Broadening the absorption of conjugated polymers by "click" functionalization with phthalocyanines

Article abstract of DOI:10.1039/c0dt01348j

Conjugated copolymer derivatives of poly[2-methoxy-5-(3′,7′- dimethyloctyloxy)-1,4-phenylenevinylene] (MDMO-PPV) and poly(3-hexylthiophene) (P3HT) containing 10% of alkyne functionalities in the side chains have been prepared using the sulfinyl precursor

Full text of DOI:10.1039/c0dt01348j

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PAPER
Broadening the absorption of conjugated polymers by “click”
functionalization with phthalocyanines
Bert J. Campo,a Jan Duchateau,a Carolina R. Ganivet,b Beatriz Ballesteros,b Jan Gilot,c Martijn M. Wienk,c
Wibren D. Oosterbaan,a Laurence Lutsen,d Thomas J. Cleij,d Gema de la Torre,b Rene´ A. J. Janssen,*c
Dirk Vanderzande*a and Toma´s Torres*b,e
Received 6th October 2010, Accepted 18th February 2011
DOI: 10.1039/c0dt01348j
Conjugated copolymer derivatives of poly[2-methoxy-5-(3¢,7¢-dimethyloctyloxy)-1,4-phenylenevinylene]
(MDMO-PPV) and poly(3-hexylthiophene) (P3HT) containing 10% of alkyne functionalities in the
side chains have been prepared using the sulfinyl precursor route and the Rieke method, respectively.
With the aim of expanding the absorption range of these conjugated polymers for their use in bulk
heterojunction (BHJ) polymer:fullerene solar cells, appropriate phthalocyanine (Pc) molecules have
been covalently bound through a post-polymerization “click chemistry” reaction between the alkyne
functionalities in the side chains of the copolymers and a Pc functionalized with an azide moiety. The
resulting poly(p-phenylenevinylene)-Pc (PPV-Pc) material holds a 9 mol% content of Pcs, while the
polythiophene-Pc material (PT-Pc) contains a 8 mol% of Pc-functionalization in the side chains. As
expected, the presence of the Pc contributes to the extension of the absorption up to 700 nm. BHJ solar
cells have been prepared using PPV-Pc and PT-Pc materials in combination with PCBM. Although the
Pc absorption contributes to the generation of photocurrent, the overall power conversion efficiencies
(PCE) obtained from these cells are lower than those obtained with BHJ P3HT:PCBM (1 : 1) and
MDMO-PPV:PCBM (1 : 4) solar cells. A plausible explanation could be the moderate solubility of the
PPV-Pc and PT-Pc materials that limits the processing into thin films.
ester (PCBM) as the electron acceptor component in the active
Introduction
layer.
Polymer:fullerene bulk heterojunction (BHJ) solar cells are
Several chemical strategies have been applied to increase the
promising candidates as sources of renewable energy.1–3 A con-
tinuous improvement on the optoelectronic properties of the
efficiency in BHJ devices. For example, the open circuit voltage
(Voc) and short-circuit current density (Jsc) may be improved by
active materials and device processing has led to solar cells with
a fine-tuning of the donor and acceptor energy levels. In this
efficiencies over 7% today.4,5 Increasing the efficiency and lifetime
regard, one of the limitations of conventional P3HT and MDMO-
of the devices is a challenge that has to be met for potential
PPV polymers is their narrow absorption window: only light with
enough energy for electrons to cross the polymer band gap can be
examples of polymer:fullerene BHJ solar cells are those contain-
absorbed, that is, only a fraction of what is emitted by the sun.
successful commercialization of this type of solar cell.1 Often cited
ing semiconducting poly[2-methoxy-5-(3¢,7¢-dimethyloctyloxy)-
1,4-phenylenevinylene] (MDMO-PPV) or poly(3-hexylthiophene)
(P3HT) as electron donors, and phenyl-C61-butyric acid methyl
The solar emission spectrum ranges from the UV to the infrared,
with a maximum flux around 700 nm. In this regard, extending the
absorption of the polymeric material would, in principle, enhance
the absorption of the active layer in the device, thus leading to
higher short-circuit currents and efficiencies. In this regard, the so-
called low band gap polymers6,7 are candidates for better overlap
with the solar spectrum.
Here, we aim to broaden the absorption window of the polymer
material following a different approach, i.e. through the covalent
attachment to the side chains of the polymer backbone of a
dye molecule that absorbs longer wavelengths compared to the
conjugated polymer. Phthalocyanines (Pcs) are thermally and
chemically stable 18-p aromatic molecules showing an intense ab-
sorption in the red/near infrared (IR) region of the solar spectrum
aHasselt University, Campus Diepenbeek Institute for Materials Re-
search Agoralaan Building D, 3590, Diepenbeek, Belgium. E-mail: dirk.
vanderzande@uhasselt.be
bDepartamento de Qu´ımica Orga´nica, Universidad Auto´noma de Madrid,
28049, Madrid, Spain. E-mail: tomas.torres@uam.es
cMolecular Materials and Nanosystems, Eindhoven University of Technol-
ogy, 5600 MB, Eindhoven, The Netherlands. E-mail: r.a.j.jannssen@tue.nl
dDivision IMOMEC, IMEC, Wetenschapspark 1, 3590, Diepenbeek, Bel-
gium
eIMDEA-Nanociencia, Facultad de Ciencias, Cantoblanco, 28049, Madrid,
Spain
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(i.e. around 700 nm) with high extinction coefficients and fluo-
rescence quantum yields, which makes them ideal chromophores
to enhance the spectral coverage.8 In addition, Pcs are good p-
type semiconductors and present rich redox chemistry, which
can be modulated as a function of the peripheral substitution
and/or thecentral metalincluded in the aromaticcavity. Therefore,
once photoexcited, Pcs are capable of acting either as electron-
donors when they are connected to appropriate electron-acceptor
moieties such as fullerene derivatives,8–10 or as electron-acceptors
when linked to donor systems such as polythiophenes.11 All
these features render Pcs valuable photoactive materials for their
incorporation in planar heterojunction10,12 or bulk heterojunction
solar cells13 with fullerenes, as well as in dye sensitized solar
cells.14,15 As far as MDMO-PPV and P3HT absorb light with
wavelengths ranging from 400 to 600 nm, the incorporation of
Pc molecules absorbing from 600 to 700 nm to the active layer
will cause a broadening of the absorption range.16–18 Recently,
photoconversion properties extended more than 150 nm toward
longer wavelengths have been demonstrated on a P3HT/PCBM
blend mixed with a peripherally substituted octabutoxy H2Pc, as
compared to a device without such Pc-sensitization.17 Maximum
internal quantum efficiencies of ca. 40% were observed in the main
absorption region of the Pc (i.e. around 700 nm) for a 10 : 10 : 1
ratio of P3HT, PCBM and H2Pc, respectively. Another recent
work by H. Ohkita and coworkers reports a power conversion
efficiency (PCE) of 2.7% of annealed, spin-coated BHJ devices
containing a 10 : 10 : 1 ratio of P3HT, PCBM and a silicon(IV)
Pc derivative, a 20% larger value than the corresponding control
device without Pc-sensitization (i.e. 2.2%).18 The key issue of this
result is that the Si(IV)Pc derivative holds axially-linked, branched
hydrocarbon chains, which avoid the formation of Pc-aggregates
and therefore, permit the allocation of the Si(IV)Pc molecules at the
donor (P3HT)/acceptor (PCBM) interface. External quantum ef-
ficiency (EQE) measurements indicate that the Si(IV)Pc molecules
can contribute to the photocurrent generation by either direct
photoexcitation or as energy funnels for P3HT excitons at the
P3HT/PCBM interface.
