Influence of a D-π-A system through a linked unit of double and triple bonds in a triarylene bridge for dye-sensitised solar cells

Article abstract of DOI:10.1039/c7nj00413c

Herein, eight metal-free organic dyes (YH-1-YH-8) containing olefin or acetylene as π-spacer linkages in a triarylene bridge were synthesised. Moreover, two dyes (1N-PPP and 1N-PPS) without olefin and triple bonds as π-spacer linkages were used as references. The photophysical and electrochemical properties of the dyes were characterised, and the dyes were then used to fabricate dye-sensitised solar cells (DSSCs). We demonstrated the use of a D-π-A dipolar system by employing arylamine derivatives as an electron donor, triarylene with iterative olefin or acetylene as a π-bridge, and cyanoacrylic acid as an electron acceptor. YH-1 had olefin as a repeating unit in the triarylene bridge and exhibited broad absorption, favourable short-circuit photocurrent density (J_sc), and favourable open-circuit voltage (V_oc) when used in a film morphology with DCA as a coabsorbent. The optimal device exhibited a J_sc of 16.23 mA cm^-2, a V_oc of 650 mV, and a fill factor of 0.67, corresponding to an overall conversion efficiency of 7.08%. The photophysical properties of the DSSCs were analysed using time-dependent density functional theory with the B3LYP functional.

Full text of DOI:10.1039/c7nj00413c

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ISSN 1144-0546
PAPER
Jason B. Benedict et al.
The role of atropisomers on the photo-reactivity and fatigue of
diarylethene-based metal–organic frameworks
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DOI: 10.1039/C7NJ00413C
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ARTICLE
Influence of D–π–A System Through Linked Unit of Double and
Triple Bonds in Triarylene Bridge for Dye-Sensitised Solar Cells
Rui-Yu Huang,a Yu-Hsiang Chiu,†a Yu-Hsuang Chang,a Kew-Yu Chen,b Pei-Ting Huang,a Ting-Hsuan
Received 00th January 20xx,
Accepted 00th January 20xx
Chiang,a and Yuan Jay Chang*a
DOI: 10.1039/x0xx00000x
Eight metal-free organic dyes (YH-1–YH-8) containing olefin or acetylene as the π-spacer linkage in the triarylene bridge
were synthesised. Two dyes (1N-PPP and 1N-PPS) without the olefin and triple bonds as π-spacer linkages were used as
references. The photophysical and electrochemical properties of the dyes were characterised, and the dyes were then to
fabricate dye-sensitised solar cells (DSSCs). We demonstrated the use of the D–π–A dipolar system by employing arylamine
derivatives as an electron donor, triarylene with iterative olefin or acetylene as a π-bridge, and cyanoacrylic acid as an
electron acceptor. YH-1 had olefin as a repeat unit in the triarylene bridge and had broad absorption, favourable short-
circuit photocurrent density (Jsc), and favourable open-circuit voltage (Voc) when used in film morphology with DCA as a
coabsorbent. The optimal device exhibited a Jsc of 16.23 mA·cm−2, a Voc of 650 mV, and a fill factor of 0.67, corresponding to
an overall conversion efficiency of 7.08%. The photophysical properties of the DSSCs were analysed using time-dependent
density functional theory with the B3LYP functional.
www.rsc.org/
A. Numerous metal-free organic dyes have been investigated
and demonstrated to exhibit a high performance level similar to
that of ruthenium-based complexes.10-17 Yano and Hanaya used
an alkoxysilyl anchor dye (ADEKA-1) as a cosensitiser and
achieved the highest performance yet reported (i.e., 14%) with
LEG-4 in metal-free organic dyes.18
To achieve an optimal D–π–A photosensitiser for DSSCs, it is
critical to improve the cell’s power conversion efficiency. The π-
bridge is a crucial factor in DSSCs not only because it connects
D and A in the electron channel, but also because a conjugated
chromophore with light harvesting ability improves the short-
circuit current (Jsc). Numerous studies have focused on
1 Introduction
Very recently, under limited stocks of fossil fuels and CO2
emission issue in global which is urged to investigate and
develop renewable and environmental friendly energy source.
Solar energy is generally acknowledged as
a potential
alternative energy source. In the past two decades, dye-
sensitised solar cells (DSSCs) based on nanocrystalline TiO2 and
photosensitisers have received considerable attention because
they are easy to fabricate, colourful and transparent devices,
low-cost devices, and can be scaled up.1-4 DSSC devices utilising
ruthenium-based polypyridyl complexes exhibit
a power
conjugated π-bridges, with the π-bridge unit in the sensitiser
19-23
mainly composed of anthracene,15,
benzene,24-25
conversion efficiency of more than 11% under AM 1.5
conditions.5-8 Diau and Yeh et al. used a porphyrin dye (YD2-o-
C8) and achieved a maximal performance of 13% with Y123 in a
cocktail system.9 However, one previous report on a metal
complex sensitiser reported a complicated synthesis route,
difficult purification, low yield, and source-limited metal. Metal-
free organic dyes are environmental friendly, have a high molar
extinction coefficient, can be synthesised at a low cost, have
high structural flexibility, and have sensitiser variety. Most
organic sensitisers with high efficiency have dye molecules with
linearly shaped structures comprising a strong D–π–A dipole
with an electron donor D, a π-bridge, and an electron acceptor
benzothiadiazole,26-29 diketopyrrolopyrrole,30-32 furan,33-34
pyrrole,35-36 and thiophene,37-38 all of which exhibit C–C linkages.
However, some π-spacers exhibit a low degree of π-conjugation
along the main chromophore through the C–C linkage, which
may reduce their electron injection efficiency.20, 39 In previous
studies, the expansion of π-conjugated chromophores has
yielded higher Jsc, which is often accompanied by a lower open-
circuit voltage (Voc). The effect of Voc on device performance has
mostly been attributed to the electron lifetime, which is the
time taken for electrons from the excited state of the
photosensitiser that have been injected into the nanoporous
TiO2 to recombine.40-41 The Voc results of previous reports can
be summarised as follows: (i) The conduction band edge of TiO2
is downshifted by electron acceptor species. (ii) Bulky
triarylamine donors and alkyl substituents result in higher Voc
and a longer electron lifetime because of the enhanced surface
blocking effect. (iii) The dye structures yield interactions
between electrolyte and dye, hence producing numerous
electrolyte acceptor species at the interface and enhancing
electron recombination. (iv) Dye structures that exhibit
favourable film morphology cover the TiO2 surface more
This journal is © The Royal Society of Chemistry 20xx
J. Name., 2013, 00, 1-3 | 1

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Journal Name
completely, thus preventing direct contact with the electron
acceptor of the electrolyte.
n-Butyllithium (1.6 M in hexane), N,N-Dimethylformamide,
sodium hydride (NaH), Palladium(II) aDceOtIa: 1t0e.10(P39d/(CO7ANJc0)20)4,135C-
View Article Online
Although some report showed fancy dye skeleton and good Bromothiophene-2-carbaldehyde,
performance, it also has complicated synthetic route, and a low Triethylamine, Diisopropylamine, Copper (I) iodide (CuI),
totally yield. 15-17, 42 We previously reported a simplify triarylene Trimethylsilylacetylene,
1-Iodo-4-bromobenzene, Tri(o-
π-bridge using C–C single bond linkage (1N-PPP and 1N-PPS tolyl)phosphine, Tetrakis(triphenylphosphine) palladium (0) (Pd
4-Bromobenzaldehyde,
)
that possessed different π-conjugated chromophores (PPh3)4), Piperidine, Cyanoacetic acid, Ammonium acetate, and
(phenylene/thiophene) and a slight twist in the bridge moiety.25 Acetic acid glacial were purchased from ACROS, Alfa, Merck,
And rare report to discuss the Influence by double and triple Lancaster,
TCI,
Sigma-Aldrich,
Showa,
respectively.
bonds linkage in triarylene Bridge for DSSCs. In this study, we Chromatographic separations were performed using Merck
designed and synthesised eight YH-series dyes (YH-1
–
YH-8
)
Kieselgel silica gel 60 (40–63 μm).
containing olefin or acetylene as the π-spacer linkage in the
triarylene bridge. To focus the effect of different dye structures
on the charge recombination rate and the electron lifetime was
investigated, and we also evaluated how the film morphology
with the co-absorbent enhanced the performance of the
resultant DSSC devices. We also discovery the thiophene
moieties can enhance light harvesting, but the sensitisers with
thiophene spacer exhibited lower Voc than dyes with phenylene
π-bridges, and discuss in the section of Photovoltaic
performance of DSSCs. The synthesis procedures are described
in Scheme 1, and all structures were confirmed using
spectroscopy.
