1-aryl-4-silylmethyl[60]fullerenes: Synthesis, properties, and photovoltaic performance

Article abstract of DOI:10.1002/asia.201200726

The efficient nucleophilic addition of aryl Grignard reagents (aryl=4-MeOC₆H₄, 4-Me₂NC₆H ₄, Ph, 4-CF₃C₆H₄, and thienyl) to C₆₀ in the presence of DMSO produced 1,2-arylhydro[60]fullerenes after acid treatment. The reactions of the anions of these arylhydro[60] fullerenes with either dimethylphenylsilylmethyl iodide or dimethyl(2- isopropoxyphenyl)silylmethyl iodide yielded the target compounds, 1-aryl-4-silylmethyl[60]fullerenes. The properties and structures of these 1-aryl-4-silylmethyl[60]fullerenes (aryl=4-MeOC₆H₄, thienyl) were examined by electrochemical studies, X-ray crystallography, flash-photolysis time-resolved microwave-conductivity (FP-TRMC) measurements, and electron-mobility measurements by using a space-charge-limited current (SCLC) model. Organic photovoltaic devices with a polymer-based bulk heterojunction structure and small-molecule-based p-n and p-i-n heterojunction configurations were fabricated by using 1-aryl-4-silylmethyl[60]fullerenes as an electron acceptor. The most efficient device exhibited a power-conversion efficiency of 3.4 % (short-circuit current density: 8.1 mA/ cm², open-circuit voltage: 0.69 V, fill factor: 0.59). Copyright

Full text of DOI:10.1002/asia.201200726

FULL PAPER
DOI: 10.1002/asia.201200726
1-Aryl-4-Silylmethyl[60]fullerenes: Synthesis, Properties, and Photovoltaic
Performance
Yutaka Matsuo,*[a] Hiromi Oyama,[a] Iwao Soga,[a, b] Toshihiro Okamoto,[a, d]
Hideyuki Tanaka,[a] Akinori Saeki,[c] Shu Seki,[c] and Eiichi Nakamura*[a]
Abstract: The efficient nucleophilic ad-
dition of aryl Grignard reagents (aryl=
4-MeOC6H4, 4-Me2NC6H4, Ph, 4-
CF3C6H4, and thienyl) to C60 in the
presence of DMSO produced 1,2-aryl-
hydro[60]fullerenes after acid treat-
ment. The reactions of the anions of
structures of these 1-aryl-4-silylme-
thyl[60]fullerenes (aryl=4-MeOC6H4,
thienyl) were examined by electro-
chemical studies, X-ray crystallography,
flash-photolysis time-resolved micro-
wave-conductivity (FP-TRMC) meas-
urements, and electron-mobility meas-
urements by using a space-charge-limit-
ed current (SCLC) model. Organic
photovoltaic devices with a polymer-
based bulk heterojunction structure
and small-molecule-based p–n and p–i–
n heterojunction configurations were
fabricated by using 1-aryl-4-silylme-
thyl[60]fullerenes as an electron ac-
ceptor. The most efficient device exhib-
ited a power-conversion efficiency of
3.4% (short-circuit current density:
these
arylhydro[60]fullerenes
with
either
dimethylphenylsilylmethyl
iodide or dimethyl(2-isopropoxyphe-
nyl)silylmethyl iodide yielded the
target compounds, 1-aryl-4-silylme-
thyl[60]fullerenes. The properties and
Keywords: conducting materials
electrochemistry fullerenes
photovoltaic devices · thiophenes
·
·
8.1 mA/cm2,
0.69 V, fill factor: 0.59).
open-circuit
voltage:
·
Introduction
enes,[4] bis-adducts, such as bis-PCBM[5] and indene C60 bis-
adducts (ICBAs),[6] and methanofullerene derivatives.[7] In-
creased variety in fullerene-based acceptors has been widely
pursued, because it would significantly expand the field of
OPV research. This pursuit is not only limited to the im-
provement of power-conversion efficiency, but also includes
fundamental research on morphology control[3e,8] and excit-
ed-state dynamics.[9]
Whilst functionalized fullerene derivatives are the most-
promising electron-accepting materials in organic photovol-
taic (OPV) devices, there is only a limited repertoire of such
fullerene electron-acceptors. Only a few types of fullerene
derivatives are known to be viable for application in OPV
devices, including [6,6]-phenyl-C61-butyric acid methyl
esters (PCBMs),[1,2] 1,4-dialkylfullerenes,[3] 1,4-diarylfuller-
Herein, we focus on 1,4-diadducts that contain one alkyl
group and one aryl group (Scheme 1). In general, 1,4-dia-
lkylfullerenes that contain insulating aliphatic groups usually
[a] Prof. Dr. Y. Matsuo, H. Oyama, Dr. I. Soga, Dr. T. Okamoto,
Dr. H. Tanaka, Prof. Dr. E. Nakamura
Department of Chemistry, School of Science
The University of Tokyo
7-3-1 Hongo, Bunkyo-ku, Tokyo 113-0033 (Japan)
Fax : (+81)3-5800-6889
E-mail: matsuo@chem.s.u-tokyo.ac.jp
nakamura@chem.s.u-tokyo.ac.jp
[b] Dr. I. Soga
Mitsubishi Chemical Group Science and
Technology Research Center, Inc.
1000 Kamoshida, Aoba-ku, Yokohama
Kanagawa 227-8502 (Japan)
Scheme 1. Molecular design of the 1,4-diadducts.
[c] Dr. A. Saeki, Prof. Dr. S. Seki
Department of Applied Chemistry
Graduate School of Engineering
Osaka University
exhibit low carrier mobility, with the exception of molecules
such
as
1,4-bis(dimethylphenylsilylmethyl)[60]fullerene
(SIMEF),[3] which form columnar arrays of C60 cores that
result in good electron mobility. On the other hand, 1,4-dia-
rylfullerenes possess comparative electronic properties, but
the rigidity of their aryl groups results in poorer solubility.