In view of these results, we envision the covalent attachment
of Pc molecules at the side chains of P3HT and MDMO-PPV
conjugated copolymers, in a proper molar ratio (i.e. around a
10% content), as a plausible route to obtain higher photocurrents
and increased PCE in BHJ devices of these materials with
PCBM. An appropriate content of Pc molecules may lead to
enhanced photocurrent generation by photoexcitation of the Pcs;
in addition, the covalent binding of the Pcs to the polymer may
avoid the aggregation phenomena and enforce the Pcs to interact
with both the main chain of the semiconducting polymer and the
acceptor PCBM, thus allowing energy transfer from the polymer
to the Pc molecules and subsequent electron transfer from the
photoexcited Pc to PCBM.
To prepare these polythiophene-Pc (PT-Pc, Scheme 1) and
poly-p-phenylenevinylene-Pc (PV-Pc, Scheme 1) materials, a post-
polymerization procedure seems to be the most convenient
approach. One of the most reliable ways to perform this function-
alization is the well-known 1,3 Huisgen cycloaddition between
an azide and an alkyne functionality.19 This “click chemistry”
reaction proceeds with very high yields and has been largely
applied to the side-chain functionalization of polymers,20 and
also exploited with success for the derivatization of materials, for
example carbon nanotubes, with Pcs.21 Therefore, PPV and P3HT-
based alkynyl-terminated copolymers have to be prepared, and
further reacted with an unsymmetrically substituted Pc containing
solubilizing groups and one azide functionality. Following this
approach, a high degree of incorporation of Pc molecules to
the functionalized side-chains of the copolymer can be achieved.
Reasonable precursors of the alkynyl-terminated PPV and P3HT-
based copolymers are the corresponding materials holding lateral
chains with ester groups, which can be easily prepared following
reported procedures.22,23
Therefore, we have synthesized PPV and PT copolymers with
approximately 10% content of ester-functionalized alkyl side
chains. Basic hydrolysis of the ester and subsequent reaction with
propargyl alcohol leads to the corresponding alkynyl-terminated
materials, which can further react with azido-containing Pc
molecules to give PT-Pc and PPV-Pc coupled materials with
a broader absorption range compared to P3HT or MDMO-
PPV. The photovoltaic performance of these materials has been
studied in polymer:PCBM BHJ solar cells with several ratios of
PCBM.
Results and discussion
Synthesis and characterization
The synthesis of PPVs has been reported by several routes.22,24,25
In this particular case, the copolymerization reaction of the
MDMO monomer 1 and an ester-containing monomer 2 was
done using the sulfinyl precursor route (Scheme 1a), yielding the
non-conjugated derivative PPV-1.22 Although both monomers are
a mixture of regioisomers, for the sake of simplicity only one
isomer is depicted in Scheme 1a. Post-polymerization treatment of
PPV-1 with toluene and potassium tert-butoxide transformed the
ester functionality in the side chains of the conjugated copolymer
to a carboxylic acid (PPV-2), which was further reacted with
propargylic alcohol to give PPV-3. This copolymer contains 9%
of triple bonds, as determined by 1H-NMR. A detailed report on
the synthesis of these and other alkyne-functionalized PPVs will
be published elsewhere.26
The synthesis of poly(3-alkylthiophenes) has been achieved
using various synthetic routes.27,28 The synthesis of the ester-
containing copolymer PT-1, displayed in Scheme 1b, was carried
out using the previously reported Rieke method,23,29 which yields
copolymers having a regio-regularity of ca. 90%. After copolymer-
ization of thiophenes 3 and 4 to give PT-1, the ester functionalities
in the alkyl side chains were converted to the corresponding acid
functions in a 2 M NaOH solution in EtOH. The conversion of the
ester-functionalized copolymer PT-1 to the acid-functionalized
copolymer PT-2 was complete after stirring for 48 h under
reflux. The full conversion was evidenced in 1H-NMR by the
disappearance of the signal originating from the O–CH2 methylene
protons in the ester functionality. Additional proof is the shift of
the C O absorption in FT-IR from 1740 cm-1 to 1710 cm-1.
The acid functional groups were reacted in a second step with
propargyl alcohol using the DCC/DMAP protocol to give PT-
3.30 The presence of the triple bond at the end of the alkyl side
chains was confirmed in 1H-NMR by the signal originating from
the O–CH2-C CH methylene protons in the ester moiety; and
the presence of the acetylene proton is visible at d = 2.42 ppm. The
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Scheme 1 Synthesis of alkyne-containing (a) MDMO-PPV-type copolymer PPV-3 and (b) P3HT-based copolymer PT-3; (c) synthesis of
azido-functionalized phthalocyanine Pc-3.
1
C
O stretch on FT-IR shifts from 1710 cm-1 in the acid group
reaction with an excess sodium azide. H-NMR spectra of these
compounds confirms the successful transformation of the OH-
moiety into the bromo and azide functionalities through the
chemical shift of the adjacent methylene signal (from 4.75, to
4.99 and 4.61, respectively). The azido-containing Pc-3 shows the
typical N3 stretching band in FT-IR at 2093 cm-1. The UV-vis
spectrum of this macrocycle exhibits a B band at 350 nm and a
single Q band with a maximum at 675 nm.
to 1740 cm-1 in the ester group. The percentage of functionalized
side chains in this copolymer was calculated by integration of
1
the H-NMR signals from the O-CH2 (4.7 ppm) of the ester-
functionalized side chains and CH3 groups (0.89 ppm) of the
hexyl side chains. The relative ratios indicate that copolymer PT-3
contains 8% alkynyl moieties.
The synthesis of the azido-phthalocyanine Pc-3 is depicted
in Scheme 1c. First, the statistical cyclotetramerization reac-
tion of 4-tert-butylphthalonitrile and 4-(4-hydroxymethylphenyl)-
phthalonitrile31 in a 3 : 1 ratio in the presence of Zn(OAc)2 afforded
the Zn(II)Pc precursor Pc-1. Bromination of this Pc using CBr4
gave Pc-2, which was converted to the azide derivative Pc-3 by
The reaction conditions for the polymer-Pc coupling via
“click chemistry” (Scheme 2) were adapted from literature
procedures.32 In order to maximize the number of Pc molecules
incorporated to the polymer, different Cu(I) salts, N-ligands
and Pc ratios were tested. Finally, the use of 2 equivalents of
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corresponding polymer (i.e. PPV-3 or PT-3) and 2 eq. of Pc-3
were dissolved in degassed THF, and then CuBr and PMDETA
were added under nitrogen flow. After work up and purification,
the reaction mixture was spotted on a TLC plate and eluted
in a THF–hexane (1 : 2) mixture. Since the resulting polymer
materials PPV-Pc and PT-Pc do not elute on the TLC plate,
the visible spots with retention factor (Rf) > 0 are due to the
smaller molecules present in the reaction mixture. Bright blue
Pc spots were visible for both experiments before purification.
