Synthesis and characterization of a bis-methanofullerene-4-nitro-α- cyanostilbene dyad as a potential acceptor for high-performance polymer solar cells

Article abstract of DOI:10.1016/j.tet.2012.05.114

We report the synthesis, characterization, and electrochemical properties of bis-PCBM dyad containing 4-nitro-α-cyanostilbene units for potential usage in efficient organic solar cells. The bis-PCBM dyad is fully characterized by NMR, UV-vis absorption, a

Full text of DOI:10.1016/j.tet.2012.05.114

Tetrahedron 68 (2012) 6696e6700
Contents lists available at SciVerse ScienceDirect
Tetrahedron
journal homepage: www.elsevier.com/locate/tet
Synthesis and characterization of a bis-methanofullerene-4-nitro-a-cyanostilbene
dyad as a potential acceptor for high-performance polymer solar cells
Boram Kim , Hye Rim Yeom , Won-Youl Choi , Jin Young Kim ,*, Changduk Yang a
a
a
c
a
,b,
*
a
Interdisciplinary School of Green Energy and KIER-UNIST Advanced Center for Energy, Ulsan National Institute of Science and Technology (UNIST), Ulsan 689-798, Republic of Korea
Low Dimensional Carbon Materials Center, UNIST, Republic of Korea
Department of Metal and Materials Engineering, Gangneung-Wonju National University, Gangneung 210-702, Republic of Korea
b
c
a r t i c l e i n f o
a b s t r a c t
Article history:
Received 20 April 2012
Received in revised form 25 May 2012
Accepted 28 May 2012
Available online 5 June 2012
We report the synthesis, characterization, and electrochemical properties of bis-PCBM dyad containing
4
-nitro-
fully characterized by NMR, UVevis absorption, and electrochemical cyclic voltammetry. It is found that
the presence of 4-nitro- -cyanostilbenes affects the cyclic voltammetry and absorption spectrum very
little. Whereas the 56 -electron system in the bis-functionalized fullerene cage significantly influences
a-cyanostilbene units for potential usage in efficient organic solar cells. The bis-PCBM dyad is
a
p
on the electrochemical and photophysical properties, resulting in up-shifted LUMO and wider absorption
compared to PCBM. Although the efficiencies of both conventional and the inverted cells based on P3HT/
bis-PCBM dyad as the preliminary results are low in comparison with the optimized high-performance
PSCs, it is believed that the efficiency would be improved through successful device optimization of
P3HT/bis-PCBM dyad cells.
Keywords:
Methanofullerene
bis-Adduct
bis-PCBM
Dyad
4
-Nitro-
a
-cyanostilbene
Ó 2012 Elsevier Ltd. All rights reserved.
1. Introduction
harvesting organofullerenes suffer from negative side effects,
such as insufficient charge transport, inefficient charge-
1
2,16
A soluble C60 derivative, [6,6]-phenyl-C61 butyric acid methyl ester
PCBM) has affirmed to be an invaluable n-type semiconductor for
dissociation, or morphology problems.
To date, only fullerene-
(
4-nitro- -cyanostilbene dyad showed superior photovoltaic per-
formance to that of the traditional PCBM.
a
1e4
28
solution-processed organic electronics.
resentedthewell-studiedbenchmarkacceptorinbulk-heterojunction
Therefore, PCBM has rep-
In this context, we have designed and synthesized a bis-PCBM
5e9
(BHJ) polymer solar cells (PSCs).
Although the modification of the
dyad incorporating 4-nitro-
a
-cyanostilbene units. Considering
-electron system by the
PCBM’s structure by changing the substituents aiming at more effi-
possible combined effects from the 56
p
cient acceptor materials for PSCs has come into focus, most of the
bis-adduct framework and the increased light absorption in the
visible region by the additional chromophores, the bis-PCBM dyad
is rationally expected to display excellent performance and its
structural motif is outlined in Fig. 1.
9e13
device performance is poorer than or similar to that of PCBM.
