J apan Advanced Institute of Science and TechnologyJ apan Advanced Institute of Science and Technology
J AIST RepositoryJ AIST Repository
Ful l erene-Based Supram ol ecul ar N anocl usters w i th
Pol y[2-m ethoxy-5-(2' -ethyl hexyl oxy)-p-
phenyl enevi nyl ene] for Li ght Energy Conversi on
H asobe, Taku; Fukuzum i , Shuni chi ; Kam at, Prashant
V. ; M urata, H i deyuki
J apanese J ournal of Appl i ed Physi cs, 47(2): 1223-
TypeJ ournal Arti cl e
URLhttp: //hdl . handl e. net/10119/8789
Thi s i s the author' s versi on of the w ork. It i s
posted here by perm i ssi on of The J apan Soci ety of
Appl i ed Physi cs. Copyri ght (C) 2008 The J apan
Soci ety of Appl i ed Physi cs. Taku H asobe, Shuni chi
Fukuzum i , Prashant V. Kam at, and H i deyuki M urata,
J apanese J ournal of Appl i ed Physi cs, 47(2), 2008,
1223-1229. http: //j j ap. i pap. j p/l i nk?J J AP/47/1223/
Fullerene-Based Supramolecular Nanoclusters with poly[2-methoxy-5-
for Light Energy Conversion
Taku Hasobe,*,a,b Shunichi Fukuzumi,c Prashant V. Kamat,d and Hideyuki Murataa
aSchool of Materials Science, Japan Advanced Institute of Science and Technology
(JAIST), 1-1, Asahidai, Nomi, Ishikawa, 923-1292, Japan
bResearch Center for Integrated Science, JAIST, Nomi, Ishikawa, 923-1292, Japan
cDepartment of Material and Life Science, Division of Advanced Science and
Biotechnology, Graduate School of Engineering, Osaka University, SORST, Japan
Science and Technology Agency (JST), Suita, Osaka 565-0871, Japan
dNotre Dame Radiation Laboratory and Departments of Chemistry & Biochemistry
and Chemical & Biomolecular Engineering, University of Notre Dame. Notre Dame
Indiana 46556-5674, USA
KEYWORDS: fullerene, MEH-PPV, porphyrin, organic solar cell, supramolecular
E-mail Address: firstname.lastname@example.org
Abstract: Organized composite molecular nanoassemblies of fullerene and poly[2-
methoxy-5-(2'-ethylhexyloxy)-p-phenylenevinylene] (MEH-PPV) prepared in
acetonitrile/toluene mixed solvent absorb light over entire spectrum of visible light. The
highly colored composite clusters can be assembled as 3 dimensional array onto
nanostructured SnO2 films using electrophoretic deposition approach. The composite
cluster films exhibit an incident photon-to-photocurrent efficiency (IPCE) as high as 18%,
which is significantly higher than that of molecular assembly composed of 5,10,15,20-
tetrakis(3,5-di-tert-butylphenyl)-21H,23H-porphyrin (H2P) and C60 prepared by the same
manner (4%). The maximum IPCE value is increased to 25% under an applied bias
potential to 0.2 V vs. SCE. The power conversion efficiency of MEH-PPV and C60
assembly-modified electrode is determined as 0.24%. The photocurrent generation
properties observed with MEH-PPV and C60 clusters demonstrate the synergy of these
systems towards yielding efficient photoinduced charge separation within these
The need to develop next generation solar cells has stimulated renewed interest in
the design of efficient, low-cost energy conversion devices.1-12) A promising and
attractive strategy is to mimic natural photosynthesis. Energy from sunlight is captured
by photosynthetic p-pigments (primarily chlorophylls and carotenoids) which cover the
wide spectral range of the solar irradiation.13,14) Light energy is absorbed by the
individual p-pigments and is quickly transferred to chlorophylls that are in a well-
organized protein environment. The energy conversion event start via electron-transfer
processes. The artificial photoconversion devices developed so far have a limited
degree of self-organization, whereas the components in the natural photosynthetic system
are highly organized in quaternary protein structures. Although exact duplication of
natural photosynthetic environment is not necessary for construction of artificial light
energy conversion devices, little attention has been given to artificial light energy
conversion devices based on highly organized light harvesting assemblies. The
construction of efficient solar cells also requires an enhanced light-harvesting efficiency
of chromophore molecules throughout the solar spectrum together with a highly efficient
conversion of the harvested light into electrical energy. Thus, useful combination and
organization of organic molecules is essential for light energy conversion properties.