After work up and purification by rinsing with acetone, no blue
spots were visible in TLC, a positive verification of removal of all
non-reacted Pc molecules. UV-Vis spectroscopy measurements in
solution of PPV-Pc and PT-Pc displayed the polymer absorption
with a maximum around 450 nm for the PT-containing material,
and a maximum at 500 nm for the PPV one, and, in both cases,
the absorption at 675 nm of the covalently bound Pc (Fig. 1).
The proof that conversion of the C C bonds towards the 1,4-
disubstituted-1,2,3-triazole moiety was fully achieved is provided
1
by the H-NMR spectrum of PT-Pc and PPV-Pc. The signal of
Scheme 2 Schematic representation of the “click” reaction of copolymers
PPV-3 and PT-3 with Pc-3 to obtain PPV-Pc and PT-Pc, respectively.
the methylene protons next to the alkyne function at d = 4.7 ppm
completely disappears, indicating that all present alkyne moieties
have reacted with a Pc molecule. Instead, new resonances of the
two different methylene moieties close to the triazole are visible in
the range of d = 5.0–5.7 ppm. In both materials, signals originating
from the incorporated Pc units are visible in the aromatic region
Pc-3 (with respect to the number of acetylene moieties present
in the copolymers), CuBr (0.1 eq) and N,N,N ¢,N¢,N¢¢,N¢¢,N¢¢¢-
pentamethyldiethylenetriamine (PMDETA) (0.1 eq) were found
to be optimum conditions for our proposed reaction. Thus, the
Fig. 1 UV-Vis absorption of (a) a solution of PPV-Pc in THF (squares) and in CB (triangles); (b) a film of PPV-3 drop-cast from a solution in THF
(squares) and films of PPV-Pc drop-cast from solution in CB (triangles) or THF (circles); (c) PT-Pc in solutions of CB (triangles) and THF (black line);
(d) films drop-cast from a solution in CB (P3HT: squares, and PT-Pc: triangles) and drop-cast from a solution in THF (PT-Pc: circles).
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between d = 7.5 and 8 ppm, together with the signal of the triazole
ring.
a better stacking of the PT chains.34 Therefore, THF seems to be
a better solvent than CB to induce a better organization of the
polymer chains in the film: THF appears to minimize the impact
of the large Pc molecules in the alkyl side chains on the structural
ordering of the polymer chains.
UV-Vis spectroscopy measurements
The UV-Vis absorption spectra of PPV-Pc solutions in THF
and chlorobenzene (CB) are displayed in Fig. 1a. The absorption
between 400 and 550 nm with wavelength of maximum absorption
(lmax) around 510 nm is due to the conjugated backbone of the
PPV, while the absorptions at ca. 350 nm and between 650 and
700 nm is due, respectively, to the Soret and Q band absorptions
of the Pc molecules covalently bound to the side chains. In THF
and CB, the lmax of the Q band is at 676 nm and 691 nm,
respectively. Red-sifting of the Q band in solutions of Pcs in
aromatic solvents has been previously observed and rationalized
in terms of stabilization of the LUMO level of the Pc through
coordination of the aromatic solvent. In fact, precursor azido-
phthalocyanine Pc-3 shows a lmax of its Q band in CB at 684 nm,
whereas this Pc exhibits a lmax at 675 in THF solution. A solvent-
induced interaction between the Pc moiety and the conjugated
PPV backbone can explain the additional red-shifting observed in
CB solution of PPV-Pc with regard to that of Pc-3.
In Fig. 1b, the UV-Vis spectra of alkyne-functionalized PPV-
3 and PPV-Pc in film are given. The absorption of PPV-3 is
comparable to the absorption of MDMO-PPV between 400 and
550 nm with lmax at 512 nm. In the PPV-Pc film, the Pc absorption
is visible with lmax at 692 nm, while the lmax of the PPV decreases
to 494 nm. The shift to lower wavelengths of the PPV absorption
in PPV-Pc as compared to PPV-3 indicates that the presence
of the Pc in the side chains disturbs the polymer organization
and lowers effective conjugation length. The lmax of the Pc Q
band in the PPV-Pc film almost coincides with that obtained
in CB solution, this fact being an indication of the interaction
between the conjugated PPV backbone and the Pc molecules,
which produces a stabilization of the LUMO level of the Pc as
in the case of dilution in aromatic solvents.
Cyclic voltammetry
Electrochemical data (V vs. Fc/Fc+) of the redox process of Pc-
2, which was used as reference compound, were obtained from
cyclic voltammetry. The measured potentials in o-DCB solution
(1 mol dm-3 TBAPF6) of the onsets of the redox waves for Pc-2
1
1
2
were: Ered = -1.373 V, Eox = 0.005 V, and Eox = 0.749 V. The
first oxidation and reduction potential are used to estimate the
energy of the HOMO and LUMO levels using Fc/Fc+ = -5.23
eV with respect to the vacuum level.35 The HOMO and LUMO
energy levels of Pc-2 were found to be -5.2 eV and -3.9 eV,
respectively. In Fig. 2, the energy levels of Pc-2 are schematically
represented in comparison with those determined for MDMO-
PPV, P3HT, and PCBM in a similar way. Considering the relative
position of the LUMO levels, the Pc molecules could, apart from
acting as an absorber, also act as an electron acceptor relative to
P3HT and as an electron donor relative to PCBM. The same
situation applies to the combination with MDMO-PPV. The
fact that the HOMO level of Pc-2 is similar to that of P3HT
and MDMO-PPV is advantageous as the Pc molecule in PT-
Pc and Pc-PPV will not act as a hole trap. In addition, the
small HOMO-HOMO offset will likely result in energy transfer
from the PT and PPV polymers to the Pc molecule, followed
by electron transfer to PCBM. These events are plausible, since
photoexcited charge transfer from the Pc component to C60 or
PCBM has been widely demonstrated in many different device
configurations, even in P3HT/PCBM BHJ solar cells containing
a 10% of free, unsubstituted Pc chromophore.17,18 On the other
hand, some previous studies performed by us in solution of related,
covalent PPV-Pc short oligomers reveal a photosensitization of the
Pc units when exciting the PPV chains.36
The absorption spectra of PT-Pc solutions in THF and CB are
displayed in Fig. 1c. The PT absorption has a lmax around 450 nm.
The contribution of the Pc in the absorption is visible at ca. 350 nm,
and between 600 and 700 nm, with lmax around 675 nm. In THF
solution, the Pc absorption appears at lmax 677 nm, while in CB
solution the lmax of the Pc was at 691 nm for PT-Pc. The UV-Vis
spectra of PT-Pcfilms drop-cast from solutions in CB and THF are
displayed in Fig. 1d, together with the absorption of regio-regular
P3HT in CB. Although the spectra are affected by scattering, they
show that, compared to the absorption in solution, the absorption
of the polymer backbone in PT-Pc broadens relative to the Q
band of the Pc component, as a consequence of the p–p stacking
of the conjugated chains of the PT part. The PT absorption is also
red-shifted compared to the spectrum in solution, with maximum
absorptions at 523 nm for the film drop-cast from CB and 564 nm
for the film drop-cast from THF, respectively. The absorption at
600 nm in both THF- and CB-drop-casted films is due to the
ordering of regio-regular PT chains.33 The contribution of the
absorption in the visible of the Pc moiety was found at around
690 nm. The higher lmax, together with the higher relative intensity
of the shoulder at 600 nm of the polymeric backbone in the film
drop-cast from THF compared to the corresponding values of the
film drop-cast from CB, seem to indicate that the former presents
Fig. 2 Energy scheme of the absorbing materials in PT-Pc:PCBM and
PPV-Pc:PCBM solar cells.
