Photosensitizing porphyrin-triazine compound for bulk heterojunction solar cells

Article abstract of DOI:10.1039/c2jm33840h

This report describes the synthesis of a novel porphyrin-triazine compound bearing three porphyrin macrocycles connected to each other via a triazine central unit, and investigation of its properties for possible use in bulk heterojunction solar cells (BHJ-SCs). The porphyrin macrocycles serve as light harvesting antennae, while the triazines have been widely known to be charge extracting promoters. According to cyclic voltammetric studies, the Highest Occupied Molecular Orbital (HOMO) and Lowest Unoccupied Molecular Orbital (LUMO) energy levels of the target compound were estimated to be at -5.4 and -3.5 eV versus vacuum, respectively. Photoluminescence measurements of the blended films of the porphyrin-triazine compound and phenyl-C₆₁-butyric acid methyl ester (PCBM) or poly(3-hexylthiophene) (P3HT) indicated that the charge transfer was possible when the target porphyrin was used as an electron donor together with PCBM as an acceptor. Additionally, the surface morphology of the films with different donor:acceptor ratios was investigated by atomic force microscopy (AFM). Upon variation of the donor:acceptor weight ratio and thickness of the organic layer, the short circuit current density (J _SC) of the BHJ-SCs fabricated herein improved up to approximately 2.25 mA cm^-2.

Full text of DOI:10.1039/c2jm33840h

View Article Online / Journal Homepage / Table of Contents for this issue
Dynamic Article Links <
C
Journal of
Materials Chemistry
Cite this: J. Mater. Chem., 2012, 22, 23030
www.rsc.org/materials
PAPER
Photosensitizing porphyrin–triazine compound for bulk heterojunction
solar cells†
Aritat Luechai,a Jacek Gasiorowski,b Amorn Petsom,c Helmut Neugebauer,b Niyazi Serdar Sariciftcib
bc
*
and Patchanita Thamyongkit
Received 14th June 2012, Accepted 7th September 2012
DOI: 10.1039/c2jm33840h
This report describes the synthesis of a novel porphyrin–triazine compound bearing three porphyrin
macrocycles connected to each other via a triazine central unit, and investigation of its properties for
possible use in bulk heterojunction solar cells (BHJ-SCs). The porphyrin macrocycles serve as light
harvesting antennae, while the triazines have been widely known to be charge extracting promoters.
According to cyclic voltammetric studies, the Highest Occupied Molecular Orbital (HOMO) and
Lowest Unoccupied Molecular Orbital (LUMO) energy levels of the target compound were estimated
to be at ꢀ5.4 and ꢀ3.5 eV versus vacuum, respectively. Photoluminescence measurements of the
blended films of the porphyrin–triazine compound and phenyl-C61-butyric acid methyl ester (PCBM)
or poly(3-hexylthiophene) (P3HT) indicated that the charge transfer was possible when the target
porphyrin was used as an electron donor together with PCBM as an acceptor. Additionally, the surface
morphology of the films with different donor : acceptor ratios was investigated by atomic force
microscopy (AFM). Upon variation of the donor : acceptor weight ratio and thickness of the organic
layer, the short circuit current density (JSC) of the BHJ-SCs fabricated herein improved up to
approximately 2.25 mA cmꢀ2
.
peripheral positions,3 thermal and photo-stabilities, and strong
two-photon absorption.4 Porphyrins have long been of interest
as light-harvesting initiators for charge separation5 in various
optoelectronic devices, for example in photovoltaic cells,6
organic light-emitting diodes (OLEDs),7 and organic field-effect
transistors (OFETs).8 Recently, porphyrins have been proven to
be one of the most promising candidates for dye-sensitized solar
cells (DSSCs)9 and bulk-heterojunction solar cells (BHJSCs).2,10
In this study, we use porphyrin macrocycles as light harvesting
antennae by attaching them via their meso-carbons on all three
peripheral sites of an electron accepting triazine ring via amino
groups. Triazine (or 1,3,5-triazine) and its derivatives have high
thermal stability, molecular symmetry,11 spatial co-planarity,12
and great potential for structural modification.13 Triazine
derivatives have been extensively studied as electron transporting
and hole blocking layers,12b,c,14 as emissive materials,12f,14b,15 and
as non-linear optical16 and two-photon absorbing compounds.17
Covalent connection of the porphyrins, which are known to be p-
type semiconductors,18 with p-electron-deficient conjugated
functionalities like the triazine unit is expected to provide func-
tions in BHJ-SCs from the possibly enhanced charge extraction
efficiency. Like other planar aromatic compounds, several
porphyrin derivatives encounter low solubility due to molecular
aggregation. As one of the most important requirements of the
photoactive compounds for organic solar cell applications, high
solubility is essential for synthetic transformations, purification
Introduction
Harvesting energy directly from sunlight using photovoltaic (PV)
technology is recognized as one of the major global energy
production approaches in future energy supply. Amongst all
types of photovoltaic cells, organic solar cells have been of great
interest due to their flexibility in chemical design and mechanical
properties as well as ultrathin, roll-to-roll fabrication possibili-
ties.1 An impressive development of their efficiency took place in
the last decade and organic solar cells pushed above the 10%
power conversion efficiency.2 Photosynthetic pigments related to
the chlorophylls, such as porphyrins, are particularly good
candidates for optical and optoelectronic applications, due to
their large molar absorption coefficients, tuneable electro-
chemical and photophysical properties via central metal insertion
and/or introduction of various substituents at the macrocycle
aProgram in Petrochemistry and Polymer Science, Faculty of Science,
Chulalongkorn University, Bangkok 10330, Thailand
bLinz Institute for Organic Solar Cells (LIOS), Institute of Physical
Chemistry, Johannes Kepler University Linz, Linz 4040, Austria
cDepartment of Chemistry, Faculty of Science, Chulalongkorn University,
Bangkok 10330, Thailand. E-mail: patchanita.v@chula.ac.th; Fax: +66 2-
254-1309; Tel: +66 2-218-7587
† Electronic supplementary information (ESI) available: spectral data,
including 1H-NMR spectra, 13C-NMR spectra and mass spectra for
new compounds, and absorption and emission spectra of Zn-2, as well
as the calibration curve of Zn-2. Absorption spectrum of a P3HT film.
