0 g) and ethyl cellulose (0.5 g) to form a slurry, and then the
3.2. Photophysical properties
slurry was sonicated for 5 min in an ultrasonic bath, finally to
form a viscous white TiO2 paste. The thickness of films was
controlled through repeating screen-printing times. After
a heating process (at 325 ꢂC for 5 min, at 375 ꢂC for 5 min, at
450 ꢂC for 15 min, and then at 500 ꢂC for 15 min) to remove the
organic substances, the TiO2 films were soaked in 0.04 M TiCl4
aqueous solution for 30 min at 70 ꢂC to improve the photovoltaic
performance. After sintering at 520 ꢂC for 30 min, the TiO2
electrode films were immerged into 0.2 mM dye (DC1, DC2, DC3
and SC) in CH3OH/CH2Cl2 (1:1; v/v), and sensitized for about 15 h
at room temperature. Afterward, these films were rinsed with
CH2Cl2 in order to remove physisorbed organic dye molecule. To
evaluate their photovoltaic performance, the dye-sensitized
TiO2/FTO glass films were sandwiched together with Pt coated
FTO glass which was used as counter electrode. Platinized
counter electrodes were fabricated by thermal depositing
H2PtCl6 solution (5 mM in isopropanol) onto FTO glass. Then the
counter electrode was placed directly on the top of the dye-
sensitized TiO2 film sealed with thermal adhesive film
The UVevis and emission spectra of the dyes in CH2Cl2/MeOH
(1:1) solution and the absorption spectra of the dyes on TiO2 films
are shown in Fig. 1 and Fig. 2, respectively, and the characteristic
data are presented in Table 1. All the dyes exhibit two distinct
absorption bands appearing at 320ꢀ390 nm and 400ꢀ600 nm,
respectively. The former is ascribed to a localized aromatic
pꢀp*
transition and the later is assigned to the intramolecular charge
transfer (ICT) between donor and acceptor. Compared to DC1, DC2
possesses a broader absorption near to 550 nm and the absorption
maximum is red-shift by 19 nm, which is due to the stronger
electron-donating ability of phenothiazine than that of carbazole
[25]. It is interesting to note that when the
p-bridge of vinyl-
thiophene is introduced into each chain of DC2, the resulting
product DC3 exhibits a broaden and more intensive absorption
compared to DC2, and a shoulder can be observed clearly near
490 nm of DC3 which perhaps is attributed to the absorption
overlap and complement of the donors and thiophene spacers in
the two independent Dꢀ ꢀA units. The overlap and complement
p
(w25
m
m). The electrolyte (0.6 M 1-methyl-3-propylimidazolium
in the absorption of DC2 or DC1 are not observed apparently.
iodide (PMII), 0.10 M guanidinium thiocyanate, 0.03 M I2, 0.5 M
tert-butylpyridine in acetonitrile and valeronitrile (85:15)) was
injected from a hole made on the counter electrode into the
space between the sandwiched cells.
However, the molar absorption coefficient (
3
¼ 39,823 Mꢀ1 cmꢀ1) of
DC2 is much higher than that of compound SB with single chain
(
3
¼ 16,000 Mꢀ1 cmꢀ1) [14], which indicates that the absorption of
the dyes is enhanced by double Dꢀ ꢀA systems in one molecule.
p
The above phenomenons can also be observed clearly from the
3. Result and discussion
3.1. Synthesis and structural characterization
The synthetic route of the dyes is shown in Scheme 1. Inter-
mediate 1 or 2 was prepared from diphenylamine via alkylation
reaction with 1,6-dibromohexane or 1-bromohexane, respectively.
Compound 1 followed further alkylation with carbazole and
phenothiazine in the presence of KOH in DMSO to afford
compounds 3 and 4, respectively. The intermediates 3, 4 and 2 were
then converted to the corresponding dialdehydes 5, 6 and aldehyde
7 by VilsmeiereHaack reaction in the presence of DMF and POCl3. 8
and 9 were obtained via Knoevenagel reaction of the 6 and 7 with
2-thiopheneacetonitrile in THF. The dialdehyde 10 and aldehyde 11
were also prepared by a similar process to 5. Finally, the dia-
ldehydes 5, 6, 10 and the aldehyde 11 were condensed with cya-
noacetic acid to yield the target dyes (DC1, DC2, DC3 and SC) by the
Knoevenagel reaction in refluxing CHCl3 in the presence of piper-
idine. All the intermediates and target dyes were confirmed by
standard spectroscopic methods.