Thus, our motivation has been to achieve a good balance be-
tween solubility and favorable electronic properties, which
are conferred by the alkyl group and the aryl group, respec-
2-1 Yamadaoka, Suita, Osaka 565-0871 (Japan)
[d] Dr. T. Okamoto
Current address:
Department of Advanced Electron Devices
The Institute of Scientific and
Industrial Research (ISIR)
8-1 Mihogaoka, Ibaraki, Osaka 567-0047 (Japan)
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Yutaka Matsuo, Eiichi Nakamura et al.
tively. Moreover, because 1,4-diadducts have smaller p-con-
jugated systems than 1,2-diadducts, their LUMO levels are
Grignard reagent and so we studied the scope and limita-
tions of this reaction.
higher, thus resulting in a higher open-circuit voltage (VOC
)
We studied the DMSO-assisted monoaddition reaction
with various aryl Grignard reagents, [Eq. (1)], including
both electron-donating- and electron-withdrawing groups, to
obtain compounds 1–5. The addition reaction of electron-
rich aryl groups, such as the anisyl and dimethyl amino
groups, occurred more smoothly and more readily than that
of electron-deficient aryl groups, such as the trifluorome-
thylphenyl group. We also included a 2-thienyl group to
in OPV devices.[3]
Herein, we report the synthesis of 1-aryl-4-silylmethyl[60]-
fullerenes, including the characterization of their electro-
chemical properties, crystal-packing structures, and photo-
voltaic performance in OPV devices. An anisyl group and
a thienyl group were chosen as the aryl groups because of
their electron-donating nature, which was expected to raise
the LUMO levels and to increase the VOC value. The addi-
tion of a thienyl group to fullerene derivatives has previous-
ly been attempted to obtain fullerene–thiophene hybrids,[10]
which were expected to exhibit properties of both fullerene
and of the standard electron donor, poly(3-hexylthiophene)
(P3HT). 1-Aryl-4-silylmethyl[60]fullerenes are regioisomers
of 1-aryl-2-silylmethyl[60]fullerenes, which have been previ-
ously synthesized by the migration of aryl groups from the
silicon side-chain to the fullerene core.[11] A respectable
power-conversion efficiency of 3.4% was achieved herein,
thus demonstrating that 1-aryl-4-silylmethyl[60]fullerenes
can serve as viable electron-acceptors to produce efficient
and competitive OPV devices.
obtain a monoACTHNUGTRNEUNG(thienyl)hydro[60]fullerene (5) in moderate
yield. To our knowledge, compound 5, a 2-substituted thien-
yl fullerene compound, is a new compound, although a 3-
substituted regioisomer had been previously synthesized by
a palladium-catalyzed hydroarylation reaction.[13b]
Results and Discussion
Synthesis of 1,2-Arylhydro[60]fullerenes
In general, there are three methods to obtain mono-
ACHTUNGTRENNUNG(aryl)hydro[60]fullerenes. The first is a sulfoxide (DMSO)-
assisted monoaddition reaction of an aryl Grignard reagent
to C60,[3] the second is an AlCl3-mediated Friedel–Crafts-
type hydroarylation reaction,[12] and the third is a transition-
metal-catalyzed arylation reaction of C60 by using arylboron-
ic acids.[13] Herein, the first method was chosen. A previous
report[1b] described only one example with
a p-anisyl
Synthesis and Properties of 1-Aryl-4-
silylmethyl[60]fullerenes
Abstract in Japanese:
Next, we deprotonated compounds 1–5 with a base to
obtain monoaryl[60]fullerene anions, which reacted with si-
lylmethyl halides to give 1-aryl-4-silylmethyl[60]fullerenes
6–10 in 18–36% yield [Eq. (2)]. We investigated the solubili-
ty of the 1-aryl-4-silylmethyl[60]fullerene products in tolu-
ene, which is a commonly used solvent for device fabrica-
tion. The solubilities were in the range 0.3–0.9 wt.%, which
are acceptable values for spin-coating processes.
The electrochemical properties of compounds 6–10 were
investigated by cyclic voltammetry in THF. Cyclic voltam-
mograms for all compounds exhibited three reversible one-
electron-reduction waves (Figure 1). The LUMO levels of
all of the compounds were calculated by using the equation:
LUMO level=À(first reduction potential versus Fc/
Fc++4.8). Compounds with electron-donating groups on the
aryl groups (compounds 6, 7, and 10) showed a LUMO level
that was approximately 0.1 eV higher than unsubstituted
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Figure 2. Crystal structure of compound 6a; all molecules are depicted
by using a space-filling model.
Figure 3. Crystal structure of compound 10a; all molecules are depicted
by using a space-filling model.
compound 6a, pairs of molecules associate through a fuller-
À
ene–aryl-group p p interaction in the manner as shown in
Figure 2, upper right.[14,15] The distance between the fuller-
ene moiety of one molecule and the aryl group of the other
molecule is very short (3.17 ꢁ; sum of van der Waals radii
of the two carbon atoms: 3.4 ꢁ). The pairs of molecules are
arranged in a grid-like structure (Figure 2, bottom) with
inter-fullerene distances of 3.38, 3.45, and 3.47 ꢁ. The pack-
ing structure of thienylfullerene 10a also showed fullerene–
aryl-group interactions, with a thiophene–fullerene distance
of 3.37 ꢁ. The fullerene and thiophene moieties are ar-
ranged in an interpenetrating way along the b and c axes
(Figure 3, bottom) to form anisotropic crystals. Inter-fuller-
ene distances in the crystal of compound 10a were 3.34 and
3.38 ꢁ.
Figure 1. Electrochemical data. a) Cyclic voltammogram of compound
6a. b) Summarized LUMO levels of compounds 6–10.
compound 8. The introduction of an electron-withdrawing
trifluoromethyl group (compound 9) led to a relative de-
crease in the LUMO level by 0.05 V. On the other hand, the
introduction of an electron-donating o-isopropoxy group
onto the phenyl group on the silicon atom (compound 10b)
did not change the LUMO level.
Performance of the Photovoltaic Device
Photoconductivity and Carrier Mobility
To determine the molecular structure of 1-aryl-4-silylme-
thyl[60]fullerenes and to examine the packing structure that
influences carrier mobility (see below), we performed X-ray
crystallography on single crystals of compounds 6a and 10a
(Figure 2 and Figure 3). In the crystal-packing structure of
Prior to the investigations of photovoltaic performance, we
investigated the photoconductivity of blended films of com-
pounds 6b and 10b with poly(3-hexylthiophene) (P3HT) by
means of a flash-photolysis time-resolved microwave-con-
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Yutaka Matsuo, Eiichi Nakamura et al.
ductivity (FP-TRMC) method (wavelength of the pulse
laser: l=515 nm).[16] The TRMC method is an electrode-
less measurement method that enables the determination of
carrier mobility, photoconductivity, the quantum yield of
carrier-generation, and the lifetime of generated carriers in
micro-sized regions of organic thin-films. In this method, the
microwave-absorption-mediated dielectric loss of carriers is
measured by time-resolved microwave spectroscopy under
the irradiation of a pulse-excitation laser.
The TRMC photoconductivity values of the blended films
of compounds 6b and 10b with P3HT were fSm=3ꢂ
10À3 cm2 VÀ1 sÀ1 and 5ꢂ10À3 cm2 VÀ1 sÀ1, respectively. We as-
cribe the higher photoconductivity of the P3HT:10b film to
both the molecular structure and the supramolecular organi-
zation of compound 10b. The conjugation between the elec-
tron-donating thiophene and the electron-accepting fuller-
ene groups enables efficient carrier generation, whilst the
closer packing of the fullerene cores permits efficient
charge-transfer processes.