Recently, progress is being made towards the development of bulk heterojunction
organic solar cells, which possess an active layer of a conjugated donor polymer and an
acceptor molecule.2-5,7,8,10-12,15) In these blend systems, efficient photoinduced electron
transfer occurs at the donor-acceptor interface, and intimate mixing of donor and acceptor
is therefore beneficial for efficient charge separation. Especially, fullerene is used as a
suitable electron acceptor component in such photovoltaic cells. The electron-transfer
reduction of C60 is highly efficient because of the minimal changes of structure and
solvation associated with the electron-transfer reduction.16-20) On the other hand, the
conjugated polymer such as poly[2-methoxy-5-(2'-ethylhexyloxy) -p-phenylenevinylene]
(MEH-PPV) has also emerged as a promising photonic and donor polymer. Photonic
devices incorporating MEH-PPV have thus far included light-emitting diodes21,22) and
photodiodes.23) MEH-PPV-C60 based photodetectors with high visible-ultraviolet
sensitivity24) and photovoltaic devices have also been fabricated.25,26)
Porphyrins with its electron donating as well as sensitizing properties are suitable
for efficient electron transfer with small reorganization energies.18-20) In addition, rich
and extensive absorption features of porphyrinoid systems guarantees increased
absorption cross-sections and an efficient use of the solar spectrum.27) Moreover,
porphyrins and fullerenes are known to form supramolecular complexes facilitating close
contact between one of the electron-rich 6:6 bonds of the guest fullerene and the
geometric center of the host porphyrin.28-33) The porphyrin-fullerene interaction energies
are reported to be in the range of -16 to -18 kcal mol-1.34) Such a strong interaction
between porphyrins and fullerenes is likely to be a good driving force for the formation
of supramolecular complexes between porphyrin and C60. Based on these ideas, we
have recently developed highly organized supramolecular photovoltaic cells composed of
fullerenes and multi-porphyrin arrays.35,36) Although construction of molecular devices
using a variety of molecular assemblies has already been attempted, new organization
strategies and approaches for efficient light energy conversion are continuously sought to
tailor their performance.
Herein we report new types of light energy conversion systems using fullerene-
based supramolecular composites with an electron donor: MEH-PPV (Fig. 1), which are
clusterized on nanostructured SnO2 electrodes. The organized molecular assembly
between fullerene and MEH-PPV prepared in acetonitrile/toluene mixed solution exhibit
efficient light-harvesting and light energy conversion properties in the visible region. In
addition, we have compared the structural and light energy conversion properties of
fullerene and MEH-PPV–based assembly films with that of fullerene and 5,10,15,20-
tetrakis(3,5-di-tert-butylphenyl)-21H,23H-porphyrin (H2P) composite films. The details
on the dependence of photoelectrochemical properties on the different molecular
organizations between donor and acceptor moieties are discussed.
2. Experimental Section
Melting points were recorded on a Yanagimoto micro-melting point apparatus and
not corrected. 1H NMR spectra were measured on a JEOL EX-270 (270 MHz) or a
JEOL JMN-AL300 (300 MHz). Matrix-assisted laser desorption/ionization (MALDI)
time-of-flight mass spectra (TOF) were measured on a Kratos Compact MALDI I
(Shimadzu). The UV-visible spectra were recorded on a Perkin Elmer LAMDA 750
spectrophotometer. Transmission electron micrographs (TEM) of porphyrin and
fullerene assemblies were recorded by applying a drop of the sample to carbon-coated
copper grid. Images were recorded using a Hitachi H7100 transmission electron
All solvents and chemicals were of reagent grade quality, obtained commercially and
used without further purification unless otherwise noted (vide infra). Thin-layer
chromatography (TLC) and flash column chromatography were performed with Art. 5554
DC-Alufolien Kieselgel 60 F254 (Merck), and Fujisilicia BW300, respectively.