See DOI: 10.1039/c2jm33840h
23030 | J. Mater. Chem., 2012, 22, 23030–23037
This journal is ª The Royal Society of Chemistry 2012

View Article Online
procedures, diverse physical, photophysical and electrochemical
studies, and device fabrication via a wet process. This three-
pointed star architecture, presented here in this work, having
three porphyrin rings attached on the triazine ring via a flexible
amino group is expected to suppress the porphyrin aggregation
without the use of solubilizing substituents on the porphyrin
rings. To the best of our knowledge, there is no porphyrin–
triazine derivative studied for organic solar cells yet. Therefore,
this work aims to demonstrate the potential use of this class of
material for BHJ SCs.
give Zn-2 quantitatively, while compound 3 was kept for other
syntheses. The disappearance of the singlet signal at d ꢀ2.84 ppm
1
in a H-NMR spectrum and an emission peak at about 720 nm
indicated the completion of the reaction. According to the
1H-NMR spectrum, small signals between d 1.00–1.50 ppm was
observed, indicating a small amount of impurities that might be
encompassed in the aggregates of Zn-2 in the synthesis and
purification processes. Solubility of Zn-2 in several common
organic solvents, such as CH2Cl2, CHCl3, toluene, chloroben-
zene, THF, etc. proved its utility for BHJ-SC preparation from a
wet process by using various kinds of solvents. In chlorobenzene,
which was a solvent employed in the device fabrication in this
study, the solubility of Zn-2 was found to be approximately 45
mg mLꢀ1, equivalent to about 6.3 ꢁ 10ꢀ5 mol tetraphenylpor-
phyrin rings per 1 mL, while that of its benchmark meso-tetra-
phenylporphinatozinc(II) (Zn-TPP) was approximately 36 mg
mLꢀ1 or 4.5 ꢁ 10ꢀ5 mol mLꢀ1. This observation indicated the
enhancement of the solubility of Zn-2 due to the presence of
the 2,4,6-triamino-1,3,5-triazine central unit that might lower the
stacking effect of the porphyrin rings.
Results and discussion
1. Synthesis
The synthesis of the target porphyrin–triazine derivative for
BHJ-SCs is illustrated in Scheme 1. Porphyrin 119 was readily
condensed with cyanuric chloride in basic condition, resulting in
compounds 2 and 3 in 55% and 44% yield, respectively. A three-
column process is required to purify the target compounds.
Firstly, the silica column was used to remove unreacted
compound 1 and other polar byproducts. Secondly, sized-
exclusion chromatography separated pure compounds 2 and 3.
Finally, to further remove the remaining impurities another silica
column chromatography followed by sonicating–centrifugating
the resulting solids in hexane and methanol were performed.
Mass spectra confirmed the formation of compounds 2 and 3 by
showing their molecular ion peaks at m/z 1964.342 and 1371.742,
respectively. Compound 2 was metallated by Zn(OAc)2$2H2O to
2. Photophysical properties of Zn-2
UV-Vis absorption spectra of a Zn-2 solution in toluene and a
Zn-2 film are shown in Fig. 1. The Zn-2 solution exhibited a
characteristic absorption pattern of a Zn-chelated porphyrin
ring having intense B-band at 431 nm and Q-bands at 552 and
601 nm with absorption coefficients of 6 ꢁ 105, 2 ꢁ 104 and 9 ꢁ
103 Mꢀ1 cmꢀ1, respectively, indicating that the photophysical
properties of the individual porphyrin macrocycle were not
significantly affected by the linking with the triazine unit, which
is consistent with a previous report.20 The absorption pattern of
the film is similar, but broader than that of the solution most
likely due to the aggregation of the macrocycle conjugation
systems.
The photoluminescence spectra of Zn-2 solution (toluene) and
film are shown in Fig. 2. Upon excitation at 431 nm, emission of
the Zn-2 solution appeared at 611 nm with a small shoulder at
659 nm, while that of the film was found at 611 and 648 nm and
the peaks were broader compared to those of the solution. The
emission peak at 648 nm in the film spectrum was significantly
more pronounced and blue shifted than that at 659 nm in the
Fig. 1 Absorption spectra of a Zn-2 solution in toluene (solid line) and a
Zn-2 film (dashed line). The inset shows a magnification of the region
between 520 and 640 nm.
Scheme 1 Synthesis of target compound Zn-2.
This journal is ª The Royal Society of Chemistry 2012
J. Mater. Chem., 2012, 22, 23030–23037 | 23031

View Article Online
to the presence of the triazine unit. According to the previous
report,12b the reversible reduction peak at about ꢀ2.0 V versus
NHE was likely to be reduction of the triazine unit. The inde-
finable anodic signal from ꢀ0.3 and ꢀ0.7 V versus NHE is likely
to be resulted from the possible formation of unknown products
from the reduction process(es) of Zn-2, which is attributed to
molecular cleavage or deformation, as this feature was more
conspicuous at higher cycle numbers and was not observed in the
case of Zn-TPP.
The onset potentials of the first oxidation and reduction (Eox
and Ered, respectively) of Zn-2 obtained from the cyclic voltam-
metric studies were found to be +0.7 and ꢀ1.3 eV, respectively.
These values were used to determine an energy gap (Eg), and the
Highest Occupied Molecular Orbital (HOMO) and Lowest
Unoccupied Molecular Orbital (LUMO) energy levels (EHOMO
and ELUMO, respectively) of Zn-2 versus vacuum with an esti-
mated energy for NHE of ꢀ4.75 eV versus vacuum.21 According
to the equations:
Fig. 2 Photoluminescence spectra of a Zn-2 solution in toluene (solid
line) and a Zn-2 film (dashed line) upon photoexcitation at 431 nm.
solution spectrum, which is commonly observed when the
aggregate is created in the bulk sample.
Eg ¼ Eox ꢀ Ered
;
3. Electrochemistry
EHOMO ¼ ꢀ(Eox + 4.75) (eV); and
ELUMO ¼ ꢀ(Ered + 4.75) (eV);22
Based on cyclic voltammetry, the Zn-2 film can be electro-
chemically oxidized and reduced (Fig. 3). The oxidation process
of the molecule to a radical cation was observed at about +0.9 V
versus a normal hydrogen electrode (NHE) and a second
the calculated Eg of Zn-2 was 1.9 eV with EHOMO and ELUMO of
ꢀ5.5 and ꢀ3.5 eV, respectively.
oxidation of the molecule to
a dication was found at
about +1.1 V versus NHE. The reduction of Zn-2 to a radical
anion and a dianion occurred at about ꢀ1.5 and ꢀ1.8 V versus
NHE, respectively. These oxidation and reduction features are
consistent with those of Zn-TPP, except that Zn-2 can be reduced
at a significantly lower potential than Zn-TPP (the onset
potentials of the first reduction of Zn-2 and Zn-TPP were ꢀ1.3
and ꢀ1.4 V versus NHE, respectively), indicating the higher
electronegative nature of Zn-2 compared to that of Zn-TPP due
In Fig. 4, we display both HOMO and LUMO levels together
with the work functions (WF) of ITO, poly(3,4-ethyl-
enedioxythiophene) : poly(styrenesulfonate) (PEDOT : PSS) and
Al, and the HOMO and LUMO levels of poly(3-hexylthiophene)
(P3HT) and phenyl-C61-butyric acid methyl ester (PCBM). For a
device with a P3HT : Zn-2 active layer, the LUMO level of Zn-2
is at a lower energy level than that of P3HT, which can allow the
acceptance of electrons from P3HT and subsequent charge
transfer to the Al electrode. Similarly, when Zn-2 is blended with
electron-accepting PCBM, the LUMO level of Zn-2 was esti-
mated to be at a higher energy than that of PCBM, while its
HOMO level lies below the WF of PEDOT : PSS, suggesting the
possibility of charge transfer in the system. The above-mentioned
electrochemical behaviour of Zn-2 and this estimation suggest
that Zn-2 should be able to serve both as donor (when used
with PCBM) or acceptor (when used with P3HT) in Zn-2-based
BHJ-SCs.