A comparative performance was also observed for com-
pound 10b in a space-charge-limited current (SCLC) mobili-
ty measurement. Because the SCLC electron mobility of
compound 10b (5ꢂ10À5 cm2 VÀ1 sÀ1) was higher than that of
compound 6b (1ꢂ10À5 cm2 VÀ1 sÀ1), we expected that the
thienyl fullerene would show better performance in the pho-
tovoltaic application compared with the anisyl fullerene.
Figure 4. Structure and obtained performance of OPV cells by using full-
erene derivatives (compounds 6b and 10b, as well as reference com-
pounds SIMEF and PCBM).
Photovoltaic Applications (Bulk Heterojunction)
Next, we evaluated the photovoltaic performance of 1-aryl-
4-silylmethyl[60]fullerenes in which the aryl groups were p-
anisyl and 2-thienyl groups. We employed o-isopropoxy-sub-
stituted compounds 6b and 10b, which had the best solubili-
ty in organic solvents; SIMEF and PCBM were used as ref-
erence materials. First, we fabricated standard bulk-hetero-
junction devices, which had an ITO/PEDOT:PSS/P3HT:ful-
lerene-derivative/NBphen/Al structure (Figure 4). The
device with 2-thienyl fullerene 10b recorded a power-con-
version efficiency (PCE) of 2.8% (VOC =0.61 V, short-circuit
current density (JSC): 8.7 mAcmÀ2, fill factor (FF): 0.53). Al-
though the efficiency was lower than those of devices that
used the standard reference materials, SIMEF (3.6%) and
PCBM (3.2%), this value is respectable when compared
with other P3HT-based bulk-heterojunction devices. Fur-
thermore, the device with compound 10b showed a higher
VOC compared to that with PCBM (VOC =0.55 V). This
result was attributed to the higher-lying LUMO level
(À3.71 eV vs. À3.80 eV for PCBM) of compound 10b,
which was derived from a 1,4-addition pattern and the elec-
tron-donating thienyl group.
Photovoltaic Applications (p–n Heterojunction)
Next, we examined compounds 6b and 10b for use in small-
molecule OPV devices by using tetrabenzoporphyrin (BP)
as a donor (Figure 4); BP was obtained from a soluble pre-
cursor material (CP) through a thermally induced retro-
Diels–Alder reaction.[17] CP is solution-processable and thin-
films of CP can be converted into insoluble crystalline thin
films of BP by heating. Subsequently, acceptor materials can
be deposited onto the BP layer by solution processing. The
BP layers for each obtained device possessed the same or-
ganization structure and, thus, had the same interfacial
structure. This result allowed us to evaluate the intrinsic
electronic performance of the acceptor materials without
the influence of morphology.
A solution of CP in a mixture of CHCl3 and chloroben-
zene (1:2, v/v) was spin-coated on a PEDOT:PSS layer that
was coated on ITO glass. The substrate was heated at 1808C
for 20 min to obtain a BP (p) layer. A solution of either
compound 6b or 10b (0.7 wt.%) in a mixture of chloroben-
zene and CS2 (1:1, v/v) was then spin-coated on top of the
p layer to form an n layer, thus giving a solution-processed
p–n heterojunction device. The device was then thermally
annealed at 1208C for 5 min. The fabricated OPV devices
with a p–n junction that were formed by using compounds
6b and 10b exhibited PCEs of 2.3% and 2.7%, respectively.
As with the bulk-heterojunction devices, a higher PCE was
On the other hand, the device with p-anisyl fullerene 6b
gave low JSC (1.7 mAcmÀ2) and FF values (0.36), thereby
leading to a low PCE of 0.38%. The lower performance of
the P3HT:6b OPV device was in good agreement with the
poorer TRMC photoconductivity that was exhibited by the
blended film that comprised P3HT and compound 6b.
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Yutaka Matsuo, Eiichi Nakamura et al.
obtained for the 2-thienyl compound (10b), thus leading to
the conclusion that the 2-thienyl compound 10b is superior
to p-anisyl compound 6b in its fundamental electronic prop-
erties.
a bulk heterojunction, p–n heterojunction, and a p–i–n junc-
tion yielded similar observations: the thienyl fullerene (10b)
exhibited better performance than the anisyl one (6b). Nev-
ertheless, both types of compounds were found to be suita-
ble for the solution-processing-based fabrication of OPVs
because of the high solubility that was conferred by the silyl-
methyl group. The 3.4% PCE that was obtained was re-
spectable, which suggests that these 1-aryl-4-silylmethyl[60]-
fullerenes, especially those that have a thienyl group as an
aryl moiety, are promising fullerene electron acceptors for
applications as OPV devices. Optimization of the donor ma-
terials and device structures will also provide further oppor-
tunities to produce efficient OPV devices.
Photovoltaic Applications (p–i–n Junction)
Finally, we fabricated devices with a p–i–n junction that had
a bulk-heterojunction interlayer (i layer) between the donor
(p) and acceptor (n) layers (Figure 4). Fabrication of the
i layer was achieved through a solution process, with the use
of a tetrabenzoporphyrin precursor, CP.[3b] After the fabrica-
tion of insoluble BP p layers, solutions of CP and the fuller-
ene derivatives (6b or 10b) were spin-coated onto the
p layer. After heating the substrate to convert CP into BP in
the i layer, subsequent spin-coating of the respective fuller-
ene derivatives formed the n layers, thereby affording p–i–n
junctions.
Experimental Section
General
All manipulations were carried out under an argon atmosphere by using
standard Schlenk techniques. KOtBu and (trimethylsilyl)methyl triflate
were purchased from Aldrich and used as received without further purifi-
cation. KI was purchased from Wako and heated at 1008C before use.
All anhydrous organic solvents were purchased from Kanto chemicals
and purified by a solvent purification system (GlassContour) that was
equipped with columns of activated alumina and a supported copper cat-
alyst (G-5) before use. Column chromatography on silica gel was per-
formed on Kanto Silica gel 60 (spherical, neutral, 140–325 mesh). NMR
spectra were measured on JEOL, ECX-400, and ECA-500 spectrometers
and reported in parts per million (ppm) relative to tetramethylsilane (d=
0.00 ppm). 1H NMR spectra were recorded in either CDCl3 or in a mix-
ture of CDCl3 and CS2 and were referenced internally to tetramethylsi-
lane as a standard; 13C NMR spectra were referenced to the solvent reso-
nance. Methyl-, methylene-, and methine signals in the 13C NMR spectra
were assigned by DEPT spectra. HPLC analysis was performed on a Shi-
madzu LC-10A system that was equipped with a SPD-M10A diode-array
The p–i–n devices with compounds 6b and 10b showed
PCE values of 2.8% and 3.4%, respectively, which were
higher than those of their corresponding p–n devices. Simi-
lar to polymer-based bulk-heterojunction devices and small-
molecule-based devices with a p–n heterojunction (see
above), 2-thienyl compound 10b performed better than
compound 6b. In comparison with the devices with a p–n
heterojunction, the JSC value was improved from approxi-
mately 6–7 mAcmÀ2 to 7–8 mAcmÀ2, presumably because of
an increase in the film-thickness of the p–i–n devices. In
general, p–i–n devices retain their effectiveness, even when
thicker films are used, because the interpenetrating i layer
enables the efficient utilization of the photogenerated exci-
tons. On the other hand, a BP:PCBM device with a similar
p–i–n junction only achieved a PCE of 2.0%.[3b] The respect-
able performance of the devices with compounds 6b and
10b indicates that there is significant potential for the use of
1,4-thienyl-alkyl fullerenes in the research of device-struc-
ture-modification on OPV cells.
detector and
a Cosmosil-Buckyprep column (4.6ꢂ250 mm, Nacalai
Tesque Co.). Atmospheric pressure chemical ionization (APCI)-HRMS
was measured on a JEOL JMS-T100 LC ESI-TOF mass spectrometer.