BHJ solar cells fabrication and characterization
PT-Pc copolymers were mixed in polymer:PCBM 1 : 1 and 1 : 2
(w/w) blends, and PPV-Pc in 1 : 4 blends. Mixed solutions in
CB were spin-coated at several spinning speeds to obtain varying
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Fig. 3 EQE of solar cells with (a) PPV-Pc:PCBM (1 : 4) active layer or (b) PT-Pc in blends with PCBM in a (1 : 1) and (1 : 2) weight ratio; and J–V curve
of ITO/PEDOT:PSS (~50 nm)/polymer:PCBM/LiF/Al devices with (c) PPV-3:PCBM (1 : 4) (squares) and PPV-Pc:PCBM (triangles); (d) PT-1:PCBM
(1 : 1) (squares) and PT-Pc:PCBM (1 : 2) (triangles).
active layer thicknesses. Therefore, devices with a configuration
ITO/PEDOT:PSS/polymer:PCBM/LiF/Al were prepared. As
mentioned above, THF seems to be the best solvent to induce
structural order of the polymer chains in the film, at least in the
case of PT-Pc. However, the use of CB is compulsory to dissolve a
sufficient amount of PCBM. In CHCl3 or THF, PCBM could not
be dissolved completely and layers spin-coated from solutions of
PT-Pc or PPV-Pc and PCBM in these solvents were rough, and
the corresponding devices were of low-efficiency or shunted.
polythiophene:PCBM also indicates a lack of crystalline ordering
of the PT part in spin-coated films as compared to drop cast films
(Fig. 1d), which is important for high conversion efficiencies in
P3HT:PCBM solar cells.
Device performances
The best PPV-3:PCBM and PPV-Pc:PCBM solar cells are dis-
played in Fig. 3c, and the device parameters of the solar cells
of each copolymer are given in Table 1. The performance of
devices with PPV-3 is quite comparable to what is reported for
MDMO-PPV:PCBM (1 : 4) BHJ solar cells.37 The presence of
10% of alkyne functionalized side chains has little or no effect
in the device, and thus, a PCE of 2.2% was achieved. In solar cells
with PPV-Pc:PCBM (1 : 4) blends, however, there is a decrease
in Jsc, Voc and fill factor (FF). The detrimental effect of the Pc
molecule on the solubility of the polymer in CB could be largely
responsible for the poor device performance, since it causes a poor
polymer organization, as was evidenced in the UV-Vis spectrum
(see Fig. 1b). This will cause an unfavourable morphology and
lower hole mobility in the blend, and consequently, low Jsc and
FF. The decrease in Voc could be due to device defects.
Photocurrent generation
In the spectral response of BHJ solar cells with a PPV-Pc:PCBM
(1 : 4) active layer (Fig. 3a), there is a clear contribution in the
EQE of the covalently bound Pc molecules. The contribution of
the PPV backbone is visible around 500 nm, and that of the Pc
around 700 nm. Comparing the EQE with the UV-Vis absorption
spectrum of a PPV-Pc film, the absorption peaks of the PPV
backbone and the Pc remain at the same wavelength: however,
the height of the Pc peak relative to the PPV signal differs. In the
spectral response the relative intensity of the Pc Q-band is higher.
Also in the spectral response of PT-Pc:PCBM solar cells
(Fig. 3b), the EQE due to the Pc component is clearly present
around 700 nm, indicating that the light absorbed by the Pc
moiety leads to charge transfer, and the generated charges are
extracted. The low values of the EQE between 350–550 nm, due to
The J–V curves of the best PT-1:PCBM and PT-Pc:PCBM
solar cells are shown in Fig. 3d. The performance of the device
PT-1 as donor component was comparable to the performance of
P3HT:PCBM solar cells prepared following the same procedure.29
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Table 1 Solar cell characteristics of the best devices of each poly-
mixed-B columns (10 mm, 30 cm ¥ 7.5 mm) Polymer Labs and a
◦
mer:PCBM combination
Shodex refractive index detector at 40 C in THF at a flow rate
of 1.0 ml min-1 were used. Molecular weight distributions were
measured relative to polystyrene standards and toluene was used
as a flow rate marker.
Layer
thickness
PCE (%) (nm)
Polymer:PCBM Jsc (mA cm-2) Voc (V) FF
Electrochemical measurements were performed at room tem-
perature under an inert atmosphere with a scan rate of 0.1 V s-1,
using 1 M tetrabutylammonium hexafluorophosphate in o-DCB
as the electrolyte. The working electrode was a platinum disk and
the counter electrode was a silver rod electrode. A silver wire
coated with silver chloride (Ag/AgCl) was used as quasi-reference
electrode in combination with Fc/Fc+ as internal standard. The
vacuum level of Fc/Fc+ is assumed at -5.23 eV. Solar cells were
made on glass substrates (3 ¥ 3 cm) with patterned ITO electrodes.
The substrates were sonicated in acetone, cleaned with soapy
water and isopropanol and treated with UV/O3 for 15 min. Typi-
cally, 50 nm poly(ethylenedioxythiophene): poly(styrenesulfonate)
(PEDOT: PSS) (CleviosTM P VP AI 4083, HC Starck) was
spin-coated at 3000 rpm. 1.0 wt% and 1.5 wt% solutions of
PCBM in chlorobenzene were added to the polymer in (1 : 1)
and (1 : 2) (w/w) ratios respectively. The solutions were stirred
at 50 ◦C before they were spin-coated at several spinning speeds to
investigate the influence of active layer thickness. The preparation
of P3HT:PCBM solar cells was with P3HT obtained from Rieke
Metals. 1 nm of LiF and 100 nm of Al were evaporated in
high vacuum (p = 10-7 mbar). J–V curves were measured under
simulated solar light (100 mW cm-2) from a tungsten-halogen lamp
filtered by a Schott GG385 UV filter and a Hoya LB120 daylight
filter using a Keithley 2400 source meter. Spectral response was
measured with monochromatic light from a 50 W tungsten halogen
lamp (Philips focusline) in combination with a monochromator
(Oriel, Cornerstone 130) and a lock-in amplifier (Stanford research
Systems SR830). A calibrated Si cell was used as reference.
The device was kept behind a quartz window in a nitrogen
filled container. To measure the cell under appropriate operation
conditions, the cell was illuminated by a bias light from a 532 nm
solid state laser (Edmund Optics).