Fig. 2. Absorption spectra of the dyes anchored on TiO2 films.

486
Y. Hong et al. / Dyes and Pigments 94 (2012) 481e489
Table 1
Absorption, emission and electrochemical properties of the dyes DC1, DC2, DC3 and SC.
Dye
Absorption
Emission
Oxidation potential data
EHOMO/ELUMOb/eV
lmax/nm
3
/Mꢀ1 cmꢀ1
lmax/nm
Eox/V (vs NHE)
E0e0/V
Eox ꢀ E0e0/V (vs.NHE)
ꢀ1.87
Egapa/V (vs NHE)
EHOMO/ELUMO/eV
ꢀ5.17/ꢀ2.38
DC1
DC2
DC3
SC
321
403
321
422
382
439
343
463
15,599
38,289
18,030
39,823
28,760
44,447
22,633
20,311
509 (403)
0.92
2.79
1.37
ꢀ5.90/ꢀ2.29c
ꢀ5.63/ꢀ2.15d
ꢀ5.61/ꢀ2.12d
ꢀ5.47/ꢀ2.50e
ꢀ5.44/ꢀ2.75d
ꢀ5.41/ꢀ2.99e
ꢀ5.33/ꢀ2.75d
610 (422)
576 (439)
599 (463)
0.99
0.93
0.96
2.44
2.34
2.31
ꢀ1.45
ꢀ1.41
ꢀ1.35
0.95
0.91
0.85
ꢀ5.24/ꢀ2.80
ꢀ5.18/ꢀ2.84
ꢀ5.21/ꢀ2.90
a
Egap is the energy gap between the Eox ꢀ E0e0 of the dye and the conductive band level of TiO2 (ꢀ0.5 V vs NHE).
Calculated at the B3LYP-31G(d) level in vacuum.
Calculated HOMOꢀLUMO levels for the chain of DC1 which employed carbazole as donor.
Calculated HOMOꢀLUMO levels for the chain of DC1, DC2, DC3 and SC which employed diphenylamine as donor.
Calculated HOMOꢀLUMO levels for the chain of DC2 and DC3 which employed phenothiazine as donor.
b
c
d
e
absorption of DC3 and SC. It is obvious that the absorption of the
conduction band (CB) of TiO2, the electrochemical behavior of the
dyes was studied by cyclic voltammetry (CV) (Table 1). The first
half-wave potentials (E1/2 vs. Fc/Fcþ) of DC1, DC2 DC3 and SC
adsorbed on TiO2 film were determined to be 0.29, 0.36, 0.30 and
dye DC3 exhibited broaden and more intensive than that of SC. The
absorption properties of the three dyes in the solution are consis-
tent with the energy optical band (E0e0) between the HOMO and
LUMO energy levels, and can also be proved by the molecular
optimization results of the dyes (Fig. 3). Compared to the absorp-
tion spectra of the dyes in the solution, the absorption spectra on
TiO2 (Fig. 2) are broadened, and the absorption intensity in the
ultraviolet region decreases; however, the absorption intensity in
the visible light region increases, accompanying with a bath-
ochromic shift of the absorption maximum [26].
0.33 V, respectively. Therefore, the first oxidation potentials (Eox
)
versus normal hydrogen electrode (NHE), corresponding to the
highest occupied molecular orbital (HOMO) levels, were 0.92, 0.99,
0.93 and 0.96 V calibrated by addition of 0.63 V to the potential vs
Fc/Fcþ (vs NHE), respectively. The estimated excited state potentials
corresponding to the lowest unoccupied molecular orbital (LUMO)
levels, were ꢀ1.87, ꢀ1.45, ꢀ1.41 and ꢀ1.33 V (vs NHE) calculated
from Eox ꢀ E0e0, where the E0e0 were calculated from intersection
of the normalized absorption and the emission spectra (lint) and
E0e0 ¼ 1240/lint (Fig. 1b). On the other hand, the HOMO values
versus vacuum were transformed via the equation EHOMO ¼ ꢀe
[4.88 þ E1/2 (vs. Fc/Fcþ)] [27], and the corresponding EHOMO of DC1-
3.3. Electrochemical properties
To evaluate the feasibility of the regeneration of the dyes and
electron injection from the excited state of the dyes to the
Fig. 3. The optimized structure and the frontier molecular orbitals of the HOMO and LUMO calculated with DFT on a B3LYP/6e31 þ G(d) level of the dyes. c: Calculated HOMO-
LUMO levels for the chain of DC1 which employed carbazole as donor; d; Calculated HOMO-LUMO levels for the chain of DC1, DC2, DC3 and SC which employed diphenylamine as
donor; e: Calculated HOMO-LUMO levels for the chain of DC2 and DC3 which employed phenothiazine as donor; f: Energy level of the conduction band edge of TiO2 (ꢀ4.00 eV vs
vacuum) [29]; g: Energy level of the I3-/I- redox couple (ꢀ4.60 eV vs vacuum) [28].