À
C
N
A solution of 4-MeOC6H4MgBr (1.89 mL, 1.10m, 2.08 mmol) in THF was
added to a solution of C60 (500 mg, 0.694 mmol) in 1,2-dichlorobenzene
(150 mL) that contained DMSO (1.48 mL, 20.83 mmol) at 258C. The
color of the solution immediately changed from purple to dark green.
After stirring for 30 min, a saturated aqueous solution of NH4Cl (1.0 mL)
was added to stop the reaction. The resulting dark-red solution was sub-
jected to vacuum distillation to remove the 1,2-dichlorobenzene. The res-
idue, which contained a small amount of 1,2-dichlorobenzene (about 0.5–
3 mL), was dissolved in toluene (200 mL) and passed through a pad of
silica gel to remove the magnesium salts. The mixture was concentrated
to obtain a solution (about 5–10 mL) that contained the product. Purifi-
cation of the product by column chromatography on silica gel (CS2/n-
hexane, 1:1 to 2:1) afforded the title compound (477 mg, 0.576 mmol,
Conclusions
We have described a method for the synthesis of 1-aryl-4-si-
lylmethyl[60]fullerenes (aryl=p-anisyl, p-dimethylamino-
phenyl, phenyl, p-trifluoromethylphenyl, and 2-thienyl), new
types of 1,4-diadducts, which possess relatively high-lying
LUMO levels and tunable aryl groups that control the pack-
ing structures. During the synthesis of the target compounds,
an efficient DMSO-assisted installation of a 2-thienyl group
on fullerene was found to produce a key intermediate com-
pound. 1-Aryl-4-silylmethyl[60]fullerenes that contained
anisyl and thienyl groups were characterized by X-ray crys-
tallography, photoconductivity experiments, and by the fab-
rication of solution-processed OPV devices. The 2-thienyl
compounds were superior to the p-anisyl compounds in
terms of both their crystal-packing structure and the TRMC
photoconductivity of the blended film that was composed of
P3HT and fullerenes. The evaluation of OPV devices with
1
83% yield) as black crystals. H NMR (500 MHz, CDCl3/CS2): d=3.98 (s,
3H), 6.72 (s, 1H), 7.27–7.29 (m, 2H), 8.34–8.37 ppm (m, 2H); 13C NMR
(500 MHz, CDCl3/CS2): d=55.34, 63.86, 67.3, 115.22, 128.71, 128.72,
135.00, 135.69, 136.31, 140.23, 140.29, 140.54, 141.17, 141.58, 141.65,
141.97, 142.02, 142.04, 142.31, 142.56, 142.57, 143.28, 144.56, 144.65,
144.73, 145.38, 145.41, 145.49, 145.51, 145.81, 145.93, 146.18, 146.20,
146.35, 146.40, 146.85, 147.27, 147.51, 152.65, 154.14, 159.32 ppm; HRMS
(APCIÀ): m/z calcd for C67H8O: 829.0575 [M]À; found: 829.0616.
À
C60(C6H4 NMe2)H (2)
The procedure described for compound 1 was performed by using 4-
À
(Me2N) C6H4MgBr in place of 4-MeOC6H4MgBr to obtain compound 2
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Yutaka Matsuo, Eiichi Nakamura et al.
(20.2 mg, 0.024 mmol, 86%) as black crystals. 1H NMR (400 MHz,
CDCl3/CS2): d=3.17 (s, 6H), 6.75 (s, 1H), 7.07–7.10 (m, 2H), 8.24–
8.27 ppm (m, 2H); 13C NMR (400 MHz, CDCl3/CS2): d=29.92, 40.51,
63.80, 67.27, 113.50, 128.15, 135.52, 136.41, 140.18, 140.22, 141.52, 141.62,
141.20, 142.03, 142.34, 142.49, 142.53, 143.23, 144.58, 144.62, 145.33,
145.35, 145.38, 145.48, 145.81, 146.09, 146.12, 146.15, 146.28, 146.36,
146.86, 147.23, 147.44, 149.84, 152.84, 154.62 ppm; HRMS (APCIÀ): m/z
calcd for C68H11N: 842.0891 [M]À; found: 842.0900.
1H NMR (500 MHz, CDCl3/CS2): d=0.60 (s, 3H), 0.64 (s, 3H), 2.55 (d,
J=14.6 Hz, 1H), 2.71 (d, J=14.6 Hz, 1H), 3.95 (s, 3H), 7.16–7.17 (m,
2H), 7.30–7.32 (m, 3H), 7.57–7.59 (m, 2H), 8.11–8.10 ppm (m, 2H);
13C NMR (500 MHz, CDCl3/CS2): d=21.91, 22.06, 29.77, 30.47, 55.35,
68.66, 110.17, 114.85, 119.86, 123.55, 125.62, 128.31, 128.71, 128.72, 131.38,
133.26, 134.17, 135.03, 135.69, 136.18, 136.31, 140.23, 140.29, 140.54,
140.58, 141.17, 141.23, 141.58, 141.65, 141.97, 142.02, 142.04, 142.11,
142.31, 142.56, 142.57, 142.93, 143.28, 143.59, 144.26, 144.31, 144.35,
144.54, 144.56, 144.65, 144.72, 144.73, 145.38, 145.41, 145.49, 145.51,
145.81, 145.93, 146.15, 146.18, 146.20, 146.28, 146.35, 146.36, 146.40,
146.67, 146.86, 147.27, 147.51, 147.82, 148.63, 154.14, 154.37, 157.47,
158.90, 159.49 ppm; HRMS (APCIÀ): m/z calcd for C76H20SiO: 977.1283
[M]À; found: 977.1330.
