8-Hydroxylquinoline-conjugated porphyrins as broadband light absorbers for dye-sensitized solar cells

Article abstract of DOI:10.1039/c3nj01643a

Three porphyrin dyes, DPZn-HOQ, PZn-HOQ and DPZn-COOH, were synthesized and characterized for dye-sensitized solar cells. Both DPZn-HOQ and DPZn-COOH exhibited a donor-π-acceptor configuration with N,N-dimethylaniline as a donor and 8-hydroxylquinoline (HOQ) and para-benzoic acid (BZA) as acceptors, respectively. PZn-HOQ is an analogue of DPZn-HOQ without a donor. It was found that DPZn-HOQ exhibited broader and stronger light absorption capability in the red region than DPZn-COOH. Theoretical calculations showed that the electrons were delocalized to the 8-hydroxylquinoline ring in DPZN-HOQ. The DPZn-HOQ-sensitized solar cells exhibited higher energy conversion efficiency (3.09%) than DPZn-COOH-sensitized solar cells (1.76%) under the same conditions. The results were consistent with the incident photon to current conversion efficiency (IPCE) spectra. The electrochemical impedance spectroscopy studies revealed that HOQ-conjugated porphyrin exhibited high electron recombination resistance and a long electron lifetime, which was attributed to the effective shielding of DPZn-HOQ from the electrolyte due to its tilted orientation on the surface of TiO₂ nanoparticles. The efficiency of DPZn-HOQ-sensitized solar cells was further increased to 3.41% when a complementary dye BET was used.

Full text of DOI:10.1039/c3nj01643a

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DOI: 10.1039/C3NJ01643A
ARTICLE
8-Hydroxylquinoline-conjugated porphyrins as
broadband light absorbers for dye-sensitized solar
cells
Cite this: DOI: 10.1039/x0xx00000x
Liping Si,a,b Hongshan Hea,b* and Kai Zhuc
Received 00th January 2012,
Accepted 00th January 2012
Three porphyrin dyes, DPZn-HOQ, PZn-HOQ and DPZn-COOH, were synthesized and
characterized for dye-sensitized solar cells. Both DPZn-HOQ and DPZn-COOH exhibited a
DOI: 10.1039/x0xx00000x
donor-π-acceptor configuration with an N,N-dimethylaniline as
a
donor and 8-
www.rsc.org/
hydroxylquinoline (HOQ) and para-benzoic acid (BZA) as acceptors, respectively. PZn-HOQ
is an analogous of DPZn-HOQ without a donor. It was found that DPZn-HOQ exhibited
broader and stronger light absorption capability in the red region than DPZn-COOH.
Theoretical calculations showed the electrons were delocalized to the 8-hydroxylquinoline ring
in DPZN-HOQ. The DPZn-HOQ-sensitized solar cells exhibited higher energy conversion
efficiency (3.09%) than DPZn-COOH-sensitized solar cell (1.76%) under the same conditions.
The results were consistent with the incident photon to current conversion efficiency (IPCE)
spectra. The electrochemical impedance spectra studies revealed that HOQ-conjugated
porphyrin exhibited high electron recombination resistance and long electron lifetime, which
was attributed to the effective shielding of DPZn-HOQ toward electrolyte due to its tilted
orientation on the surface of TiO2 nanoparticles. The efficiency of DPZn-HOQ-sensitized solar
cell was further increased to 3.41% when c complementary dye BET was used.
bandgap of dyes in order to convert solar energy to electricity
efficiently.
1. Introduction
Low-cost and easy fabrications of dye-sensitized solar cells
(DSCs) make this type of devices very promising for future
indoor and outdoor applications.1-3 Recently greater than 12%
energy conversion efficiency has been achieved in a zinc
porphyrin-sensitized solar cell in combination with a cobalt-
based redox couple.4 However, low energy conversion
efficiency and poor long-term stability are of two major
concerns in regard to its competitiveness to other types of solar
cells.5 The concerns are linked tightly to the narrow absorption
of sunlight and the weak adsorption strength of current dyes.5
One strategy to broaden the absorption spectra is to expand the
π-conjugation. Ball6 et al fused an anthracene into porphyrin
and extended the absorption to 900 nm. However, the resulting
solar cell only produced less than 0.1% energy conversion
efficiency due to energetically unfavourable electron injection
from its LUMO (lowest unoccupied molecular orbital) to the
conduction band of TiO2 nanoparticle (TiO2 NP). Reddy7 et al
found conjugation of 4-carboxylanthrancence to porphyrin ring
extended the absorption edge to 800 nm and resulted in energy
conversion efficiency of 8.21%. Therefore, it is critical to
balance the energy level of frontier molecular orbitals and
Dye molecules have to bind strongly on TiO2 nanoparticles
without significant dissociation during the operation.5 This is
usually achieved by coordination of a benzoic acid (BZA)
group of dye molecules to titanium atom of TiO2 nanoparticle.8
In the state-of-the-art DSC, a single BZA group was used to
attach the porphyrin molecules to TiO2 nanoparticles.4, 9 During
the solar cell operation, the porphyrin dye molecule dissociates
slowly from TiO2 surface and eventually loses its ability to
convert sunlight into electricity. Multiple BZA groups were
introduced into porphyrin dyes in order to increase their
binding capability.10-15 However, a compromise to solar cell
efficiency was observed. Imahori16 et al found energy
conversion efficiency decreased when a second BZA group was
introduced into the porphyrin. Rochford17 et al found the
introduction of four BZA groups to porphyrin ring eliminated
aggregation. Binding capability and electron injection were
enhanced; however, this design limits the further structural
modifications. It is imperative to find a simple alternative
anchoring group to replace the benzoic acid group (BZA) to
address this concern.