PT-1 (1 : 1)
5.81
1.79
1.46
4.25
3.36
0.65
0.67
0.68
0.85
0.66
0.49 1.86
73
42
33
80
PT-Pc (1 : 2)
PT-Pc (1 : 1)
PPV-3 (1 : 4)
PPV-Pc (1 : 4)
0.34 0.41
0.33 0.32
0.62 2.22
0.35 0.77
100
The best performing PT-Pc:PCBM solar cells (Table 1) were
obtained using a relatively thin layer (42 nm). Better current
densities and efficiencies were achieved with higher amounts of
PCBM. The low Jsc values of PT-Pc:PCBM solar cells compared
to P3HT:PCBM solar cells, together with the fact that the best
current densities were obtained for very thin layers (thickness <
50 nm), indicated that the charge transport properties in the
blend were unfavourable. The low FF of the devices and the
need of more PCBM to improve the extraction of charges indicate
that also the morphology of the blended layer is poor. Thermal
treatment of P3HT:PCBM solar cells has been reported to result
in better hole transport in the polymer phase because of closer
stacking of the conjugated polymer backbones and a phase
separated morphology.38 However, annealing treatments of the
PT-Pc devices did not lead to better results. The Pc molecules in the
side chains may prevent the PT chains from self-organizing, this
fact explains why no better results are obtained after annealing. A
better p–p stacking would be obtained by processing from THF,
but the solubility of PCBM in this solvent was too low for device
preparation. A better solubility in the processing solvent might
lead to an enhanced polymer organization in the blend and to an
improved morphology, both increasing the PCE.
Experimental
General
Synthesis of PPV and PT precursors
The preparation of monomers 2 and 4, the copolymerization
reactions to prepare PPV-1 and PT-1 and post-polymerization
transformations to give PPV-2 and PPV-3 will be reported
elsewhere. 1H-NMR spectra were recorded on a Varian Inova
300 spectrometer at 300 MHz in a 5 mm probe using deuterated
chloroform or tetrahydrofuran, obtained from Cambridge Isotope
Laboratories. Chemical shifts are reported in ppm downfield
from tetramethylsilane (TMS) using the peak of residual CHCl3
as an internal standard at d = 7.24 ppm in chloroform, or
the polythiophene aromatic proton peak at d = 6.96 ppm in
tetrahydrofuran. Fourier transform infrared spectroscopy (FT-
IR) was performed on a Perkin Elmer Spectrum One FT-IR
spectrometer using pellets in KBr or films drop-cast on a NaCl
disk from solution in chlorobenzene or tetrahydrofuran. Gas
chromatography/mass spectrometry (GC-MS) was carried out on
TSQ-70 and Voyager mass spectrometers. UV-Vis spectra were
recorded on a Varian CARY 500 UV-Vis-NIR spectrophotometer
from 200 to 800 nm at a scan rate of 600 nm min-1. Size exclusion
chromatography (SEC) was performed with a 1 wt% polymer
solution in THF, which was filtered with a 0.45 mm pore PTFE
syringe filter. A Spectra Physics P100 pump equipped with two
Poly([2-methoxy-5-(3¢,7¢-dimethyloctyloxy)-1,4-phenylenevinyl-
ene]-co-[2-methoxy-5-(6-(prop-2-yn-oxy carbonyl)hexyloxy)-1,4-
phenylenevinylene]) (PPV-3). Copolymer PPV-3 containing 9%
of akynyl-terminated side chains was obtained and characterized.
Characterization is given to enable interpretation of results. GPC
(THF): Mw = 380 000 g mol-1, Mw/Mn = 5.2; lmax(THF)/nm 507;
n
max/cm-1 3058, 2954, 2927, 2868, 1745, 1505, 1464, 1414, 1384,
1352, 1258, 1158, 1092, 1037, 969 and 860; dH(300 MHz; CDCl3)
7.6–7.4 (2 H, m, olef. H) 7.2–7.1 (2 H + 2 Hf , m, arH), 4.65 (2
Hf , s, OCH2), 4.1–3.8 (5 H + 5 Hf , m, OCH2, OCH3), 2.4 (2 Hf ,
m, CH2COO), 2.3 (2H + 2Hf , m, CH2CH2O) and 1.8–0.6 (15 H,
m, CHC C, CH, CH2 and CH3).
Poly([3-hexylthiophene-2,5-diyl]-co-[3-(6-ethoxycarbonylhexyl)-
thiophene-2,5-diyl]) (PT-1). Copolymer PT-1 containing 10%
of functionalized side chains was obtained and characterized.
Characterization is given to enable interpretation of results. GPC
(THF): Mw = 76 700 g mol-1, Mw/Mn = 1.9; lmax (Film)/nm
555 and 602(sh); nmax/cm-1 3053, 2954 s, 2925 vs, 2855 s, 1738,
1562, 1509, 1455, 1377, 1261, 1180 1094, 1030, 821 and 725;
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dH(300 MHz; CDCl3) 6.96 (1 H + 1 Hf , s, Th), 4.10 (2Hf , c,
OCH2), 2.79 (2 H, t, a-CH2), 2.56 (2 H + 2 Hf , t, a-CH2), 2.31 (2
Hf , t, CH2COOEt), 1.7 (2 H + 2 Hf , m, b-CH2), 1.5–1.2 (6 H +
4Hf , m, g, d, e-CH2) and 0.90 (3 H + 3 Hf , t, CH3).
with a saturated aqueous solution of NaHCO3, dried over
MgSO4, and vacuum concentrated. Purification by column
chromatography on silica gel with hexane/dioxane (3 : 1) as eluent
afforded Pc-2 as a blue solid (174 mg, 88%). Mp > 250 ◦C;
l
max(THF)/nm 675 (log e 5.3), 609 (4.6) and 350 (4.9); nmax/cm-1
Poly([3-hexylthiophene-2,5-diyl]-co-[3-(6-carboxyhexyl)thio-
phene-2,5-diyl]) (PT-2). 1.00 g of the 9/1 copolymer PT-1 was
stirred for 48 h in 100 ml of a 2 M NaOH solution in EtOH under
reflux. The mixture was poured out in a MeOH/2 M HCl mixture
and filtrated. The isolated copolymer was dried to obtain 0.95 g
(96%) of PT-2. GPC (THF): Mw = 51 000 g mol-1, Mw/Mn = 1.7;
2959, 1728, 1607, 1483, 1090, 1047, 831 and 764; dH(300 MHz;
DMSO) 9.4–8.9 (8 H, m, Pc-H), 8.4–8.1 (6 H, m, Pc-H and
phenyl-H), 7.8–7.7 (2 H, m, phenyl-H), 4.99 (2 H, s, CH2Br)
and 1.80 (27 H, s, C(CH3)3); m/z (MALDI-TOF) 912–919,
C51H45BrN8Zn (912.22).
n
max/cm-1 2954, 2924, 2853, 1710, 1635, 1507, 1457, 1377, 1261,
Zinc(II)
2,9,16–tri-tert-butyl-23-(4¢-azidomethyl
phenyl)
1077, 820, 803 and 725; dH(300 MHz; CDCl3) 6.96 (1 H + 1 Hf , s,
Th), 2.79 (2 H, t, a-CH2), 2.56 (2 H + 2 Hf , t, a-CH2), 2.37 (2 Hf ,
m, CH2COOH), 1.7 (2 H + 2 Hf , m, b-CH2), 1.4, 1.3 and 1.2 (6
H + 4 Hf , m, g, d, e-CH2) and 0.90 (3 H, CH3).