C60ACHTUNGTRENNUNG(C6H5)H (3)
The procedure described for compound
1
was performed by using
C6H5MgBr in place of 4-MeOC6H4MgBr to obtain compound 3 (205 mg,
1
0.257 mmol, 37%) as black crystals. H NMR (500 MHz, CDCl3/CS2): d=
6.73 (s, 1H), 7.08–7.11 (m, 2H), 7.22–7.25 (m, 1H), 7.28–7.31 ppm (m,
2H); 13C NMR (500 MHz, CDCl3/CS2): d=63.86, 66.54, 113.22, 128.31,
128.82, 128.94, 135.51, 136.62, 140.23, 140.29, 141.52, 141.61, 141.98,
142.03, 142.35, 142.48, 142.55, 143.31, 144.56, 144.62, 145.32, 145.35,
145.40, 145.47, 145.82, 146.09, 146.12, 146.15, 146.27, 146.36, 146.86,
147.07, 147.34, 149.85, 152.08 ppm; HRMS (APCIÀ): m/z calcd for
C66H6: 799.0470 [M]À; found: 799.04900.
À
C60(C6H4 NMe2)
G
The procedure described for compound 6a was performed by using com-
pound in place of compound to obtain compound (205 mg,
2
7
0.257 mmol, 37%) as black crystals. H NMR (500 MHz, CDCl3/CS2): d=
0.56 (s, 3H), 0.58 (s, 1H), 2.51 (d, J=14.6 Hz, 1H), 2.81 (d, J=14.7 Hz,
1H), 3.05 (s, 6H), 6.94–6.95 (m, 2H), 7.27–7.28 (m, 3H), 7.56–7.58 (m,
2H), 8.00–8.02 ppm (m, 2H); 13C NMR (500 MHz, CDCl3/CS2): d=21.95,
22.16, 29.76, 30.50, 55.35, 68.66, 110.14, 114.84, 117.26, 123.52, 125.66,
128.32, 131.71, 131.72, 134.17, 136.18, 135.69, 136.18, 136.31, 140.23,
140.29, 140.54, 140.58, 141.17, 141.23, 141.58, 141.65, 141.97, 142.02,
142.04, 142.11, 142.31, 142.56, 142.57, 142.93, 143.28, 143.59, 144.26,
144.31, 144.35, 144.54, 144.56, 144.65, 144.72, 144.73, 145.38, 145.41,
145.49, 145.51, 145.81, 145.93, 146.15, 146.19, 146.22, 146.27, 146.32,
146.36, 146.40, 146.67, 146.86, 146.93, 147.21, 147.59, 147.85, 148.65,
154.44, 154.36, 157.56, 158.79, 158.88 ppm; HRMS (APCIÀ): m/z calcd
for C77H23SiN: 990.1600 [M]À; found: 990.1624.
C60ACHTUNGTRENNUNG(C6H4CF3)H (4)
The procedure described for compound 1 was performed by using 4-
FC6H4MgBr in place of 4-MeOC6H4MgBr to obtain compound
4
(173 mg, 0.120 mmol, 48%) as black crystals. 1H NMR (500 MHz,
CDCl3): d=7.04 (s, 1H), 7.94–7.96 (d, J=8.3 Hz, 2H), 8.47–8.49 ppm (d,
J=8.3 Hz, 2H); 13C NMR (500 MHz, CDCl3/CS2): d=63.58, 65.43,
114.22, 128.77, 128.73, 135.42, 135.66, 140.18, 140.27, 141.51, 141.62,
141.65, 141.99, 142.03, 142.04, 142.53, 143.22, 143.57, 144.57, 144.62,
145.33, 145.34, 145.41, 145.47, 145.49, 145.81, 146.08, 146.13, 146.35,
146.43, 146.75, 147.27, 147.23, 147.77, 151.45, 154.16, 154.62 ppm; HRMS
(APCIÀ): m/z calcd for C67H5F3: 867.0343 [M]À; found: 867.0359.
C CHUTTGNERN(NNUG C6H5)AHCUTNGTREN(NGNU CH2Si(Me)2Ph) (8)
60A
The procedure described for compound 6a was performed by using com-
pound in place of compound to obtain compound (102 mg,
3
1
7
C60ACHTUNGTRENNUNG(C4H3S)H (5)
1
0.128 mmol, 18%) as black crystals. H NMR (500 MHz, CDCl3/CS2): d=
0.65 (s, 3H), 0.66 (s, 3H), 2.55 (d, J=14.6 Hz, 1H), 2.71 (d, J=14.6 Hz,
1H), 7.25–7.27 (m, 2H), 7.29–7.31 (m, 4H), 7.52–7.53 (m, 1H), 7.60–7.62
(m, 2H), 7.64–7.66 ppm (m, 1H); 13C NMR (500 MHz, CDCl3/CS2): d=
22.01, 22.04, 29.77, 30.47, 55.35, 68.66, 110.17, 114.85, 119.86, 123.55,
125.62, 128.31, 128.71, 128.72, 131.38, 133.26, 134.17, 135.03, 135.69,
136.18, 136.31, 140.23, 140.29, 140.54, 140.58, 141.17, 141.23, 141.58,
141.65, 141.97, 142.02, 142.04, 142.11, 142.31, 142.56, 142.57, 142.93,
143.28, 143.59, 144.26, 144.31, 144.35, 144.54, 144.56, 144.65, 144.72,
144.73, 145.38, 145.41, 145.49, 145.51, 145.81, 145.93, 146.15, 146.18,
146.20, 146.28, 146.35, 146.36, 146.40, 146.67, 146.86, 147.27, 147.59,
147.82, 148.58, 148.72, 149.43, 149.55, 154.52, 155.26, 158.00, 158.03 ppm;
HRMS (APCIÀ): m/z calcd for C75H18Si: 947.1178 [M]À; found:
947.1206.
A solution of (C4H3S)MgBr (5.37 mL, 0.85m, 4.58 mmol) in THF was
added to a solution of C60 (550 mg, 0.764 mmol) in 1,2-dichlorobenzene
(150 mL) that contained DMSO (0.33 mL, 4.58 mmol) at 258C. The color
of the solution gradually changed from purple to dark green. After stir-
ring for 48 h, a saturated aqueous solution of NH4Cl (1.0 mL) was added
to stop the reaction. The resulting dark-red solution was subjected to
vacuum distillation to remove the 1,2-dichlorobenzene. The residue,
which contained a small amount of 1,2-dichlorobenzene (about 0.5–
3 mL) was dissolved in toluene (200 mL) and passed through a pad of
silica gel to remove the magnesium salts. The mixture was concentrated
to obtain a solution (about 5–10 mL) that contained the product. Purifi-
cation of the product by column chromatography on silica gel (CS2/n-
hexane, 1:1 to 1:0) afforded the title compound (477 mg, 0.576 mmol,
1
56% yield) as black crystals. H NMR (500 MHz, CDCl3/CS2): d=6.95 (s,
À
C
(C6H4 CF3)
N
1H), 7.20–7.26 (m, 1H), 7.63–7.65 (dd, 1H), 7.92–7.93 ppm (dd, 1H);
13C NMR (500 MHz, CDCl3/CS2): d=63.68, 65.44, 103.77, 125.80, 126.11,
127.89, 133.33, 135.25, 136.31, 136.84, 140.23, 140.29, 140.32, 140.33,
140.54, 141.62, 141.65, 142.07, 142.60, 143.02, 143.24, 145.49, 145.51,
145.81, 144.69, 145.62, 146.19, 146.22, 146.35, 146.42, 146.72, 148.54,
151.95, 153.31 ppm; HRMS (APCIÀ): m/z calcd for C64H4S: 805.0034
[M]À; found: 805.0054.
