New diarylmethanofullerene derivatives and their properties for organic thin-film solar cells

Article abstract of DOI:10.3762/bjoc.5.7

A number of diarylmethanofullerene derivatives were synthesized. The cyclopropane ring of the derivatives has two aryl groups substituted with electron-withdrawing and -donating groups, the latter with long alkyl chains to improve solubility in organic so

Full text of DOI:10.3762/bjoc.5.7

New diarylmethanofullerene derivatives and their
properties for organic thin-film solar cells
Daisuke Sukeguchi, Surya Prakash Singh, Mamidi Ramesh Reddy,
Hideyuki Yoshiyama, Rakesh A. Afre, Yasuhiko Hayashi, Hiroki Inukai,
Tetsuo Soga, Shuichi Nakamura, Norio Shibata* and Takeshi Toru
Full Research Paper
Open Access
Address:
Beilstein Journal of Organic Chemistry 2009, 5, No. 7.
Department of Frontier Materials, Graduate School of Engineering,
Nagoya Institute of Technology, Gokiso, Showa-ku, Nagoya 466
8555, Japan
doi:10.3762/bjoc.5.7
Received: 17 December 2008
Accepted: 09 February 2009
Published: 24 February 2009
Email:
Norio Shibata* - shibata.norio@nitech.ac.jp
Associate Editor: P. Skabara
* Corresponding author
© 2009 Sukeguchi et al; licensee Beilstein-Institut.
License and terms: see end of document.
Keywords:
bulk heterojunction solar cells; fullerene derivatives; high open-circuit
voltage
Abstract
A number of diarylmethanofullerene derivatives were synthesized. The cyclopropane ring of the derivatives has two aryl groups
substituted with electron-withdrawing and -donating groups, the latter with long alkyl chains to improve solubility in organic
solvents, an important property in processing cells. First reduction potentials of most derivatives were less negative than that of
[6,6]-phenyl-C61-butyric acid methyl ester (PCBM), which is possibly ascribed to their electron-withdrawing nature. Organic thin-
film photovoltaic cells fabricated with poly(3-hexylthiophene) (P3HT) as the electron-donor and diarylmethanofullerene derivatives
as the electron-acceptor material were examined. The {(methoxycarbonyl)phenyl[bis(octyloxy)phenyl]methano}fullerene showed
power conversion efficiency as high as PCBM, but had higher solubility in a variety of organic solvents than PCBM. The Voc value
was higher than that of PCBM, which is derived from the electron-donating (octyloxy)phenyl group, possibly raising the LUMO
level. Photovoltaic effects of the devices fabricated with the derivatives having some electron-withdrawing groups were also
examined.
Introduction
Bulk heterojunction photovoltaic cells consisting of thin-film Significant efforts have been made to optimize the power-
composites of conjugated polymers (donors) and fullerene conversion efficiency (PCE) of solar cells based on poly(3-
derivatives (acceptors) are promising candidates for inex- hexylthiophene) (P3HT) as a donor and [6,6]-phenyl-C61-
pensive, renewable solar energy conversion [1-6]. These butyric acid methyl ester (PCBM) as an acceptor [7-10]. Using
organic thin films could also be used as flexible solar cells. a combination of these donor and acceptor molecules together
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Beilstein Journal of Organic Chemistry 2009, 5, No. 7.
with the optimized solvent processing, composition, and effect expected to increase the electron-accepting ability of fullerene,
of device annealing, PCE has reached up to 5% [11-17]. In while the electron-donating groups would decrease the LUMO
addition to PCBM widely studied as the bulk heterojunction energy level which leads to an increase of the open-circuit
(BHJ) acceptor, several methanofullerene derivatives have so voltage (Voc) values of the solar cell. These diarylmethan-
far been studied for the development of efficient acceptors such ofullerenes have long alkyl chain(s) to increase the solubility
as spiroannulated methanofullerenes [18], diarylmethan- and hopefully to cause the interaction with the donor P3HT
ofullerenes [19,20], alkoxy-substituted PCBM derivatives [21], polymer, being related to the morphology of the heterojunction
and bisPCBM [22]. These derivatives have been shown to have thin film.
excellent properties as acceptors, but it is still important to
Synthesis of diarylmethanofullerene
study the structure-efficiency relationship of the fullerene struc-
ture in order to develop highly efficient OPVs. The design of derivatives
highly soluble derivatives of PCBM has also attracted much Diarylmethanofullerene derivatives were synthesized according
attention because 3D architectures such as vesicles and fibers to the method cited in the literature [26]. Synthetic routes are
are highly dependent on the solvent used [23,24]. Recently, we shown in Scheme 1.
briefly communicated a soluble bulk-heterojunction organic
photovoltaic P3HT device using a newly synthesized methan- Generally, the Friedel–Crafts acylation of benzene derivatives
ofullerene derivative 1a [25]. In this paper, we give a full 10–14 with acid chlorides 3–9 in the presence of anhydrous
account of our studies on new bulk-heterojunction (BHJ) AlCl3 gave the carbonyl compounds 15a–k which were treated
devices composed of P3HT and a variety of newly synthesized with p-toluenesulfonylhydrazine to afford the hydrazones
diarylmethanofullerene derivative 1a–k, 2 blends.