Fig. 3 Cyclic voltammograms of a Zn-2 (solid line) and ZnTPP (dashed
line) films in the range between (a) 0 and ꢀ2.2 V and (b) 0 and +1.8 V.
Fig.
4 Comparative energy diagram of a Zn-2-based BHJ-SC
architecture.
23032 | J. Mater. Chem., 2012, 22, 23030–23037
This journal is ª The Royal Society of Chemistry 2012

View Article Online
4. Photoluminescence studies of the blend films
In order to study if Zn-2 is able to serve as a donor and/or
as an acceptor material, photoluminescence studies of the
Zn-2 : PCBM (1 : 1 w/w) and P3HT : Zn-2 (1 : 1 w/w) blended
films were performed. The photoactive layers were photoexcited
at the absorption maximum of the donor, i.e. Zn-2 (lmax ¼ 431
nm) in the case of the Zn-2 : PCBM film and P3HT (lmax ¼ 517
nm, see ESI†) in the case of the P3HT : Zn-2 film. The results
shown in Fig. 5 reveal that the porphyrin emission was
completely quenched by PCBM, indicating electron transfer
from Zn-2 (donor) to PCBM (acceptor). In the contrary, such
complete emission quenching was not observed in the case of the
P3HT : Zn-2 blend, indicating that the charge transfer from
P3HT (donor) to Zn-2 (acceptor) was not efficient. Therefore,
only the Zn-2 : PCBM blended film were employed as a photo-
active layer in the BHJ-SCs. The use of the blends of porphyrin
derivatives and fullerenes as active layers in BHJ-SCs has been
demonstrated to efficiently harvest solar energy and to facilitate
the photo-induced charge separation process.6h,18b,23 Some
reports described the formation of a crystallite network between
porphyrins and fullerenes in the blends23,24 that have proven
useful for BHJ-SCs.25
Fig. 6 Schematic setup of a BHJ-SC based on Zn-2 : PCBM.
As
a control experiment, a standard device having a
P3HT : PCBM (2 : 1 w/w) active layer (device ‘Standard’,
Table 1) was prepared in the same batch as the devices based on
Zn-2 : PCBM to ensure a high standard and reproducibility of
the device fabrication procedure. The standard device exhibited a
cell efficiency (h) of 3.4% with a short circuit current density
(JSC), and an open circuit voltage (VOC) and a fill factor (FF) of
9.78 mA cmꢀ2, 0.6 V and 55%, respectively. These results are
in good agreement with those of the ITO/PEDOT : PSS/
P3HT : PCBM/Al device previously prepared by a similar
procedure.26
Table 1 Characteristics of Zn-2 based BHJ-SCs
Zn-2 : PCBM ratio
Device
By weight By mol JSC/mA cmꢀ2 VOC/V FF/% h/%
A
B
C
D
E
F
G
H
I
1 : 4
1 : 6
1 : 8
0.106 : 1 1.68
0.070 : 1 1.95
0.053 : 1 2.24
0.042 : 1 2.25
0.035 : 1 2.06
0.030 : 1 1.89
0.042 : 1 1.80
0.042 : 1 1.77
0.4
0.5
0.6
0.6
0.6
0.6
0.6
0.5
28
32
32
32
32
32
31
30
0.2
0.3
0.4
0.5
0.4
0.4
0.3
0.3
1 : 10a
1 : 12
1 : 14
1 : 10b
1 : 10c
Zn-2
n/ad
n/ad
J
PCBM
P3HT : Zn-2 ratio
K
L
M
1 : 10
1 : 1
10 : 1
<0.01
0.12
0.02
0.2
0.4
0.1
27
31
24
<0.1
<0.1
<0.1
Standard P3HT : PCBM 2 : 1 9.78
0.6
55
3.4
a
A Zn-2 : PCBM mixed solution was prepared from a 18 mg mLꢀ1 stock
solution of each compound. A Zn-2 : PCBM mixed solution was
b
c
prepared from a 9 mg mLꢀ1 stock solution of each compound. A Zn-
2 : PCBM mixed solution was prepared from a 36 mg mLꢀ1 stock
solution of each compound. No significant JSC and/or VOC was
measured.
d
Fig. 5 Results of photoluminescence study of the (a) Zn-2 : PCBM and
(b) the P3HT : Zn-2 blended films.
The Zn-2 : PCBM weight ratio was varied from 4 : 1 to 1 : 14,
corresponding to a molar ratio from 1.70 : 1 to 0.030 : 1. The use
of a ratio from 4 : 1 to 1 : 2 gave an h of less than 0.1% and
therefore is not described in the table. The results clearly showed
that the variation of the Zn-2 : PCBM weight ratio from 1 : 4 to
1 : 10 (devices A–D) led to the increase in JSC, while VOC and FF
increased and reached maximum values at weight ratios of 1 : 8
and 1 : 10, indicating the better charge transfer when the PCBM
amount in the Zn-2 : PCBM film is higher within this weight
5. Photovoltaic characteristics
To determine the potential of Zn-2 as the photoactive compound
in the BHJ-SCs, Zn-2-based devices having different weight ratio
of Zn-2 : PCBM as well as thicknesses were fabricated. As shown
in Fig. 6, a 60 nm layer of electron blocking PEDOT : PSS was
patterned on an ITO-coated glass substrate. The Zn-2 : PCBM
blended film was sandwiched between the PEDOT : PSS layer
and a 150 nm Al top contact layer.
ratio range. The optimum h of 0.5% with JSC of 2.25 mA cmꢀ2
,
This journal is ª The Royal Society of Chemistry 2012
J. Mater. Chem., 2012, 22, 23030–23037 | 23033

View Article Online
VOC of 0.6 V and FF of 32% was obtained when the Zn-
2 : PCBM weight ratio was 1 : 10 (device D, Table 1). Additional
attempts to improve the cell efficiency by adjusting the thickness
of the Zn-2 : PCBM (1 : 10) film via the use of the two-fold lower
(device G) and higher (device H) concentrations of the Zn-
2 : PCBM (1 : 10) spin-casting solution were done. The increase
or decrease in thickness results mainly in the drop of JSC and
therefore the cell efficiencies. It should be noted that, for the
optimum case, with the Zn-2 : PCBM weight ratio of 1 : 10, the
Zn-2 : PCBM mole ratio is equivalent to 0.042 : 1 or, in other
words, the porphyrin ring : PCBM mole ratio is approximately
0.13 : 1. It can also be considered that under this condition the
porphyrin stacking effect tended to be reduced, leading to the
increase in the porphyrin–PCBM interface and the improved
donor–acceptor electronic communication.
and VOC. High series resistance and low parallel resistance
worked as limiting factors in the cell performance. Incident
photon-to-current efficiency (IPCE) spectrum of device D upon
excitation at 431 nm exhibited a similar spectral behaviour as the
absorption spectrum of Zn-2 (lmax ¼ 431 nm) films (Fig. 7b). The
maximum value of IPCE was found to be 22%.