(E)-2-cyano-3-(5-((E)-4-((E)-4-(naphthalen-1-yl(phenyl)amino)
-styryl)styryl)thiophen-2-yl)acrylic acid (YH-1). A mixture of 4a (1.05
g, 1.96 mmol), cyanoacetic acid (168 mg,1.96 mmol), and piperidine
(1 mL, 10 mmol) in acetic acid was placed in a three-necked flask with
15 mL chloroform and stirred at 70 °C for 6 h. After cooling, the
reaction was quenched by adding distilled water, and extracted with
CH2Cl2. The organic layer was dried over anhydrous MgSO4 and
evaporated under vacuum. The product was purified by silica gel
column chromatograph eluted with CH2Cl2/acetic acid (19/1). The
black solid was isolated in 77% yield (904 mg, 1.51 mmol). δH (400
MHz, THF-d8) 8.35 (s, 1H), 7.96 (d, 1H, J = 8.4 Hz), 7.94 (d, 1H, J = 8.04
Hz), 7.84 (d, 1H, J = 8.16 Hz), 7.79 (d, 1H, J = 3.92 Hz), 7.61 (d, 2H, J
=8.36 Hz), 7.55 (d, 2H, J = 9.08 Hz), 7.27-7.37 (m, 3H), 7.19-7.24 (m,
3H), 7.09 (d, 2H, J = 7.44 Hz), 7.06 (d, 1H, J = 16.0 Hz), 6.95-6.98 (m,
3H). δC (100 MHz, THF-d8) 163.1, 152.4, 148.2, 148.1, 145.4, 143.3,
138.9, 138.4, 135.5, 135.1, 134.7, 132.4, 131.2, 130.7, 128.9, 128.7,
128.2, 127.3, 127.2, 127.0, 126.9, 126.4, 126.2, 126.1, 125.9, 125.7,
123.9, 122.4, 122.0, 121.0, 120.2, 115.6, 98.6. MS (ESI, 70 eV): m/z
(relative intensity) 599 (M+, 100); HRMS calcd for C40H27N2O2S:
599.1793, found 599.1789.
(E)-3-(5-((E)-4-((E)-4-(bis(4-(hexyloxy)phenyl)amino)styryl)-
styryl)thiophen-2-yl)-2-cyanoacrylic acid (YH-2). Compound YH-2
was synthesized according to the same procedure as that of YH-1.
Dark red solid of YH-2 was obtained in 75% yield. δH (400 MHz, CDCl3)
8.31 (s, 1H), 7.70 (d, 1H, J = 4.12 Hz), 7.50 (s, 3H), 7.34 (d, 2H, J = 8.72
Hz), 7.28 (s, 3H), 7.23 (d, 2H, J = 1.2 Hz), 7.85 (d, 1H, J = 3.96 Hz), 7.07
(d, 4H, J = 8.88 Hz), 6.94 (d, 2H, J = 15.88 Hz), 6.91 (d, 1H, J = 8.56 Hz),
6.85 (d, 4H, J = 8.96 Hz), 3.95 (t, 4H, J = 6.52 Hz), 1.76-1.83 (m, 4H),
1.45-1.50 (m, 4H), 1.34-1.38 (m, 8H), 0.93 (t, 6H, J = 6.96 Hz). δC (100
MHz, CDCl3) 166.3, 155.6, 154.5, 148.7, 147.5, 140.3, 140.0, 138.9,
134.3, 134.1, 133.8, 129.4, 128.9, 127.4, 127.3, 126.9, 126.7, 126.6,
125.0, 120.0, 119.7, 115.8, 115.3, 68.2, 31.6, 29.3, 25.7, 22.6, 14.0.
MS (ESI, 70 eV): m/z (relative intensity) 750 (M+, 100); HRMS calcd
for C48H50N2O4S: 750.3491, found 750.3494.
Fig.1 Organic dye structures of YH-series.
2 Experimental
2.1 Characterization and reagents
All reactions and manipulations were performed under a
nitrogen atmosphere, and solvents were freshly distilled
according to standard procedures. 1H and 13C nuclear magnetic
resonance (NMR) spectra were recorded using a Bruker (AVIII
HD 400) spectrometer with CDCl3, THF-d8, or DMSO-d6 as the
solvent. Chemical shifts (δ) were reported downfield from the
peak with respect to tetramethylsilane. Absorption spectra
were recorded using a Shimadzu UV-1800 spectrophotometer,
and emission spectra were obtained using a Hitachi F-4500
spectrofluorometer. Redox potentials were measured through
cyclic voltammetry on a CHI 620 analyser. All measurements
were performed in tetrahydrofuran solutions containing 0.1 M
tetrabutylammonium hexaflourophosphate as the supporting
electrolyte under ambient conditions after purging for 10 min
with N2. Furthermore, the conventional three-electrode
configuration was employed, comprising a glassy carbon
working electrode, a platinum counter electrode, and an Ag/Ag+
reference electrode calibrated using ferrocene/ferrocenium as
an internal reference. Mass spectra were recorded using a JEOL
JMS-700 double-focusing mass spectrometer.
(E)-2-cyano-3-(4-((E)-4-((E)-4-(naphthalen-1-yl(phenyl)-
amino)styryl)styryl)phenyl)acrylic acid (YH-3). Compound YH-3 was
synthesized according to the same procedure as that of YH-1. Dark
red solid of YH-3 was obtained in 78% yield. δH (400 MHz, DMSO-d6)
8.30 (s, 1H), 8.06 (d, 2H, J = 8.04 Hz), 8.02 (d, 1H, J = 8.16 Hz), 7.92 (d,
2H, J = 8.24 Hz), 7.85 (d, 1H, J = 8.32 Hz), 7.80 (d, 2H, J = 7.72 Hz), 7.63
(d, 2H, J = 7.92 Hz), 7.57-7.60 (m, 3H), 7.42-7.54 (m, 5H), 7.38 (d, 2H,
J = 6.8 Hz), 7.31 (d, 1, J = 19.16 Hz), 7.25 (d, 2H, J = 8.04 Hz), 6.97-7.09
(m, 4H), 6.87 (d, 2H, J = 7.84 Hz). δC (100 MHz, DMSO-d6) 163.9, 153.9,
148.0, 147.8, 142.9, 142.5, 138.0, 135.8, 135.4, 132.0, 131.7, 131.0,
130.8, 130.6, 129.8, 129.0, 128.9, 128.1, 127.8, 127.7, 127.5, 127.3,
127.1, 127.0, 126.8, 126.3, 123.8, 122.8, 122.5, 121.0, 116.9, 103.0.
2 | J. Name., 2012, 00, 1-3
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MS (ESI, 70 eV): m/z (relative intensity) 593 ((M-H)-, 100); HRMS calcd intensity) 589 ((M-H)-, 100); HRMS calcd for C42H25N2O2: 589.1916,
View Article Online
DOI: 10.1039/C7NJ00413C
for C42H29N2O2: 593.2229, found 593.2227.
found 589.1916.