Y. Hong et al. / Dyes and Pigments 94 (2012) 481e489
487
Table 2
3 and SC versus vacuum were ꢀ5.17, ꢀ5.24, ꢀ5.18 and ꢀ5.21 eV,
respectively. The ELUMO calculated by [EHOMO E0e0
Photovoltaic parameters of DSSCs.
þ
]
Dye
Jsc/mA cmꢀ2
Voc/mV
FF
h/%
were ꢀ2.38, ꢀ2.80, ꢀ2.84 and ꢀ2.90 eV, respectively. The results
showed that the HOMO levels of all the dyes were sufficiently
higher than that of Iꢀ/I3ꢀ redox potential value (0.4 V vs NHE
or ꢀ4.60 eV vs vacuum) [28], indicating that the oxidized dyes
formed after electron injection into the CB of TiO2 could thermo-
dynamically accept electrons from Iꢀ ions and then were regen-
erated. The LUMO levels of these dyes were significantly lower than
that of the conduction band edge energy level of the TiO2 electrode
(ꢀ0.5 V vs NHE or ꢀ4.00 eV vs vacuum) [29], and provided that an
energy gap (Egap) of 0.2 eV [30] was necessary for efficient electron
injection. Hence, an effective electron transfer from the excited dye
to TiO2 was ensured.
DC1
DC2
DC3
SC
5.73
8.98
10.79
8.20
715
756
687
655
0.69
0.69
0.70
0.71
2.82
4.66
5.19
3.80
4.66, 2.82 and 3.80%, respectively. The highest
DC3 due to its relatively higher Jsc, which could be ascribed to its
higher light harvesting efficiency in the visible region.
h of the cell based on
The incident monochromatic photon-to-current conversion
efficiency (IPCE) spectra of the DSSCs are plotted in Fig. 5. For DC3
based cell, a high IPCE (above 50%) was obtained in the range from
400 to 560 nm with a maximum value of 68% at 480 nm, and the
onset of IPCE tails off toward 705 nm. In the cases of DC2, DC1 and
SC, the IPCE exceeded 50% in a relatively narrow range of
400e523 nm, 400ꢀ467 nm and 435ꢀ532 nm and reached their
maximum of 68% at 450 nm (for DC2), 63% at 401 nm (for DC1) and
59% at 469 nm (for SC), respectively. On the other hand, the onset of
IPCE for DC2, DC1 and SC was extended to 623 nm, 534 nm and
653 nm, which corresponds to blue-shifts of 82 nm, 171 nm and
52 nm, compared to DC3, respectively. The higher IPCE values for
DC3 based DSSC should be attributed to its broader absorption and
enhanced molar extinction coefficient in the visible region, which
matched well with the absorbance spectra of the dyes in solution.
The higher and broader IPCE of the cell based on DC3 could lead to
a higher short-circuit photocurrent density (Table 2).