The procedure described for compound 6a was performed by using com-
pound in place of compound 1 to obtain compound (11.0 mg,
4
9
1
0.190 mmol, 19%) as black crystals. H NMR (500 MHz, CDCl3/CS2): d=
0.51 (s, 3H), 0.57 (s, 3H), 2.53 (d, J=14.6 Hz, 1H), 2.73 (d, J=14.6 Hz,
1H), 7.26–7.29 (m, 2H), 7.31–7.34 (m, 4H), 7.52–7.53 (m, 1H), 7.57–7.59
(m, 2H), 7.64–7.66 ppm (m, 1H); 13C NMR (500 MHz, CDCl3/CS2): d=
22.87, 27.66, 29.77, 29.93, 55.37, 69.25, 110.17, 114.85, 119.86, 123.55,
125.62, 128.31, 128.71, 128.72, 131.38, 133. 26, 134.17, 135.03, 135.69,
136.18, 136.31, 140.23, 140.29, 140.54, 140.58, 141.17, 141.23, 141.58,
141.65, 141.97, 142.02, 142.04, 142.11, 142.31, 142.56, 142.57, 142.93,
143.28, 143.59, 144.35, 144.59, 144.63, 144.67, 144.91, 144.96, 144.98,
145.30, 145.34, 145.49, 146.70, 146.72, 146.81, 146.84, 147.02, 147.05,
147.13, 147.53, 147.76, 147.99, 148.45, 148.46, 148.72, 151.20, 154.23,
157.65, 158.25 ppm; HRMS (APCIÀ): m/z calcd for C76H17SiF3:
1015.1052 [M]À; found: 1015.1084.
À
C
(C6H4 OMe)
N
A solution of KOtBu (0.184 mL, 1.0m, 0.184 mmol) in THF (1.0m) was
added to a solution of compound 1 (76.0 mg, 0.0918 mmol) in PhCN at
258C. A dark-green solution of the potassium salt of compound 1 was im-
mediately obtained. After stirring for 30 min, PhSi(Me)2CH2Cl (0.33 mL,
1.86 mmol) and potassium iodide (0.305 g, 1.86 mmol) were added to the
solution. After stirring for 18 h at 1108C, a saturated aqueous solution of
NH4Cl (1.0 mL) was added to stop the reaction. Evaporation of volatile
compounds gave crude product 6a. Purification of the product by column
chromatography on silica gel (CS2/n-hexane, 1:4 to 1:1) and by prepara-
tive HPLC (Buckyprep column; eluent: toluene/2-propanol, 6:4) afforded
the title compound (18.8 mg, 0.0193 mmol, 21% yield) as black crystals.
Chem. Asian J. 2013, 8, 121 – 128
126
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www.chemasianj.org
Yutaka Matsuo, Eiichi Nakamura et al.
C
G
G
(CV) was performed at a scan rate of 100 mVsÀ1. The potential was cor-
rected against Fc/Fc+.
The procedure described for compound 6a was performed by using com-
pound 5 in place of compound 1 to obtain compound 10a (24% yield) as
black crystals. 1H NMR (500 MHz, CDCl3/CS2): d=0.64 (s, 3H), 0.67 (s,
3H), 2.55 (d, J=14.6 Hz, 1H), 2.71 (d, J=14.6 Hz, 1H), 7.25–7.27 (m,
2H), 7.29–7.31 (m, 4H), 7.52–7.53 (m, 1H), 7.60–7.62 (m, 2H), 7.64–
7.66 ppm (m, 1H); 13C NMR (500 MHz, CDCl3/CS2): d=29.77, 30.47,
55.35, 68.66, 111.14, 115.85, 118.53, 122.34, 124.92, 125.11, 128.31, 128.72,
133.38, 133.46, 135.17, 135.44, 135.49, 135.68, 136.31, 140.23, 140.29,
140.54, 140.58, 141.17, 141.23, 141.58, 141.65, 141.97, 142.02, 142.04,
142.11, 142.31, 142.56, 142.57, 142.93, 143.28, 143.59, 144.26, 144.31,
144.35, 144.54, 144.56, 144.65, 144.72, 144.73, 145.38, 145.41, 145.49,
145.51, 145.81, 145.93, 146.15, 146.16, 146.24, 146.30, 146.32, 146.39,
146.40, 146.65, 146.88, 147.63, 147.78, 147.92, 149.73, 154.06, 154.32,
157.34 ppm; HRMS (APCIÀ): m/z calcd for C73H16SiS: 953.0742 [M]À;
found: 953.0763.
X-ray Crystallographic Analysis
Single crystals of compounds 6a and 10a that were suitable for X-ray
analysis were obtained by the slow diffusion of EtOH into solutions of
compounds 6a and 10a in CS2. X-ray crystallographic measurements
were performed on a Rigaku R-AXIS RAPID II (imaging plate detec-
tor) by using graphite-monochromated CuKa radiation (l=1.5405 ꢁ).
The positional- and thermal parameters were refined by using the full-
matrix least-squares method with the SHELXL97 program.
CCDC 895606 (6a) and CCDC 895605 (10a) contain the supplementary
crystallographic data for this paper. These data can be obtained free of
charge from The Cambridge Crystallographic Data Centre via
www.ccdc.cam.ac.uk/data_request/cif.
FP-TRMC Measurements
À
À
C60ACHTUNGTRENNUNG(C6H4 OMe)ACHTUNGTRENNUNG(CH2Si(Me)2C6H4 OiPr) (6b)
Samples for flash-photolysis time-resolved microwave-conductivity (FP-
TRMC) measurements were prepared by drop-casting blended solutions
that contained P3HT (0.5 wt.% in chlorobenzene) and the corresponding
fullerene derivative (6a: 0.25 wt.% in chlorobenzene; 10a: 0.5 wt.% in
chlorobenzene) onto UV/O3-pretreated quartz substrates. These drop-
cast films were thermally annealed at 1208C for 10 min.
A solution of KOtBu (0.899 mL, 1.0m, 0.899 mmol) in THF (1.0m) was
added to a solution of compound 1 (372.3 mg, 0.450 mmol) in PhCN at
258C. A dark-green solution of the potassium salt of compound 1 was im-
mediately obtained. After stirring for 30 min, (2-iPrOC6H4)Si(Me)2CH2Cl
(1.61 mL, 8.99 mmol) and potassium iodide (1.49 g, 8.99 mmol) were
added to the solution. After stirring for 18 h at 1108C, a saturated aque-
ous solution of NH4Cl (1.0 mL) was added to stop the reaction. Evapora-
tion of volatile compounds gave the crude product. Purification by
column chromatography on silica gel (CS2/n-hexane, 1:1) and preparative
HPLC (Buckyprep column; eluent: toluene/2-propanol, 6:4) afforded the
title compound (177 mg, 0.162 mmol, 36% yield) as black crystals.