16a–k. Treatment of 16a–k with sodium methoxide or
LiHMDS in o-dichlorobenzene (ODCB) gave a mixture of
isomeric diarylmethanofullerenes. After purification, thermal
Results and Discussion
We prepared new diarylmethanofullerene derivatives which treatment under reflux in toluene gave diarylmethanofullerenes
were studied as electron-accepting materials in the bulk-hetero- 1a–k in good yields. The C70 derivative 2, a mixture of isomers,
junction device of organic thin-film photovoltaic cells (Figure was prepared from 16a by a procedure similar to those of C60
1). The new diarylmethanofullerenes have two aromatic rings derivatives 1a–k using C70 instead of C60. As expected, all the
on the cyclopropane, having electron-withdrawing and electron- compounds were soluble in all organic solvents tested such as
donating groups. The electron-withdrawing groups were AcOEt, THF, acetone, dichloromethane, toluene and xylenes,
Figure 1: Diarylmethanofullerene derivatives.
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Beilstein Journal of Organic Chemistry 2009, 5, No. 7.
Scheme 1: Synthesis of diarylmethanofullerene derivatives.
while conventional PCBM has high solubility in toluene and showed
a
more negative value than mono- and
xylenes, but limited solubility in AcOEt, THF, and acetone.
bis(octyloxy)phenylmethanofullerenes 1c and 1a. When
compared with PCBM, most derivatives except 1e showed first
reduction potentials with less negative values. It is reasonable
Electrochemical Studies
Electrochemical studies were performed by differential pulse that less negative values are derived from the electron-with-
voltammetry (DPV) using a platinum electrode and drawing nature of the (methoxycarbonyl)phenyl, cyanophenyl,
tetrabutylammonium hexafluorophosphate as the supporting nitrophenyl, (methylsulfonyl)phenyl, and (trifluoromethylsulf-
electrolyte in THF. Reduction potentials are listed in Table 1. onyl)phenyl groups attached to the cyclopropane ring, enough
The obtained cyclic voltammetry data were reversible. The first to compensate the opposite effect of the electron-donating
reduction potentials depend on the electron-donating nature of mono-, bis-, or tris(octyloxy)phenyl group [19]. These first
the substituents, in which tris(octyloxy)phenyl compound 1b reduction potential data showed that the diarylmethan-
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Beilstein Journal of Organic Chemistry 2009, 5, No. 7.
Table 1: DPV Data for soluble fullerene derivatives in ODCBa
Derivative
E1red
E2red
E3red
E4red
E5red
E6red
1a
1b
1c
1d
1e
1f
−0.900
−0.945
−0.905
−0.835
−1.050
−0.915
−0.905
−0.890
−0.890
−0.883
−0.897
−0.915
−1.049
−1.205
−1.376
−1.285
−1.210
−1.320
−1.290
−1.455
−1.270
−1.290
−1.253
−1.279
−1.385
−1.290
−1.420
−1.885
−1.505
−1.715
−1.800
−1.530
−1.836
−1.770
−1.590
−1.780
−1.737
−1.565
−1.535
−1.770
−2.100
−1.775
−2.155
−2.275
−1.705
−2.275
−2.245
−1.885
−2.252
−1.873
−1.725
−1.785
−2.270
−2.395
−2.265
−2.320
−2.170
1g
1h
1i
−2.350
−2.125
1j
1k
2
−1.865
−2.285
PCBM
aA 3 mm platinum plate was used as working electrode and a platinum wire as counter electrode. Ag/AgNO3 (0.01 M in MeCN/0.1 M TBAPF) was used
as reference electrode separated by Vycor® glass, and all potentials are given in relation to this electrode. The measurements were performed using a
concentration of approximately 0.5 mM of the compounds.
ofullerene derivatives can be a better electron acceptor than PCBM in a 1:1 weight ratio [28] prepared by stirring for a day
PCBM [27].
was spin-coated and subsequently the device was heated at
130 °C for 30 min. The Al cathode layer was deposited with a
thickness of ~100 nm by thermal evaporation in a vacuum
Photovoltaic Devices
A series of solar cells was fabricated with P3HT as the electron- chamber under 3 × 10−4 Pa. After thermal evaporation of the Al
donor and diarylmethanofullerene derivatives as the electron- cathode layer, the device was annealed at 140 °C for 10 min in a
acceptor material. Sandwich configurations are described as glove box. The active area of the device was defined in an area
ITO/PEDOT:PSS/P3HT:diarylmethanofullerene derivatives/Al of 3 mm2 with a shadow mask (Figure 2).