An
important breakthrough was achieved when PCBM was replaced by
1
4e18
bis-functionalized 56
p
-electron fullerenes
_ENREF_16, such as
These bis-adducts pos-
bis-PCBM16 and bis-indene-C60 adducts.
17,18
sess higher LUMO energy levels, resulting in higher VOC as well as
higher power conversion efficiency (PCE) of the P3HT-based
16e18
PSCs.
Another important development was accomplished by
the synthesis of [6,6]-phenyl-C71 butyric acid methyl ester (PC71BM)
that has a broader absorption in the visible region than PCBM, leading
8
,19e23
to a positive effect on current generation in PSCs.
Despite the enormous advances in the synthesis of fullerene-
2
4e27
based dyads and triads to further increase visible absorption,
limited success in PSCs has been reported since most of the light-
*
Corresponding authors. Interdisciplinary School of Green Energy and KIER-
UNIST Advanced Center for Energy, Ulsan National Institute of Science and Tech-
nology (UNIST), Ulsan 689-798, Republic of Korea; e-mail addresses: jykim@uni-
st.ac.kr (J.Y. Kim), yang@unist.ac.kr (C. Yang).
Fig. 1. Rational design motif of bis-PCBM dyad; 4-nitro-
additional light-harvesting unit to provide a higher Jsc. In principle, the LUMO can be
raised by bis-adduct framework due to 56 -electron system.
a-cyanostilbene was chosen as
p
0
040-4020/$ e see front matter Ó 2012 Elsevier Ltd. All rights reserved.
http://dx.doi.org/10.1016/j.tet.2012.05.114

B. Kim et al. / Tetrahedron 68 (2012) 6696e6700
6697
2
. Results and discussion
The synthesis of the intermediates and bis-PCBM dyad is shown
in Scheme 1. Previously, Sharma and co-workers prepared the 4-
nitro-4-hydroxy- -cyanostilbene as a dark green solid via Knoe-
a
venagel condensation between 4-hydroxybenzaldehyde and 4-
nitrobenzylcyanide in ethanol in the presence of sodium hydrox-
2
9
ide. Later, aiming at improving the PSCs, they reported the syn-
thesis and evaluation of a 4-nitro- -cyanostilbene-based PCBM,
which, given its high device performance, identified a new effective
a
2
8
modification strategy for fullerenes in PSCs.
Fig. 2. 1H NMR (a) of 1 and 1H & 13C NMR (b, c) spectra of bis-PCBM dyad in CDCl
digital photographs of 1 and bis-PCBM dyad.
3
. The
turned out to be a dark red solid (see the digital photograph in
1
Fig. 2b). In the H NMR spectrum, as a result of the successful ester
formation, we can clearly see a disappearance of the
at 5.75 ppm as well as an apparent up-field shift of the peaks
¼6.98 ppm) denoting the aromatic signals ortho to the phenolic
dOH resonances
(
d
Scheme 1. Synthetic route to bis-PCBM dyad.
1
3
benzene ring unit in 4-nitro-4-hydroxy-
a
-cyanostilbene. The
C
NMR spectroscopy shows a resonance in the carbonyl region at
2
d
¼170.22 ppm and a lot of carbon signals in the sp region
(d
¼127e150 ppm). Additionally, the spectrum displays two single
However, our initial attempt to synthesize 4-nitro-4-hydroxy-a-
3
intensity resonances assigned to sp -hybridized bridgehead carbon
atoms at
¼79.83 ppm and 79.25 ppm as well as signals at around
0 ppm corresponding to the quaternary carbon atoms of the ful-
cyanostilbene by the procedure described in the literature above,
1
d
gave, by the inspection of the H NMR spectrum, inseparable
5
complex mixtures. Despite the utilization of various purification
tools, the pure greenish product could not be isolated. A charac-
teristic solubility of the mixtures in water was a main problem of
the product separation. This is probably due to the formation of salt
sodium phenoxides since sodium hydroxide is strong enough base
to react with 4-hydroxybenzaldehyde as acidic phenolic com-
pound. We then proceeded to investigate the synthesis of 4-nitro-
lerene unit, in accordance with a [6,6]-closed methanofullerene.