6. Thin film nanomorphology
Nanoscale phase separation between the two compounds and
film morphology were found to have significant importance for
achieving efficient devices.27 Surface topography of the Zn-
2 : PCBM films with different Zn-2 : PCBM weight ratios was
investigated by atomic force microscopy (AFM). The results
showed that the surface morphology of the films looked very
similar with no observable pinhole, suggesting good blending of
the two materials. As shown in Fig. 8, an AFM image of the Zn-
2 : PCBM film of device D having the weight ratio of 1 : 10
indicates the relatively smooth and evenly distributed blend of
Zn-2 and PCBM with root-mean-square (rms) roughness of 0.5
nm. Additionally, the AFM technique was used to determine the
film thickness of the Zn-2 : PCBM film at the weight ratio of
1 : 10. The results showed that the use of the Zn-2 and PCBM
stock solutions at concentrations of 9, 18 and 36 mg mLꢀ1
(devices G, D and H, respectively) gave the Zn-2 : PCBM film a
thickness of approximately 60, 80 and 120 nm, respectively.
As reference systems, solar cells based on pristine Zn-2 and
PCBM (devices I and J, respectively) were fabricated and char-
acterized in the same manner. The results revealed that no
significant current was generated from these devices under illu-
mination, indicating that Zn-2 and PCBM are not suitable for
being used as a single component in the photoactive layer of
organic solar cells. Additionally, BHJ-SC bearing P3HT : Zn-2
blended films with the weight ratio of 1 : 10, 1 : 1 and 10 : 1
(devices K, L and M, respectively) were also prepared to examine
whether the results correspond to those obtained from the above-
mentioned photoluminescence study of the P3HT : Zn-2 blended
film. As a result, the JSC, VOC and FF of these devices were found
to be relatively low compared to those of the BHJ-SCs based on
Zn-2 : PCBM, which is likely the result of poor charge transfer
from P3HT to Zn-2 as demonstrated in the photoluminescence
study section.
Current density–voltage (J–V) curves of device D obtained
from the measurement in the dark and under illumination are
shown in Fig. 7a. The dark curve shows the diode performance.
A rectification ratio of around 50 was obtained. Upon illumi-
nation, a photovoltaic effect was observed with moderate JSC
Fig. 8 AFM image of device D.
Experimental section
Material and methods
All chemicals were analytical grade, purchased from commercial
suppliers and used as received without further purification.
Chemical shifts (d) of 1H-NMR and 13C-NMR measurement are
reported in parts per million (ppm) relative to the residual CHCl3
peak (7.26 ppm for 1H-NMR and 77.0 ppm for 13C-NMR).
Coupling constants (J) are reported in Hertz (Hz). Mass spectra
were obtained by matrix-assisted laser desorption ionization
mass spectrometry (MALDI-MS) using dithranol as a matrix
and electron spray ionization mass spectrometry (ESI-MS).
Absorption and emission spectra of the solutions were measured
in toluene at room temperature, and those of the films were
obtained from the drop-casted films on a glass substrate.
Fig. 7 (a) J–V curve and (b) IPCE plot of device D.
23034 | J. Mater. Chem., 2012, 22, 23030–23037
This journal is ª The Royal Society of Chemistry 2012

View Article Online
Non-commercial compound
through 0.45 mm PTFE syringe filters. The solution of Zn-2 was
mixed with that of P3HT or PCBM in weight ratio of 1 : 1. The
resulting P3HT : Zn-2 and Zn-2 : PCBM 1 : 1 (w/w) mixture was
spin-coated on 15 mm ꢁ 15 mm glass substrates, that were
cleaned by consecutive sonication in acetone, isopropanol and
deionized water, and then dried by purging with air, with 800
rpm for 25 s.
5-(4-Aminophenyl)-10,15,20-triphenylporphyrin (1) was prepared
according to the previous published literature.17
Synthesis of compound Zn-2
Following a previously published procedure,28 a solution of
compound 1 (0.2317 g, 0.3684 mmol) and K2CO3 (0.5103 g,
0.3692 mmol) in THF (5 mL) was treated with cyanuric chloride
(0.0175 g, 0.0949 mmol) at room temperature. The resulting
solution was refluxed for 8 h and then cooled down to room
temperature. After removal of the solvent, the crude product was
purified by column chromatography [silica, 1%EtOH in CH2Cl2]
and the purple fraction was collected. Compound 2 was isolated
from 3 by consequent size-exclusion column chromatography
using THF as eluent and then purified again by a silica column
[1% EtOH in CH2Cl2], leading to compound 2 (0.1036 g, 56%) as
a purple solid. MALDI-MS obsd 1964.241 ([M]+), calcd
1964.280 ([M]+; M ¼ C135H90N18). Compound 3 was treated in
the same manner and obtained as a purple solid (0.0578 g, 44%).
MALDI-MS obsd 1371.742 ([M]+), calcd avg mass 1371.998
([M]+; M ¼ C91H61ClN13). Optimized synthesis and detailed
characterization of compound 3 and its derivatives will be
described elsewhere.
Device fabrication and characterization
Following a previously reported procedure with slight modifi-
cation,26 the above-mentioned stock solutions of Zn-2, PCBM
and P3HT in chlorobenzene were used to prepare the mixed
solution of Zn-2 : PCBM with the weight ratio varying from 4 : 1
to 1 : 14, that of P3HT : Zn-2 with weight ratios of 1 : 10, 1 : 1
and 10 : 1, and that of P3HT : PCBM with the weight ratio of
2 : 1. The 15 mm ꢁ 15 mm ITO-coated glass substrates were first
wiped with toluene and cleaned by consecutive sonication in
acetone, isopropanol and deionized water, and then dried by
purging with air. PEDOT/PSS solution (Heraeus Cleviosꢀ
PH1000 Clevios P VP AI 4083) was spin-coated on top of the
ITO with 2000 rpꢂm for 1 s and 4000 rpm for 45 s, followed by
annealing at 150 C for 10 min. After that, the organic mixed
solution was spin-coated on top of this PEDOT/PSS layer at 800
rpm for 25 s. The resulting samples were dried under vacuum at
ambient temperature for 1–2 h before a 150 nm thick Al top
electrode was deposited by thermal evaporation in a vacuum of
about 10ꢀ6 mbar in a glovebox. The active area of the devices
was between 6 and 10 mm2. Current–voltage (I–V) characteris-
tics of the devices were measured in the dark and under simulated
100 mW cmꢀ2 AM 1.5 solar irradiation in a glovebox using a
Keithley 236 source measurement unit. The intensity of the
illumination was verified prior to each individual measurement
using a calibrated silicon diode with known spectral response.