Previously, He18 et al found that 8-hydroxyquinoline (HOQ)
could be an excellent candidate to replace the BZA group. The
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HOQ is an organic molecule with very strong binding to the porphyrin plane. The HOMO (highest occupied
capability to various metal ions including Ti atom.19 It was molecular orbital) and LUMO energy levels of DPZn-HOQ
View Article Online
found that HOQ-modified porphyrin dyes exhibited strong were respectively -4.78 eV and -2.63 eV,DrOesI:u1l0ti.1n0g39in/Ca3nNJe0n1e64rg3Ay
resistance toward acidic solution. The energy conversion gap of 2.15 eV. This energy gap was smaller (0.01 eV) than its
efficiency was comparable to those that were sensitized by counterpart DPZn-COOH. Its LUMO energy level was also
BZA-modified counterparts. To explore the potential of this higher than the conduction band of TiO2 NPs. As shown in Fig.
finding in DSCs, we adopted a premium donor-π-acceptor 2, the electrons in the LUMO were delocalized from porphyrin
configuration and conjugated the HOQ to the porphyrin ring ring to the HOQ group, which would be beneficial to the
through a triple bond as shown in Fig. 1. It was found that the electron injection. There is no clear disjoint between donor and
new porphyrin dyes not only maintained the strong binding acceptor. We also performed time-dependent DFT calculations.
capability to TiO2 nanoparticles, but also exhibited up to 770 The predicted absorption spectrum was shown in Fig. 3. The
nm photon-to-electron response. In this report, synthesis, DPZn-HOQ showed strong peaks at 450 nm and 665 nm with
characterization, photophysical properties, and photovoltaic an absorption onset around 800 nm. These results indicated the
properties will be described. The theoretical calculations and promise of HOQ-conjugated porphyrins for spectral broadening
electrochemical impedance spectroscopic investigation were and adsorption enhancement for DSCs.
also carried out to support observed phenomena.
Fig. 2 Electron density distribution profiles of porphyrin dyes
Table 1 Frontier molecular energy levels of PZn-HOQ, DPZn-HOQ and
DPZn-COOH
Fig. 1 Structures of 8-hydroxylquinoline-modified porphyrin dyes (PZn-
HOQ and DPZn-HOQ), a benzoic acid-modified porphyrin dye (DPZn-
COOH), and a complementary dye (BET).
HOMO
-4.7765
-4.6937
-4.9195
LUMO
-2.6275
-2.5339
-2.3878
LUMO-HOMO
2.1875
DPZn-HOQ
DPZn-COOH
PZn-HOQ
2.1598
2.5316
2. Results and Discussion
Design of Dyes
Three dyes were designed for this study: DPZn-HOQ, PZn-
HOQ and DPZn-COOH. The DPZn-HOQ featured a premium
donor-π-acceptor configuration, in which N,N-dimethylaniline
(D) and HOQ were acted as a donor and an acceptor,
respectively. Both were conjugated to the porphyrin ring
through triple bonds. The DPZn-COOH was designed as a
reference. Its structure was quite similar to DPZn-HOQ except
a benzoic acid (BZA) was used as an acceptor. PZn-HOQ was
selected to evaluate the impact of donor on the overall
performance of the devices. It is expected that HOQ group will
not only maintain the strong binding capacity on the TiO2, but
will also broaden the absorption spectrum due to its large π
conjugation compared to the BZA group. The density
functional theory (DFT) calculations were first performed to
provide some evidence to support these expectations. The
geometry-optimized structures of three dyes and the electron
density distribution profiles were shown in Fig. 2. In the
geometry-optimized structure, the HOQ group was tilted ~ 45°
Fig. 3 Predicted absorption spectrum of DPZn-HOQ from DFT calculations
in acetonitrile.
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DOI: 10.1039/C3NJ01643A
Fig. 4 Synthesis of DPZn-HOQ, DPZn-COOH and PZn-HOQ. Reaction conditions: (a) CHCl3, TFA, DDQ; (b) ZnOAc)2, CHCl3/MeOH (v/v: 10:2) (c) NBS,
CHCl3, 0○C; (d) CuI, Pd(PPh3)2Cl2, THF, TEA, 60○C; (e) Piperidine, CHCl3, r.t.
Synthesis and Characterization
Fig. 4 showed the synthetic procedure of three porphyrin dyes.
