Semiconductor amphiphilic block copolymers for hybrid donor-acceptor nanocomposites

Article abstract of DOI:10.1039/c2jm34033j

Block copolymers feature unique properties for organizing in a well-defined pattern on length scales of several tenths of nanometers. This special attribute enables the formation of ideal donor and acceptor domains for photovoltaic devices in the size of the exciton diffusion length. Thus we designed an amphiphilic block copolymer, able to act as a hole conductor and to coordinate inorganic semiconductor nanoparticles as electron acceptors. Utilizing controlled radical polymerization techniques, defined polymers were synthesized consisting of triphenylamine pendant groups in the hole conductor block and a hydrophilic polystyrene sulfonate block. This particular combination creates narrowly distributed micelles in aqueous solution exhibiting domain sizes suitable for photovoltaic applications. The strong anionic sulfonate groups offer high loading capacities for modified cationic nanoparticles. To guarantee a broad absorption and good conductivity, we synthesized cationic CdSe nanorods and combined them with our hole conductor micelles. The advantage of high loading combined with the processability from aqueous dispersions promises a novel green alternative for preparation of hybrid solar cells with controlled domain sizes in the desired length scale. The Royal Society of Chemistry 2012.

Full text of DOI:10.1039/c2jm34033j

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PAPER
Semiconductor amphiphilic block copolymers for hybrid donor–acceptor
nanocomposites†
*
Johannes C. Brendel, Hubertus Burchardt and Mukundan Thelakkat
Received 21st June 2012, Accepted 31st July 2012
DOI: 10.1039/c2jm34033j
Block copolymers feature unique properties for organizing in a well-defined pattern on length scales of
several tenths of nanometers. This special attribute enables the formation of ideal donor and acceptor
domains for photovoltaic devices in the size of the exciton diffusion length. Thus we designed an
amphiphilic block copolymer, able to act as a hole conductor and to coordinate inorganic
semiconductor nanoparticles as electron acceptors. Utilizing controlled radical polymerization
techniques, defined polymers were synthesized consisting of triphenylamine pendant groups in the hole
conductor block and a hydrophilic polystyrene sulfonate block. This particular combination creates
narrowly distributed micelles in aqueous solution exhibiting domain sizes suitable for photovoltaic
applications. The strong anionic sulfonate groups offer high loading capacities for modified cationic
nanoparticles. To guarantee a broad absorption and good conductivity, we synthesized cationic CdSe
nanorods and combined them with our hole conductor micelles. The advantage of high loading
combined with the processability from aqueous dispersions promises a novel ‘‘green’’ alternative for
preparation of hybrid solar cells with controlled domain sizes in the desired length scale.
equilibrium state. We and others have earlier shown the advan-
Introduction
tages of donor–acceptor BCPs, using perylene as an electron
acceptor.8,9 Here, the copolymer exhibited superior device effi-
ciencies compared to the corresponding blend.8,10 However, the
number of soluble, stable and efficient organic electron acceptors
is limited. Promising alternatives are n-type inorganic semi-
conductor nanoparticles, due to their high stability and electron
transport mobilities.11 Combinations of inorganic semi-
conductors in various shapes and forms are well studied in blend
devices with donor polymers.12 However due to the strong
tendency to aggregate high contents of nanoparticles are neces-
sary to guarantee good charge percolation pathways.13 While
blend devices of homopolymers and nanoparticles suffer from
the lack of control of morphology and interface, BCPs featuring
coordinative groups are able to organize the particles in micro-
phase domains.14 Here the amount of particles required can be
much less than in usual blends due to advantages of confine-
ment.15 This is the attractiveness of self-assembled systems
compared to usual blends. Despite the various detailed studies on
self-assembled hybrid materials,16–21 to our knowledge only a few
reports combine functional hole conductor BCPs with inorganic
semiconductors suitable for solar cell applications. Lechman
et al. prepared hybrid devices utilizing the amphiphilic polymer
poly(ethylene oxide)-b-polytriphenylamine (PEO-b-PTPA),
whereat titanium dioxide was hydrolyzed in the PEO-block using
sol–gel chemistry precursors.22 Secondly, hybrid structures could
be generated with poly(vinyl-N,N0-bis(4-methoxyphenyl)-
N,N0-diphenyl-(1,10-biphenyl)-4,40-diamine)-block-poly(4-vinyl-
pyridine) (PDMTPD-block-P4VP). CdSe nanoparticles could be
Considering the last few decades of research a countless number