Incident photon to current efficiency (IPCE) measurements were
taken using a fiber optical light source from a 90 W Xenon lamp,
which is connected to an ACTON Spectra Pro150 mono-
chromator and EG & G 7260 DSP Lock amplifier to measure the
current. Three to six samples for each cell condition were
prepared to test the reproducibility and reliability of the results.
Following recently published procedure29 with slight modifi-
cation, compound 2 (0.1036 g, 0.05263 mmol) was dissolved in
THF (10 mL) and then reacted with
a solution of
Zn(OAc)2$2H2O (0.1743 g, 0.5263 mmol) in methanol (10 mL) at
room temperature for 8 h. After removal of the solvent, the
reaction mixture was redissolved in CH2Cl2, washed with water,
dried (Na2SO4), and concentrated to dryness. Purification by
column chromatography [silica, 1% EtOH in CH2Cl2] followed
by sonicating–centrifugating in hexane and methanol gave a
purple solid (100.7 mg, 89%). dH (400 MHz; CDCl3) 6.47 (3H, s),
7.29–7.59 (m, 6H), 7.60–7.75 (m, 27H), 7.75–7.88 (m, 6H), 7.90–
8.29 (m, 18H), 8.76–8.97 (m, 18H), 8.97–9.15 (m, 6H); dC (100
MHz; CDCl3) 119.0, 120.7, 121.1, 124.3, 126.4, 126.5, 127.3,
127.4, 132.0, 134.4, 134.9, 137.7, 138.0, 142.7, 142.8, 143.1, 150.1,
150.2, 150.3, 163.9; MALDI-MS obsd 2154.516; calcd avg mass
2154.462 ([M]+;
M
¼
C135H84N18Zn3); ESI-HRMS obsd
2177.5169 ([M + Na]+), calcd 2177.4513 ([M + Na]+), 2154.5145
([M]+); labs/nm 431, 552 and 601 (3/dm3 molꢀ1 cmꢀ1 6 ꢁ 105, 6 ꢁ
104 and 9 ꢁ 103); lem/nm 612 (lex ¼ 431 nm).
Film morphology study
An atomic force microscope setup with Digital Instruments
Dimension 3100 (Veeco Metrology group), working in tapping
mode, was used in order to investigate the surface morphology
and determine the thickness of the samples.30
Electrochemical studies
Electrochemical properties of compoundZn-1 were determined by
cyclic voltammetry in acetonitrile containing 0.1 M Bu4NPF6 by
using a ITO-coated glass working electrode, a Pt wire counter
electrode and an Ag/AgCl quasi-reference electrode (QRE) with a
scan rate of 20 mV sꢀ1. The resulting redox potentials were
externally calibrated with a ferrocene/ferrocenium couple of which
the potentialvalue of0.40V versusNHEwasused. Thevalue ofthe
NHE versus vacuum level used in this work is ꢀ4.75 eV.21
Conclusions
The novel soluble porphyrin derivative having three porphyrin
macrocycles linked by the triazine central unit (Zn-2) was
successfully synthesized and characterized by spectroscopic
techniques. Based on cyclic voltammetric analysis, Zn-2 was
found to have appropriate HOMO–LUMO energy levels to
possibly serve as both donor and acceptor in ITO/PEDOT : PSS/
Zn-2 : PCBM/Al and ITO/PEDOT : PSS/P3HT : Zn-2/Al solar
cells, respectively. However, photoluminescence measurements
of the blended films of the organic active layers indicated that an
electron transfer was observed in the Zn-2 : PCBM film, but not
Photoluminescence studies
Stock solutions of Zn-2, P3HT and PCBM in chlorobenzene
were prepared in the concentration of 18 mg mLꢀ1 and filtered
This journal is ª The Royal Society of Chemistry 2012
J. Mater. Chem., 2012, 22, 23030–23037 | 23035

View Article Online
€
X. X. Zhang, K. N. Mohammad and M. Gratzel, J. Phys. Chem. A,
2009, 113, 10119.
in the P3HT : Zn-2 one. The results from the device study
confirmed the possible usage of Zn-2 as donor material in
organic BHJ-SCs. Our best ITO/PEDOT : PSS/Zn-2 : PCBM/Al
device exhibited an energy conversion maximum efficiency of
0.5% with JSC, VOC and FF of 2.25 mA cmꢀ2, 0.6 V and 32%,
respectively. The studies showed that porphyrin rings in the Zn-2
molecule were useful as light-harvesting units in BHJ-SCs and,
with the good collaboration of the triazine core, Zn-2 could
transfer electrons to PCBM, resulting in a photovoltaic effect.
7 Selected publications: (a) M. A. Baldo, D. F. O’Brien, Y. You,
A. Shoustikov, S. Sibley, M. E. Thompson and S. R. Forrest,
Nature, 1998, 395, 151; (b) R. C. Kwong, S. Sibley, T. Dubovoy,
M. Baldo, S. R. Forrest and M. E. Thompson, Chem. Mater., 1999,
11, 3709; (c) T. F. Guo, S. C. Chang, Y. Yang, R. C. Kwong and
W. E. Thompson, Org. Electron., 2000, 1, 15; (d) E. M. Gross,
N. R. Armstrong and R. M. Wightman, J. Electrochem. Soc., 2002,
149, E137; (e) V. A. Montes, C. Perez-Bolivar, N. Agarwal,
J. Shinar and P. Anzenbacher, J. Am. Chem. Soc., 2006, 128, 12436;
(f) X. Wang, H. Wang, Y. Yang, Y. He, L. Zhang, Y. Li and X. Li,
Macromolecules, 2010, 43, 709.
8 Selected publications: (a) Y. Y. Noh, K. Yase and S. Nagamatsu,
Appl. Phys. Lett., 2003, 83, 1243; (b) Y. Y. Noh, J. J. Kim,
Y. Yoshida and K. Yase, Adv. Mater., 2003, 15, 699; (c)
P. Checcoli, G. Conte, S. Salvatori, R. Paolesse, A. Bolognesi,
A. Berliocchi, F. Brunetti, A. D’Amico, A. Di Carlo and P. Lugli,
Synth. Met., 2003, 138, 261; (d) P. B. Shea, J. Kanicki and N. Ono,
J. Appl. Phys., 2005, 98, 014503; (e) C.-M. Che, H.-F. Xiang,
S. S.-Y. Chui, Z.-X. Xu, V. A. L. Roy, J. J. Yan, W.-F. Fu,
P. T. Lai and I. D. Williams, Chem.–Asian J., 2008, 3, 1092; (f)
X. B. Huang, C. L. Zhu, S. M. Zhang, W. W. Li, Y. L. Guo,
X. W. Zhan, Y. Q. Liu and Z. Z. Bo, Macromolecules, 2008, 41,
6895; (g) P. Ma, Y. Chen, X. Cai, H. Wang, Y. Zhang, Y. Gao and
J. Jiang, Synth. Met., 2010, 160, 510.
Acknowledgements
This research was partially supported by Marie Curie Interna-
tional Incoming Fellowship (PIIF-GA-2008-220272), Thailand
Research Fund-Master Research Grants-Window II (TRF-
MRG-WII 525S022), National Research University Project of
Thailand, Office of the Higher Education Commission (Project
No: EN1250B), the Center of Excellence of Petroleum, Petro-
chemicals and Advance Material, and Graduate School of
Chulalongkorn University (The 90th Anniversary of Chula-
longkorn University Fund, Ratchadaphiseksomphot Endow-
ment Fund).