phthalocyaninato(2-)- N29, N30, N31, N32 (Pc-3) (only one
regioisomer is named). Sodium azide (1.21 g, 18.6 mmol) and
Pc-2 (0.170 g, 0.186 mmol) were dissolved in DMF–H2O (10 : 1)
(22 mL) and heated to 70 ◦C for 4 h. After cooling down to room
temperature, the solvent was removed and the crude was extracted
with CH2Cl2 and dried over Na2SO4. Solvent was evaporated and
the resulting solid filtered and washed with hexane to give Pc-3
as a blue solid (0.149 g, 91%). Mp > 250 ◦C; lmax(THF)/nm 675
(log e 5.6), 609 (4.9) and 350(5.2); nmax/cm-1 2959, 2093 (N3),
1728, 1607, 1483, 1090, 1047, 831 and 764; dH(300 MHz; THF)
9.5–9.1 (9 H, m, arom. H), 8.4–8.1 (7 H, m, arom. H), 4.61 (2
H, s, CH2N3) and 1.84 (27 H, s, C(CH3)3); m/z (MALDI-TOF)
875–882, C51H45N11Zn (875.32).
Poly([3-hexylthiophene-2,5-diyl]-co-[3-(6-(prop-2-yn-oxycar-
bonyl)hexyl)thiophene-2,5-diyl]) (PT-3). 100 mg of the (x/y)
0.90/0.10 acid functionalized polymer PT-2 was dissolved in
chlorobenzene before addition of propargylic alcohol (90 mg),
DCC (80 mg) and DMAP (4 mg). The reaction was stirred for
48 h at 50 ◦C. The mixture was precipitated in MeOH, stirred
for 1 h and filtrated to obtain 60 mg of the alkyne-functionalized
copolymer PT-3 with x/y = 0.92/0.08. GPC (THF): Mw = 31 800 g
mol-1, Mw/Mn = 1.9; nmax/cm-1 3055, 2956 s, 2926 vs, 2855 s, 1746,
1656, 1562, 1509, 1455, 1377, 1261, 1156, 1092, 1021, 820, 801 and
725; dH(300 MHz; CDCl3) 6.96 (1 H + 1 Hf , s, Th), 4.65 (2 Hf , s,
OCH2), 2.78 (2 H, t, a-CH2), 2.54 (2 H + 2 Hf , t, a-CH2), 2.42
(1 Hf , s, CHC C), 2.37 (2 Hf , t, CH2COOR), 1.7, 1.4 and 1.3 (8
H + 6 Hf , m, b, g, d, e-CH2) and 0.89 (3 H, t, CH3).
Synthesis of PPV-Pc and PT-Pc
General procedure. Dry THF was degassed by sonicating while
an argon flow was sent continuously through the solvent. The
polymer was dissolved in THF by stirring at 50 ◦C, before adding
Pc-3 and other reagents. Equivalents were calculated relative
to the number of alkyne functions present in the copolymer.
The reactions were stirred in the dark under reflux and inert
atmosphere. CuBr (0.1 eq) and PMDETA (0.1 eq.) were added
to the polymer with 2 eq. of Pc-3 in THF (10 mL). The work-up
was carried out by filtering the reaction over Al2O3 and washing
with THF and CH2Cl2 (PPV-Pc) or CHCl3 (PT-Pc). Subsequently,
the total volume was reduced to 15 mL by evaporation under
reduced pressure and the resulting solution was precipitated
dropwise in MeOH. The resulting copolymer was filtered off,
washed extensively with MeOH and acetone and dried at room
temperature under reduced pressure.
Synthesis of phthalocyanine precursors
Zinc(II) 2,9,16–tri-tert-butyl-23-(4¢-hydroxymethyl phenyl)
phthalocyaninato(2-)- N29, N30, N31, N32 (Pc-1) (only one
regioisomer is named). 4-tert-butylphthalonitrile (709 mg, 3.84
mmol), 4-(4¢-hydroxymethylphenyl) phthalonitrile31 (300 mg, 1.28
mmol) and Zn(OAc)2 (305 mg, 1.66 mmol) in DMAE (5 mL)
were stirred at 110 ◦C under argon atmosphere for 16 h. After
cooling to room temperature, the reaction mixture was treated
with MeOH–H2O (3 : 1) (15 mL), and the solid obtained was
filtered, washed with MeOH and vacuum-dried. The resulting
blue solid was purified by column chromatography on silica
gel using hexane/dioxane (2 : 1) as eluent. The symmetrically
tert-butyl substituted phthalocyanine was firstly eluted followed
by the unsymmetrically derivative Pc-1. The latter was obtained
as a blue solid (250 mg, 25%). Mp > 250 ◦C; lmax(THF)/nm 675
(log e 5.3), 609 (4.5) and 350 (4.8); nmax/cm-1 2959, 1728, 1607,
1483, 1090, 1047, 831 and 764; dH(300 MHz; DMSO) 9.4–8.9 (8
H, m; Pc-H), 8.4–8.1 (6 H, m, Pc-H and phenyl-H), 7.8–7.7 (2
H, m, phenyl-H), 5.45 (1 H, s, CH2OH), 4.75 (2 H, s, CH2OH)
and 1.81 (27 H, s, C(CH3)3); m/z (MALDI-TOF) 850-857,
C51H46N8OZn (850.31).
PPV-Pc. PPV-3 (50 mg) was dissolved before adding Pc-3
(31 mg, 0.036 mmol), distilled PMDETA (0.3 mg, 0.0017 mmol)
and Cu(I)Br (0.3 mg, 0.0020 mmol). After purification, PPV-Pc
(60 mg) was isolated. GPC (THF): Mw = 302 000 g mol-1, Mw/Mn =
4.0; lmax(THF)/nm 352, 509 and 676; lmax(CB)/nm 358, 510 and
691; lmax(Thin film)/nm 494 and 692; nmax/cm-1 3058, 2959, 2927,
2869, 1737, 1504, 1464, 1414, 1385, 1351, 1260, 1205, 1027, 970,
862 and 800; dH(300 MHz; THF) 9.58–9.38, 8.30, 8.11, 7.90, 7.55–
7.4, 7.3–7.1, 5.70, 5.21, 4.1–3.8, 2.4–2.3 and 1.8–0.7.
PT-Pc. PT-3 (60 mg) was dissolved, and Pc-3 (61 mg, 0.070
mmol), PMDETA (0.6 mg, 0.0035 mmol) and CuBr (0.5 mg,
0.0035 mmol) were subsequently added. After purification, PT-
Pc (36 mg) was isolated. GPC (THF): Iw = 58 600 g mol-1,
Mw/Mn = 1.8; lmax(THF)/nm 352, 459 and 677; lmax(CB)/nm
358, 458 and 691; lmax(Thin film, drop-cast from THF)/nm 564
and 694; lmax(Thin film, drop-cast from CB)/nm 523 and 692;
Zinc(II)
2,9,16–tri-tert-butyl-23-(4¢-bromomethyl
phenyl)
phthalocyaninato(2-)- N29, N30, N31, N32 (Pc-2) (only one
regioisomer is named). PPh3 (197 mg, 0.75 mmol) and CBr4
(249 mg, 0.75 mmol) were added to a solution of Pc-1 (200 mg,
0.23 mmol) in dry CH2Cl2 (8 mL) under an argon atmosphere.