The remaining signals are attributable to the carbon atoms of the
butyl chains in PCBM.
Fig. 3 depicts the UVevis absorption characteristics of 4-nitro-4-
hydroxy-a-cyanostilbene (1), PCBM, bis-PCBM, and bis-PCBM dyad
in chloroform solution. PCBM shows strong absorption at 330 nm
whereas the absorption maximum of 1 is at 365 nm. The absorption
of bis-PCBM dyad is non-superimposable on the sum of the ab-
sorption spectra of 1 and bis-PCBM (see bis-PCBM in Fig. 3 as well),
4
-hydroxy-
catalyzed by piperidine in ethanol, successfully affording a pure
red’ product in quantitative yield, an observation at odds with the
a-cyanostilbene (1) through the Knoevenagel reaction
‘
1
color reported by Sharma et al. (see the digital photograph and H
13
NMR in Fig. 2a as well as C NMR in the SI for further information).
As well, bis-PCBM was obtained as a by-product of the prepa-
ration of PCBM.1 After isolating the unreacted C60 and PCBM by
column chromatography in the regular manner, the isomeric bis-
PCBMs were collected upon elution with dichloromethane. And
then, the esters were hydrolyzed with hydrochloric acid/acetic acid
to the corresponding dicarboxylic acid-functionalized bis-PCBA.
The acid bis-PCBA was found to be insoluble in most organic sol-
vents, most likely due to the combination of intermolecular hy-
3
2
2
1
.0
.5
.0
.5
bis-PCBM dyad
bis-PCBM
PCBM
0
.15
,16
0.10
1
0.05
0.00
4
00
500
600
700
800
Wavelength(nm)
1.0
0.5
0.0
1
drogen bonding and C60eC60 interactions. Finally, bis-PCBM dyad
3
0,31
was prepared by a Steglich esterification (DCC/DMAP)
of 1 with
bis-PCBA. The structure of bis-PCBM dyad was fully identified by
1
13
H and C NMR (Fig. 2b and c). Owing to two large substituents, the
target product is easily soluble in chloroform, tetrahydrofuran
THF), chlorobenzene (CB) and ortho-dichlorobenzene (o-DCB). In
contrast to the color previously described for 4-nitro- -cyanos-
tilbene-PCBM (dark green), the obtained product bis-PCBM dyad
300
400
500
600
700
800
Wavelength (nm)
(
a
Fig. 3. UVeVis absorption of 1, PCBM, bis-PCBM, and bis-PCBM dyad in CHCl
3
solution.

6698
B. Kim et al. / Tetrahedron 68 (2012) 6696e6700
implying an evidence of the electronic interaction of the two
chromophores.32,33 Interestingly, the spectrum of bis-PCBM dyad
displays an increased and wider absorption compared to PCBM,
with a shoulder peak at ca. 430 nm as characteristic of [6,6]-closed
ring isomer. The relatively higher absorption of bis-PCBM dyad in
the visible region can be attributed, in part, to a highly broken
symmetry of the fullerene core, leading to the lowest-energy
illumination from a calibrated solar simulator with irradiation in-
tensity of 100 mW/cm . The device performance of a solar cell is
determined by the open-circuit voltage (VOC), short-circuit current
2
(JSC), and fill factor (FF). The power conversion efficiency (
e
h ) of
a solar cell is given as
h
e
¼(JSC$VOC$FF)$100/PINC, where PINC is the
intensity of incident light. Higher values of those three parameters
yield larger light-to-electricity power conversion efficiency.
The PCE up to 0.76% is observed for the conventional P3HT:bis-
PCBM dyad solar cells with a VOC of 0.69 V, a short circuit current
3
4,35
transitions being formally dipole allowed.