9 A. Yella, H.-W. Lee, H. N. Tsao, C. Yi, A. K. Chandiran,
M. K. Nazeeruddin, E. W.-G. Diau, S. M. Zakeeruddin and
€
M. Gratzel, Science, 2011, 334, 629.
10 R. F. Service, Science, 2011, 332, 293.
Notes and references
11 Selected publications: (a) M. Kucharski and W. Mazurkiewicz,
Polymer, 1982, 23, 1688; (b) T. Fang and D. A. Shimp, Prog.
Polym. Sci., 1995, 20, 61; (c) T. Nishikubo, A. Kameyama and
C. Saito, J. Polym. Sci., Part A: Polym. Chem., 2000, 38, 3604.
12 Selected publications: (a) I. Nenner and G. J. Schulz, J. Chem. Phys.,
1975, 62, 1747; (b) R. Fink, C. Frenz, M. Thelakkat and H. Schmidt,
Macromolecules, 1997, 30, 8177; (c) R. Fink, Y. Heischkel,
M. Thelakkat and H. Schmidt, Chem. Mater., 1998, 10, 3620; (d)
H. Meier, H. C. Holst and A. Oehlhof, Eur. J. Org. Chem., 2003,
4173; (e) H. Meier, E. Karpuk and H. C. Holst, Eur. J. Org. Chem.,
2006, 2609; (f) Q. Fang, S. Ren, B. Xu, J. Du and A. Cao, J.
Polym. Sci., Part A: Polym. Chem., 2006, 44, 3797; (g)
T. Yamamoto, S. Watanabe, H. Fukumoto, M. Sato and
T. Tanaka, Macromol. Rapid Commun., 2006, 27, 317; (h) L. Zou,
Y. Fu, X. Yan, X. Chen and J. Qin, J. Polym. Sci., Part A: Polym.
Chem., 2008, 46, 702.
13 Selected publications: (a) J. A. Zerkowski, J. P. Mathias and
G. M. Whitesides, J. Am. Chem. Soc., 1994, 116, 430; (b)
C. M. Drain, K. C. Russell and J.-M. Lehn, J. Comb. Chem., 1996,
3, 337; (c) J. L. Sessler, C. T. Brown, D. O’Connor, S. L. Springs,
R. Wang, M. Sathiosatham and T. Hirose, J. Org. Chem., 1998, 63,
7370; (d) A. Osuka, R. Yoneshima, H. Shiratori, T. Okada,
S. Taniguchi and N. Mataga, Chem. Commun., 1998, 1567; (e)
K. A. Jolliffe, P. Timmerman and D. N. Reinhoudt, Angew. Chem.,
Int. Ed., 1999, 38, 933; (f) M. H. Al-Sayah and N. R. Branda, Org.
Lett., 2002, 4, 881; (g) T. Carofiglio, A. Varotto and U. Tonellato,
J. Org. Chem., 2004, 69, 8121.
1 (a) A. J. Heeger, N. S. Sariciftci and E. B. Namdas, Semiconducting
and Metallic Polymers, Oxford University Press, New York, 1st
edn, 2010; (b) C. J. Brabec, V. Dyakonov, J. Parisi and
N. S. Sariciftci, Organic Photovoltaics: Concepts and Realization
(Springer Series in Materials Science), Springer, Heidelberg, 2010;
(c) S.-S. Sun and N. S. Sariciftci, Organic Photovoltaics:
Mechanisms, Materials, and Devices (Optical Science and
Engineering), Taylor & Francis, Boca Raton, 1st edn, 2005; (d)
M. Kaltenbrunner, M. S. White, E. D. G1owacki, T. Sekitani,
T. Someya, N. S. Sariciftci and S. Bauer, Nat. Commun., April 3,
2012, DOI: 10.1038/ncomms1772.
2 Mitsubishi Chemical Holdings Corporation, http://www.m-
kagaku.co.jp/english/aboutmcc/RC/special/feature1.html, accessed
17 April 2012.
3 K. M. Kadish, E. V. Caemelbecke and G. Royal, in The Porphyrin
Handbook, ed. K. M. Kadish, K. M. Smith and R. Guilard,
Acedemic Press, New York, 2000, vol. 8, ch. 55.
4 F. C. Krebs and H. Spanggaard, Sol. Energy Mater. Sol. Cells, 2005,
88, 363.
5 (a) D. Gust, T. A. Moore and A. L. Moore, Acc. Chem. Res., 2001, 34,
40; (b) H. Imahori and S. Fukuzumi, Adv. Funct. Mater., 2004, 14,
525.
6 Selected publications: (a) K. Kalyanasundaram, N. Vlachopoulos,
€
V. Krishnan, A. Monnier and M. Gratzel, J. Phys. Chem., 1987, 91,
2342; (b) A. Kay and M. Gratzel, J. Phys. Chem., 1993, 97, 6272;