The DPZn-HOQ was synthesized by direct reaction of 5, 15-
dibromo-10,20-dimesitylporphyrin zinc (Br-PZn-Br), one molar
equivalent 4-ethynyl-N,N-dimethylaniline (D), and one molar
equivalent
8-tert-butoxycarbonyloxy-5-ethynylquinoline
(HQQ-Boc) in THF under a typical Sonogashira coupling
20
condition.4,
The reaction produced five compounds
corresponding to one or two Br atoms were replaced by HOQ-
Boc or D. The target compound was separated on column
chromatography using chloroform and methanol as elute,
followed by removal of the protecting group Boc in chloroform
in the presence of piperidine with an overall yield of ~ 40%.
The DPZn-HOQ was a green powder, soluble in chloroform,
dichloromethane, methanol, ethanol, THF and insoluble in
hexane. The other two porphyrin dyes PZn-HOQ and DPZn-
HOQ were prepared in a similar manner. The 1H NMR and MS
confirmed the structure of these dyes.
Fig. 5 Normalized absorption spectra of DPZn-HOQ (red), PZn-HOQ
(black), and DPZn-COOH (blue) in CHCl3.
As shown in Fig. 6, the overall absorption spectral features of
porphyrin dyes on the TiO2 nanoparticles were quite similar to
their solution spectra. However, an obvious red-shift of
absorption peaks was observed for the DPZn-HOQ, indicating
the strong electronic coupling between HOQ and TiO2
nanoparticles. A blue-shift was observed for PZn-HOQ. The
Soret peak became quite broader indicating the existence of dye
aggregation due to the lack of a donor group. The peak position
of DPZn-COOH did not change too much. These results
indicated that the desired absorption capability of the DPZn-
HOQ for DSCs.
Absorption spectra
The normalized absorption spectra of DPZn-HOQ, PZn-HOQ
and DPZn-COOH in CHCl3 were shown in Fig. 5. The DPZn-
HOQ exhibited two strong peaks at 461 and 672 nm, which
matched the predicted spectrum very well. The peak at 672 nm
was quite broad and intense. A shoulder between 550 and 650
nm was also observed. The DPZn-COOH exhibited one strong
peak at 443 nm and three weak peaks at 575, 634 and 671 nm.
The PZn-HOQ showed three peaks: 443, 568 and 622 nm.
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dimethylimidazolium iodide, 0.05
butylpyridine in acetonitrile.
M I2, 0.1 M LiI, and 0.5 M tert-
View Article Online
DOI: 10.1039/C3NJ01643A
Table 2. Photovoltaic parameters for porphyrin-sensitized solar cellsa.
JSC (mA/cm2)
VOC (V)
FF
η (%)
PZn-HOQ
DPZn-HOQ
DPZn-COOH
PZn-HOQ/BETb
DPZn-HOQ/BET
6.48
7.81
4.22
6.87
8.33
0.576
0.595
0.602
0.573
0.605
0.678
0.664
0.694
0.668
0.677
2.53
3.09
1.76
2.63
3.41
aAll dyes were dissolved in methanol for dye loading; bThe molar ratio of
porphyrin to BET is 3:1.
The energy conversion efficiency was consistent to the
IPCE spectra as shown in Fig. 8. The DPZn-HOQ exhibited
much broader and stronger photon-to-current response than
DPZn-COOH in the red region, which was coincident to their
absorption spectra. It should be mentioned that the PZn-HOQ
without a donor also exhibited better performance than DPZn-
COOH (2.53% vs 1.76%). Co-sensitization of DPZn-HOQ with
BET dye resulted in 10% increase of energy conversion
efficiency, leading to overall energy conversion efficiency of
3.41%. The enhancement was consistent with the strong
complementary absorption of BET around 510 nm, which may
also occur through the Förster resonance energy transfer
process.21-25
Fig. 6. The absorption spectra of DPZn-HOQ and DPZn-COOH on the
TiO2 films.
Photovoltaic studies
The photovoltaic performances of three porphyrin dyes were
studied. A typical “sandwich” configuration of the DSC was
adapted for this investigation. The dye-loading time was fixed
to four hours as the efficiency decreased when the dye-loading
time was increased. In these cells, the thickness of TiO2
nanocrystalline layer was fixed to ~7 µm. No scattering layer
was applied. The results are listed in Table 2. The J-V curves
are depicted in Fig. 7. The DPZn-HOQ gave 3.09% energy
conversion efficiency, whereas DPZn-COOH only gave 1.76%
energy conversion efficiency under same conditions. Thus, the
efficiency increased by 75% after the conventional benzoic acid
group was replaced by HOQ. It was found the open-circuit
voltages (VOC) of DPZn-HOQ and DPZn-COOH sensitized
cells were quite similar to each other (0.595 vs 0.602 V),
whereas the short-circuit current (JSC) was quite different (7.81
vs 4.22 mA/cm2). We concluded that the increase of energy
conversion efficiency of DPZn-HOQ–sensitized solar cell
mainly came from the increase of JSC.