1H NMR (500 MHz, CDCl3/CS2): d=0.50 (s, 3H), 0.55 (s, 3H), 1.17 (d,
J=6.3 Hz, 3H), 1.25 (d, J=6.3 Hz, 3H), 2.58 (d, J=14.3 Hz, 1H), 2.71
(d, J=14.3 Hz, 1H), 3.90 (s, 3H), 4.41 (m, 1H), 6.56–6.58 (d, 1H), 6.74–
6.76 (t, 1H), 7.13–7.14 (m, 2H), 7.35–7.36 (m, 2H), 8.15–8.17 ppm (m,
2H); 13C NMR (500 MHz, CDCl3/CS2): d=21.91, 22.06, 29.77, 30.47,
55.35, 68.66, 110.17, 114.85, 119.86, 123.55, 125.62, 128. 31, 128.71, 128.72,
131.38, 133.26, 134.17, 135.03, 135.69, 136.18, 136.31, 140.23, 140.29,
140.54, 140.58, 141.17, 141.23, 141.58, 141.65, 141.97, 142.02, 142.04,
142.11, 142.31, 142.56, 142.57, 142.93, 143.28, 143.59, 144.26, 144.31,
144.35, 144.54, 144.56, 144.65, 144.72, 144.73, 145.38, 145.41, 145.49,
145.51, 145.81, 145.93, 146.15, 146.18, 146.20, 146.28, 146.35, 146.36,
146.40, 146.67, 146.86, 147.27, 147.51, 147.82, 148.63, 154.14, 154.37,
157.47, 158.90, 159.49 ppm; HRMS (APCIÀ): m/z calcd for C85H26SiO:
1091.1753 [M]À; found: 1091.1176.
FP-TRMC measurements were carried out at 258C in air, where the reso-
nant frequency and microwave power were properly adjusted to 9.1 GHz
and 3 mW, respectively. Charge carriers were photochemically generated
by using a 515 nm light pulse from an optical parametric oscillator
(OPO) that was equipped with a Spectra-Physics model INDI Nd:YAG
laser with a pulse duration of 5–8 ns. The excitation photon density was
3.8ꢂ1015/(cm2 pulse). Transient conductivities (Ds) were evaluated ac-
cording to: Ds=(1A)ACHTNUGRTNEUNG(DPr/Pr), where A, DPr, and Pr represent the sensi-
tivity factor, the change in reflected microwave power, and the reflected
microwave power, respectively. Subsequently, Ds was converted into the
product of the quantum yield (f) and the sum of charge-carrier mobili-
ties, Sm=(mh+me), according to fSm=Ds(eI0Flight)
À1, where e, I0, and Flight
are the unit charge of a single electron, the incident photon density of
the excitation laser (photonsmÀ2), and a correction (or filling) factor
(mÀ1), respectively.
SCLC Measurements (Determination of Electron Mobility)
The single-layered cells were prepared on ITO-coated glass substrates
that were provided by GEOMATEC. ITO substrates were treated with
UV/O3 prior to spin-coating onto PEDOT:PSS. The PEDOT:PSS-coated
substrate was dried in air at 1208C for 10 min, then dried in a nitrogen
glove box at 1808C for 3 min prior to use. Subsequently, the fullerene de-
rivative was spin-coated from a chlorobenzene/CS2 (1:1) solution and was
thermally annealed at 1208C for 10 min. For the top electrode, 0.5 nm-
thick LiF and 80 nm-thick Al were deposited. The J–V curves were mea-
sured by a computer-controlled Keithley 2400 source meter. The electron
mobility was determined by fitting to a space-charge-limited-current
(SCLC). The SCLC is given by J=(9/8)e0ermV2/d3, where J is the current,
e0 is the permittivity of free space, er is the relative permittivity of the
material, m is the (electron) mobility, V is the applied voltage, and d is
the thickness of the fullerene-derivative layer. The estimated thicknesses
of thienyl fullerene and anisyl fullerene were 75 nm and 50 nm, respec-
tively.
À
C
(C4H3S)
(CH2Si(Me)2C6H4 OiPr) (10b)
The procedure described for compound 6b was performed by using com-
pound 5 in place of compound 1 to obtain compound 10b (28% yield) as
black crystals. 1H NMR (500 MHz, CDCl3/CS2): d=0.54 (s, 3H), 0.56 (s,
3H), 1.24 (d, J=6 Hz, 3H), 1.31 (d, J=6 Hz, 3H), 2.62 (d, J=17.2 Hz,
1H), 2.75 (d, J=17.2 Hz, 1H), 3.94 (s, 3H), 4.46 (m, 1H), 6.59–6.61 (d,
2H), 6.76–6.77 (t, 1H), 7.17–7.19 (m, 2H), 7.23–7.38 (m, 1H), 8.17–
8.19 ppm (m, 2H); 13C NMR (400 MHz, CDCl3/CS2): d=21.89, 22.08,
30.69, 53.14, 56.35, 68.62, 110.06, 110.60, 114.85, 115.07, 116.28, 119.86,
119.96, 122.59, 125.56, 125.68, 127.51, 130.62, 131.37, 136.31, 136.53,
137.81, 139.38, 140.22, 140.26, 140.29, 140.43, 140.58, 140.61, 141.10,
141.13, 141.58, 141.62, 141.65, 141.96, 142.01, 142.04, 142.09, 143.43,
143.59, 143.94, 144.15, 144.26, 144.31, 144.73, 145.27, 145.38, 145.41,
145.81, 145.93, 146.15, 146.18, 146.20, 146.28, 146.35, 146.36, 146.59,
146.67, 146.74, 146.86, 147.27, 147.31, 147.51, 147.62, 147.64, 148.00,
148.63, 154.08, 154.15, 154.37, 157.47, 158.42, 159.39 ppm; HRMS
(APCIÀ): m/z calcd for C76H22SiSO: 1011.1161 [M]À; found: 1011.0079.