€
(c) D. Wohrle, B. Tennigkeit, J. Elbe, L. Kreienhoop and
G. Schurpfeil, Mol. Cryst. Liq. Cryst., 1993, 230, 221; (d)
S. Cherian and C. C. Wamser, J. Phys. Chem. B, 2000, 104, 3624;
(e) F. Odobel, E. Blart, M. Lagree, M. Villieras, H. Boujtita, N. El
Murr, S. Caramori and C. A. Bignozzi, J. Mater. Chem., 2003, 13,
502; (f) W. M. Campbell, A. K. Burrell, D. L. Officer and
K. W. Jolly, Coord. Chem. Rev., 2004, 248, 1363; (g) H. Imahori, J.
Phys. Chem. B, 2004, 108, 6130; (h) T. Hasobe, P. V. Kamat,
M. A. Absalom, Y. Kashiwagi, J. Sly, M. J. Crossley,
K. Hosomizu, H. Imahori and S. Fukuzumi, J. Phys. Chem. B,
2004, 108, 12865; (i) Q. Wang, W. M. Campbell, E. E. Bonfantani,
K. W. Jolley, D. L. Officer, P. J. Walsh, K. Gordon, R. Humphry-
14 Selected publications: (a) J. M. Lupton, L. R. Hemingway,
W. I. D. Samuel and P. L. Burn, J. Mater. Chem., 2000, 10, 867; (b)
J. Pang, Y. Tao, S. Freiberg, X. P. Yang, M. D’Iorio and S. Wang,
J. Mater. Chem., 2002, 12, 206; (c) H. Inomata, K. Goushi,
T. Masuko, T. Konno, T. Imai, H. Sasabe, J. J. Brown and
C. Adachi, Chem. Mater., 2004, 16, 1285; (d) H. Namazi and
M. Adeli, J. Polym. Sci., Part A: Polym. Chem., 2005, 43, 28; (e)
E. J. Acosta, S. O. Gonzalez and E. E. Simanek, J. Polym. Sci.,
ꢀ
ꢀ
Part A: Polym. Chem., 2005, 43, 168; (f) R. Juarez, R. Gomez,
J. L. Segura and C. Seoane, Tetrahedron Lett., 2005, 46, 8861; (g)
J. Kang, D. Lee, H. Park, Y. Park, J. W. Kim, W. Jeong, K. Yoo,
K. Go, S. Kim and J. Kim, J. Mater. Chem., 2007, 17, 3714; (h)
A. Richard, H. A. Klenklera, A. Tranc, D. Z. Popovic and G. Xu,
Org. Electron., 2008, 9, 285; (i) H. Zhong, E. Xu, D. Zeng, J. Du,
J. Sun, S. Ren, B. Jiang and Q. Fang, Org. Lett., 2008, 10, 709.
15 (a) S. W. Kim, S. C. Shim, B.-J. Jung and H.-K. Shim, Polymer, 2002,
43, 4297; (b) Q. Fang and T. Yamamoto, Macromol. Chem. Phys.,
2004, 205, 795; (c) T. Murase and M. Fujita, J. Org. Chem., 2005,
€
Baker, M. K. Nazeeruddin and M. Gratzel, J. Phys. Chem. B, 2005,
109, 15397; (j) T. Hasobe, S. Fukuzumi and P. V. Kamat, J. Phys.
Chem. B, 2006, 110, 25477; (k) W. M. Campbell, K. W. Jolly,
P. Wagner, K. Wagner, P. J. Walsh, K. C. Gordon, L. S. Mende,
€
M. K. Nazeerruddin, Q. Wang and M. Gratzel, J. Phys. Chem. C,
2007, 111, 11760; (l) H. Imahori, T. Umeyama and S. Ito, Acc.
Chem. Res., 2009, 42, 1809; (m) R. M. Ma, P. Guo, H. J. Cui,
23036 | J. Mater. Chem., 2012, 22, 23030–23037
This journal is ª The Royal Society of Chemistry 2012

View Article Online
70, 9269; (d) S. Ren, Q. Fang, F. Yu and D. Bu, J. Polym. Sci., Part A:
Polym. Chem., 2005, 43, 6554; (e) W. Jia, Y. Hu, J. Gao and S. Wang,
Dalton Trans., 2006, 1721; (f) C. K. Kim, E. S. Song, H. J. Kim,
C. Park, J. K. Kim, Y. C. Kim, J. W. Yu and C. Kim, J. Polym.
Sci., Part A: Polym. Chem., 2006, 44, 5855; (g) G. Wen, Y. Xin,
X. Zhu, W. Zeng, R. Zhu, J. Feng, Y. Cao, L. Zhao, L. Wang,
W. Wei, B. Peng and W. Huang, Polymer, 2007, 48, 1824.
H. Lemmetyinen, Chem.–Eur. J., 2007, 13, 10182; (m) T. Hasobe,
ꢀ
K. Saito, P. V. Kamat, V. Troiani, H. Qiu, N. Solladie, K. S. Kim,
J. K. Park, D. Kim, F. D’Souza and S. Fukuzumi, J. Mater. Chem.,
2007, 17, 4160; (n) A. Kira, M. Tanaka, T. Umeyama, Y. Matano,
N. Yoshimoto, Y. Zhang, S. Ye, H. Lehtivuori, N. V. Tkachenko,
H. Lemmetyinen and H. Imahori, J. Phys. Chem. C, 2007, 111,
13618; (o) T. Umeyama, T. Takamatsu, N. Tezuka, Y. Matano,
Y. Araki, T. Wada, O. Yoshikawa, T. Sagawa, S. Yoshikawa and
H. Imahori, J. Phys. Chem. B, 2011, 113, 10798; (p) C.-L. Wang,
W.-B. Zhang, C.-H. Hsu, H.-J. Sun, R. M. V. Horn, Y. Tu,
D. V. Anokhin, D. A. Ivanov and S. Z. D. Cheng, Soft Matter,
2011, 7, 6135.
16 (a) Q. Y. Hu, W. X. Lu, H. D. Tang, H. H. Y. Sung, T. B. Wen,
I. D. Williams, G. K. L. Wong, Z. Lin and G. Jia, Organometallics,
2005, 24, 3966; (b) K. Srinivas, S. Sitha, V. J. Rao,
K. Bhanuprakash and K. Ravikumar, J. Mater. Chem., 2006, 16, 496.
17 (a) R. Kannan, G. S. He, T.-C. Lin, P. N. Prasad, R. A. Vaia and
L.-S. Tan, Chem. Mater., 2004, 16, 185; (b) Y. Z. Cui, Q. Fang,
G. Xue, G.-B. Xu, L. Yin and W.-T. Yu, Chem. Lett., 2005, 34,
644; (c) L. Zou, Z. Liu, X. Yan, Y. Liu, Y. Fu, J. Liu, Z. Huang,
X. Chen and J. Qin, Eur. J. Org. Chem., 2009, 5587–5593.
18 (a) Y. Harima, K. Takeda and K. Yamashita, J. Phys. Chem. Solids,
1995, 56, 1223; (b) T. Hasobe, H. Imahori, P. V. Kamat, T. K. Ann,
S. K. Kim, D. Kim, A. Fujimoto, T. Hirakawa and S. Fukuzumi, J.
Am. Chem. Soc., 2005, 127, 1216; (c) Q. Sun, L. Dai, X. Zhou,
L. Li and Q. Li, Appl. Phys. Lett., 2007, 91, 253505; (d) T. Hasobe,
A. S. D. Sandanayaka, T. Wada and Y. Araki, Chem. Commun.,
2008, 3372; (e) Y. Matsuo, Y. Sato, T. Niinomi, I. Soga, H. Tanaka
and E. Nakamura, J. Am. Chem. Soc., 2009, 131, 1127.