Fig. 8 IPCE spectra of DPZn-HOQ, DPZn-COOH, PZn-HOQ and BET
sensitized solar cells.
Electrochemical Impedance Spectroscopy
To explore whether the structural modification affected the
electron recombination resistance in the devices, we performed
electrochemical impedance spectroscopy (EIS)26-28 with an AC
perturbation superimposed on the CW bias light illumination in
the frequency range of 10-2–105 Hz. As shown in Fig. 9, the
measured electron recombination resistance (Rct) of DPZn-
HOQ at TiO2 NP/electrolyte interface was about 6-fold larger
than that of DPZn-COOH. The larger recombination resistance
(or reduced recombination) could be attributed to the steric
hindrance associated with the DPZn-HOQ adsorption geometry
Fig. 7 The J-V curves of porphyrin-sensitized solar cells under AM1.5G
condition.
The
electrolyte
composition:
0.6
M
1-propyl-2,3-
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that presumably limits the accessibility of the oxidized species each other and form an effective layer to block the direct
of redox couple in the electrolyte from reaching the TiO2 NP contact between TiO2 surface and electrolyte. As a result, the
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surface. Consistent with the impedance result, the measured electron recombination will be significaDnOtlIy: 10r.e1d0u39c/eCd3.NJO0n164th3Ae
electron lifetime (τr) of DPZn-HOQ sensitized solar cell was contrary, the DPZn-COOH will chelate to Ti atoms vertically.
also much (about a factor of three) longer than that of the The mesityl groups will not be able to stack over each other.
DPZn-COOH sensitized solar cell as shown in Fig. 10.
There will be large void between porphyrin dyes allowing the
electrolyte to penetrate inside and contact directly with TiO2
surface. To support this explanation, we measured the total
amounts of DPZn-HOQ and DPZn-COOH on a 0.16 cm2 TiO2
coated FTO glass. It was found that the amount of DPZn-HOQ
was 31% higher than that of DPZn-COOH (12.37 ×10-9 vs
16.05 × 10-9 mol), which was very close to the estimated
increase (33%) of volume of DPZn-COOH compared to DPZn-
HOQ (assume porphyrins align as depicted in the Fig. 12 and
the distances of d1 and d2 are 15 and 20 Å, respectively).
Fig. 9 The electron recombination resistance as a function of the bias
voltage from EIS measurements.
Fig. 11. The electron diffusion coefficient as a function of photoelectron
density from IMPS measurements.
Fig. 10. Plots of the recombination lifetime from IMVS measurements
Intensity-modulated photocurrent spectroscopy (IMPS)
showed that replacing the benzoic acid with HOQ did not show
significant impact on the electron diffusion coefficient (D) in
the TiO2 matrix as shown in Fig. 11. However, introducing a
donor increased the D values, which may come from increased Fig. 12 Proposed alignments of DPZn-COOH and DPZn-HOQ dyes on the
surface of TiO2 nanoparticles.
electric dipole moment (4.32 and 7.05 debyes for PZn-HOQ
and DPZn-HOQ respectively from the calculation) for more
effective electron diffusion from top to the bottom of TiO2 NPs.
We were unable to obtain reliable data to evaluate the long-
Co-sensitization of DPZn-HOQ with BET dye showed
term stability of the solar cells due to the leakage of liquid
negligible effect on electron transport.
electrolyte during the test. However, we tested the resistance of
The EIS results could be explained by unique alignment of
porphyrin-coated TiO2 film toward the base and the acid, which
DPZn-HOQ on TiO2 NP surface. DPZn-HOQ will chelate to
can be used as an indirect measure of long-term stability. When
TiO2 NPs in a bidentate mode, resulting in a non-vertical
DPZn-COOH-coated film was immersed into 0.05 mM NaOH
alignment as illustrated in Fig. 12. The mesityl groups, which
in ethanol/water (1:1) the dye de-adsorbed from TiO2 film
are perpendicular to the porphyrin plane, will likely stack over
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completely within one hour, whereas only a slight color change Syntheses
was observed for DPZn-HOQ after three days. The optical
images of these films were shown in Fig. 13. A similar
resistance toward acid was also observed.
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PZn-HOQ. PZn-Br (100 mg, 0.145 mmol) was mixed with 8-tert-
butoxycarbonyloxy-5-ethynylquinoline (98.3D4OmI:g1,00.1.033695/Cm3mNJo0l,1624.53A
eq.) in 6 mL anhydrous THF and 1mL triethylamine. Then 15 mol.