Nanostructured SnO2 films were cast on an optically transparent electrode (OTE) by
applying a 2% colloidal solution obtained from Alfa Chemicals. The air-dried films
were annealed at 673 K. The details of the preparation of SnO2 films on conducting
glass substrate were reported elsewhere.37) The nanostructured SnO2 film electrode is
referred as OTE/SnO2. Poly[2-methoxy-5-(2-ethylhexyloxy)-1,4-phenylenevinylene]
(MEH-PPV) were purchased from Aldrich (Mn:~51,000). Preparation of H2P have been
2.3 Electrophoretic Deposition of Molecular Cluster Films
A known amount of MEH-PPV, porphyrin, and C60 or mixed cluster solution in
acetonitrile/toluene (3/1, v/v, 2 mL) was transferred to a 1 cm cuvette in which two
electrodes (viz., OTE/SnO2 and OTE) were kept at a distance of 6 mm using a Teflon
spacer. A dc electric field (~200V/cm) was applied between these two electrodes using
a Fluke 415 power supply. The deposition of the film can be visibly seen as the solution
becomes colorless with simultaneous brown coloration of the OTE/SnO2 electrode. The
OTE/SnO2 electrode coated with MEH-PPV and C60 clusters is referred as
OTE/SnO2/(MEH-PPV+C60)n. Preparation of (H2P+C60)n is also adopted by the same
method as H2P-C60 composites ([H2P] = 0.19 mM and [C60] = 0.31 mM in
acetonitrile/toluene = 3/1, v/v). The weight % ratio of MEH-PPV : C60 is ~ 1 : 4. The
final concentration of C60 is 0.31 mM.
2.4 Photoelectrochemical Measurements
Photoelectrochemical measurements were carried out using a working electrode and a
Pt gauge counter electrode in the cell assembly using a Keithley model 617
programmable electrometer. The electrolyte was 0.5 M NaI and 0.01 M I2 in acetonitrile.
A collimated light beam from a 150 W Xenon lamp with a 400 nm cut-off filter was used
for excitation of (MEH-PPV+C60)m films deposited on SnO2 electrodes. A Bausch and
Lomb high intensity grating monochromator was introduced into the path of the
excitation beam for the selected wavelength.
The incident photon to photocurrent efficiency (IPCE) values were calculated by
normalizing the photocurrent values to incident light energy and intensity using eq 1,38)
IPCE (%) = 100 ¥ 1240 ¥ Isc /(Iinc ¥ l ) (1)
where Isc is the short circuit photocurrent (A/cm2), Iinc is the incident light intensity
(W/cm2), and l is the wavelength (nm).
Power conversion efficiency, h is calculated by eq 2,38)
h = FF x Isc x Voc/Win
where the fill factor (FF) is defined as FF = [IV]max/ Isc Voc, where Voc is the open circuit
photovoltage, and Isc is the short circuit photocurrent.
3. Result and Discussion
3.1 Construction of Molecular Assemblies of Fullerenes and Donor moieties
C60, MEH-PPV and porphyrin are soluble in nonpolar solvents such as toluene, but
sparingly soluble in polar solvents such as acetonitrile.38,39) When a concentrated
solution of these molecules in toluene is mixed with acetonitrile by fast injection method,
the molecules aggregate and form stable clusters. The final solvent ratio of mixed
solvent employed in the present experiments was 3 : 1 (v/v) acetonitrile : toluene. The
same strategy can be extended to prepare mixed or composite molecular clusters
consisting of donor moieties and C60 molecules. Mixed cluster aggregates in the present
investigation were prepared by mixed solution containing constant molar ratio of donor
moieties (MEH-PPV or H2P) and C60 in toluene (0.5 ml), and then injecting into a pool of
acetonitrile (1.5 ml). These optically transparent composite clusters [denoted as (MEH-
PPV+C60)n and (H2P+C60)n] are stable at room temperature and they can be reverted back
to their monomeric forms by diluting the solution with toluene.
The absorption spectra of donor moieties (MEH-PPV and H2P) and C60 in neat
toluene are compared with the absorption spectrum of [(MEH-PPV+C60)n or (H2P+C60)n]
clusters in acetonitrile/toluene (3/1, v/v) in Fig. 2. In both cases, the composite clusters
[(MEH-PPV+C60)n or (H2P+C60)n] in the mixed solvent (spectra a) exhibit much broader
and more intense absorption in the visible and near infrared regions than those of parent
MEH-PPV (or H2P) in spectra b and C60 in spectra c. For example, earlier studies on the
porphyrin clusters have shown that the intermolecular interactions have significant
impact on the intensity and position of the Soret and Q-bands.40) In the case of
(H2P+C60)n, although Soret band of unaggregated monomeric H2P remains, Q-bands
become red-shifted. The presence of C60 induces further enhancement of absorption of
these clusters in the visible region. This demonstrates that the composite clusters of
donor moieties and C60 are superior light absorbers as compared to that of the
corresponding single component since they absorb throughout the visible part of the solar
spectrum. A charge transfer type interaction between the two molecules may be
responsible for the long-wavelength absorption of the composite clusters. Similar
charge transfer interactions leading to extended absorption has been observed for donor-
C60 composites41-43) linked at close proximity.