A closer view of
the two spectra (PCBM and bis-PCBM dyad) discloses, furthermore,
a red-shifted band at w707 nm relative to the PCBM (697 nm).
From the herein observed spectral features, it is safe to assume that
bis-PCBM dyad would be able to absorb more solar energy and
contribute to an improved performance.
The electrochemical properties of bis-PCBM dyad were studied
by cyclic voltammetry (CV), where PCBM data obtained in this
study for comparison is also shown in Fig. 4. In o-ODCB, each
compound exhibits three well-defined, single-electron, quasir-
eversible waves, which is in sharp contrast with the results repor-
2
density (JSC) of 3.05 mA/cm , and a fill factor (FF) of 36%. On the
other hand, under the same white light illumination, the P3HT:bis-
2
PCBM dyad-based inverted cells exhibit a JSC of 1.06 mA/cm ,
a VOC of 0.47 V, and a FF of 31%. It yields a substantially lower PCE of
0.16% because of its decreased photocurrent. Work is in progress in
order to find optimal conditions for the PSCs based on P3HT/bis-
PCBM dyad.
ted for 4-nitro-
peak. The half-cell potentials (defined as E
a
-cyanostilbene-PCBM with only one reduction
(a)
2
8
1
¼0.5(Ep,cþEp,a)) for the
0.0
reduction of the PCBM and bis-PCBM dyad relative to Fc/Fcþ
are ꢀ1164, ꢀ1540, ꢀ2036 mV, and ꢀ1261, ꢀ1587, ꢀ2260 mV, re-
spectively. The bis-PCBM dyad lifts its LUMO level by w100 meV,
from ꢀ3.636 eV (PCBM) to ꢀ3.539 eV, because of the extraction of
two more
p-electrons from the fullerene core. This reveals an ob-
-2.0
vious similarity to the difference between LUMO levels of PCBM
and bis-PCBM.16 We do not observe an additional up-shift of the
LUMO because of the inductive effect of the strong electron with-
drawing nitro and cyano groups in the bis-PCBM dyad on the redox
2
8
behavior, as opposed to the report by Sharma et al. The fully
optimization of the PSC device based on P3HT/bis-PCBM dyad is an
extraordinarily time-consuming process since a complex region
isomeric mixture of the bis-adduct has any negative side effects on
-0.2
0.0
0.2
0.4
0.6
0.8
Voltage (V)
0.5
16
(b)
the chargeetransport properties.
0
.0
1
0
0
.0
.5
.0
bis-PCBM dyad
PCBM
-0.5
-1.0
-1.5
-
-
-
-
-
0.5
1.0
1.5
2.0
2.5
0.0
0.2
0.4
Voltage (V)
-
2.5
-2.0
-1.5
-1.0
-0.5
Fig. 5. JeV characteristics of conventional (a) and the inverted (b) devices under AM
2
1.5G illumination from a calibrated solar simulator with an intensity of 100 mW/cm .
Electrode Potential (mV vs Fc/Fc+)
Inset is a schematic of the device architectures, respectively.
Fig. 4. Cyclic voltammograms of PCBM and bis-PCBM dyad in o-DCB solution. Ex-
þ
ꢀ4
ꢀ3
perimental conditions: values for 0.5(EpaþEpc) in V versus Fc/Fc ; 10 e10 mol/L
o-DCB solution; Bu NClO (0.1 M) as supporting electrolyte; Pt wire as counter elec-
trode; 50 mV/s scan rate.