(E)-3-(4-((E)-4-((E)-4-(bis(4-(hexyloxy)phenyl)amino)styryl)-
(E)-3-(4-((4-((4-(bis(4-(hexyloxy)phenyl)amino)phenyl)-
styryl)phenyl)-2-cyanoacrylic acid (YH-4). Compound YH-4 was ethynyl)phenyl)ethynyl)phenyl)-2-cyanoacrylic
acid
(YH-8).
synthesized according to the same procedure as that of YH-1. Black Compound YH-8 was synthesized according to the same procedure
solid of YH-4 was obtained in 78% yield. δH (400 MHz, THF-d8) 8.24 (s, as that of YH-1. Dark red solid of YH-8 was obtained in 82% yield. δH
1H), 8.08 (d, 2H, J = 7.88 Hz), 7.74 (d, 2H, J = 8.24 Hz), 7.60 (d, 2H, J = (400 MHz, THF-d8) 8.29 (s, 1H), 8.11 (d, 2H, J = 8.52 Hz), 7.70 (d, 2H,
8.32 Hz), 7.54 (d, 2H, J = 8.36 Hz), 7.36-7.43 (m, 3H), 7.29 (d, 1H, J = J = 8.48 Hz), 7.56 (d, 2H, J = 8.52 Hz), 7.51 (d, 2H, J = 8.32 Hz), 7.31 (d,
16.28 Hz), 7.18 (d, 1H, J = 16.28 Hz), 7.01-7.06 (m, 5H), 6.85-6.89 (m, 2H, J = 8.88 Hz), 7.08 (d, 4H, J = 8.84 Hz), 6.90 (d, 4H, J = 8.88 Hz), 6.84
6H), 3.97 (t, 4H, J = 6.44 Hz), 1.80-1.83 (m, 4H), 1.48-1.54 (m, 4H), (d, 2H, J = 8.84 Hz), 3.97 (t, 4H, J = 6.48 Hz), 1.76-1.83 (m, 4H), 1.50-
1.37-1.42 (m, 8H), 0.96 (t, 6H, J = 6.92 Hz). δC (100 MHz, THF-d8) 155.9, 1.54 (m, 4H), 1.37-1.42 (m, 8H), 0.96 (t, 6H, J = 7.12 Hz). δC (100 MHz,
152.6, 148.6, 142.3, 140.4, 138.2, 135.5, 131.5, 131.2, 130.9, 129.4, THF-d8) 162.6, 156.4, 152.4, 149.3, 139.7, 132.1, 131.8, 131.5, 131.1,
128.7, 127.1, 126.7, 126.5, 126.3, 125.0, 119.8, 115.0, 67.7, 31.6, 130.7, 127.4, 127.2, 124.7, 121.6, 118.3, 115.1, 113.0, 104.3, 92.6,
29.3, 25.7, 22.5, 13.4. MS (ESI, 70 eV): m/z (relative intensity) 744 90.1, 87.3, 67.7, 31.6, 29.3, 25.7, 22.5, 13.3. MS (ESI, 70 eV): m/z
(M+, 100); HRMS calcd for C50H52N2O4: 744.3927, found 744.3927.
(relative intensity) 740 (M+, 100); HRMS calcd for C50H48N2O4:
740.3614, found 740.3608.
(E)-2-cyano-3-(5-((4-((4-(naphthalen-1-yl(phenyl)amino)-
phenyl)ethynyl)phenyl)ethynyl)thiophen-2-yl)acrylic acid (YH-5).
Compound YH-5 was synthesized according to the same procedure 2.2 Fabrication and Characterization of DSSCs.
as that of YH-1. Black solid of YH-5 was obtained in 82% yield.δH (400 Fluorine-doped tin oxide (FTO) conducting glass (FTO glass, Solaronix
MHz, DMSO-d6) 8.50 (s, 1H), 8.03 (d, 1H, J = 8.12 Hz), 7.99 (d, 1H, J = TCO22-7; sheet resistance = 7 Ω square−1) and titania oxide pastes of
3.96 Hz), 7.95 (d, 1H, J = 8.2 Hz), 7.83 (d, 1H, J = 8.36 Hz), 7.52-7.62 Ti-Nanoxide T/SP and R/SP were purchased from Solaronix. A thin
(m, 7H), 7.41-7.48 (m, 4H), 7.30 (t, 2H, J = 8.04 Hz), 7.04-7.10 (m, 3H), film of TiO2 (10–12-μm transparent layer + 5-μm scattering layer) was
6.82-6.88 (m, 2H). δC (100 MHz, DMSO-d6) 168.9, 163.5, 149.0, 147.5, coated onto a 0.28-cm2 FTO glass substrate, which was then
147.2, 145.9, 142.5, 139.9, 137.3, 136.4, 135.4, 133.8, 133.2, 132.3, immersed in a THF solution containing 3 × 10−4 M dye sensitiser for
131.9, 131.0, 130.5, 130.1, 130.0, 129.0, 127.9, 127.8, 127.6, 127.3, 12 h, rinsed with anhydrous acetonitrile, and dried. Another piece of
127.2, 127.1, 126.8, 126.3, 123.8, 123.7, 123.5, 123.2, 119.8, 119.3, FTO glass with a 100-nm-thick layer of sputtered Pt was used as a
116.9, 113.7, 98.7, 83.4. MS (FAB, 70 eV): m/z (relative intensity) 597 counter electrode. The active area was controlled at a dimension of
((M+H)+, 100); HRMS calcd for C40H25N2O2S: 597.1631, found 0.28 cm2 by adhering a 60-μm-thick piece of polyester tape to the Pt
597.1630.
electrode. The photocathode was placed on the top of the counter
electrode and tightly clipped to form a cell, and an electrolyte was
injected into the seam between the two electrodes. An acetonitrile
(E)-3-(5-((4-((4-(bis(4-(hexyloxy)phenyl)amino)phenyl)-
ethynyl)phenyl)ethynyl)thiophen-2-yl)-2-cyanoacrylic acid (YH-6). solution containing LiI (0.5 M), I2 (0.05 M), and 4-tert-butylpyridine
Compound YH-6 was synthesized according to the same procedure (TBP; 0.5 M) was used as electrolyte. Devices composed of the
as that of YH-6. Dark red solid of YH-6 was obtained in 80% yield. δH commercial dye N719 under the same conditions (3 × 10−4 M,
(400 MHz, THF-d8) 8.39 (s, 1H), 7.84 (d, 1H, J = 3.64 Hz), 7.58 (d, 2H, Solaronix S.A., Switzerland) were used as references. The cell
J = 8.12 Hz), 7.52 (d, 2H, J = 7.96 Hz), 7.43 (d, 1H, J = 3.84 Hz), 7.30 (d, parameters were obtained under incident light with an intensity of
2H, J = 8.44 Hz), 7.09 (d, 4H, J = 8.6 Hz), 6.90 (d, 4H, J = 8.6 Hz), 6.83 100 mW·cm−2 (as measured using a thermopile probe; Oriel 71964)
(d, 2H, J = 8.44 Hz), 3.98 (t, 4H, J = 6.32 Hz), 1.76-1.82 (m, 4H), 1.51- that was generated using a 300-W solar simulator (Oriel Sol3A Class
1.54 (m, 4H), 1.39-1.42 (m, 8H), 0.96 (t, 6H, J = 6.24 Hz). δC (100 MHz, AAA Solar Simulator 9043A, Newport) and passed through an AM 1.5
THF-d8) 156.4, 149.4, 144.9, 139.7, 137.5, 132.6, 132.2, 131.4, 131.1, filter (Oriel 74110). The light intensity was further calibrated using an
127.2, 125.1, 120.9, 118.2, 115.4, 115.1, 112.9, 97.7, 92.9, 87.3, 83.2, Oriel reference solar cell (Oriel 91150) and adjusted to 1.0 sun. The
67.8, 31.6, 29.3, 25.7, 22.5, 13.4. MS (FAB, 70 eV): m/z (relative monochromatic quantum efficiency was recorded using
a
intensity) 746 (M+, 100); HRMS calcd for C48H46N2O4S: 746.3178, monochromator (Oriel 74100) under short-circuit conditions. The
found 746.3176.
electrochemical impedance spectra of the DSSCs were recorded
using an impedance/charge extraction method (CEM)/intensity-
modulated photovoltage spectroscopy (IMVS) analyser (Zahner
(E)-2-cyano-3-(4-((4-((4-(naphthalen-1-yl(phenyl)amino)-
phenyl)ethynyl)phenyl)ethynyl)phenyl)acrylic
acid
(YH-7). Ennium).