Fig. 3 shows transmission electron micrographs (TEM) images of (MEH-PPV+C60)n
and (H2P+C60)n to examine the structural properties of these molecular assemblies. The
TEM image of (MEH-PPV+C60)n (Fig. 3A) displays well-controlled size and shape of
nanoclusters with a diameter of ~50 nm. These clusters are in sharp contrast with the
TEM image of (H2P+C60)n exhibiting irregular and larger size (Fig. 3B). Judging from
the molecular scales of these molecules, one can safely conclude that MEH-PPV is self-
assembled with C60 molecules in the mixed solution to yield large donor–acceptor (D-A)
nanoclusters with an interpenetrating network.
3.2 Solar Energy Conversion Properties of (MEH-PPV+C60)n and (H2P+C60)n
Assemblies-Modified Electrode using Two-electrode System
As shown earlier,44,45) clusters of C60 prepared in acetonitrile/toluene mixed solvent can
be assembled electrophoretically as thin films on a conducting glass electrode surface.
A similar electrodeposition approach was adopted to prepare film of (MEH-PPV+C60)n or
(H2P+C60)n on nanostructured SnO2 films cast on an optically conducting glass electrode
(referred as OTE/SnO2). Upon application of the DC electric field of ~200 V/cm
between OTE/SnO2 and OTE electrodes which were immersed parallel in a mixed
acetonitrile/toluene (3/1, v/v) solution containing (MEH-PPV+C60)n or (H2P+C60)n
clusters we can achieve deposition of mixed clusters on SnO2 nanocrystallites. As the
deposition continues we can visually observe discoloration of the solution and coloration
of the electrode that is connected to positive terminal of the dc power supply. Fig. 4
shows an absorption spectrum of OTE/SnO2/(MEH-PPV+C60)n film prepared by
electrophoretic deposition. The absorption spectrum exhibits a broad photoresponse,
which is consistent with the absorption spectrum of aggregated molecular clusters in
acetonitrile/toluene (spectrum a in Fig. 2A).46) The ability to assemble clusters from
solution onto electrode surface demonstrates that electrophoretic deposition is useful for
fabrication of organic thin films.
In order to evaluate the photoelectrochemical performance of the (MEH-PPV+C60)n,
we used the OTE/SnO2/(MEH-PPV+C60)n electrode as a photoanode in a
photoelectrochemical cell. Photocurrent measurements were performed in acetonitrile
containing NaI (0.5 M) and I2 (0.01 M) as redox electrolyte using a Pt gauge counter
electrode (Fig. 5).38) We also constructed an OTE/SnO2/(H2P+C60)n electrode to compare
the light energy conversion properties in the presence and absence of MEH-PPV (Fig. 5).
The photocurrent and photovoltage responses recorded following the excitation of
OTE/SnO2/(MEH-PPV+C60)n electrode are shown in Fig. 6A and B, respectively. The
photocurrent response is prompt, steady and reproducible during repeated on/off cycles of
the visible light illumination. The short circuit photocurrent density (isc) is 0.31 mA/cm2,
and open circuit voltage (Voc) is 220 mV were reproducibly obtained during these
measurements. Blank experiments conducted with OTE/SnO2 [i.e., by excluding
composite clusters: (MEH-PPV+C60)n] produced no detectable photocurrent under the
similar experimental conditions. These experiments confirmed the role of (MEH-
PPV+C60)n assemblies towards harvesting light energy and generating photocurrent
during the operation of a photoelectrochemical cell.
Fig. 5 and Fig. 6
We also evaluated the power characteristics of the photoelectrochemical cell by
varying the load resistance. A drop in the photovoltage and an increase in the
photocurrent are observed with decreasing the load resistance (Fig. 7). The fill factor
for the (MEH-PPV+C60)n-based photoelectrochemical cell was determined to be 0.40.
Net power conversion efficiency obtained for the same cell was 0.24% (input power: 11.2
mW/cm2). This value is ~7 times larger than 0.035% of OTE/SnO2/(H2P+C60)n (trace b).