of publications were presented on block copolymers (BCP), due
to their unique morphologies with nanoscale domain sizes and
highly ordered structures in bulk and solution.1,2 The self-
assembly process of these materials is considered to be ideal for
‘‘Bottom-up’’ approaches towards patterned functional thin
films.3,4
Referring to photovoltaic devices these unique properties
perfectly match the desired interface distance in the range of the
exciton diffusion length.5,6 However, the synthesis of functional
BCPs for highly efficient solar cells remains challenging. So far
only a few reports could prove the advantages of BCPs on solar
cells, including the stability of the equilibrated morphology and
improved device efficiency. Hashimoto and co-workers synthe-
sized stiff conjugated block copolymers of poly(3-hexylth-
iophene) (P3HT) and fullerenes attached to the side chains of a
second polythiophene block.7 As a result the stability of the
devices was preserved under long term annealing tests due to the
equilibrated morphology. In contrast blends of materials are
trapped in a non-equilibrium state and on a long time-scale the
morphology reaches an undesirable macrophase separated
Applied Functional Polymers, Macromolecular Chemistry I, University of
Bayreuth, 95440 Bayreuth, Germany. E-mail: mukundan.thelakkat@
uni-bayreuth.de; Fax: +49 921 553109; Tel: +49 921 553108
† Electronic supplementary information (ESI) available. See DOI:
10.1039/c2jm34033j
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selectively incorporated into the P4VP phase of the lamellar
morphology.23
Motivated by the requirement of novel materials for this
promising field, we synthesized the new amphiphilic BCP poly-
(bis(4-methoxyphenyl)-40-vinylphenylamine)-block-poly(tetra-
butylammonium styrene sulfonate) (PDMTPA-b-PBu4N+SS)
(Scheme 1).
PDMTPA is an amorphous hole conductor polymer that has
been well-studied by our group before.24 Hole mobilities up to
5 ꢀ 10ꢁ5 cm2 Vꢁ1 sꢁ1 were found.25 As hydrophilic block we
chose PBu4N+SS, due to its sufficient solubility and the high
charge density even at low pH. As previously reported, the
sulfonate groups feature the catalytic crystallization of TiO2 at
room temperature.26,27 Furthermore, the strong coulomb inter-
actions of the polyelectrolyte enable high loading capacities with
oppositely charged nanoparticles, while maintaining a high
solubility.28 The close arrangement of the nanoparticles is crucial
for the percolation of charges and conductivity. The desired
block copolymer was synthesized by reversible addition frag-
mentation chain transfer polymerization (RAFT). Therefore, we
first needed to optimize the polymerization conditions in order to
get well-defined molecular weights and low polydispersities.23
The sulfonated block was prepared via polymerization of the
protected monomer, neopentyl styrene sulfonate (NeoSS). This
allows the use of common high boiling solvents such as anisole or
toluene and the neopentyl group can be easily removed after-
wards.29,30 The resulting amphiphilic polymer was studied for its
morphology in aqueous solution by dynamic light scattering
(DLS) and transmission electron microscopy (TEM). We
combined these micelles with highly crystalline CdSe nanorods to
ensure the absorption of visible light and good electron trans-
port. The particles can be modified with aminoethanethiol
hydrochloride to get a high positive surface charge gaining
solubility in water.31 Due to the strong attraction to the nega-
tively charged PBu4N+SS-block, mixing of both components
results in a stable colloidal solution of donor and acceptor
materials in water.
Results and discussion
During the last decade RAFT polymerization has become an
important technique among the controlled radical polymeriza-
tions for macromolecule design.32–34 But actually there are only a
few reports on the polymerization of functional semiconductor
monomers.35 Due to the larger size of these monomers compared
to simple styrene or acrylate monomers and the sensitivity
against radical oxidation, particular attention has to be paid to
the polymerization conditions.
The order of monomer addition is crucial for well-defined
block copolymers by RAFT.36 Especially triphenylamine
monomers (TPA) are able to stabilize the propagating radical
altering the reactivity of the active chain end. In consequence
we first prepared the individual homopolymers PDMTPA and
poly(neopentyl styrene sulfonate) (PNeoPSS) and verified
their ability to initiate the respective counterpart. Both
polymerizations were carried out using 2-cyano-2-pro-
Scheme
1
Synthesis of poly(4,40-dimethoxytriphenylamine)-block-
ꢂ
pylbenzodithioate as chain transfer agent (CTA) and at 80 C
poly(tetrabutylammonium styrene sulfonate) (PDMTPA-b-PBu4N+SS)
in anisole, which is a suitable high boiling solvent for both
monomers.
using 2-cyano-2-propylbenzodithioate as chain transfer agent (CTA).