(Figure 2). The ITO/PEDOT:PSS/P3HT:PCBM/Al cell was
also fabricated for a comparative study. The conducting Current density–voltage (J–V) characteristics of the device were
polymer, poly(3,4-ethylenedioxythiophene):poly(styrenesulf- measured under one-sun illumination using an AM1.5G filter
onate) (PEDOT:PSS), acting as a buffer layer for hole transport with a white light xenon lamp under a nitrogen atmosphere. A
and reducing the roughness of the ITO surface, was spin-coated photovoltaic effect of these devices was clearly visible under
by 2000 rpm on the ITO-glass substrate with a thickness of exposure to light. OPVs fabricated with P3HT:diarylmethan-
~80 nm from aqueous solution. The layer was then annealed at ofullerene derivatives having electron-withdrawing groups such
120 °C for 10 min to remove the residual water. An ODCB as bis(methoxycarbonyl)phenyl, cyanophenyl, 3- and
solution of P3HT and the diarylmethanofullerene derivative or 4-nitrophenyl, (methylsulfonyl)phenyl, and (trifluoromethyl-
sulfonyl)phenyl groups, taking a P3HT:PCBM-blended cell as a
reference, were examined. Table 2 shows the current
density–voltage (J–V) characteristic parameters of the devices
structured from P3HT:diarylmethanofullerene derivatives
1a–1k, 2 and P3HT:PCBM blends.
Derivative 1a having methoxycarbonylphenyl and
bis(octyloxy)phenyl groups was shown to be a superior acceptor
in combination with P3HT and PCE of the P3HT:1a blended
cell was as high as that of PCBM. Especially, the Voc value of
the P3HT:1a cell was 0.61 V, 0.09 V higher than that of the
P3HT:PCBM cell. This could be generally ascribed to the
reduced LUMO level of the methanofullerene by the electron-
Figure 2: Device layout of the solar cell.
donating bis(octyloxy)phenyl group, since the band gap
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Beilstein Journal of Organic Chemistry 2009, 5, No. 7.
ofullerenes 1b and 1c with less negative first reduction poten-
tial also showed enhanced Voc values. The electron-donating
(octyloxy)phenyl groups seemingly mainly worked on this
effect. The first reduction potentials of the derivatives 1d,
1f–1k, and 2 having electron-withdrawing groups are also less
negative than that of PCBM. It should be noted that the
derivatives 1a–1c having the methoxycarbonylphenyl group
exhibited enhanced Voc values as compared with lower Voc
values for the cells fabricated with other derivatives 1d, 1f–1k,
and 2. The reason is not clear but the lower Voc values may be a
consequence of negative effects such as morphology problems
relating to inefficient charge transfer or charge separation. A
more detailed study is necessary to elucidate these results.
Short-circuit current (Jsc) and fill factor (FF) values for 1a–1c
were lower in comparison with that for PCBM. Dimeth-
oxyphenyl- and (methoxycarbonyl)phenyl-substituted, and
phenyl- and (methoxycarbonyl)phenyl-substituted methan-
ofullerenes 1d and 1e did not work as acceptors, probably
because of their low solubility in ODCB. The bis(methoxycar-
bonyl)phenyl- and cyanophenyl-substituted methanofullerenes
Table 2: J–V characteristic parameters of bulk–heterojunction solar
cells
Derivative Eff (%)a
FFb
Vocc
Jscd
1a
1b
1c
1d
1e
1f
1.93
1.50
1.05
0.022
–e
0.59
0.49
0.39
0.18
–
0.61
0.66
0.60
0.49
–
5.41
4.60
4.43
0.25
–
1.00
0.84
0.051
–e
0.59
0.40
0.21
–
0.54
0.52
0.35
–
3.13
4.09
0.69
–
1g
1h
1i
1j
1.24
0.86
1.60
1.98
0.50
0.43
0.55
0.56
0.56
0.48
0.60
0.52
4.43
4.20
4.90
6.82
1k
2
PCBM
aPower-conversion efficiency bFill factor cOpen-circuit voltage dOpen-
circuit current ePower conversion was not observed.
between the HOMO level of the P3HT and the LUMO level of 1f and 1g showed good PCE, whereas nitrophenyl-substituted
the acceptor is related to the Voc value, the higher band gap methanofullerenes 1h and 1i did not work as acceptors. (Meth-
corresponding to the higher Voc value [20,27,29-31]. More oxycarbonyl)phenylmethano-C70 derivative 2 showed excellent
negative first reduction potentials of the methoxy-substituted PCE. (Methylsulfonyl)phenyl- and (trifluoromethylsulfonyl)-
PCBM derivatives in comparison with that of PCBM have been phenyl-substituted methanofullerenes 1j and 1k also worked
shown to be well correlated to the Voc values of the solar cells fine.