In order to further evaluate the response of (MEH-PPV+C60)n clusters towards the
photocurrent generation a series of photocurrent action spectra were recorded and
compared against the (H2P+C60)n clusters. The photocurrent action spectrum of
OTE/SnO2/(MEH-PPV+C60)n produced by the electrodeposition of MEH-PPV and C60 is
shown in spectrum a of Fig. 8. The photocurrent action spectrum exhibits a broad
photoresponse, which approximately parallel the corresponding absorption spectrum.47)
The maximum IPCE value of OTE/SnO2/(MEH-PPV+C60)n attains 18% at 480 nm, which
is ~5 times larger than 4% of OTE/SnO2/(H2P+C60)n. Both the I-V characteristic (trace b
in Fig. 7) and the intensity dependence of the efficiency (spectrum b in Fig. 8) in
OTE/SnO2/(H2P+C60)n show that charge recombination and charge transport within the
nanostructure assembly is a major limiting factor in achieving higher photoconversion
efficiencies. However, we have recently reported that composite clusters of multi-
porphyrin arrays such as porphyrin alkanethiolate monolayer-protected gold
nanoparticles and fullerenes (C60), which were assembled on a nanostructured SnO2
electrode using a similar deposition technique, exhibited much enhanced light energy
conversion properties (h: ~1.5%) as compared with the non-organized systems
(0.035%).35,36) This drastic enhancement (~45 times) of the power conversion efficiency
is largely ascribed to the organization between donor and acceptor moieties on the
OTE/SnO2 electrode for the efficient initial photoinduced electron transfer.
3.3 Photoelectrochemical Properties of (MEH-PPV+C60)n and (H2P+C60)n
Assemblies-Modified Electrode using Three-Electrode System
The charge separation in the OTE/SnO2/(MEH-PPV+C60)n electrode assembly can
be further modulated by using them in a standard three-compartment cell as a working
electrode along with Pt wire gauze counter electrode and saturated calomel reference
electrode (SCE).48) Figure 9A shows I-V characteristics of the OTE/SnO2/(MEH-
PPV+C60)n electrode under the visible light illumination. The photocurrent increases as
the applied potential is scanned towards more positive potentials. Increased charge
separation and the facile transport of charge carriers under positive bias are responsible
for enhanced photocurrent generation. At potentials greater than +0.4 V vs. SCE direct
electrochemical oxidation of iodide interferes with the photocurrent measurement.
Since we can control the photocurrent generation property by applying bias to OTE/SnO2,
we have also optimized a photocurrent action spectrum of OTE/SnO2/(MEH-PPV+C60)n
under an applied bias potential of 0.2 V vs. SCE (spectrum a in Fig. 9B). The action
spectrum also shows a broad photoresponse and a maximum IPCE value of 25%. This
value is larger than the value measured in two electrode system (18%: spectrum b).
3.4 Photocurrent Generation Mechanism
The photoinduced charge separation processes in MEH-PPV-C60 and H2P-C60 are
already established.35,49,50) The primary process responsible for the photocurrent
generation is the photoinduced charge separation between the excited state of MEH-PPV
or H2P38) to C60 (C60/C60
•– = -0.2 V vs NHE) in the donor mieties-C60 supramolecular
complex. This electron transfer process within the aggregated cluster is fast compared
to the direct electron injection to the conduction band of SnO2 (0 V vs NHE) system. As
the reduced C60 injects electrons into the SnO2 nanocrystallites, the oxidized MEH-PPV
(MEH-PPV/MEH-PPV•+ = 1.0 vs NHE)51) or H2P (H2P/H2P•+ = 1.2 V vs NHE) undergoes
electron transfer with iodide ion (I3
-/I- = 0.5 V vs NHE) in the electrolyte.38) Such a
photocurrent generation mechanism is consistent with the earlier reported reaction
scheme involving organized donor-acceptor assemblies.35,36,48)
The supramolecular assemblies of fullerene-based composites composed of MEH-
PPV provide useful systems for fulfilling an enhanced light-harvesting efficiency of
chromophores throughout the solar spectrum and a highly efficient conversion of the
harvested light into the high energy state of the charge separation by photoinduced
electron transfer. Especially, the structure of (MEH-PPV+C60)n has well-controlled size
and shape as compared to that of (H2P+C60)n. The photoelectrochemical behavior of
OTE/SnO2/(MEH-PPV+C60)n also exhibits much enhancement as compared to those of
(H2P+C60)n. Such systems based on supramolecular approach have promising
perspective for the development of efficient light energy conversion devices.