◦
After stirring at 50 C for 1 h, the reaction mixture was washed
3986 | Dalton Trans., 2011, 40, 3979–3988
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©

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n
max/cm-1 2957 s, 2927 vs, 2856 s, 1739, 1644 br, 1511 w, 1487 w,
3 M. C. Scharber, D. Wuhlbacher, M. Koppe, P. Denk, C. Waldauf, A. J.
Heeger and C. L. Brabec, Adv. Mater., 2006, 18, 789.
4 M. A. Green, K. Emery, Y. Hishikawa and W. Warta, Progr. Photovolt.:
Res. Appl., 2009, 17, 320.
5 (a) Y. Y. Liang, D. Q. Feng, Y. Wu, S. T. Tsai, G. Li, C. Ray and L. P.
Yu, J. Am. Chem. Soc., 2009, 131, 7792; (b) C. Hsiang-Yu, H. Jianhui,
Z. Shaoqing, L. Yongye, Y. Guanwen, Y. Yang, Y. Luping, W. Yue
and L. Gang, Nat. Photonics, 2009, 3, 649; (c) Y. Liang, Z. Xu, J. Xia,
S.-T. Tsai, Y. Wu, G. Li, C. Ray and L. Yu, Adv. Mater., 2010, 22,
E135.
1456, 1390 w, 1363 w, 1331 w, 1261, 1231 w, 1186 w, 1152 w, 1092,
1048, 1024, 920, 820, 800 and 748; dH(300 MHz; THF) 8.14, 7.97,
7.76, 7.44, 7.35, 6.96, 6.89 6.83, 6.79, 5.60, 5.06, 2.80, 2.67, 2.40,
2.04, 1.91, 1.77, 1.34, 1.27 and 0.91.
Conclusions
6 C. Winder and N. S. Sariciftci, J. Mater. Chem., 2004, 14, 1077.
7 (a) J. Peet, J. Y. Kim, N. E. Coates, W. L. Ma, D. Moses, A. J. Heeger
and G. C. Bazan, Nat. Mater., 2007, 6, 497; (b) J. Hou, H.-Y. Chen, S.
Zhang, R. I. Chen, Y. Yang, Y. Wu and G. Li, J. Am. Chem. Soc., 2009,
131, 15586; (c) S. H. Park, A. Roy, S. Beaupre´, S. Cho, N. Coates, J. S.
Moon, D. Moses, M. Leclerc, K. Lee and A. J. Heeger, Nat. Photonics,
2009, 3, 297.
8 (a) G. de la Torre, C. G. Claessens and T. Torres, Chem. Commun., 2007,
2000; (b) Y. Rio, M. S. Rodr´ıguez-Morgade and T. Torres, Org. Biomol.
Chem., 2008, 6, 1877; (c) E. M. Maya, C. Garc´ıa, E. M. Garc´ıa-Frutos,
P. Va´zquez and T. Torres, J. Org. Chem., 2000, 65, 2733.
9 (a) A. de la Escosura, M. V. Martinez-Diaz, D. M. Guldi and T. Torres,
J. Am. Chem. Soc., 2006, 128, 4112; (b) M. Quintiliani, A. Kahnt,
T. Wolfle, W. Hieringer, P. Vazquez, A. Gorling, D. M. Guldi and T.
Torres, Chem.–Eur. J., 2008, 14, 3765; (c) B. Ballesteros, G. de la Torre,
A. Shaerer, A. Hausmann, M. A. Herranz, D. M. Guldi and T. Torres,
Chem.–Eur. J., 2010, 16, 114.
Conjugated polythiophene- and polyphenylenevinylene-type
copolymers decorated with Pc molecules (PT-Pc and PPV-Pc)
have been successfully synthesized by post-polymerization “click
chemistry” reactions. Copolymers containing ca. 10% alkyne func-
tions in the side chains (i.e. PT-3 and PPV-3) react with an azido-
functionalized Pc molecule (Pc-3) to yield the corresponding
Pc-containing polymers PPV-Pc and PT-Pc. Integration of the
1H-NMR signals of the alkyl side chains indicated that the Pc
content in the final copolymers is 8% in the case of PT-Pc, and
9% for the PPV-Pc material. These Pc-containing polymers were
applied in BHJ solar cells with PCBM in 1 : 4 blends for PPV-
Pc, and 1 : 1 and 1 : 2 blends for PT-Pc. The spectral response
showed, in both materials, a clear contribution of the Pc around
700 nm to the photocurrent, this fact indicating that the light
absorbed by the Pc moiety leads to charge transfer processes,
and that the generated charges are collected. Therefore, with
this approach we succeeded in broadening the absorption of the
active layer in polymer solar cells. However, solubility of the
materials in CB (the processing solvent) is not good enough
for a correct processing, especially in the case of PT-Pc, and,
therefore, the nanoscale organization of the materials in the active
layer is not appropriate to achieve efficient devices. Nevertheless,
continued efforts in materials design, namely, incorporation of
other peripheral substituents to the Pc core to enhance the
solubility of the final material and/or changes in the ratio of
covalently bound Pcs, can lead to better processed polymer-Pc
materials which could lead to more efficient devices.
10 G. Bottari, G. de la Torre, D. M. Guldi and T. Torres, Chem. Rev., 2010,
110, 6768.
11 M. V. Martinez-Diaz, S. Esperanza, A. de la Escosura, M. Catellani,
S. Yunus, S. Luzzati and T. Torres, Tetrahedron Lett., 2003, 44,
8475.
12 (a) J. Xue, S. Uchida, B. P. Rand and S. R. Forrest, Appl. Phys. Lett.,
2004, 84, 3013; (b) W.-B. Chen, H.-F. Xiang, Z.-X. Xu, B.-P. Yan,
V. A. L. Roy, C.-M. Che and P.-T. Lai, Appl. Phys. Lett., 2007, 91,
191109; (c) V. Kim, H. M. Haverinen, Z. Wang, S. Madakuni, Y. Kim,
J. Li and G. E. Jabbour, Chem. Mater., 2009, 21, 4256; (d) N. Li, B. E.
Lassiter, R. R. Lunt, G. Wei and S. R. Forrest, Appl. Phys. Lett., 2009,
94, 023307; (e) D. Placencia, W. N. Wang, R. C. Shallcross, K. W.
Nebesny, M. Brumbach and N. R. Armstrong, Adv. Funct. Mater.,
2009, 19, 1913; (f) Z. R. Hong, R. Lessmann, B. Maennig, Q. Huang,
K. Harada, M. Riede and K. Leo, J. Appl. Phys., 2009, 106, 064511;
(g) B. Yu, L. Huang, H. Wang and D. Yan, Adv. Mater., 2010, 22, 1017.
13 M. K. R. Fischer, I. Lopez-Duarte, M. M. Wienk, M. V. Martinez-
Diaz, R. A. J. Janssen, P. Bauerle and T. Torres, J. Am. Chem. Soc.,
2009, 131, 8669.