[20]. On the other hand, the first reduction potential of 1a is less
negative than that of PCBM (Table 1). In addition, a higher Voc The current density–voltage (J–V) characteristics of the OPVs
value was shown for the P3HT-1a cell. The structured from P3HT:1a and P3HT:PCBM blends were
tris(octyloxy)phenyl- and (octyloxy)phenyl-substituted methan- annealed at 140, 130, and 100 °C for 30 min after cathode (Al)
Figure 3: (A) J–V characteristics of the P3HT:1a-blended device annealed at 100–140 °C (black: 100 °C, red: 130 °C, blue: 140 °C, solid line: current
under light, dashed line: current under dark). (B) J–V characteristics of the P3HT:PCBM-blended device annealed at 100–140 °C (black: 100 °C, red:
130 °C, blue: 140 °C, solid line: with light current, dashed line: with dark current).
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Beilstein Journal of Organic Chemistry 2009, 5, No. 7.
Figure 4: (A) Spectral responsivity of the P3HT:1a-blended film on the ITO glass annealed at 100–140 °C (100 °C: black, 130 °C: red, 140 °C: blue).
(B) Spectral responsivity of the P3HT:PCBM-blended film on the ITO glass annealed at 100–140 °C (100 °C: black, 130 °C: red, 140 °C: blue).
deposition. The PCE values of the P3HT:1a-blended cell temperatures with slight decrease of that at 140 °C. The
increased slightly as the annealing temperature decreased from P3HT:1a-based cell showed a maximum at around 550 nm,
140 to 100 °C; thus, the PCE values of 1.91, 1.93, and 2.06% whereas the P3HT:PCBM annealed at 100 and 130 °C exhib-
were obtained at the annealing temperatures of 140, 130, and ited the maxima at around 505 nm as shown in Figure 4(B).
100 °C, respectively. Figure 3 shows the J–V characteristics of Since these responsivities are definitely derived from the
the P3HT:1a and P3HT:PCBM solar cells. Figure 4 shows the absorption of P3HT, this notable bathochromic shift in the
spectral responsibilities for both solar cells. Jsc, Voc and FF responsivity maxima of P3HT:1a in comparison with
values of the P3HT:1a-blended cell did not significantly alter at P3HT:PCBM can be ascribed to the change in the alignment of
these annealing temperatures [Figure 3(A)]. On the other hand, the P3HT polymer chain induced by the long octyloxy chains of
the J–V characteristics of the P3HT:PCBM-blended cell varied 1a. A change of the annealing temperature may also be related
significantly depending on the annealing temperatures [Figure to the growth of the domain size of derivative 1a, as observed in
3(B)].
the case of PCBM [32-34], which possibly makes the conjuga-
tion length of P3HT longer. AFM measurements were
Figure 4(A) shows the spectral responsivities of the P3HT:1a- performed on P3HT:1a and P3HT:PCBM films with different
based cell with annealing at 140, 130, and 100 °C. Similar spec- annealing temperatures. Different results were obtained
tral responsivities were obtained irrespective of the annealing between P3HT/1a and P3HT/PCBM: substantially similar low
roughness values were observed in the AFM image of P3HT/1a
annealed at 100, 130, 140 °C (r.m.s. = 0.9–1.1 nm). On the
Table 3: J–V characteristic parameters of P3HT:1a- and P3HT:PCBM-
other hand, films of P3HT/PCBM showed similar roughness at
130 and 140 °C (r.m.s. = 1.4–1.6 nm), but a coarser surface was
observed at 100 °C (r.m.s. = 2.2–2.6 nm). The P3HT/PCBM
cell showed the highest efficiency. This is in accord with the
data in which higher roughness gives a more efficient device
[32-34]. As shown in Table 3, the highest efficiency was
obtained for the P3HT:1a cell when annealed at 100 °C with a
small PCE change in between 100 and 140 °C (Figure 5).
blended solar cells at different annealing temperatures
Cell
Temperature (°C) Eff (%) FF
Voc Jsc
P3HT:1a
60
1.93
1.88
2.06
1.93
1.91
0.54 0.55 6.41
0.56 0.57 5.80
0.57 0.61 5.83
0.59 0.61 5.41
0.58 0.61 5.47
80
100
130
140
P3HT:PCBM 100
2.19
1.98
1.84
0.64 0.55 6.31
0.56 0.52 6.82
0.56 0.49 6.69
Conclusion
130
140
In conclusion, a variety of new and highly soluble diarylmeth-
anofullerene derivatives 1a–k having electron-withdrawing and
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Beilstein Journal of Organic Chemistry 2009, 5, No. 7.