Compound YH-7 was synthesized according to the same procedure
as that of YH-1. Red solid of YH-7 was obtained in 80% yield. δH (400
MHz, DMSO-d6) 8.29 (s, 1H), 8.05 (d, 2H, J = 8.32 Hz), 8.02 (d, 1H, J =
8.16 Hz), 7.93 (d, 1H, J = 8.44 Hz), 7.84 (d, 1H, J = 8.36 Hz), 7.72 (d,
2H, J = 8.2 Hz), 7.51-7.61 (m, 6H), 7.39-7.47 (m, 4H), 7.28 (t, 2H, J =
7.72 Hz), 7.07 (d, 2H, J = 7.92 Hz), 7.03 (t, 1H, J = 7.92 Hz), 6.82-6.86
(m, 3H). δC (100 MHz, DMSO-d6) 168.9, 163.4, 162.7, 152.4, 148.9,
147.4, 147.3, 142.5, 136.0, 135.4, 132.7, 132.2, 131.0, 129.9, 129.0,
127.9, 127.6, 127.3, 127.1, 126.8, 126.7, 126.2, 123.7, 123.4, 123.1,
120.5, 119.8, 116.9, 113.7, 93.3, 90.2. MS (ESI, 70 eV): m/z (relative
2.3 Quantum Chemistry Computations
The structures of dyes were optimized using the B3LYP/6-31G(d)
hybrid functional. For the excited states, a time-dependent
density functional theory (TDDFT) with the B3LYP functional
was employed. All analyses were performed using the Q-Chem
3.0 software. The frontier orbital plots of the highest and lowest
occupied molecular orbitals (hereafter referred to as the HOMO
and LUMO, respectively) were drawn using GaussView 04.
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DOI: 10.1039/C7NJ00413C
Scheme 1. Organic dye synthesis route. Reagents and conditions: (i) n-BuLi, DMF, THF, −78 °C; (ii) (a) NaH, CH3PPh3I, THF, 25–60 °C; (b) Pd(OAc)2, P(o-tolyl)3,
4-bromobenzaldehyde or 5-bromothiophene-2-carbaldehyde, triethylamine, 80 °C; (iv) piperidine, CNCH2COOH, CH2Cl2, 70 °C; (v) Pd (PPh3)4,
trimethylsilylacetylene, CuI, i-Pr2NH, toluene, 80 °C; (vi) (a) K2CO3, THF/MeOH; (b) Pd (PPh3)4, 1-bromo-4-iodobenzene, CuI, i-Pr2NH, toluene, 80 °C; (vii) Pd
(PPh3)4, CuI, i-Pr2NH, toluene, 80 °C.
reactions to yield compounds 10 and 11, and all aldehyde groups
were verified using proton NMR (ESI). The compounds 4, 5, 10, and
3 Results and discussion
11 that contained aldehyde groups were used to yield final products
through Knoevenagel condensation reactions. Eight final products
were obtained with high yields of cyanoacrylic acid acceptor units
that were easily purified. The structures of the eight compounds
were characterised using spectroscopy.
3.1 Synthesis
The structures of the dyes are illustrated in Fig. 1, and their synthesis
procedures are presented in Scheme 1. The YH-series contained
olefin or acetylene as the π-spacer linkage in the triarylene bridge
between the arylamine donor and acceptor of cyanoacrylic acid in
the sensitiser. The synthesis of the dyes began with 4-Bromo-
diarylaniline yielding the aldehyde group of compound 2 through 3.2 Absorption spectra
formylation. An aldehyde group extended the π-bridge through
The ultraviolet–visible absorption spectra of all sensitisers in
Wittig and Heck reactions to yield compounds 4 and 5. The π-spacer CH2Cl2 solution are presented in Fig. 2, and the parameters of the
linkage of acetylene was constructed by repeating Sonogashira sensitisers are listed in Table 1. The YH-series sensitisers exhibited
4 | J. Name., 2012, 00, 1-3
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two or three broad, high-intensity absorption peaks within the range
of 344–504 nm. The short wavelength region (265–383 nm) was
attributed to localised π–π* transitions, whereas the long
wavelength region (405–490 nm) was attributed to intramolecular
charge transfer (ICT) transitions. Compared with 1N-PPP and 1N-PPS,
extending π-conjugation by insertion of π-spacer linkage, the
absorption spectra of the dyes were red-shifted by approximately
30–64 nm with respect to those in the solution, except for YH-5,
which had a slightly blue-shifted spectrum. The ICT absorption band
was stronger when the olefin bonds were used π-spacer linkages
than when triple bonds were used as π-spacer linkages, indicating
that the full conjugation of the olefin linkage enhanced π-overlapping
and led to increased red shift and an extensive absorption region.
Hence, YH-1~YH-4 exhibited broader, high-intensity ICT transitions
and approximately 25–87 nm red-shifted ICT transitions in CH2Cl2
solution. The acetylene moiety was more electronegative than the
olefin bonds, and the electronegativity of the triple bonds weakened
the electron-withdrawing ability of the electron acceptor because of
the opposite dipole moment of the triple bond and electron acceptor.
Thus, the absorption spectra of the dyes with triple bonds were blue-
shifted compared with those of dyes with double bonds.19,43 The
absorption photocurrent (Jsc) and the intensity of absorption
exhibited the same π-spacer linkage trend for dyes in solution.
Compared with the absorption spectra in methylene chloride,
all dyes exhibited red-shift and spectral broadening on the TiO2
film, because of intermolecular J-aggregation of sensitizer or
strong interaction between the dye and semiconductor surface
when it is anchored onto the TiO2 surface.19, 43-44 And those
absorption spectra of sensitizers with alkoxy long chain are
broader than without, representing an advantageous spectral
property for light harvesting.
View Article Online
DOI: 10.1039/C7NJ00413C
6.0x104
4.0x104
YH-1
YH-2
YH-3
YH-4
YH-5
YH-6
YH-7
YH-8
2.0x104
0.0
300
400
500
600
700
Wavelength (nm)
Fig. 2 Absorption spectra of dyes in CH2Cl2 solution.
1.0
0.8
0.6
0.4
0.2
0.0
YH-1
YH-2
YH-3
YH-4
YH-5
YH-6
YH-7
YH-8
400
500
600
700
3.3 Electrochemical Properties
Wavelength (nm)
The first oxidation potentials (Eox) corresponding to the HOMO
level of the photosensitisers were measured using cyclic
voltammetry (Fig. S28). Two long hexyloxy chains in the arylamine
donor moiety strongly affected the electron delocalisation and
oxidation potential, increased the HOMO energy level to 0.29–0.32
eV, and reduced the HOMO–LUMO energy gap. The introduction of
olefin and acetylene moieties as π-spacer linkages had nearly no
effect on the HOMO energy level of the dyes but reduced the energy
gap, indicating that the coplanarity and π-conjugation in the
triarylene bridge was increased. Compared with the dye with
acetylene as π-spacer linkage, the introduction of the olefin π-spacer
linkage slightly increased the HOMO level. The lowest ionisation
potentials of the dyes in CH2Cl2 solution decreased in the following
order: YH-5 ≈ YH-7 > YH-1 ≈ YH-3 ≈ 1N-PPS ≈ 1N-PPP > YH-6 ≈ YH-8
> YH-2 ≈ YH-4 (Fig. 4 and S31). Moreover, the LUMO levels of the
dyes were estimated according to Eox and the zero–zero band gaps
at the onset of the absorption spectra (Table 1). The reduction of
energy gap energies not only the hexyloxy chains in the arylamine
donor group, but along with the thiophene unit in bridge. YH-1 and
YH-2 had narrow HOMO–LUMO energy gaps, a trend consistent with
the wider absorption ranges illustrated in Fig. 4. This trend was also
confirmed using theoretical calculations, as discussed in the
following section.
Fig. 3 Absorption spectra of dyes absorbed on TiO2.