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Fig. 1 GPC-plots of the homopolymers poly(bis(4-methoxyphenyl)-40-
vinylphenylamine) (PDMTPA, red) and poly(neopentyl styrene sulfo-
nate) (PNeoSS, blue), eluent: THF, calibration with polystyrene.
Fig.
3
Comparison of GPC plots of the initiating macro-CTA
PDMTPA (dashed line) and the resulting block copolymer PDMTPA-b-
PNeoSS (continuous line).
Then, we studied the sequential polymerization of DMTPA
using the macro-CTA PNeoSS under similar conditions. The
GPC trace of sample PNeoSS-b-PDMTPA displays no signifi-
cant shift of the main peak in comparison to the macro-CTA
(Fig. 2). Furthermore a broad underlying peak was formed
characteristic for a free radical polymerization. This indicates
that PNeoSS was not able to initiate the polymerization of
DMTPA and a broadly distributed homopolymer was formed in
addition to the macro-CTA. Changing the synthesis conditions
such as variation of temperature and concentration unfortu-
nately had no influence on this process (Fig. S1 in the ESI†).
Alternatively we started the polymerization of NeoSS as
second monomer from PDMTPA as macro-CTA. Here the GPC
traces clearly indicated the formation of a block copolymer.
However, a second peak was observed at the original elution
volume of PDMTPA (Fig. 3). This suggests that a considerable
part of the macro-CTA remained unreactive. Keeping a retarded
initiation in mind, one could expect a statistical distribution
covering the macro-CTA and the associated BCPs, resulting in
one broad peak. But a bimodal distribution indicates that the
main part of the PDMTPA homopolymer was able to initiate the
controlled polymerization of NeoSS, while a second part
remained without addition of further monomer units. In
Fig. 2 Comparison of GPC plots of the initiating macro-CTA PNeoSS
(dashed line) and the resulting block copolymer PNeoSS-b-PDMTPA
(continuous line).
Both the resulting homopolymers showed narrow molecular
weight distributions (Fig. 1), which implies good control of the
RAFT polymerization of the monomers.
Table 1 Synthesis conditions and characterization for the macro-CTAs and the respective block copolymers
Monomer/CTA/AIBN
ratio
T
Solvent
Mn (kg molꢁ1 a
)
Mp1 (kg molꢁ1 a,b
)
Mp2 (kg molꢁ1 a,b
)
PDI
Macro-CTA
PDMTPA(1)
PDMTPA(2)
PDMTPA(3)
PDMTPA(4)
BCP
50/1/0.2
50/1/0.2
50/1/0.2
50/1/0.2
60 ꢂC
80 ꢂC
100 ꢂC
60 ꢂC
Anisole
Anisole
Anisole
Benzene
3.21
5.80
4.97
4.52
3.66
6.64
5.73
4.94
—
—
—
—
1.09
1.12
1.11
1.07
PDMTPA(1)-b-PNeoSS
PDMTPA(2)-b-PNeoSS
PDMTPA(3)-b-PNeoSS
PDMTPA(4)-b-PNeoSS
100/1/0.4
100/1/0.4
100/1/0.4
100/1/0.4
80 ꢂC
80 ꢂC
80 ꢂC
80 ꢂC
Anisole
Anisole
Anisole
Anisole
4.78
8.67
8.77
11.55
4.06
6.31
5.73
5.00
8.55
1.30
1.28
1.34
1.37
15.23
15.47
18.95
a
GPC was calibrated with polystyrene as standard. b Mp was defined as the molecular weight of single peaks.
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DMTPA. For verification we altered the conditions of the
macro-CTA synthesis and consequently tested the macro-initi-
ator efficiency of the macro-CTAs prepared in different solvents
and at different temperatures keeping the concentration and
ratio of components the same. Thus, the temperature was varied
from 60 to 100 ꢂC and secondly the polarity of the medium was
changed. A summary of these reactions and the corresponding
polymer characteristics are given in Table 1.
The reduced reaction temperature (60 ꢂC) in anisole of the
macro-CTA PDMTPA(1) reduced the polymerization rate, so
that only a conversion of 44% was reached after 22 h. All other
samples were stopped at higher conversions of 55–60%, yielding
similar molecular weights and narrow distributions. Those
macro-CTAs were then employed in the polymerization of
NeoSS under conditions summarized in Table 1. The GPC plots
of the resulting BCPs and the respective macro-CTAs are shown
in Fig. 4.