Figure 5: The AFM images of the P3HT:1a- and P3HT:PCBM-blended films annealed at different temperatures. (A) P3HT:1a-blended film annealed
at 100 °C for 30 min, Ra:0.8161 nm, P-V: 15.02 nm: RMS: 1.110. (B) P3HT:1a-blended film annealed at 130 °C for 30 min Ra: 0.6775 nm, P-V: 17.51
nm, RMS: 0.9067 nm. (C) P3HT:1a-blended film annealed at 140 °C for 30 min, Ra: 0.8884 nm, P-V: 69.73 nm, RMS: 1.734 nm. (D) P3HT:PCBM-
blended film annealed at 100 °C for 30 min, Ra: 1.531 nm, P-V: 35.72 nm, RMS: 2.159 nm. (E) P3HT:PCBM-blended film annealed at 130 °C for 30
min, Ra: 1.083 nm, P-V: 15.34 nm, RMS: 1.418 nm. (F) P3HT:PCBM-blended film annealed at 140 °C for 30 min, Ra: 1.135 nm, P-V: 13.47 nm, RMS:
1.573.
Experimental
-donating groups were studied as acceptors of the BHJ device.
Compared with the P3HT:PCBM blend, the P3HT:diarylmeth- Representative procedure: Preparation of 1a
anofullerene derivatives blend had decreased first reduction Methyl 4-[3,4-bis(octyloxy)benzoyl]benzoate (15a)
potential due to the electron-withdrawing aryl groups attached To a solution of terephthalic acid monomethyl ester chloride (3,
to the cyclopropane ring, possibly enhancing the acceptability 268 mg, 1.35 mmol) in CH2Cl2 (6 mL) was added aluminium
of the fullerene moiety. Higher Voc values were obtained due trichloride (199 mg, 1.49 mmol) in portions at 0 °C and
mainly to the electron-donating group, while the Jsc values were subsequently a solution of 1,2-bis(octyloxy)benzene (10,
l o w e r e d . I n p a r t i c u l a r , d e r i v a t i v e 1 a h a v i n g 500 mg, 1.49 mmol) in CH2Cl2 (4 mL). The reaction mixture
(methoxycarbonyl)phenyl and bis(octyloxy)phenyl groups was was stirred for 45 min. The resultant clear solution was stirred
shown to be a superior acceptor in combination with P3HT and for an additional 20 min at 40 °C, when the color of the reac-
the PCE of the P3HT:1a blended cell was as high as that of tion mixture turned reddish brown. The reaction mixture was
PCBM. The annealing conditions were shown to be important washed with brine. The organic layer was dried over MgSO4
in further improvement of the PCE values. The highest PCEs of and evaporated under vacuum to leave a solid which was puri-
both cells were obtained at a lower annealing temperature fied by silica gel column chromatography (ethyl acetate/hexane
(100 °C). Their spectral responsivities and the AFM measure- = 10:90 as eluent) to give 15a (624 mg, 93%). 1H NMR
ments suggested a change of the P3HT alignment depending on (CDCl3, 200 MHz): δ 8.14 (d, J = 7.8 Hz, 2H), 7.79 (d, J = 8.0
the annealing temperatures. These observations will lead the Hz, 2H), 7.46 (s, 1H), 7.32 (dd, J = 2.0, 13.6 Hz, 1H), 6.88 (d, J
way to further development of highly efficient acceptors for = 8.4 Hz, 1H), 4.10–4.00 (m, 4H), 3.96 (s, 3H), 1.89–1.80 (m,
organic thin-film solar cells.
4H), 1.56–1.28 (m, 20H), 0.91 (t, J = 6.6 Hz, 6H); 13C (CDCl3,
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Beilstein Journal of Organic Chemistry 2009, 5, No. 7.
50.3 MHz): δ 194.32, 166.00, 153.33, 148.59, 142.01, 132.33, 26.22, 22.86, 14.38; FT-IR (KBr, cm−1): 2923, 2853, 1725,
129.14, 129.09, 129.03, 125.36, 113.85, 111.13, 69.21, 69.04, 1608, 1511, 1464, 1430, 1275, 1186, 1136, 1107; MALDI-TOF
52.42, 31.91, 29.47, 29.44, 29.37, 29.24, 29.14, 26.12, 26.09, MS: m/z 1200; Anal. calcd. for C91H44O4: C; 90.98, H; 3.69.
22.81, 14.27; FT-IR (KBr, cm−1): 2954, 2929, 2856, 1725, Found: C; 89.41, H; 3.45.