DC3 based cell exhibited a higher Jsc but lower Voc value
compared to that of DC2 sensitized cell. In general, the Voc value is
quite sensitive to the electron lifetime in the conduction band of
TiO2 [31]. To further shed light on the difference in Voc among the
dyes sensitized solar cells, the electrochemical impedance spec-
troscopy (EIS) of the DSSCs based on different dyes were measured
in the dark under a forward bias of ꢀ0.7 V. As shown in Fig. 6, two
semicircles were observed in the Nyquist plots. The smaller and
larger semicircles in the Nyquist plots were attributed to the charge
transfer at the counter electrode/electrolyte interface and the TiO2/
dye/electrolyte interface, respectively. As shown in Fig. 6a, the
radius of the larger semicircle was decreased gradually in the order
of DC2, DC1, SC and DC3 cell, which may result in the longest
electron lifetime of DC2 and shortest lifetime of DC3. Seemingly
there will be a different conclusion compared to IMVS. However,
according to the impedance parameters fitted by the equivalent
3.4. Molecular orbital calculations
To gain an insight into the molecular structure and electron
distribution, density functional theory (DFT) calculations were
performed on a B3LYP/6e31 þ G (d) level with Gaussian 03. The
electron distributions of the HOMO and LUMO of the dyes are
shown in Fig. 3. At the ground state for all the dyes, electrons are
homogeneously distributed in both the donors (diphenylamine,
carbazole and phenothiazine) and
p-bridge, and upon the light
illumination, electrons move from the HOMO to the LUMO by an
intramolecular charge transfer, and are finally located in anchoring
groups through the
p-bridge. The results indicated that the high
electron density from the donor units moved to the cyanoacrylic
acid moieties in the HOMOꢀLUMO excitation induced by light, thus
allowing an efficient photoinduced electron transfer from the dye
to the TiO2 electrode.
3.5. Photovoltaic performances of the DSSCs
The currentꢀvoltage (JꢀV) curves of DSSCs based on DC1-3 and
SC are shown in Fig. 4. The detailed parameters of short-circuit
current density (Jsc), open-circuit voltage (Voc), fill factor (FF) and
overall conversion efficiency (
h
) are summarized in Table 2. Among
of 5.19%
these dyes, the cell based on DC3 exhibited a maximum
h
(Jsc ¼ 10.79 mA cmꢀ2, Voc ¼ 687 mV, FF ¼ 0.70) under standard
global AG 1.5G solar light irradiation (100 mW cmꢀ2). Under the
same measuring conditions, while the cells sensitized with DC2,
DC1 and SC gave Jsc of 8.98, 5.73 and 8.20 mA cmꢀ2, Voc of 756, 715
and 655 mV and FF of 0.69, 0.69 and 0.71, corresponding to
h of
Fig. 4. JꢀV curves of DSSCs sensitized by DC1, DC2, DC3 and SC.
Fig. 5. IPCE spectra of DSSCs based on varied dyes.

488
Y. Hong et al. / Dyes and Pigments 94 (2012) 481e489
Fig. 6. Electrochemical impedance spectra (a) measured in the dark and electron lifetime (b) Incident light intensity dependent electron lifetime measured at 457 nm LED illu-
mination for DSSCs sensitized by DC1, DC2, DC3 and SC, respectively.
Table 3
Acknowledgments
Electrochemical parameters of DSSCs.
This work was financially supported by the National Natural
Science Foundation of China (20872038, 20873183, 21072064),
Jiangxi Province Natural Science Foundation of China
(2009GQC0055) and the Natural Science Foundation of Guangdong
Province, China (10351064101000000).
Dye
C/F (10ꢀ3
)
R/U
Electron Lifetime/ms
DC1
DC2
DC3
SC
1.14
1.37
5.37
0.42
87.25
107.1
17.35
69.4
99.7
146.7
93.2
29.1
circuit (inset in Fig. 6a) with the fitted values listed in Table 2,
where the electron lifetime can be estimated by sn ¼ Rrec ꢁ CPE2
(CPE2: chemical capacitance) [32,33]. DC3 based cell exhibits
a smaller recombination resistance (Rrec) compared to SC based
cell; however, the value of chemical capacitance (CPE2) of the DSSC
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based on DC3 is larger. As a result, the electron lifetimes (sn) of
DSSCs calculated by EIS showed the same order as the IMVS
outcomes, although these values are usually larger than those
obtained from IMVS, since the EIS measurement was performed in
the dark. Hence, the electron lifetime values were in the order of
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DC2
> DC1 > DC3 > SC implying the order of Voc of
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those of the electron lifetime values calculated by the Nyquist
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p
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Diphenylamine, carbazole and phenothiazine were used as electron
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Relatively high molar extinction coefficient of the DC series dyes
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