3.4 Computational analysis
The effect of the use of dyes YH-1~8 on device performance was
further explored through theoretical models. Complete geometrical
optimisations were performed using TDDFT with the B3LYP
functional in combination with the standard 6-31G(d) basis set within
Q-Chem 3.0.45 The use of olefin or acetylene as the π-spacer linkage
in the triarylene bridge led to similar coplanarity, as demonstrated
by the optimised structure determined using theoretical
computation (Fig. S25). The frontier orbital electron distributions of
the dyes are illustrated in Figs. 5 and S26. The electron densities in
the HOMO and LUMO were mainly distributed around the
triphenylamine donor moieties and the cyanoacrylic acid of the
acceptor moieties, respectively. Previous relevant studies have
reported that a disturbance to charge delivery, either through a
distortion of the molecular geometry or intramolecular aggregation,
may reduce the charge migration rate. As long as the charge-
separated state has a long lifetime, high device quantum efficiency
can be achieved.39, 46 A delicate balance between charge separation
and recombination must be maintained by modifying the molecular
structures, bulky structures, and hydrophobic long chains that may
reduce intermolecular aggregation and dark current.
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The difference in the Mulliken charge distributions of the ground
state (S0) and excited state (S1) according to the estimate generated
using TDDFT/B3LYP is presented in Fig. 6 and Table S2.†† Dyes
containing alkoxy chains exhibited optimal charge separation in the
ICT state (bar chart, Fig. 6), because the chains enhance the electron-
donating ability of arylamine donors.
Journal Name
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DOI: 10.1039/C7NJ00413C
Photoexcitation pumps an electron from the HOMO to the LUMO
and thus shifts a considerable number of electrons from the donor
to the acceptor. Consequently, the HOMO–LUMO energy gap of dyes
YH-2, YH-4, YH-6, and YH-8 that contained alkoxy chains was lower
than that of dyes YH-1, YH-3, YH-5, and YH-7 that did not contain
alkoxy chains. Therefore, the ICT band in the even-numbered dyes
exhibited a bathochromic shift compared with that in the odd-
numbered dyes. A similar trend was identified for the dipole moment
(YH-2: 11.6309 D > YH-1: 9.7556 D) and CT transition excitation in the
YH-series sensitisers (Table S1).
Fig. 6 Difference of Mulliken charges between ground state (S0) and excited
state (S1 and S2), estimated by time dependent DFT/B3LYP model.
The transition probability was estimated according to the
excitations using TDDFT/B3LYP, and the calculated oscillator strength
(f) is presented in Table S1.†† The f values for the lowest energy ICT
transitions (S1 state) were all relatively high, ranging from 0.58 to
0.98. The results were consistent with the absorptivity of the dyes in
solution.
3.5 Photovoltaic performance of DSSCs
The DSSC devices composed of the designed photosensitisers were
absorbed on the TiO2 surface using a standard procedure. The
electrolyte used to investigate the performance of the devices
contained LiI (0.5 M), I2 (0.05 M), and TBP (0.5 M) in MeCN. The
experiments involving coabsorption were conducted using
deoxycholic acid (DCA). The incident photocurrent conversion
efficiency (IPCEs) and photocurrent–voltage (J–V) curve of all dyes
were measured under AM 1.5 solar light (100 mW·cm−2). The short-
circuit current (Jsc), open-circuit voltage (Voc), fill factor (FF), and
solar-to-electrical photocurrent density (η) are summarised in Table
1, wherein N719 serves as a reference dye.
The J–V curve and IPCE of all devices are plotted in Fig. 7. An
apparent improvement of 2–53 mV in Voc was observed for dyes YH-
1, YH-3, YH-5, and YH-7 without long alkoxy chains, compared with
Voc obtained without DCA coabsorbent (Table 1). Favourable
morphology and coverage of the dyes on the TiO2 film reduced the
Li+ or I3− ions in contact with the TiO2 surface, enhancing Voc because
of an improved surface blocking effect and subsequently increasing
the gap between the conduction bands of the TiO2 and electrolyte.47-
Fig. 4 HOMO - LUMO energy levels of the YH-series sensitizer.
49
Dyes YH-1, YH-3, YH-5, and YH-7 without long alkoxy chains had
higher Voc than the other dyes with alkoxy chains, indicating that they
reduced dark current in the device by substantially reducing the
charge recombination rate.
We modified the dyes’ structures by using thiophene moieties as
π-bridges near the anchoring group. Thiophene moieties can
enhance light harvesting. However, the organic dyes with thiophene
spacer exhibited lower Voc than dyes with phenylene π-bridges. Dyes
with more active sulphur sites had a higher tendency to form dye–
iodine complexes because of the strong interactions between iodine
and sulphur atoms.50
Compared with devices using reference dyes without double or
triple bond linkage units (such as 1N-PPP or 1N-PPS), we discovered
that the devices using double-bond dyes had dramatically improved
energy conversion efficiency η because of a large enhancement of Jsc
(YH-1 and YH-3). However, the introduction of triple bonds reduced
η because of a low Jsc (YH-5 and YH-7). This lower Jsc was because
these dyes had narrower absorption spectra than the dyes with
double bonds, and this result was consistent with the dye loading
results for dyes on TiO2 films (Table 1). After adding DCA (10 mM) as
co-absorbent to all YH-series dyes improved the Jsc and quantum
Fig. 5 The frontier HOMO and LUMO orbitals of YH-series dyes estimated by
time-dependent DFT/B3LYP (6-31G* basis set).
6 | J. Name., 2012, 00, 1-3
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View Article Online
Table 1 Photochemical and electrochemical parameters of the dyes.
DOI: 10.1039/C7NJ00413C
b
c
dye
λmaxa (nm)/
ε (104 M-1cm-1)
476 (3.86)
490 (3.83)
439 (4.30)
450 (3.23)
406 (4.00)
403 (3.10)
405 (4.52)
420 (3.20)
375 (3.74)
422 (3.63)
---
EHOMO
(V)
Eg
ELUMO
Jsc (mA·cm-2)
Voc (mV)
FF
ηd ,e (%)
Dyes Loading
(10-7mol/cm-2)
(eV)
2.20
2.14
2.36
2.25
2.53
2.36
2.61
2.53
2.78
2.52
2.60g
(V)
YH-1
YH-2
YH-3
YH-4
YH-5
-5.33
-5.01
-5.29
-5.00
-5.36
-5.06
-5.36
-5.06
-5.33
-5.32
-5.60g
-3.13
-2.87
-2.93
-2.75
-2.83
-2.70
-2.75
-2.53
-2.55
-2.80
-3.00g
14.80
11.80
13.80
10.10
7.62
9.13
8.48
8.84
635
582
695
693
644
602
704
693
680
660
744
0.65
0.60
0.67
0.66
0.69
0.62
0.68
0.68
0.60
0.60
0.66
6.14
4.16
6.47
4.63
3.37
3.43
4.07
4.17
4.60
5.68
7.29
15.82
9.63
11.27
9.05
4.79
7.75
5.96
6.88
---
YH-6
YH-7
YH-8
1N-PPPf
1N-PPSf
N719
11.24
14.20
14.86
---
---
a Absorption and Emission are in CH2Cl2. b Oxidation potential in CH2Cl2 (10-3 M) containing 0.1 M (n-C4H9)4NPF6 with a scan rate 50 mV·s-1. c ELUMO calculated
by EHOMO – Eg. d Performance of DSSCs measured in a 0.28 cm2 working area on a FTO (7Ω/square) substrate. e Electrolyte : LiI (0.5 M), I2 (0.05 M), and TBP
(0.5 M) in MeCN. f see reference 25. g see reference 62.