1642; MS (EI) m/z 496; Anal. calcd. for C31H44O5: C, 74.96; H,
8.93. Found: C; 75.03, H; 8.92.
Photovoltaic cells
After rubbing with cloth to remove the protrusions, the ITO-
glass (FINE brand, Furuuchi Co. Ltd., 15 Ω/cm2) substrate was
cleaned successively with acetone, methanol, and a copious
Methyl 4-{1-(2-tosylhydrazono)-1-[3,4-
bis(octyloxy)phenyl]methyl}benzoate (16a)
A solution of 15a (1 g, 2.01 mmol) and p-toluenesulfonylhy- amount of water, and dried by a N2 blower. The conducting
drazine (937 mg, 5.03 mmol) in methanol (15 mL) was heated polymer, poly(3,4-ethylenedioxythiophene):poly(styrenesulf-
under reflux for 5 h. The solvent was removed under vacuum to onate) (PEDOT:PSS, Sigma-Aldrich), acting as a buffer layer
give a solid which was purified by silica gel column chromato- for hole transport and reducing the roughness of the ITO
graphy (ethyl acetate/hexane = 25:75 as eluent) to give 16a surface, was spin-coated by 2000 rpm on the ITO-glass
(800 mg, 63%). 1H NMR (CDCl3, 200 MHz): δ 8.17 (d, J = 8.2 substrate with a thickness of ~80 nm from the aqueous solution.
Hz, 2H), 7.85 (d, J = 8.2 Hz, 2H), 7.32–7.17 (m, 5H), 6.65–6.61 These layers were then annealed at 100 °C for 10 min to remove
(m, 2H), 3.98–3.90 (m, 4H, s, 3H), 2.43 (s, 3H), 1.85–1.58 (m, the residual water. P3HT was purchased from Sigma-Aldrich.
4H), 1.57–1.29 (m, 20H), 0.90 (t, J = 6.4 Hz, 6H); 13C (CDCl3, An ODCB solution (15 mg/mL) of P3HT and the diarylmethan-
50.3 MHz): δ 165.63, 153.10, 150.78, 148.44, 143.79, 135.69, ofullerene derivatives 1a–k, 2 in a 1:1 weight ratio prepared by
135.05, 131.17, 130.37, 129.28, 129.02, 128.36, 128.29, 127.7, stirring for a day was spin-coated by 2000 rpm and the resultant
125.94, 121.51, 111.85, 111.37, 69.05, 68.91, 52.46, 31.89, layers were heated at appropriate temperatures. The Al cathode
31.85, 29.48, 29.38, 29.31, 29.27, 29.15, 29.16, 26.05, 22.78, layer was deposited on the film with a thickness of ~100 nm by
22.75, 21.73, 14.23; FT-IR (KBr, cm−1): 2928, 2854, 1725, thermal evaporation in a vacuum chamber under 3 × 10−4 Pa.
1509; MS (EI) m/z 664; Anal. calcd. for C38H52N2O6S: C; The active area of the device was defined in an area of 3 mm2
68.64, H; 7.88, N; 4.21. Found: C; 68.92, H; 8.19, N; 4.21. with a shadow mask. After thermal evaporation of the Al
cathode layer, the device was annealed at 140 °C for 10 min.
Methyl 4-{[6,6]-1-[3,4-bis(octyloxy)phenyl]C61}-
All the above operations were conducted in a glove box filled
benzoate (1a)
with nitrogen. Current density–voltage (J–V) characteristics of
To a solution of 16a (613 mg, 0.92 mmol) in dry pyridine (5.0 the device was measured by a JASCO instrument under one-sun
mL) was added sodium methoxide (50 mg, 0.92 mmol). After illumination using an AM 1.5G filter with a white light xenon
stirring for 30 min at room temperature, a solution of C60 lamp (100 mW/cm2) under the nitrogen atmosphere. Optical
(398 mg, 0.55 mmol) of in dry ODCB (10 mL) was added. The absorption spectra of the device were measured by UV/VIS/
resulting mixture was stirred at 80 °C for 24 h. The reaction NIR spectrophotometer (V-570 JASCO). The device with
mixture was washed with diluted HCl aqueous solution and P3HT:PCBM was also fabricated for a comparative study and
brine successively. Solvents were removed under vacuum to characterized as in the case of the P3HT:diarylmethan-
give the crude product which was purified by column chromato- ofullerene derivatives device.
graphy (silica gel; toluene). First fraction was unreacted C60.
Fractions containing brown color were collected and the solvent
Supporting Information
was evaporated to leave a solid. This compound was dissolved
in toluene and refluxed for 24 h to complete the isomerisation.
Experimental procedures for the preparation of derivatives
The isomerisation was confirmed by HPLC (Develosil ODS-
1b–k, 2.
HG-5, MeOH/CHCl3) and 13C NMR. Further purification by
Supporting Information File 1
Experimental methods
column chromatography as above yielded 1a (112 mg, 17%).