% eq of CuI (4.14 mg, 0.022 mmol) and Pd(PPh3)Cl2 (15.27 mg,
0.022 mmol) were added as catalysts. The reaction was carried out
under N2 protection at 40℃ for 24h. Solvent was then removed and
solid was re-dissolved in chloroform and loaded on a silica column
for purification. CHCl3 was used as eluent. The third band was
collected as PZn-Boc and crystallized from chloroform/hexane as
green solid. PZn-Boc (68 mg, 0.077 mmol) was then dissolved in 10
mL dichloromethane at room temperature. Then 3 eq. of piperidine
was added. The reaction was run for 30 min. After all the solvent
was removed by evaporating under vacuum, the residue was re-
dissolved in chloroform and loaded on a silica column for
Fig. 13 Optical images of porphyrin-coated TiO2 film in 0.05 mM NaOH in
ethanol/water (1:1) at room temperature. (1): PZn-HOQ; (2) DPZn-HOQ;
(3) DPZn-C6-HOQ; (4) DPZn-COOH. DPZn-C6-HOQ is an analogous of
DPZn-HOQ with multiple alkyl groups. The study of this new dye is under
investigation and the results will be reported in due course.
purification. Chloroform was used as eluent. The main band was
collected and re-crystallized from hexane as green solid. Yield: 36%.
1H NMR data (in CDCl3): 10.10 (s, 1H); 9.85 (d, 2H); 9.27 (d,3H);
8.93 (d,1H); 8.89 (d, 2H); 8.85 (d,2H); 8.404 (d, 2H); 8.22 (d, 1H);
7.72 (tri, 1H); 7.32 (m, 5H); 2.65 (s, 6H);1.85 (s, 12H).
3. Conclusion
In conclusion, we demonstrated for the first time that
conjugation of an 8-hydroxylquinoline to the porphyrin ring
through a triple bond not only broadened the absorption spectra
with increased absorption coefficient, but also reduced the
electron recombination at TiO2/electrolyte interface. The
electron lifetimes were increased two times compared to the p-
benzoic acid functionalized porphyrins. This resulted in a
significant increase of energy conversion efficiency.
Considering the versatile coupling capability of HOQ to many
other organic dyes, this study demonstrated the potential of
HOQ in DSCs applications for high efficiency and excellent
long-term stability
DPZn-HOQ. Br-PZn-Br (114 mg, 0.148 mmol) was mixed with 8-
tert-butoxycarbonyloxy-5-ethynylquinoline (39.86 mg, 0.145 mmol)
4-ethynyl-N,N-dimethylaniline (21.49 mg, 0.148 mmol) in
anhydrous THF ( 20 mL) and triethylamine (1.4 mL). Then 30 mol.
% eq of CuI (8.38 mg, 0.044 mmol) and Pd(PPh3)4 (51.31 mg, 0.044
mmol) were added as catalyst. The reaction was carried out under N2
protection at 40℃ for 24h. Solvent was then removed and solid was
re-dissolved in chloroform and loaded on a silica column for
purification. CHCl3 was used as eluent. The third band was collected
as DPZn-Boc and crystallized from chloroform/hexane as green
solid. DPZn-Boc (18 mg, 0.018 mmol) was then dissolved in 10 mL
dichloromethane at room temperature. After 3 eq. of piperidine was
added, the reaction was run for 30 min. After all the solvent was
removed by evaporating under vacuum, the residue was re-dissolved
in chloroform, and loaded on a silica column for purification.
Chloroform was used as eluent, the main band was collected and
recrystallized from hexane as green solid. Yield: 13%. 1H NMR data
(in CDCl3): 9.75 (d, 2H); 9.58 (d, 2H); 9.27 (d, 1H); 8.89 (d, 1H);
8.82 (d, 2H); 8.73 (d, 2H); 8.22 (d, 1H);7.88 (d, 1H); 7.35 (m, 7H);
5.00 (s, 2H)2.75 (bd, 6H); 1.97 (s, 12H); 0.53 (s, 6H).
4. Experimental
General Methods and Materials
All solvents were treated by standard methods prior to use.
Chemicals were analytical grade and used as received. The
FTO (fluorine-tine-oxide) glass with sheet resistance 7 Ω/cm2
from Hartfort Glass (USA) was used for cell fabrication.
Absorption spectra were obtained on an HP Agilent 8543 UV-
visible spectrophotometer in CHCl3 at room temperature. The
DPZn-COOH. Br-PZn-Br (100 mg, 0.130 mmol) was mixed with
4-ethynyl-N, N-dimethylaniline (18.88 mg, 0.130 mmol) and 4-
ethynylbenzoic acid (18.98 mg 0.130 mmol) in anhydrous THF (10
mL) and triethylamine (1.0 mL). Then 30 mol.% eq of CuI (47.43
mg, 0.039 mmol) and Pd(PPh3)4 (45.06 mg, 0.039 mmol) were
added as catalyst. The reaction was carried out under N2 protection
at 40℃ for 24h. Solvent was then removed and solid was re-
dissolved in chloroform and loaded on a silica column for
purification. CHCl3 was used as eluent. The main band was collected
and recrystallized from hexane as green solid. Yield: 26%. 1H NMR
data (in CDCl3): 9.70 (d, 2H); 9.58 (d, 2H); 8.65 (d, 2H); 8.58 (d,
2H); 8.10 (m, 4H); 7.50 (m, 4H); 6.60 (d, 4H); 1.80 (d, 6H); 1.25 (s,
12H); 0.90 (s, 6H).