3. Conclusion
4
4
Aspiring to improve efficiency of the PSCs, we have presented
To demonstrate potential applications of the bis-PCBM dyad in
PSCs, we used P3HT as an electron donor and bis-PCBM dyad as an
electron acceptor. The blends were spin-coated from a mixture of
solvents (chloroform/5% acetone) containing the P3HT/bis-PCBM
dyad and subsequent thermal annealing 120 C. The device archi-
tectures of the conventional and the inverted devices are ITO/
a novel type of fullerene, bis-PCBM dyad bearing 4-nitro-
a-cya-
1
nostilbene moieties, clearly identified through a combination of H
13
and C NMR spectra. From the electrochemical and photophysical
properties of the bis-PCBM dyad, one can conclude that the 4-
ꢁ
nitro-
electronic energy levels of the C60 derivatives very little. By virtue of
56 -electron system in fullerene framework, the bis-PCBM dyad
a-cyanostilbene chromophores influence the absorption and
PEDOT:PSS/P3HT:bis-PCBM dyad (1:1 w/w)/Al and ITO/TiO
P3HT:bis-PCBM dyad (1:1 w/w)/MoO /Au, respectively. In the
inverted devices, MoO as the hole transport layer and TiO as the
x
/
p
3
has a higher LUMO level and stronger absorption than PCBM, which
should potentially be a highly helpful for minimizing the energy
loss in the electron transfer from the donor to the acceptor material
as well as increasing current generation in BHJ solar cells. By op-
timizing the device fabrication process, the photovoltaic
3
x
electron transport layer were deposited. The device structures of
the regular and inverted polymer solar cells are shown in Fig. 5a
and b. All data were obtained under white light AM 1.5G

B. Kim et al. / Tetrahedron 68 (2012) 6696e6700
6699
performance of bis-PCBM dyad as acceptor blended with P3HT
would be significantly superior to that of the traditional PCBM. As
initial results, the efficiency obtained from the conventional
structure device is 0.76%, while the PCE of the inverted device
reaches 0.16%. Through successful device optimization of P3HT/bis-
PCBM dyad cells, the high efficiency would be expected in the near
future.
unit. The JeV curves for the devices were measured under AM 1.5G
illumination at 100 mA/cm .
2
4.3. Synthesis of 4-nitro-4-hydroxy-a-cyanostilbene (1)
To mixture of the 4-hydroxylbenezaldehyde (2.0 g,
a
16.39 mmol) and 4-nitrobenzylcyanide (2.66 g, 16.39 mmol) in
absolute EtOH (40 mL), was added with piperidine (2.43 mL,
24.58 mmol) portionwise, stirred at room temperature for 3 h,
Thus, future efforts will focus on testing the influence of bis-
PCBM dyad in combination with P3HT on the performance of PSCs.
ꢁ
cooled to 0 C, and filtered. The precipitate was washed with EtOH,
1
4
4
. Experimental section
dried to yield 1 (95%). H NMR (600 MHz, CDCl
3
):
d
(ppm) 8.30 (d,
J¼9 Hz, 2H), 7.92 (d, J¼8.4 Hz, 2H), 7.82 (d, J¼9 Hz, 2H), 7.60 (s, 1H),
1
3
.1. Materials and instruments
6.98 (d, J¼8.4 Hz, 2H), 5.75 (s, 1H). C NMR (150 MHz, acetone-d
6
):
d
(ppm) 161.50, 147.37, 145.81, 141.52, 132.32, 126.36, 124.75, 123.92,
All starting materials were purchased either from Aldrich or
117.79. Elemental analysis: C, 67.67; H, 3.79; N, 10.52; O, 18.03;
ꢁ
Acros and used without further purification. All solvents are ACS
grade unless otherwise noted. Anhydrous THF was obtained by
distillation from sodium/benzophenone prior to use. Anhydrous
Found: C, 67.90; H, 3.89; N, 10.78; O, 18.15. Mp 204 C. FTIR (
cm ): 3417, 2171, 1585, 1525, 1322.
n
/
ꢀ1
1
13
toluene was used as received. H NMR and C NMR spectra were
recorded on a Varian VNMRS 600 spectrophotometer and MALDI-
MS spectra were obtained from Ultraflex III (Bruker, Germany).