14 (a) M. V. Mart´ınez-D´ıaz, G. de la Torre and T. Torres, Chem. Commun.,
2010, 46, 7090; (b) M. V. Mart´ınez-D´ıaz, T. Torres, in Handbook of
Porphyrin Sciences, K. Kadish, K. M. Smith and R. Guilard, Vol 10, p.
141, World Scientific Press, 2010; (c) M. V. Mart´ınez-D´ıaz, M. Ince and
T. Torres, Monatsh. Chem., 2011, DOI: 10.1007/s00706-010-0431-0.
15 (a) J.-J. Cid, J. H. Yum, S.-R. Jang, M. K. Nazeeruddin, E. Mart´ınez-
Ferrero, E. Palomares, J. Ko, M. Gra¨tzel and T. Torres, Angew. Chem.,
Int. Ed., 2007, 46, 8358; (b) B. C. O’Regan, I. Lopez-Duarte, M. V.
Martinez-Diaz, A. Forneli, J. Albero, A. Morandeira, E. Palomares, T.
Torres and J. R. Durrant, J. Am. Chem. Soc., 2008, 130, 2906; (c) J. J.
Cid, M. G. Iglesias, J. H. Yum, A. Forneli, J. Albero, E. M. Ferrero, P.
Va´zquez, M. Gra¨tzel, M. K. Nazeeruddin, E. Palomares and T. Torres,
Chem.–Eur. J., 2009, 15, 5130; (d) M. Garc´ıa-Iglesias, J.-J. Cid, J.-H.
Yum, A. Forneli, P. Va´zquez, M. Kd. Nazeeruddin, E. Palomares, M.
Gra¨tzel and T. Torres, Energy Environ. Sci., 2011, 4, 189–194.
16 A. Ltaief, R. B. Chaabane, A. Bouazizi and J. Davenas, Mater. Sci.
Eng., C, 2006, 26, 344.
Acknowledgements
The authors gratefully acknowledge the funding of the Ph.D.
grant of B.J.C. by the Institute for the Promotion of Innovation
through Science and Technology in Flanders (IWT-Vlaanderen),
as well as the received support from the European Science
Foundation (ESF) for the activity entitled ‘New Generation of
Organic based Photovoltaic Devices’. This work was supported
by the European Union (SOLAR N-TYPE, MRTN CT-2006-
035533) and COST Action D35. Financial support by the MEC,
Spain (CTQ2008-00418/BQU, CONSOLIDER-INGENIO 2010
CDS 2007-00010, PLE2009-0070), and CAM (MADRISOLAR-
2, S2009/PPQ/1533) and the FWO (G.0685.06) is also gratefully
acknowledged. The research was further supported by the Euro-
pean Union (the European Regional Development Fund - ERDF)
in the Interreg IV-A project Organext.
17 E. M. J. Johansson, A. Yartsev, H. Rensmo and V. J. Sundstro¨m, J. Phys.
Chem. C, 2009, 113, 3014.
18 S. Honda, T. Nogami, H. Ohkita, H. Benten and S. Ito, ACS Appl.
Mater. Interfaces, 2009, 1, 804.
19 V. V. Rostovtsev, L. G. Green, V. V. Fokin and K. B. Sharpless, Angew.
Chem., Int. Ed., 2002, 41, 2596.
20 W. H. Binder and R. Sachsenhofer, Macromol. Rapid Commun., 2008,
29, 952.
Notes and references
21 (a) B. Ballesteros, G. de la Torre, C. Ehli, G. M. A. Rahman, F. Agullo-
Rueda, D. M. Guldi and T. Torres, J. Am. Chem. Soc., 2007, 129, 5061;
(b) S. Campidelli, B. Ballesteros, A. Filoramo, D. D. Diaz, G. de la
Torre, T. Torres, G. M. A. Rahman, C. Ehli, D. Kiessling, F. Werner,
1 G. Dennler, M. C. Scharber and C. J. Brabec, Adv. Mater., 2009, 21,
1323.
2 B. C. Thompson and J. M. J. Frechet, Angew. Chem., Int. Ed., 2008, 47,
58.
This journal is
The Royal Society of Chemistry 2011
Dalton Trans., 2011, 40, 3979–3988 | 3987
©

View Article Online
V. Sgobba, D. M. Guldi, C. Cioffi, M. Prato and J. P. Bourgoin, J. Am.
Chem. Soc., 2008, 130, 11503.
31 B. Ballesteros, S. Campidelli, G. de la Torre, C. Ehli, D. M. Guldi, M.
Prato and T. Torres, Chem. Commun., 2007, 2950.
32 T. L. Benanti, A. Kalaydjian and D. Venkataraman, Macromolecules,
2008, 41, 8312.
22 L. Lutsen, P. Adriaensens, H. Becker, A. J. Van Breemen, D. Van-
derzande and J. Gelan, Macromolecules, 1999, 32, 6517.
23 B. J. Campo, W. D. Oosterbaan, J. Gilot, T. J. Cleij, L. Lutsen, R. A. J.
Janssen and D. Vanderzande, Proceedings of SPIE, 2009, 7416.
24 H. G. Gilch and W. L. J. Wheelwright, J. Polym. Sci., Part A-1, 1966,
4, 1337.
33 P. J. Brown, D. S. Thomas, A. Ko¨hler, J. S. Wilson, J.-S. Kim, C. M.
Ramsdale, H. Sirringhaus and R. H. Friend, Phys. Rev. B: Condens.
Matter, 2003, 67, 064203.
34 F. C. J. Spano, Chem. Phys., 2005, 122, 234701.
25 R. A. Wessling, J. Polym. Sci., Polym. Symp., 1985, 72, 55.
26 J. Duchateau, L. Lutsen, D. Vanderzande, T. J. Cleij, unpublished
results.
27 I. Osaka and R. D. McCullough, Acc. Chem. Res., 2008, 41, 1202.
28 R. D. McCullough, Adv. Mater., 1998, 10, 93.
29 B. J. Campo, J. Gilot, H. J. Bolink, J. Zhao, J. C. Bolse´e, W. D.
Oosterbaan, S. Bertho, B. Ruttens, J. D’Haen, T. J. Cleij, J. Manca, L.
Lutsen, G. Van Assche, R. A. J. Janssen, D. Vanderzande, unpublished
results.
35 (a) J. O. M. Bockris, S. U. M. Khan, Surface Electrochemistry. A
Molecular Level Approach, Kluwer Academic/Plenum Publishers, New
York 1993; (b) V. V. Pavlishchuk and A. W. Addison, Inorg. Chim. Acta,
2000, 298, 97.
36 J.-J. Cid, C. Ehli, C. Atienza-Castellanos, A. Gouloumis, E. M. Maya,
P. Va´zquez, T. Torres and D. M. Guldi, Dalton Trans., 2009, 3955.
37 S. E. Shaheen, C. J. Brabec, N. S. Sariciftci, F. Padinger, T. Fromherz
and J. C. Hummelen, Appl. Phys. Lett., 2001, 78, 841.
38 R. Padinger, R. S. Rittberger and N. S. Sariciftci, Adv. Funct. Mater.,
2003, 13, 85.
30 B. Neises and W. Steglich, Angew. Chem. Int. Ed., 1973, 17, 522.
3988 | Dalton Trans., 2011, 40, 3979–3988
This journal is
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