By raising the temperature for the macro-CTA synthesis from
60 ꢂC to 80 ꢂC the amount of unreactive PDMTPA increased
slightly. Considerable improvements were observed at a high
temperature of 100 ꢂC, but still a substantial part of the macro-
CTA remained unreactive in polymerization using macro-CTA
PDMTPA(3). The best result was obtained with macro-CTA
PDMTPA(4) by changing the solvent from anisole to benzene
and thus reducing the polarity of the surrounding medium.
Despite a small part of unreacted homopolymer was still visible,
a low polydispersity index (PDI) of 1.37 was reached for the as-
synthesized BCP. The final polymer PDMTPA(4)-b-PNeoSS was
purified by preparative GPC to remove the last traces of the
homopolymer. The GPC trace of the final polymer is shown in
Fig. 5. These results obviously prove the influence of the initial
macro-CTA synthesis on the final initiator efficiency.
Fig.
4 GPC-traces of the samples PDMTPA(1)-b-PNeoSS,
PDMTPA(2)-b-PNeoSS, PDMTPA(3)-b-PNeoSS and PDMTPA(4)-b-
PNeoSS (solid lines) and the respective macro-CTAs (dashed lines). The
variations in synthesis of the macro-CTA are shown on the left, while the
BCP was formed under similar conditions (Experimental section).
Further evidence of a loss of the chain transfer agent was
attained by matrix-assisted laser desorption/ionization time-of-
flight (MALDI-TOF) measurements, which provides detailed
consequence, the functional chain transfer end group of the
PDMTPA must be partially disabled or lost. As no intermediate
steps of purification are involved in the macro-CTA synthesis,
this process must already occur during the polymerization of
Fig.
6 Matrix-assisted laser desorption/ionization time-of-flight
measurements of macro-CTA PDMTPA(2) and PDMTPA(4). The
major peak series corresponds to the macro-CTA and the minor one to
the homopolymer with dead chain ends.
Fig. 5 GPC-trace of the purified sample PDMTPA(4)-b-PNeoSS.
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polymers after 23 h (Fig. S6 in the ESI†). In comparison to the
self-initiation radical polymerization of styrene, here first a
cycloaddition step is involved.37 The electron donating effect of
the nitrogen in the triphenylamine monomer and the increased
number of active phenyl rings enhance this effect. Free hydrogen
radicals are created in this reaction to retain the aromaticity in
the resulting molecule after the cycloaddition, which may start or
quench a radical polymerization. However, for a detailed
mechanism further studies have to be performed to get insight
into this phenomenon, which are not part of this research. But
the presented results certainly depict the importance of detailed
kinetic studies in optimization of synthesis of functional block
copolymers.
With a well-defined polymer in hand, we consequently studied
the assembly and coordination properties of PDMTPA-b-PSS.
After deprotection of the sulfonate groups, the BCP showed a
distinct amphiphilic character. The complete deprotection was
confirmed by NMR analysis (Fig. S7 in the ESI†). Thus the
polymer showed micelle formation in aqueous solutions. These
assembly structures were characterized by dynamic light scat-
tering (DLS) to obtain the hydrodynamic radius Rh. For
consistent values we measured the decay rate G, calculated from
the autocorrelation function (1. order of cumulant fit), for
multiple angles q and plotted it against q2 with q ¼ 4pn/l ꢀ
sin(q/2) (n: refractive index; l: wavelength of the laser). The
respective linear slope of the plot is correlated to the diffusion
coefficient D by G ¼ Dq2. With D the hydrodynamic radius Rh
can be calculated as Rh ¼ (kBT)/(6phD) (kB: Boltzmann
constant; T: temperature; h: viscosity of the medium).
The plot in Fig. 7 clearly displays a linear relation between G
and q2. From the slope a hydrodynamic radius Rh of 22 nm ꢃ
0.23 nm was determined. While this value reflects the size of the
micelles in solution, including the hydrated polyelectrolyte shell,
Fig. 7 A representative distribution of micelles for an angle of 120ꢂ (top)
and the plot of Plot of G against q2 for various measured angles (bottom).
information on the end-group distribution. For comparison the
measurements of macro-CTAs PDMTPA(2) and PDMTPA(4)
are plotted in Fig. 6. The full MALDI spectra of all samples are
given in the ESI (Fig. S2–S5†). The second peak series clearly
indicate a change in the polymer end groups. The difference of
221 g molꢁ1 correlates well with the loss of the chain transfer
agent 2-cyano-2-propylbenzodithioate. Furthermore comparing
the intensities of the second peak the ratio of active species to
dead chain end moieties decreases from macro-CTA
PDMTPA(2) to PDMTPA(4). This is in good agreement with the
GPC traces of the block copolymers, where the part of unreactive
homopolymer decreases, too.