Fabrication of Bulk-Heterojunction OPV Devices
P3HT was purchased from Aldrich and PCBM was purchased from Fron-
tier Carbon Corporation. The bulk-heterojunction cells were fabricated
on patterned ITO-coated glass substrates. The substrate was ultrasonical-
ly cleaned by using a surfactant, rinsed in deionized water, and finalized
by treatment with UV/ozone. A thin layer of PEDOT:PSS (Baytron AI
4083 from H. C. Starck) was spin-coated onto the ITO glass at a speed of
3000 rpm for 30 s in a glove box that was filled with nitrogen. Blended
solutions of P3HT:fullerenes (thiophene-unit/fullerene, 1.1:0.9 molar
ratio) in 1,2-dichlorobenzene (2.0 wt%) were prepared and spin-coated
onto the PEDOT:PSS layer. Then, the Ca/Al electrode was evaporated
Electrochemical Measurements
Electrochemical measurements were performed on a Hokuto DenkoHZ-
5000 voltammetric analyzer. A glassy carbon electrode, a platinum coil,
and a Ag/Ag+ electrode were used as the working electrode, the counter
electrode, and the reference electrode, respectively. Cyclic voltammetry
Chem. Asian J. 2013, 8, 121 – 128
127
ꢀ 2013 Wiley-VCH Verlag GmbH & Co. KGaA, Weinheim

www.chemasianj.org
Yutaka Matsuo, Eiichi Nakamura et al.
onto the film through a shadow mask, thereby giving an active area of
4.00 mm2. The photovoltaic cells were encapsulated with backing glass by
using UV-curable resin under a nitrogen atmosphere.
Kastenberg, L. M. Popescu, W. J. H. Verhees, J. M. Kroon, J. C.
Hummelen, Org. Lett. 2007, 9, 551.
[2] G. Yu, J. Gao, J. C. Hummelen, F. Wudl, A. J. Heeger, Science 1995,
270, 1789.
Fabrication of OPV Devices with a p–n Heterojunction
[3] a) Y. Matsuo, A. Iwashita, Y. Abe, C. Z. Li, K. Matsuo, M. Hashigu-
chi, E. Nakamura, J. Am. Chem. Soc. 2008, 130, 15429; b) Y.
Matsuo, Y. Sato, T. Niinomi, I. Soga, H. Tanaka, E. Nakamura, J.
Am. Chem. Soc. 2009, 131, 16048; c) H. Tsuji, K. Sato, Y. Sato, E.
Nakamura, Chem. Asian J. 2010, 5, 1294; d) H. Tsuji, Y. Yokoi, Y.
Sato, H. Tanaka, E. Nakamura, Chem. Asian J. 2011, 6, 2005; e) H.
Tanaka, Y. Abe, Y. Matsuo, J. Kawai, I. Soga, Y. Sato, E. Nakamura,
Adv. Mater. 2012, 24, 3521.
[4] a) Y. Matsuo, Y. Zhang, I. Soga, Y. Sato, E. Nakamura, Tetrahedron
Lett. 2011, 52, 2240; b) A. Varotto, N. D. Treat, J. Jo, C. G. Shuttle,
N. A. Batara, F. G. Brunetti, J. H. Seo, M. L. Chabinyc, C. J.
Hawker, A. J. Heeger, F. Wudl, Angew. Chem. 2011, 123, 5272;
Angew. Chem. Int. Ed. 2011, 50, 5166.
1,4:8,11:15,18:22,25-Tetraethano-29H,31H-tetrabenzoACTHUNRTGNEUNG[b,g,L,q]porphyrin
(CP) was prepared according to literature procedures.[17] PCBM was pur-
chased from Frontier Carbon Corporation and used as received. PE-
DOT:PSS (Baytron PH and AI4083) was purchased from H. C. Starck.
Organic photovoltaic cells that had a p–n structure were fabricated ac-
cording to the following typical procedure: The layer of ITO on the glass
substrate was 145 nm thick with a sheet resistance of 8 ohms/square; the
surface roughness (Ra) was 0.7 nm and Rmax was 8.1 nm. A stripe pattern
with a 2 mm-wide layer of ITO was etched by using a conventional pho-
tolithographic technique. Prior to the formation of the buffer layer, the
patterned ITO glass was ultrasonically cleaned by using a surfactant,
rinsed with water, and then finally treated with UV/ozone. A conducting
[5] M. Lenes, G.-J. A. H. Wetzelaer, F. B. Kooistra, S. C. Veenstra, J. C.
Hummelen, P. W. M. Blom, Adv. Mater. 2008, 20, 2116.
[6] a) D. W Laird, H. Richter, V. Vejins, L. Scott, T. A Lada, II, WO/
2008/018931; US Patent Application 20090176994; b) Y. He, H.-Y.
Chen, J. Hou, Y. Li, J. Am. Chem. Soc. 2010, 132, 1377; c) Y. He, G.
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poly(3,4-ethylenedioxylenethiophene)–polystyrene-sulfonic-acid
(PE-
DOT:PSS, Baytron PH or AI4083) layer was formed on the ITO sub-
strate by spin-coating an aqueous dispersion to obtain a smooth 30 nm-
thick film. The PEDOT:PSS-coated substrate was dried in air for 10 min
at 1208C, then dried in a nitrogen glove box for 3 min at 1808C prior to
use. A precursor solution that contained 0.5 wt.% of CP in a CHCl3/
chlorobenzene mixture (1:2) was spin-coated (1500 rpm) onto the PE-
DOT:PSS layer. Thermal conversion was carried out at 1808C for 20 min
to obtain a layer of BP. After this, the fullerene derivative (0.8 wt.%)
was spin-coated (3000 rpm) from a solution of CS2/chlorobenzene (1:1, v/
v) to obtain the n layer. After drying this film for 10 min at 1208C, the
device substrate was transferred from the glove box into the vacuum
chamber without exposure to air. The evaporation of a NBphen-buffer
layer was carried out at a pressure of about 2ꢂ10À4 Pa. The deposition
rate was typically 0.1 nmsÀ1. After the deposition of the NBphen layer
(6–8 nm), the top electrode (Al, 80 nm) was deposited with a metal
shadow mask, which defined a 2 mm stripe pattern that was perpendicu-
lar to the ITO stripe. Finally, the fabricated organic photovoltaic cell was
encapsulated with backing glass by using a UV-curable resin under a ni-
trogen atmosphere.
Fabrication of OPV Devices with a p–i–n Junction
Organic photovoltaic cells that had a p–i–n structure were fabricated in
the same manner as those with a p–n heterojunction (see above), except
for the following point: An i layer was deposited on top of the BP layer
(p layer) by spin-coating (1500 rpm) a mixture of CP and a fullerene de-
rivative (CP, 0.3 wt.%; fullerene, 0.7 wt.%) in a CHCl3/chlorobenzene/
CS2 mixture (1:1:1). The i layer was heated at 1808C for 20 min. After
this, the n layer was spin-coated in the same manner.
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This work was generously supported by the Funding Program for Next-
Generation World-Leading Researchers (Y.M.), MEXT, Japan (KAKEN-
HI to E.N., 22000008), and the Strategic Promotion of Innovative Re-
search and Development from the Japan Science and Technology Agency
(JST).
[1] a) J. C. Hummelen, B. W. Knight, F. LePeq, F. Wudl, J. Yao, C. L.
Received: August 8, 2012
Wilkins, J. Org. Chem. 1995, 60, 532; b) F. B. Kooistra, J. Knol, F.
Published online: September 28, 2012
Chem. Asian J. 2013, 8, 121 – 128
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