1H NMR (CDCl3, 200 MHz): δ 8.15 (br s, 4H), 7.61 (m, 2H),
6.96 (d, J = 8.0 Hz, 2H), 4.12–3.98 (m, 4H), 3.92 (s, 3H),
1.83–1.79 (m, 4H), 1.56–1.28 (m, 20H), 0.87 (br s, 6H); 13C
(CDCl3, 50.3 MHz) δ 166.23, 149.18, 148.30, 147.60, 147.54,
144.99, 144.82, 144.42, 144.36, 144.33, 143.97, 143.50, 142.62,
[http://www.beilstein-journals.org/bjoc/content/
supplementary/1860-5397-5-7-S1.pdf]
142.57, 141.94, 141.88, 141.80, 140.58, 138.12, 137.67, 130.60, Acknowledgments
130.04, 129.85, 129.51, 123.95, 117.10, 113.05, 78.78, 69.81, This work was supported by the Incorporated Administrative
68.98, 57.46, 52.31, 32.00, 31.96, 29.65, 29.54, 29.44, 26.26, Agency New Energy and Industrial Technology Development
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Beilstein Journal of Organic Chemistry 2009, 5, No. 7.
24.Nakanishi, T.; Miyashita, N.; Michinobu, T.; Wakayama, Y.; Tsuruoka,
T.; Ariga, K.; Kurth, D. G. J. Am. Chem. Soc. 2006, 128, 6328–6329.
doi:10.1021/ja061450f
Organization (NEDO) under the Japanese Ministry of
Economy, Trade and Industry (METI).
25.Toru, T.; Shibata, N.; Nakamura, S.; Soga, T.; Hayashi, Y.; Singh, S. P.
Soluble Fullerene Derivatives. Jpn. Pat. Appl. 07309476, November
29, 2007.
References
1. Sariciftci, N. S.; Smilowitz, L.; Heeger, A. J.; Wudl, F. Science 1992,
258, 1474–1476. doi:10.1126/science.258.5087.1474
2. Yu, G.; Gao, J.; Hummelen, J. C.; Wudl, F.; Heeger, A. J. Science
1995, 270, 1789–1791. doi:10.1126/science.270.5243.1789
3. Brabec, C. J.; Sariciftci, N. S.; Hummelen, J. C. Adv. Funct. Mater.
2001, 11, 15–26.
26.Hummelen, J. C.; Knight, B. W.; LePeq, F.; Wudl, F.; Yao, J.; Wilkins,
C. L. J. Org. Chem. 1995, 60, 532–538. doi:10.1021/jo00108a012
27.Brabec, C. J.; Cravino, A.; Meissner, D.; Sariciftci, N. S.; Fromherz, T.;
Rispens, M. T.; Sanchez, L.; Hummelen, J. C. Adv. Funct. Mater. 2001,
11, 374–380.
doi:10.1002/1616-3028(200102)11:1<15::AID-ADFM15>3.0.CO;2-A
4. Hoppe, H.; Sariciftci, N. S. J. Mater. Res. 2004, 19, 1924–1945.
doi:10.1557/JMR.2004.0252
doi:10.1002/1616-3028(200110)11:5<374::AID-ADFM374>3.0.CO;2-W
28.Shrotriya, V.; Ouyang, J.; Tseng, R. J.; Li, G.; Yang, Y. Chem. Phys.
Lett. 2005, 411, 138–143. doi:10.1016/j.cplett.2005.06.027
The best performance has been reported with a 1:1 ratio of P3HT and
PCBM.
5. Brabec, C. J. Sol. Energy Mater. Sol. Cells 2004, 83, 273–292.
doi:10.1016/j.solmat.2004.02.030
6. Günes, S.; Neugebauer, H.; Sariciftci, N. S. Chem. Rev. 2007, 107,
1324–1338. doi:10.1021/cr050149z
29.Koster, L. J. A.; Mihailetchi, V. D.; Ramaker, R.; Blom, P. W. M. Appl.
Phys. Lett. 2005, 86, No. 123509. doi:10.1063/1.1889240
30.Ohkita, H.; Cook, S.; Astuti, Y.; Duffy, W.; Tierney, S.; Zhang, W.;
Heeney, M.; McCulloch, I.; Nelson, J.; Bradley, D. D. C.; Durrant, J. R.
J. Am. Chem. Soc. 2008, 130, 3030–3042. doi:10.1021/ja076568q
31.The HOMO and LUMO energies of the diarylmethanofullerene
derivatives were estimated by the method reported. See [35]. The
HOMO and LUMO values were calculated by using the following
general equations: EHOMO = E1ox + 4.4 eV ELUMO = EHOMO − Eopt. The
energy gap between the HOMO and LUMO energies was estimated to
be 2.70 by the tarc plots derived from the absorption in the UV
spectrum. Thus, the LUMO energy of 1a was estimated to be 2.95 eV.
The HOMO and LUMO values of other derivatives obtained by analogy
were not significantly changed from those of 1a. Unfortunately, we
could not compare these LUMO levels with that of PCBM, because the
oxidation potential of PCBM was not observed.