24 (a) M. M. Olmstead, D. A. Costa, K. Maitra, B. C. Noll,
S. L. Phillips, P. M. Van Calcar and A. L. Balch, J. Am. Chem.
Soc., 1999, 121, 7090; (b) P. D. W. Boyd, M. C. Hodgson,
C. E. F. Rickard, A. G. Oliver, L. Chaker, P. J. Brothers,
R. D. Bolskar, F. S. Tham and C. A. Reed, J. Am. Chem. Soc.,
1999, 121, 10487; (c) N. Armaroli, G. Marconi, L. Echegoyen,
J.-P. Bourgeois and F. Diederlich, Chem.–Eur. J., 2000, 6, 1629; (d)
N. V. Tkachenko, C. Guenther, H. Imahori, K. Tamaki, Y. Sakata,
S. Fukuzumi and H. Lemmetyinen, Chem. Phys. Lett., 2000, 326,
344; (e) H. Imahori, N. V. Tkachenko, V. Vehmanen, K. Tamaki,
H. Lemmetyinen, Y. Sakata and S. Fukuzumi, J. Phys. Chem. A,
2001, 105, 1750; (f) P. D. W. Boyd and C. A. Reed, Acc. Chem.
Res., 2005, 38, 235; (g) N. Armaroli, G. Accorsi, F. Song,
A. Palkar, L. Echegoyen, D. Bonifazi and F. Diederlich,
ChemPhysChem, 2005, 6, 732; (h) H. Imahori, Bull. Chem. Soc.
Jpn., 2007, 80, 621.
19 G. Yan, D. Bischa and S. E. Bottle, Free Radical Biol. Med., 2007, 43,
111.
20 K. P. Ghiggino, J. A. Hutchison, S. J. Langford, M. J. Latter and
M. Takezaki, J. Phys. Org. Chem., 2006, 19, 491.
21 (a) R. Gomer and G. Tryson, J. Chem. Phys., 1977, 66, 4413; (b)
C. M. Cardona, W. Li, A. E. Kaifer, D. Stockdale and
G. C. Bazan, Adv. Mater., 2011, 23, 2367.
25 (a) P. D. W. Boyd, M. C. Hodgson, C. E. F. Rickard, A. G. Oliver,
L. Chaker, P. J. Brothers, R. D. Bolskar, F. S. Tham and
C. A. Reed, J. Am. Chem. Soc., 1999, 121, 10487; (b) T. Ishii,
N. Aizawa, R. Kanehama, M. Yamashita, K. Sugiura and
H. Miyasaka, Coord. Chem. Rev., 2002, 226, 113; (c)
D. V. Konarev, A. Y. Kovalevsky, X. Li, I. S. Neretin,
A. L. Litvinov, N. V. Drichko, Y. L. Slovokhotov, P. Coppens and
R. N. Lyubovskaya, Inorg. Chem., 2002, 41, 3638; (d)
P. D. W. Boyd and C. A. Reed, Acc. Chem. Res., 2005, 38, 235; (e)
P. C. Dastoor, C. R. McNeill, H. Frohne, C. J. Foster, B. Dean,
C. J. Fell, W. J. Belcher, W. M. Campbell, D. L. Officer,
I. M. Blake, P. Thordarson, M. J. Crossley, N. S. Hush and
J. R. Reimers, J. Phys. Chem. C, 2007, 111, 15415; (f)
W. J. Belcher, K. I. Wagner and P. C. Dastoor, Sol. Energy Mater.
Sol. Cells, 2007, 91, 447; (g) T. Oku, A. Takeda, A. Nagata,
T. Noma, A. Suzuki and K. Kikuchi, Energies, 2010, 3, 671; (h)
N. Cooling, K. B. Burke, X. Zhou, S. J. Lind, K. C. Gordon,
T. W. Jones, P. C. Dastoor and W. J. Belcher, Sol. Energy Mater.
Sol. Cells, 2011, 95, 1767.
22 D. Baran, A. Balan, S. Celebi, B. M. Esteban, H. Neugebauer,
N. S. Sariciftci and L. Toppare, Chem. Mater., 2010, 22, 2978.
23 (a) H. Imahori, K. Hagiwara, M. Aoki, T. Akiyama, S. Taniguchi,
T. Okada, M. Shirakawa and Y. Sakata, J. Am. Chem. Soc., 1996,
118, 11771; (b) H. Imahori and Y. Sakata, Adv. Mater., 1997, 9,
537; (c) D. M. Guldi, C. Luo, M. Prato, E. Dietel and A. Hirsch,
Chem. Commun., 2000, 373; (d) C. Luo, D. M. Guldi, H. Imahori,
K. Tamaki and Y. Sakata, J. Am. Chem. Soc., 2000, 122, 6535; (e)
D. M. Guldi, C. Luo, M. Prato, A. Troisi, F. Zerbetto,
M. Scheloske, E. Dietel, W. Bauer and A. Hirsch, J. Am. Chem.
Soc., 2001, 123, 9166; (f) T. Hasobe, Y. Kashiwagi,
M. A. Absalom, J. Sly, K. Hosomizu, M. J. Crossley, H. Imahori,
P. V. Kamat and S. Fukuzumi, Adv. Mater., 2004, 16, 975; (g)
H. Imahori, A. Fujimoto, S. Kang, H. Hotta, K. Yoshida,
T. Umeyama, Y. Matano, S. Isoda, M. Isosomppi,
N. V. Tkachenko and H. Lemmetyinen, Chem.–Eur. J., 2005, 11,
ꢀ
7265; (h) T. Hasobe, P. V. Kamat, V. Troiani, N. Solladie,
26 P. A. Troshin, H. Hoppe, J. Renz, M. Egginger, J. Y. Mayorava,
A. E. Goryachev, A. S. Peregudov, R. N. Lyubovskaya,
G. Gobsch, N. S. Sariciftci and V. F. Razomov, Adv. Funct. Mater.,
2009, 19, 779.
T. K. Ahn, S. K. Kim, D. Kim, A. Kongkanand, S. Kuwabata and
S. Fukuzumi, J. Phys. Chem. B, 2005, 109, 19; (i) D. M. J. Guldi, J.
Phys. Chem. B, 2005, 109, 11432; (j) H. Imahori, K. Mitamura,
Y. Shibano, T. Umeyama, Y. Matano, K. Yoshida, S. Isoda,
Y. Araki and O. Ito, J. Phys. Chem. B, 2006, 110, 11399; (k)
T. Hasobe, S. Fukuzumi, S. Hattori and P. V. Kamat, Chem.–Asian
J., 2007, 2, 265; (l) H. Imahori, M. Ueda, S. Kang, H. Hayashi,
S. Hayashi, H. Kaji, S. Seki, A. Saeki, S. Tagawa, T. Umeyama,
Y. Matano, K. Yoshida, S. Isoda, M. Shiro, N. V. Tkachenko and
27 W. L. Ma, C. Y. Yang, X. Gong, K. Lee and A. J. Heeger, Adv. Funct.
Mater., 2005, 15, 1617.
28 K. Ichihara and Y. Naruta, Chem. Lett., 1995, 24, 631.
29 J. Jiao, P. Thamyongkit, I. Schmidt, J. S. Lindsey and D. F. Bocian, J.
Phys. Chem. C, 2007, 111, 12693.
30 C. Teichert, Phys. Rep., 2002, 365, 335.
This journal is ª The Royal Society of Chemistry 2012
J. Mater. Chem., 2012, 22, 23030–23037 | 23037