16
14
12
10
8
100
investigated whether adding DCA as a coabsorbent prevented the
YH-1
YH-3
YH-5
YH-7
YH-1
YH-3
YH-5
YH-7
horizontal alignment of the sensitiser on the TiO2 surface. For dyes
that cannot form high quality films, adding DCA can effectively
improve dye alignment and consequently reduce the charge
recombination rate.56-58
Adding DCA (10 mM) to all dyes improved the quantum
efficiency of the resultant DSSCs by 1%–33% (Table 2). DSSCs
containing YH-1 and YH-2 exhibited dramatic enhancements of
15.3% and 32.9%, respectively. It’s observed enhancement in
Fig. S30, dyes with thiophene moiety showed lower Voc because
of the strong interactions between iodine and sulphur atoms
80
60
40
20
0
6
4
2
0
400
500
600
700
0.0
0.2
0.4
0.6
Wavelength (nm)
Voltage(VOC
)
16
14
12
10
8
YH-2
YH-4
YH-6
YH-8
YH-2
YH-4
YH-6
YH-8
80
60
40
20
0
(
YH-1, YH-2, YH-5, and YH-6). Addition of DCA can be
6
suppressed to form dye–iodine complexes, and formed the
good morphology on TiO2 film. Adding DCA considerably
increased Voc and Jsc, indicating an improvement in dye
morphology. Thus, the addition of a DCA coabsorbent enabled
the more vertical alignment of the dye on the TiO2 surface. This
effect was confirmed by the DSSCs’ higher resistance
determined using electrochemical impedance spectroscopy
(EIS), as presented in the following section. The optimal
photovoltaic efficiency was that of YH-1, with a Jsc of 16.23
mA·cm−2, a Voc of 650 mV, and an FF of 0.67, corresponding to
an overall conversion efficiency of 7.08%.
4
2
0
0.0
400
500
600
700
0.2
0.4
Voltage(VOC
0.6
)
Wavelength (nm)
Fig. 7 J-V plots and IPCE of DSSCs devices of YH-1~8 without DCA co-absorbent.
The plots were measured under the light intensity of 1.0 sun.
efficiency of the resultant DSSCs, the YH-5 and YH-7 still
displayed lower Jsc than YH-1 and YH-3. The result consisted
with dye loading with DCA co-absorbent in Table 2. More
confirmed the olefin π-spacer linkages of organic dyes showed
better light harvesting effect than triple bonds π-spacer linkages
of organic dyes.
16
14
12
10
8
16
14
12
10
8
(a)
(b)
Previous reports have revealed that long hydrophobic chains may
prevent contact between I3− ions and the TiO2 surface, and in this
study, the compounds with long chains exhibited higher Voc than
those sensitisers without long chains.10,
However, the
51-52
6
YH-2
YH-4
YH-6
YH-8
6
YH-2(DCA)
YH-4(DCA)
YH-6(DCA)
YH-8(DCA)
YH-1
YH-3
YH-5
YH-7
YH-1(DCA)
YH-3(DCA)
YH-5(DCA)
YH-7(DCA)
4
4
introduction of long hydrophobic chains may not always improve Voc,
because some reports have calculated higher Voc when fewer or no
long alkyl chains have been used.53-55 Our investigation revealed that
sensitisers without long alkyl chains had higher Voc (YH-1, YH-3, YH-
5, and YH-7), indicating that the HOMO energy level of the sensitisers
2
2
0
0
0.0
0.2
0.4
0.6
0.0
0.2
0.4
0.6
Voltage(VOC
)
Voltage(VOC
)
was near the I−/I3 energy level, which may have reduced dye
−
Fig. 8 J–V curves of DSSCs fabricated w/wo a DCA co-absorbent at a light
intensity of 1.0 sun.
regeneration and increased the charge recombination rate.
The morphology of sensitisers on the TiO2 surface is also a crucial
factor for optimising the performance of DSSCs. The sensitiser must
be placed sufficiently vertically on the TiO2 film to prevent
intermolecular aggregation that causes dark current. We also
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plots with the largest semicircles and longest electron lifetimes,
View Article Online
100
80
60
40
20
0
100
80
60
40
20
DOI: 10.1039/C7NJ00413C
respectively.
YH-1
YH-3
YH-2
YH-4
(a)
(b)
We further validated the correlation between Voc and the electron
lifetime of a device. The electron lifetime (τr) was measured using
IMVS, and the results are presented in Fig. 10. The electron lifetime
reduced in the order YH-7 (40.59 ms) > YH-3 (35.80 ms) > YH-5 (31.33
ms) > YH-1 (27.39 ms) for devices under the same light intensity and
with DCA addition, which was consistent with the data obtained from
the Bode plot fits. Voc is defined as the energy gap between the Fermi
levels of TiO2 and the redox couple of the electrolyte.60-61 A positive
shift in the conduction band of TiO2 may have reduced Voc and the
electron lifetime. YH-7 and YH-3, which did not contain more active
sulphur sites of the thiophene moieties to form dye–iodine
complexes, had reduced charge recombination and a higher electron
lifetime than the other dyes. The CEM revealed that the conduction
band edge of TiO2 was more downshifted for YH-1 and YH-5 than for
the other dyes, which again was consistent with the Nyquist plots.
YH-5
YH-6
YH-7
YH-8
with DCA
with DCA
0
0
0
50
100
150
200
50
100
Z'/ohm
150
200
Z'/ohm
60
50
40
30
20
10
0
60
50
40
30
20
10
YH-2
YH-4
YH-6
YH-8
with DCA
YH-1
YH-3
YH-5
YH-7
with DCA
(d)
(c)
0
10-1
100
101
102
103
104
105
10-1
100
101
102
103
104
105
Frequency (Hz)
Frequency (Hz)
Fig. 9. Impedance spectra of YH-series dyes in CH2Cl2 by using DCA as YH-3 without DCA coabsorbent exhibited a favourable Voc of 695 mV
co-absorbent. (a-b) Nyquist plots (i.e., minus imaginary part of the and an overall conversion efficiency of 6.47%.
impedance –Zʺ vs. the real part of the impedance Zʹ when sweeping the
frequency). (c-d) Bode phase plots at -0.73 V bias in the dark. The
electron diffusion lifetime τe = 1/2πf.
Table 2 Photovoltaic parameters of DSSCs fabricated using YH-1~8 with and
without DCA (10 mM)
dye
DCAa
(mM)
0
Jsc
(mA·cm-2)
14.80
16.23
11.80
13.24
13.80
14.07
10.10
10.84
7.62
8.21
9.13
9.46
8.48
8.60
8.84
8.98
Voc
(mV)
635
650
582
651
695
703
693
705
644
652
602
653
704
713
693
714
FF
ηb
(%)
Dyes
Loadingc
15.82
19.80
9.63
10.98
11.27
14.65
9.05
250
200
YH-1
YH-3
YH-5
YH-7
(b)
YH-1
YH-3
YH-5
YH-7
(a)
0.72
0.68
0.64
0.60
150
100
YH-1
YH-2
YH-3
YH-4
YH-5
YH-6
YH-7
YH-8
0.65
0.67
0.60
0.64
0.67
0.66
0.66
0.63
0.69
0.70
0.62
0.65
0.68
0.67
0.68
0.68
6.14
7.08
4.16
5.53
6.47
6.58
4.63
4.81
3.37
3.74
3.43
4.05
4.07
4.11
4.17
4.34
10
0
10
0
10
0
10
0
10
0
10
0
50
0.1
1
10
0.60
0.64
0.68
0.72
Electron density (1018 cm-3
)
V
/V
oc
9.88
4.79
5.32
7.75
8.05
Fig. 10. IMVS and CEM of YH-series dyes by using DCA as co-absorbent in
CH2Cl2. (a) Electron lifetime as a function of Voc was measured by IMVS
method. (b) Electron density as a function of Voc was measured by CEM
method.