UVevis spectra were taken on Cary 5000 (Varian USA) spectro-
photometer. Cyclic voltammetry (CV) measurements were per-
formed on AMETEK VersaSTAT 3 with a three-electrode cell in
a nitrogen 0.1 M tetrabutylammonium perchlorate solution in o-
4.4. Synthesis of bis-[6,6]-phenyl C61-butyric acid (bis-PCBA)
To a solution containing bis-PCBM (1.0 g, 0.90 mmol) in chlo-
robenzene was added acetic acid (70 mL) and concentrated
hydrochloric acid (20 mL). The mixture was heated to reflux over-
night. The solvent was removed in vacuo and the precipitate was
collected by filtration. The course of the reaction was followed by
DCB at a scan rate of 50 mV/s at room temperature. Ag used as the
f
TLC (after complete conversion, R is 0.0) The crude product was
þ
Ag/Ag (0.1 M of AgNO
3
in acetonitrile) reference electrode, plati-
washed with methanol and a solvent mixture of MeOH:diethy-
ꢁ
num counter electrode, and polymer coated platinum working
lether (1:1 v/v) several times to give quantitative yield. Mp 302 C.
þ
ꢀ1
electrode, respectively. The Ag/Ag reference electrode was cali-
FTIR (
n
/cm ): 1711, 1438, 1421, 1210, 1190, 1157, 734. 573, 511.
brated using a ferrocene/ferrocenium redox couple as an internal
standard, whose oxidation potential is set at ꢀ4.8 eV with respect
to zero vacuum level. The LUMO levels of polymers were obtained
4.5. Synthesis of bis-PCBM dyad
onset
onset
opt
from the equation LUMO¼ꢀ(Ered ꢀE(ferrocene)þ4.8) eV. E
g
¼1240/
Compound 1 (0.18 g, 0.69 mmol) was mixed with bis-PCBA
(0.17 g, 0.15 mmol) and 4-N,N-dimethylaminopyridine (DMAP)
opt
l
edge. HOMO¼ꢀ(E
g
ꢀLUMO).
(0.4 g, 3.40 mmol) in o-DCB (60 mL). This mixture was treated in an
ꢁ
4
.2. Fabrication of conventional and inverted photovoltaic cells
ultrasonicator bath for 10 min, then cooled down to 0 C in an ice/
0
water bath. Finally, N,N -dicyclohexylcarbodiimide (DCC) (1.58 g,
Two-type photovoltaic cells were fabricated on ITO-coated glass
7.65 mmol) was added to the mixture quickly with a syringe. The
mixture was stirred at 0 C for 5 h and then warmed up to room
ꢁ
substrates. The ITO-coated glass substrates were first cleaned with
detergent, ultrasonicated in water, acetone and isopropyl alcohol,
and dried overnight in an oven. In conventional cells, PEDOT:PSS
temperature with continuously stirring for 3 d. The mixture was
concentrated to ca. 3 mL using a rotary evaporator, followed by
addition of excess MeOH. The solid was separated by centrifugation
(3000 rpm/30 min), washed with MeOH twice and then with
diethyl ether twice, and further purified by column chromatogra-
(
Al 4083) was spin-cast on cleaned ITO substrates after a UVeozone
ꢁ
treatment for 15 min and heated at 140 C for 10 min in air. Sub-
sequently, the active layer was coated in a glove box. The solution
containing a mixture of P3HT:bis-PCBM dyad (1:1 w/w) in a mix-
ture of solvents (chloroform/5% acetone) with a concentration of
phy on silica gel with dichloromethane as eluent to yield bis-PCBM
1
dyad (75%) as a dark red solid. H NMR (600 MHz, CDCl
3
):
d
(ppm)
1
(
1 mg/mL and P3HT:bis-PCBM dyad (1:1) in a mixture of solvents
chloroform/5% acetone) with a concentration of 13 g/mL was spin-
cast on top of PEDOT:PSS film. After then, the top electrode (Al) was
8.20e8.15 (m, 4H), 7.99e7.91 (m, 4H), 7.87e7.81 (m, 4H), 7.75e7.61
(m, 4H), 7.52e7.21 (m, 12H). C NMR (150 MHz, CDCl ): d (ppm)
3
13
170.22, 149.94, 149.81, 149.21, 147.81, 146.75, 146.61, 146.45, 146.43,
146.40, 164.20, 146.12, 146.08, 146.00, 145.92, 145.84, 145.77, 145.39,
145.34,145.23,145.12,144.99, 144.29 ,144.23, 144.07,144.04,143.88,
143.74, 143.16, 143.09, 142.81, 141.66, 141.50, 140.47, 140.26, 137.70,
137.56, 137.31, 136.89, 132.13, 131.90, 131.77, 128.30, 128.15, 128.02,
127.88, 127.85, 79.83, 79.25, 51.05, 51.00, 50.96, 49.48, 49.38, 33.92,
33.83, 33.77, 33.64, 33.18, 33.06, 32.60, 32.57, 30.78, 30.71, 30.64,
29.48, 26.28, 26.22, 25.30, 25.09, 24.54, 24.31, 22.52, 22.47, 22.41.