7. Janssen, R. A. J.; Hummelen, J. C.; Lee, K.; Pakbaz, K.; Sariciftci, N.
S.; Heeger, A. J.; Wudl, F. J. Chem. Phys. 1995, 103, 788–793.
doi:10.1063/1.470110
8. Camaioni, N.; Ridolfi, G.; Casalbore-Miceli, G.; Possamai, G.; Maggini,
M. Adv. Mater. 2002, 14, 1735–1738.
doi:10.1002/1521-4095(20021203)14:23<1735::AID-ADMA1735>3.0.C
O;2-O
9. Riedel, I.; Dyakonov, V. Phys. Status Solidi A 2004, 201, 1332–1341.
doi:10.1002/pssa.200404333
10.Padinger, F.; Rittberger, R. S.; Sariciftci, N. S. Adv. Funct. Mater. 2003,
13, 85–88. doi:10.1002/adfm.200390011
11.Janssen, R. A. J.; Hummelen, J. C.; Sariciftci, N. S. MRS Bull. 2005,
30, 33–36.
12.Li, G.; Shrotriya, V.; Huang, J.; Yao, Y.; Moriarty, T.; Emery, K.; Yang,
Y. Nat. Mater. 2005, 4, 864–868. doi:10.1038/nmat1500
13.Ma, W.; Yang, C.; Gong, X.; Lee, K.; Heeger, A. J. Adv. Funct. Mater.
2005, 15, 1617–1622. doi:10.1002/adfm.200500211
14.Reyes-Reyes, M.; Kim, K.; Carroll, D. L. Appl. Phys. Lett. 2005, 87, No.
083506. doi:10.1063/1.2006986
32.Li, G.; Shrotriya, V.; Yao, Y.; Yang, Y. J. Appl. Phys. 2005, 98, No.
043704. doi:10.1063/1.2008386
33.Matsumoto, F.; Moriwaki, K.; Takao, Y.; Ohno, T. Beilstein J. Org.
Chem. 2008, 4, No. 33. doi:10.3762/bjoc.4.33
34.Chiu, M.-Y.; Jeng, U.-S.; Su, C.-H.; Liang, K. S.; Wei, K.-H. Adv. Mater.
2008, 20, 2573–2578. doi:10.1002/adma.200703097
15.Kim, Y.; Cook, S.; Tuladhar, S. M.; Choulis, S. A.; Nelson, J.; Durrant,
J. R.; Bradley, D. D. C.; Giles, M.; McCulloch, I.; Ha, C.-S.; Ree, M.
Nat. Mater. 2006, 5, 197–203. doi:10.1038/nmat1574
16.Kim, J. Y.; Kim, S. H.; Lee, H.-H.; Lee, K.; Ma, W.; Gong, X.; Heeger,
A. J. Adv. Mater. 2006, 18, 572–576. doi:10.1002/adma.200501825
17.Kim, K.; Liu, J.; Namboothiry, M. A. G.; Carroll, D. L. Appl. Phys. Lett.
2007, 90, No. 163511. doi:10.1063/1.2730756
35.Chen, Z.-K.; Huang, W.; Wang, L.-H.; Kang, E.-T.; Chen, B. J.; Lee, C.
S.; Lee, S. T. Macromolecules 2000, 33, 9015–9025.
doi:10.1021/ma0005670
18.Knight, B.; Martín, N.; Ohno, T.; Ortí, E.; Rovira, C.; Veciana, J.;
Vidal-Gancedo, J.; Viruela, P.; Viruela, R.; Wudl, F. J. Am. Chem. Soc.
1997, 119, 9871–9882. doi:10.1021/ja962299k
19.Riedel, I.; von Hauff, E.; Parisi, J.; Martín, N.; Giacalone, F.; Dyakonov,
V. Adv. Funct. Mater. 2005, 15, 1979–1987.
doi:10.1002/adfm.200500097
20.Kooistra, F. B.; Knol, J.; Kastenberg, F.; Popescu, L. M.; Verhees, W.
J. H.; Kroon, J. M.; Hummelen, J. C. Org. Lett. 2007, 9, 551–554.
doi:10.1021/ol062666p
21.Yang, C.; Kim, J. Y.; Cho, S.; Lee, J. K.; Heeger, A. J.; Wudl, F. J. Am.
Chem. Soc. 2008, 130, 6444–6450. doi:10.1021/ja710621j
22.Lenes, M.; Wetzelaer, G.-J. A. H.; Kooistra, F. B.; Veenstra, S. C.;
Hummelen, J. C.; Blom, P. W. M. Adv. Mater. 2008, 20, 2116–2119.
doi:10.1002/adma.200702438
23.Nakanishi, T.; Schmitt, W.; Michinobu, T.; Kurth, D. G.; Ariga, K. Chem.
Commun. 2005, 5982–5984. doi:10.1039/b512320h
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