5.96
10
0
10
6.23
6.88
7.08
3.6 Electrochemical impedance spectroscopy and electron lifetime
by CEM / IMVS
a
b
Concentration of dye is 3 × 10-4 M in CH2Cl2. Performance of DSSCs
measured in a 0.28 cm2 working area on an FTO (7Ω/square) substrate
under AM 1.5 condition with electrolyte 1 (E1). c (10-7mol/cm-2)
EIS was performed to further illustrate the photovoltaic properties
of the DSSCs. Nyquist and Bode plots were constructed under a
forward bias and dark conditions (Fig. 9). Semicircles were observed
in the Nyquist plots for each sensitiser, which are associated with
transport at the TiO2/electrolyte/dye interfaces. A larger semicircle
corresponds to larger charge recombination resistance at a low
frequency, indicating a lower charge recombination rate and smaller
dark current.59 The radii of the semicircles increased in the orders
YH-1 < YH-5 < YH-3 < YH-7 and YH-2 < YH-6 < YH-4 < YH-8, which was
consistent with the Voc of the dyes. The electron diffusion lifetime (τe)
of the device was estimated by fitting the equation in a Bode plot,
and a shift to a low frequency (f) corresponded to a longer electron
lifetime. YH-3, YH-4, YH-7, and YH-8 displayed higher Voc than the
dyes without coabsorbent DCA addition, indicating a lower charge
recombination rate (Fig. 9b). Particularly, YH-7 (34.9 ms) and YH-8
(37.2 ms) had the highest Voc, as verified by the Nyquist and Bode
Conclusions
We demonstrated that a simple D–π–A dipolar system and high-
performance DSSC can be achieved using olefin or acetylene as the π-
spacer linkage in the triarylene bridge. Eight metal-free organic dyes (YH-
1–YH-8) were synthesised. The olefin π-spacer linkages of YH-1~YH-4
exhibited broader, high-intensity absorption than the acetylene-based
linkages in CH2Cl2 solution and a higher IPCE and short-circuit
photocurrent density. Organic dyes containing thiophene moieties with
more active sulphur sites had a higher tendency to form dye–iodine
complexes because of the strong interactions between iodine and
sulphur atoms. Thus, organic dyes possessing thiophene spacers
displayed lower Voc than those with phenylene π-bridges. YH-3 without
DCA coabsorbent exhibited a favourable Voc of 695 mV and an overall
conversion efficiency of 6.47%.
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Zakeeruddin, M. Grätzel, J. L. Delgado and N. Martín, ChVeimew. EAurtric.lJe.O20nl1in2e,
YH-1 contained thiophene spacers and displayed a low Voc of 635
mV, but thiophene moieties may enhance light harvesting. YH-1 had
olefin as a repeat unit in the triarylene bridge and had broad
absorption, leading to improved Jsc and film morphology with the
DCA coabsorbent, resulting in favourable Voc. A typical device
fabricated using YH-1 had a Jsc of 16.23 mA·cm−2, a Voc of 650 mV, and
a FF of 0.67, corresponding to an overall conversion efficiency of
7.08%.
18, 11621.
DOI: 10.1039/C7NJ00413C
22 Y.-Z. Lin, C. H. Huang, Y. J. Chang, C.-W. Yeh, T.-M. Chin, K.-M. Chi, P.-T.
Chou, M. Watanabe, T. J. Chow, Tetrahedron, 2014, 70, 262.
23 H. Li, Y. Yang, Y. Hou, R. Tang, T. Duan, J. Chen, H. Wang, H. Han, T. Peng,
X. Chen, Q. Li and Z. Li, ACS Sustainable Chem. Eng., 2014, 2, 1776.
24 Y. J. Chang, Y.J. Wu, P.-T. Chou, M. Watanabe and T. J. Chow, Thin Solid
Film, 2014, 558, 330.
25 Y. J. Chang and T. J. Chow, Tetrahedron, 2009, 65, 4726.
26 M. Velusamy, K. R. Justin Thomas, J. T. Lin, Y.-C. Hsu and K.-C. Ho, Org.
Lett., 2005, 7, 1899.
27 W. Zhu , Y. Wu , S. Wang , W. Li , X. Li , J. Chen, Z.-S. Wang, and H. Tian,
Adv. Funct. Mater., 2011, 21, 756.
28 S. Haid, M. Marszalek, A. Mishra, M. Wielopolski, J. Teuscher, J.-E. Moser,
R. Humphry-Baker, S. M. Zakeeruddin, M. Grätzel and P. Bäuerle, Adv.
Funct. Mater., 2012, 22, 1291.
Acknowledgements
Financial supports from the Ministry of Science and Technology of
Taiwan (MOST 105-2119-M-029 -001 -) and Academia Sinica are
gratefully acknowledged. Special thanks to Professor C.-P. Hsu at the
Institute of Chemistry Sinica of Taiwan for her assistance on quantum
chemistry computations.
29 S. Chen, H. Jia, M. Zhang, K. Shen and H. Zheng, Phys.Chem.Chem.Phys.,
2016, 18, 29555.
30 S. Qu, W. Wu, J. Hua, C. Kong, Y. Long and H. Tian, J. Phys. Chem. C, 2010,
114, 1343.
31 S. Qu, B. Wang, F. Guo, J. Li, W. Wu, C. Kong, Y. Long and J. Hua, Dyes
and Pigments, 2012, 92, 1384.
32 T. W. Holcombe, J.-H. Yum, Y. Kim, K. Rakstys and M. Grätzel, J. Mater.
Chem. A, 2013, 1, 13978.
33 J. T. Lin, P.-C. Chen, Y.-S. Yen, C.-Y. Hsu, H.-H, Chou and M.-C. P. Yeh, Org.
Lett., 2009, 11, 97.
34 S. Qu, C. Qin, A. Islam, Y. Wu, W. Zhu, J. Hua, H. Tian and L. Han, Chem.
Commun., 2012, 48, 6972.
35 H. Li, Y. Hou, Y. Yang, R. Tang, J. Chen, H. Wang, H. Han, T. Peng, Q, Li
and Z. Li, ACS Appl. Mater. Interfaces, 2013, 5, 12469.
36 H. Li, L. Yang, R. Tang, Y. Hou, Y. Yang, H. Wang, H. Han, J. Qin, Q, Li and
Z. Li, Dyes and Pigments, 2013, 99, 863.
References
1
2
3
4
B. O’Regan and M. Grätzel, Nature, 1991, 353, 737.
M. Grätzel, Nature, 2001, 414, 338.
M. Grätzel, Inorg. Chem., 2005, 44, 6841.
M. K. Nazeeruddin, S. M. Zakeeruddin, R. Humphry-Baker, M. Jirousek,
P. Liska, N. Vlachopoulous, V. Shklover, C. H. Fischer and M. Grätzel,
Inorg. Chem., 1999, 38, 6298.
5
6
Md. K. Nazeeruddin, A. Key, I. Rodicio, R. Humphry-Baker, E. Müller, P.
Liska, N. Vlachopoulous and M. Grätzel, J. Am. Chem. Soc., 1993, 115,
6382.
M. K. Nazeeruddin, P. Péchy, T. Renouard, S. M. Zakeeruddin, R.
Humphry-Baker, P. Comte, P. Liska, L. Cevey, E. Costa, V. Shklover, L.
Spiccia, G. B. Deacon, C. A. Bignozzi and M. Grätzel, J. Am. Chem. Soc.,
2001, 123, 1613.
37 N. Koumura, Z.-S. Wang, S. Mori, M. Miyashita, E. Suzuki and K. Hara, J.
Am. Chem. Soc., 2006, 128, 14256.
38 Z.-S. Wang, N. Koumura, Y. Cui, M. Takahashi, H. Sekiguchi, A. Mori, T.
Kubo, A. Furube and K. Hara, Chem. Mater., 2008, 20, 3993.
39 Y. J. Chang, M. Watanabe, P.-T. Chou and T. J. Chow, Chem. Commun,
2012, 48, 726.
7
8
P. Wang, S. M. Zakeeruddin, J. E. Moser, M. K. Nazeeruddin, T. Sekiguchi
and M. Grätzel, Nature Materials, 2003, 2, 402.
F. Gao, Y. Wang, D. Shi, J. Zhang, M. Wang, X. Jing, R. Humphry-Baker, P. 40 K. Hara, T. Sato, R. Katoh, A. Furube, Y. Ohga, A. Shinpo, S. Suga, K.
Wang, S. M. Zakeeruddin, and M. Grätzel, J. Am. Chem. Soc., 2008, 130,
10720.