This work was partially supported by Grant–in–Aids for Scientific Research (No.
19710119 to T.H.) and special coordination funds for promoting science and technology
from the Ministry of Education, Culture, Sports, Science and Technology, Japan. T.H.
also acknowledges the partial support from Kao Foundation for Arts and Sciences,
Iketani Science and Technology Foundation, and Kansai Research Foundation for
Technology Promotion. P.V.K. acknowledges the support from the Office of Basic
Energy Science of the U.S. Department of Energy. This is contribution no. NDRL 4734
from the Notre Dame Radiation Laboratory.
Fig. 1 Molecular structures of MEH-PPV and H2P used in this study.
300 400500 600700 800
Fig. 2 (A) Absorption spectra of (a) (MEH-PPV+C60)n in acetonitrile/toluene (3/1, v/v).
The weight % ratio of MEH-PPV : C60 is ~ 1 : 4; [C60] = 0.31 mM. (b) C60 (75 mM) in
toluene and (c) MEH-PPV in toluene. (B) Absorption spectra of (a) (H2P+C60)n in
acetonitrile/toluene (3/1, v/v); [H2P] = 0.19 mM and [C60] = 0.31 mM, (b) C60 (75 mM)
in toluene and (c) H2P (11 mM) in toluene.
Fig. 3 Transmission electron micrograph (TEM) images of (A) (MEH-PPV+C60)n and
Fig. 4 Absorption spectrum of OTE/SnO2/(MEH-PPV+C60)n film.
OTE: Optically Transparent Electrode
Fig. 5 Operation of a photochemical solar cell using molecular assembly of MEH-PPV
and C60 [(MEH-PPV+C60)n], and schematic illustrations of (MEH-PPV+C60)n and
(H2P+C60)n as the photoactive layers.
0.1 mA cm-2
On OffOn OffOn Off
Fig. 6 (A) Photocurrent response and (B) photovoltage response of OTE/SnO2/(MEH-
PPV+C60)n electrode prepared from cluster solution of ([C60] = 0.31 mM: weight % ratio
of MEH-PPV : C60 is ~ 1 : 4 ) to visible light illumination (l > 400 nm); electrolyte: 0.5
M NaI and 0.01M I2 in acetonitrile; Input Power: 11.2 mW cm-2.
0 0.05 0.10 0.15 0.20 0.25 0.30 0.35
Photocurrent, mA cm-2
Fig. 7 Power characteristic of the photoelectrochemical cell under white light (l > 400
nm) illumination. Electrodes: (a) OTE/SnO2/(MEH-PPV+C60)n, (b) OTE/SnO2/(H2P+C60)n
and Pt counter electrode, Electrolyte: 0.5 M NaI and 0.01M I2 in acetonitrile, Input
power: 11.2 mW/cm2.
Fig. 8 The photocurrent action spectra (presented in terms of % IPCE) of (a)
OTE/SnO2/(MEH-PPV+C60)n electrode and (b) OTE/SnO2/(H2P+C60)n electrode.
Electrolyte: 0.5 M NaI and 0.01M I2 in acetonitrile.
Voltage, V vs. SCE
Current, mA cm-2
Fig. 9 (A) I-V characteristics of OTE/SnO2/(MEH-PPV+C60)n electrode using saturated
calomel reference electrode (SCE) under white light (l > 400 nm) illumination;
electrolyte: 0.5 M NaI and 0.01M I2 in acetonitrile, input power: 11.2 mW/cm2. (B) The
photocurrent action spectra of (a) OTE/SnO2/(MEH-PPV+C60)n electrode (a) at an applied
bias of 0.2 V vs. SCE and (b) with no applied bias potential. Electrolyte: 0.5 M NaI and
0.01M I2 in acetonitrile.
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The broadness of absorption property of OTE/SnO2/(MEH-PPV+C60)n in long
wavelength region relative to that in acetonitrile/toluene (3/1, v/v) is due to
In photoelectrochemical measurement of OTE/SnO2/(MEH-PPV+C60)n, thin film
is excited from the backside of an active layer of (MEH-PPV+C60)n as shown in
Fig. 5. The difference between photocurrent action and absorption spectra of
OTE/SnO2/(MEH-PPV+C60) is likely ascribed to the complementary behavior
between absorption of SnO2 colloids (short wavelength) and scattering effects
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