Elemental Analysis: C, 85.71; H, 2.57; N, 3.57; O, 8.15; Found: C,
ꢀ
6
deposited on the active layer in a vacuum (<10 Torr) thermal
evaporator. Inverted solar cells were fabricated on ITO-coated glass
substrates. A TiO
method. The TiO
substrates after a UVeozone treatment for 15 min and heated at
x
precursor solution was prepared using the sol-gel
precursor solution was spin-cast on cleaned ITO
x
ꢁ
8
0
C for 10 min in air for conversion to TiO
x
by hydrolysis. Sub-
sequently, the TiO
box. A solution containing a mixture of P3HT:bis-PCBM dyad (1:1
w/w) in a mixture of solvents (chloroform/5% acetone) was spin-
x
-coated substrates were transferred into a glove
þ
ꢂ
85.37; H, 2.34; N, 3.47; O, 8.12. MALDI-TOF-MS m/z: [M] ¼1569.
ꢁ
ꢀ1
cast on top of TiO
x
films. Then, a thin layer of MoO
3
film (z5 nm)
Mp 242 C. FTIR (n/cm ): 2195, 1705, 1575, 1543, 1517, 1443, 1431,
was evaporated on top of the active layer. Finally, the anode
1335, 1312, 1233, 1201,1149, 701, 521.
ꢀ
6
(
Au,z95 nm) was deposited on the active layer in a vacuum (<10
Torr) thermal evaporator. The cross-sectional area of each of the
electrode defines the active area of the device as 13.5 mm . Pho-
Acknowledgements
2
tovoltaic cell measurements were carried out inside the glove box
using a high quality optical fiber to guide the light from the solar
simulator equipped with a Keithley 2635A source measurement
This work was supported by Basic Science Research Program
through the National Research Foundation of Korea (NRF) funded
by the Ministry of Education, Science and Technology (2010-

6700
B. Kim et al. / Tetrahedron 68 (2012) 6696e6700
0
002494) and the National Research Foundation of Korea Grant
funded by the Korean Government (MEST) (2010-0019408), (2010-
026163), (2010-0026916) (NRF-2009-C1AAA001-0093020).
13. Kim, J.; Yun, M. H.; Lee, J.; Kim, J. Y.; Wudl, F.; Yang, C. Chem. Commun. 2011,
078e3080.
4. Kang, H.; Cho, C. H.; Cho, H. H.; Kang, T. E.; Kim, H. J.; Kim, K. H.; Yoon, S. C.;
Kim, B. J. ACS Appl. Mater. Interfaces 2012, 4, 110e116.
5. Kim, K. H.; Kang, H.; Nam, S. Y.; Jung, J.; Kim, P. S.; Cho, C. H.; Lee, C.; Yoon, S. C.;
Kim, B. J. Chem. Mater. 2011, 23, 5090e5095.
3
1
0
1
Supplementary data
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