A. Yella, H. W. Lee, H. N. Tsao, C. Yi, A. K. Chandiran, M. K. Nazeeruddin,
E. W. G. Diau, C. Y. Yeh, S. M. Zakeeruddin and M. Grätzel, Science, 2011,
334, 629.
Sayama, H. Sugihara, H. Arakawa, J. Phys. Chem. B 2003, 107, 597.
41 T. Marinado, K. Nonomura, J. Nissfolk, M. K. Karlsson, D. P. Hagberg, L.
Sun, S. Mori and A. Hagfeldt, Langmuir, 2010, 26, 2592.
42 Z. Shen, B. Xu, P. Liu, Y. Hu, Y. Yu, H. Ding, L. Kloo, Jianli Hua, L. Sun, H.
Tian, J. Phys. Chem. A, 2017, 5, 1242.
9
10 H. Choi, C. Baik, S. O. Kang, J. Ko, M.-S. Kang, M. K. Nazeeruddin and M.
43 C. Teng, X. Yang, C. Yang, S. Li, X. Wang, A. Hagfeldt and L. Sun, J. Phys.
Chem. C 2010, 114, 11305.
Grätzel, Angew. Chem., Int. Ed., 2008, 47, 327.
11 S. Ito, H. Miura, S. Uchida, M. Takata, K. Sumioka, P. Liska, P. Comte, P.
Péchy and M. Grätzel, Chem. Commun., 2008, 5194.
12 G. Zhang, H. Bala, Y. Cheng, D. Shi, X. Lv, Q. Yu and P. Wang, Chem.
Commun., 2009, 2198.
44 W. Wu, B. Peng, J. Chen, M. Liang, and F. Cai, J. Phys. Chem. C 2008, 112,
874.
45 Y. Shao, L. F. Molnar, Y. Jung, J. Kussmann, C. Ochsenfeld, S. T. Brown, A.
T. B. Gilbert, L. V. Slipchenko, S. V. Levchenko, D. P. ONeill, R. A. Jr.
DiStasio, R. C. Lochan, T. Wang, G. J. O. Beran, N. A. Besley, J. M. Herbert,
C. Y. Lin, T. V. Voorhis, S. H. Chien, A. Sodt, R. P. Steele, V. A. Rassolov,
P. E. Maslen, P. P. Korambath, R. D. Adamson, B. Austin, J. Baker, E. F. C.
Byrd, H. Dachsel, R. J. Doerksen, A. Dreuw, B. D. Dunietz, A. D. Dutoi, T.
R. Furlani, S. R. Gwaltney, A. Heyden, S. Hirata, C.-P. Hsu, G. Kedziora, R.
Z. Khalliulin, P. Klunzinger, A. M. Lee, M. S. Lee, W. Z. Liang, I. Lotan, N.
Nair, B. Peters, E. I. Proynov, P. A. Pieniazek, Y. M. Rhee, J. Ritchie, E.
Rosta, C. D. Sherrill, A. C. Simmonett, J. E. Subotnik, H. L., III Woodcock,
W. Zhang, A. T. Bell, A. K. Chakraborty, Phys. Chem. Chem. Phys. 2006,
8, 3172.
46 C. H. Huang and Y. J. Chang, Tetrahedron Lett., 2014, 55, 4938.
47 G. Boschloo, L. Häggman, A. Hagfeldt, J. Phys. Chem. B 2006, 110, 13144.
48 Z. Ning, Y. Fu, H. Tian, Energy Environ. Sci., 2010, 3, 1170.
49 S. A. Haque, E. Palomares, B. M. Cho, A. N. M. Green, N. Hirita, D. R. Klug,
J. R. Durrant, J. Am. Chem. Soc. 2005, 127, 3456.
13 Y. Wu, M. Marszalek, S. M. Zakeeruddin, Q. Zhang, H. Tian, M. Grätzel
and W. Zhu, Energy Environ. Sci., 2012, 5, 8261.
14 N. Cai, R. Li, Y. Wang, M. Zhang and P. Wang, Energy Environ. Sci., 2013,
6, 139.
15 R. Y.-Y. Kin, H.-W. Lin, Y.-S. Yen, C.-H. Chang, H.-H, Chou, P.-W. Chen, C.-
Y. Hsu, Y.-C. Chen, J. T. Lin and K.-C. Ho, Energy Environ. Sci., 2013, 6,
2477.
16 N. Zhou, K. Prabakaran, B. Lee, S. H. Chang, B. Harutyunyan, P. Guo, M.
R. Butler, A. Timalsina, M. J. Bedzyk, M. A. Ratner, S. Vegiraju, S. Yau, C.-
G. Wu, R. P. H. Chang, A. Facchetti, M.-C. Chen and T. J. Marks, J. Am.
Chem. Soc., 2015, 137, 4414.
17 Z. Yao, M. Zhang, H. Wu, L. Yang, R. Li and P. Wang, J. Am. Chem. Soc.,
2015, 137, 3799.
18 K. Kakiage, Y. Aoyama, T. Yano, K. Oya, J. Fujisawa and M. Hanaya, Chem.
Commun., 2015, 51, 15894.
19 C. Teng, X. Yang, C. Yang, S. Li, M. Cheng, A. Hagfeldt and L. Sun, J. Phys.
Chem. C 2010, 114, 9101.
20 K.R. Justin Thomas, P. Singh, A. Baheti, Y.-C. Hsu, K.-C. Ho, J. T. Lin, Dyes
and Pigments, 2011, 91, 33.
21 P.-A. Bouit, M. Marszalek, R. Humphry-Baker, R. Viruela, E. Ortí, S. M.
50 M. Zhang, J. Liu, Y. Wang, D. Zhou and P. Wang, Chem. Sci., 2011, 2, 1401.
51 Z. Ning, Q. Zhang, H. Pei, J. Luan, C. Lu, Y. Cui and H. Tian, J. Phys. Chem.
C, 2009, 113, 10307.
52 Y. J. Chang, P.-T. Chou, Y.-Z. Lin, M. Watanabe, C.-J. Yang, T.-M. Chin and
T. J. Chow, J. Mater. Chem., 2012, 22, 21704.
This journal is © The Royal Society of Chemistry 20xx
J. Name., 2013, 00, 1-3 | 9

New Journal of Chemistry
Page 10 of 10
ARTICLE
Journal Name
53 J. E. Kroeze, N. Hirata, S. Koops, M. K. Nazeeruddin, L. Schmidt-Mende,
M. Grätzel and J. R. Durrant, J. Am. Chem. Soc. 2006, 128, 16376.
54 C. Kim, H. Choi, S. Kim, C. Baik, K. Song, M.-S. Kang, S. O. Kang and J. Ko,
J. Org. Chem., 2008, 73, 7072.
View Article Online
DOI: 10.1039/C7NJ00413C
55 W. Li, Y. Wu, X. Li, Y. Xie and W. Zhu, Energy Environ. Sci., 2011, 4, 1830.
56 R. Kern, R. Sastrawan, J. Ferber, R. Stangl, J. Luther, Electrochim. Acta
2002, 47, 4213.
57 J. Bisquert, J. Phys. Chem. B, 2002, 106, 325.
58 Q. Wang, J. Moser and M. Grätzel, J. Phys. Chem. B, 2005, 109, 14945.
59 Z. Ning, Q. Zhang, W. Wu, H. Pei, B. Liu and H. Tian, J. Org. Chem., 2008,
73, 3971.
60 R. Chen, G. Zhao, X. Yang, X. Jiang, J. Liu, H. Tian, Y. Gao, X. Liu, K. Han,
M. Sun and L. Sun, Journal of Molecular Structure., 2008, 876, 102.
61 H. Tian, X. Yang, R. Chen, R. Zhang, A. Hagfeldt and L. Sun, J. Phys. Chem.
C, 2008, 112, 11203.
62 M. K. Nazeeruddin, F. D. Angelis, S. Fantacci, A. Selloni, G. Viscardi, P.
Liska, S. Ito, B.Takeru and M. Grätzel, J. Am. Chem. Soc., 2005, 127,
16835.
10 | J. Name., 2012, 00, 1-3
This journal is © The Royal Society of Chemistry 20xx