steady-state fluorescence spectra were obtained on
fluorescence spectrometer (FS920, Edinburg Instrument, Inc,
UK) with Xenon arc lamp as light source. 5,10-
dimesitylporphyrin
a
a
29
zinc
(PZn),
5-bromo-10,20-
dimesitylporphyrin zinc (PZn-Br), and 5, 15-diboromo-10,20-
dimesitylporphyrin (Br-PZn-Br) were prepared according to
literature methods4 and confirmed by 1H NMR. 8-tert-
Butoxycarbonyl-5-ethynylquinoline (HOQ-Boc) was prepared
using
a
method as described by Montes et al.30 The
complementary dye BET was prepared according to a method
in our previous publication21, 31 and its purity was confirmed by
thin-layer-chromatography (TLC) and 1H NMR.
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Fabrication of DSCs
functional and 6-31G(D) basis set in acetonitrile solution by
means of the conductor-like polarizable continuum model
(CPCM) solvation model as implementeDdOiI:n10t.h10e3V9Gie/wCauA3rNstiscJil0ea1On6n4l0i3nA9e
program package.32 The acetonitrile was used to mimic the
solvents in electrolyte. Molecular orbitals were visualized by
GaussView 3.0. The method has been used widely for geometry
optimization and electronic calculations of porphyrins
derivatives for its accuracy.12, 18, 19, 33-36
Nanocrystalline TiO2 paste (Dyesol, 18 NR-T, ~ 20 nm in
diameter) was coated on a commercial fluorine-tin-oxide (FTO)
using a doctor-blade method. After air-drying for about 30
minutes, the sample was put into an oven for sintering (500°C
for 30 min) in ambient oxygen. The sample was then cooled to
the room temperature, and a scattering layer (Dyesol, WER2-O,
~ 400 nm in diameter) was coated again using a doctor-blade
method. The sample was put into an oven for sintering (500°C
for 30 min) in ambient oxygen. The sample was then cooled to
the room temperature and was immersed in a TiCl4 aqueous
solution (20 mM) for one hour. The film was air-dried and
sintered again at 500°C for 30 minutes. The film was then put
into the dye solution (~ 0.3 mM in methanol) at room
temperature and kept for four hours. The film was then taken
out, flushed with methanol, and vacuum dried for one hour. The
thickness of the film was ~ 17 µm determined from a
profilometer. The counter-electrode was prepared by sputtering
a 16 nm-thick film of the Pt on the FTO glass. A mask made
from the Parafilm was used as a spacer for two electrodes and
sealing material. The electrolyte solution was injected from two
pre-drilled holes on counter electrode. The cell was sealed by
hot glue. The electrolyte is an acetonitrile solution having 0.6
M 1-propyl-2,3-dimethylimidazolium iodide, 0.05 M I2, 0.1 M
LiI, 0.1 M guanidine thiocynate and 0.5 M tert-butylpyridine.
Photoelectrochemical measurements
Charge transport and recombination were studied respectively
by intensity-modulated photocurrent (IMPS) and photovoltage
(IMVS) spectroscopies as detailed previously.37-39 In brief, the
cells were probed with a small sinusoidally modulated beam of
660 nm LED light superimposed on a relatively large
background (bias) illumination also at 660 nm. The probe and
bias light entered the cell from the substrate side. Neutral
density filters were used to vary the illumination intensity. The
amplitude of the modulated photocurrent density was kept at
10% or lower compared to the steady-state photocurrent
density. Electrochemical impedance spectroscopy (EIS)
measurements were performed with a potentiostat/frequency
analyzer (PARSTAT 2273) using a two-electrode configuration
with the modulation frequencies ranging from 10-2 to 105 Hz
and the modulation amplitude of 10 mV. Z-view 2.9c (Scribner
Associates) was used to fit the EIS spectra to the equivalent
circuit based on the transmission line model.27
Solar cell characterization
The applied potential and cell current were measured using an
Agilent 4155C semiconductor parameter analyzer using a
450W Xenon light source. The light intensity at the surface of
the cell was calibrated to 100 mW/cm2, equivalent to one sun at
air mass 1.5G condition. Efficiency (η) and the fill factor (ff)
were calculated by η (%) = Pmax × 100/(Pin × A) and FF =
Pmax/(ISC × VOC), where Pmax is the maximum output power of
cells (mW), Pin is the power density of the light source
(mW/cm2), Isc is the short-circuit current (mA), Voc is the
open-circuit voltage (V), A is the active area (0.16 cm2) of the
cell. Incident photon to current efficiency (IPCE) experiments
was performed on an Agilent semiconductor parameter
analyzer with a Xe arc lamp and a Newport monochromator.
Monochromatic light was incident on the sample through
focusing lenses. The National Renewable Energy Laboratory
(NREL) calibrated photodetector was used as a reference. The
samples were scanned from 350 – 850 nm and the voltage was
recorded. The IPCE was calculated using the equation IPCE =
(Sample Voltage × Reference IPCE)/Reference Voltage. The
reference IPCE was supplied by the NREL calibrated DSC
under AM1.5 photon flux.
Acknowledgements
This work was partially supported by the Council of Faculty
Research Grant, Eastern Illinois University (H.H.) and the
National Science Foundation/EPSCoR, Grant No. 0903804
(H.H). This work was also supported by the Division of
Chemical Sciences, Geosciences, and Biosciences, Office of
Basic Energy Sciences, U.S. Department of Energy, under
contract No. DE-AC36-08GO28308 (K.Z.).
Notes and references
aDepartment of Chemistry, Eastern Illinois University, Charleston, IL
62910, USA; Tel: +1 217 581 6231; Email: hhe@eiu.edu
bCenter for Advanced Photovoltaics, South Dakota State University,
Brookings, SD 67006, USA.
c Renewable Energy Laboratory, Golden, CO 80401, USA; Fax: +1 303
384 6150;Tel: +1 303 384 6353; E-mail: kai.zhu@nrel.gov
1. A. Hagfeldt, G. Boschloo, L. Sun, L. Kloo and H. Pettersson, Chem.
Rev., 2010, 110, 6595–6663.
2. J. Halme, P. Vahermaa, K. Miettunen and P. Lund, Adv. Mater.,
2010, 22, E210-E234.
Theoretical calculations
3. B. O'Regan and M. Grätzel, Nature, 1991, 353, 737-740.
4. 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, 629-634
Theoretical calculations were performed at density functional
theory level. The single-crystal structures of porphyrins were
used as a framework for the construction of initial input
structures of calculations. Geometry optimization and
electronic structure calculations were performed using B3LYP
5. L.-L. Li and E. W.-G. Diau, Chem. Soc. Rev., 2012, 42, 291-304.
This journal is © The Royal Society of Chemistry 2012
J. Name., 2012, 00, 1-3 | 7

Page 9 of 9
ARTICLE
New Journal of Chemistry
Journal Name
6. J. M. Ball, N. K. S. Davis, J. D. Wilkinson, J. Kirkpatrick, J. 31. Y. Zhong, L. Si, H. He and A. G. Sykes, Dalton Trans., 2011, 40,
Teuscher, R. Gunning, H. L. Anderson and H. J. Snaith, RSC
Advances, 2012, 2, 6846-6853.
11389-11395.
32. M. J. T. Frisch, G. W.; Schlegel, H. B.; Scuseria, G. EV.;ieRwoAbrtbic,leMO.nAlin.e;
DOI: 10.1039/C3NJ01643A
7. N. M. Reddy, T.-Y. Pan, Y. C. Rajan, B.-C. Guo, C.-M. Lan, E. W.-
G. Diau and C.-Y. Yeh, Phys. Chem. Chem. Phys., 2013, 15, 8409-
8415.
Cheeseman, J. R.; Scalmani, G.; Barone, V.; Mennucci, B.; Petersson,
G. A.; Nakatsuji, H.; Caricato, M.; Li, X.; Hratchian, H. P.; Izmaylov,
A. F.; Bloino, J.; Zheng, G.; Sonnenberg, J. L.; Hada, M.; Ehara, M.;
Toyota, K.; Fukuda, R.; Hasegawa, J.; Ishida, M.; Nakajima, T.;
Honda, Y.; Kitao, O.; Nakai, H.; Vreven, T.; Montgomery, Jr., J. A.;
Peralta, J. E.; Ogliaro, F.; Bearpark, M.; Heyd, J. J.; Brothers, E.;
Kudin, K. N.; Staroverov, V. N.; Kobayashi, R.; Normand, J.;
Raghavachari, K.; Rendell, A.; Burant, J. C.; Iyengar, S. S.; Tomasi,
J.; Cossi, M.; Rega, N.; Millam, N. J.; Klene, M.; Knox, J. E.; Cross,
J. B.; Bakken, V.; Adamo, C.; Jaramillo, J.; Gomperts, R.; Stratmann,
R. E.; Yazyev, O.; Austin, A. J.; Cammi, R.; Pomelli, C.; Ochterski,
J. W.; Martin, R. L.; Morokuma, K.; Zakrzewski, V. G.; Voth, G. A.;
Salvador, P.; Dannenberg, J. J.; Dapprich, S.; Daniels, A. D.; Farkas,
Ö.; Foresman, J. B.; Ortiz, J. V.; Cioslowski, J.; Fox, D. J., Gaussian,
Inc., Wallingford CT, 2009.
8. F. Ambrosio, N. Martsinovich and A. Troisi, J. Phy. Chem. Lett.,
2012, 3, 1531-1535.
9. P. Gao, H. N. Tsao, M. Grätzel and M. K. Nazeeruddin, Org. Lett.,
2012, 14, 4330-4333.
10. S. Eu, S. Hayashi, T. Umeyama, Y. Matano, Y. Araki and H. Imahori,
J. Phys. Chem. C, 2008, 112, 4396-4405.
11. H. Imahori, Y. Matsubara, H. Iijima, T. Umeyama, Y. Matano, S. Ito,
M. Niemi, N. V. Tkachenko and H. Lemmetyinen, J. Phys. Chem. C,
2010, 114, 10656–10665.
12. R. Ambre, K.-B. Chen, C.-F. Yao, L. Luo, E. W.-G. Diau and C.-H.
Hung, J. Phy. Chem. C, 2012, 116, 11907-11916.
13. D. Cao, J. Peng, Y. Hong, X. Fang, L. Wang and H. Meier, Org.
Lett., 2011, 13, 1610–1613.
33. M. P. Balanay and D. H. Kim, Phys. Chem. Chem. Phys., 2008, 10,
5121-5127.
14. D. Choi, J. G. Rowley, M. Spitler and B. A. Parkinson, Langmuir,
2013, 29, 9410-9419.
34. C.-F. Lo, S.-J. Hsu, C.-L. Wang, Y.-H. Cheng, H.-P. Lu, E. W.-G.
Diau and C.-Y. Lin, J. Phy. Chem. C, 2013, 114, 12018-12023.
15. Q. Wang, W. M. Campbell, E. E. Bonfantani, K. W. Jolley, D. L.
Officer, P. J. Walsh, K. Gordon, R. Humphry-Baker, M. K. 35. H. He, A. Gurung, L. Si and A. G. Sykes, Chem.Comm., 2012, 48,
Nazeeruddin and M. Grätzel, J. Phys. Chem. B, 2005, 109, 15397-
15409.
7619-7621.
36. H. He, M. Dubey, Y. Zhong, M. Shrestha and A. G. Sykes, Eur. J.
Inorg. Chem., 2011, 3731-3738.
16. H. Imahori, T. Umeyama and S. Ito, Acc. Chem. Res., 2009, 42, 1809-
1818.
37. L. Dloczik, O. Ileperuma, I. Lauermann, L. M. Peter, E. A.
Ponomarev, G. Redmond, N. J. Shaw and I. Uhlendorf, J. Phy. Chem.
B, 1997, 101, 10281-10289.
17. J. Rochford, D. Chu, A. Hagfeldt and E. Galoppini, J. Am. Chem.
Soc., 2007, 129, 4655-4665.
18. H. He, A. Gurung and L. Si, Chem.Comm., 2012, 48, 5910-5912.
19. Y. Zhu, S. Zhou, Y. Kan and Z. Su, Int. J. Quantum Chem., 2007,
107, 1614-1623.
38. G. Schlichthörl, S. Y. Huang, J. Sprague and A. J. Frank, J. Phy.
Chem. B, 1997, 101, 8141-8155.
39. A. C. Fisher, L. M. Peter, E. A. Ponomarev, A. B. Walker and K. G.
U. Wijayantha, J. Phy. Chem. B, 2000, 104, 949-958.
20. T. Ripolles-Sanchis, B.-C. Guo, H.-P. Wu, T.-Y. Pan, H.-W. Lee, S.
R. Raga, F. Fabregat-Santiago, J. Bisquert, C.-Y. Yeh and E. W.-G.
Diau, Chem. Commun., 2012, 48, 4368-4370.
21. M. Shrestha, L. Si, C.-W. Chang, H. He, A. Sykes, C.-Y. Lin and E.
W.-G. Diau, J. Phy. Chem. C, 2012, 116, 10451-10460.
22. M. D. Brown, P. Parkinson, T. Torres, H. Miura, L. M. Herz and H. J.
Snaith, J. Phy. Chem. C, 2011, 115, 23204-23208.
23. N. Humphry-Baker, K. Driscoll, A. Rao, T. Torres, H. J. Snaith and
R. H. Friend, Nano Lett., 2012, 12, 634-639.
24. B. E. Hardin, A. Sellinger, T. Moehl, R. Humphry-Baker, J.-E.
Moser, P. Wang, S. M. Zakeeruddin, M. Grätzel and M. D. McGehee,
J. Am. Chem. Soc., 2011, 133, 10662-10667.
25. E. T. Hoke, B. E. Hardin and M. D. McGehee, Opt. Express, 2010,
18, 3893-3904.
26. J. Bisquert and I. Mora-Sero, J. Phys. Chem. Lett., 2009, 1, 450-456.
27. F. Fabregat-Santiago, G. Garcia-Belmonte, J. Bisquert, A. Zaban and
P. Salvador, J. Phy. Chem. B, 2001, 106, 334-339.
28. A. F. Halverson, K. Zhu, P. T. Erslev, J. Y. Kim, N. R. Neale and A.
J. Frank, Nano Letters, 2012, 12, 2112-2116.
29. C.-L. Wang, C.-M. Lan, S.-H. Hong, Y.-F. Wang, T.-Y. Pan, C.-W.
Chang, H.-H. Kuo, M.-Y. Kuo, E. W.-G. Diau and C.-Y. Lin, Energy
Environ. Sci., 2012, 5, 6933-6940.
30. V. A. Montes, R. Pohl, J. Shinar and P. Anzenbacher, Chem. Eur. J.,
2006, 12, 4467-4467.
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