The lost CTA is possibly caused by the formation of additional
free radicals, which terminate the active polymer. As the polymer
distribution remains narrow, this process seems to be suppressed
at the beginning of the polymerization, but increases drastically
with higher conversion. For styrene monomers self-initiation and
radical formation is already well studied and we assumed a
similar process for this system.2,37 Therefore the polymerization
was examined under similar conditions, without using any AIBN
initiator. GPC traces at different reaction times evidently present
the formation of oligomers first and higher molecular weight
Fig. 8 Transmission electron micrographs of the dried micelles stained
with ruthenium tetroxide.
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Fig. 11 Transmission electron micrographs of the CdSe nanorods
attached to the block copolymer micelles.
The respective individual sizes of the core and the shell (ꢄ14
nm) are in good agreement with theoretical values for a coiled
solid PDMTPA-block and a highly stretched PBu4N+SS-block,
which is characteristic for strong polyelectrolytes in deionised
water.38 Aqueous dispersions of those micelles are stable and
showed no precipitation, even after storage under ambient
conditions for several months.
We have studied earlier the coordination capabilities of PSS
containing spherical polyelectrolyte brushes.26,28 Building upon
this experience, we studied the coordination abilities of the
PDMTPA-b-PBu4N+SS micelles. In contrast to the spherical
colloidal particles, no time-consuming solvent exchange is
necessary, as the micelles can be freeze dried and well dispersed in
various suitable polar solvents. Non-toxic solvents such as water
or alcohols are highly preferred in technological applications.
Therefore, we focused on a system using water soluble semi-
conductor nanoparticles.39 Furthermore, to guarantee an effi-
cient absorption of the visible light, the particles need to have
good absorption coefficients in this range. CdSe nanoparticles
fulfil these requirements and they are well studied in solar
cells.11,12 A general scheme of this colloidal assembly route is
shown in Fig. 9.
Fig. 9 General preparation scheme of hybrid colloidal composites.
adjacent transmission electron micrographs (TEM) of the dried
micelles stained with ruthenium tetroxide reveal a core diameter
of approximately 16 nm (Fig. 8).
Recently Zentel et al. presented a comparable BCP in combi-
nation with CdSe quantum dots for application in light emitting
devices.40 A similar colloidal arrangement was shown by Winnik
et al. using commercial block copolymers.41 The synthesis of
CdSe nanoparticles with various shapes and high crystallinity is
well controlled using various phosphonic acid ligands.42,43 To
enable the solubility in water we exchanged this ligand with the
hydrophilic 2-aminoethanethiol (AET) according to Krauss
et al.31 The resulting nanoparticles exhibit a good solubility in
water and good absorption up to 630 nm (Fig. 10). According to
Fig. 10 Absorption of the prepared CdSe nanoparticles with 2-amino-
ethanethiol ligand in water (0.5 mg mlꢁ1).
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electron micrographs in Fig. 11. The weight ratio of nano-
particles against polymer was as high as 1 : 1.
Only a few single nanoparticles are obviously seen in the
images, which confirm the strong interaction. The high loading
facilitates a better packing of the nanoparticles, which is crucial
for high charge carrier mobility.45 A major advantage of this
separate synthesis of polymer and inorganic semiconductor is the
variability of the nanoparticle synthesis. In literature the prepa-
ration of several highly crystalline nanoparticles is well-known
and they all can be combined with these micelle structures by
electrostatic interaction.46
Finally the resulting donor–acceptor (D–A) micelles can be
used to prepare devices with microstructures on the length scale
of the exciton diffusion length. A general scheme of this concept
with spherical nanoparticles is shown in Fig. 12. The nano-
composite micelles can be assembled onto a conducting substrate
and dried to get a smooth film, which can be annealed or pressed
above Tg to get bicontinuous domains. The amorphous
PDMTPA softens and forms a continuous phase. Simulta-
neously the particles aggregate to create the required percolation
once the concentration increases on drying and annealing as
shown in Fig. 12. In such a system the charge transfer and
transport required for a solar cell are feasible.
Conclusion
The ability of block copolymers to create domains in the nano-
meter scale reveals them to be ideal for structured organic or
hybrid solar cells. Here we developed an innovative colloidal
organization of inorganic semiconductors and semiconductor
amphiphilic block copolymers. The polymer consists of a well-
known hole conductor block and a water soluble styrene sulfo-
nate block, able to coordinate nanoparticles by electrostatic
interaction. We optimized the synthesis conditions to accomplish
narrow distributions and create well-defined micelle dispersions.
Crucial in this context are the order of monomer addition and the
reactivity of the triphenylamine monomer. The latter resulted in
the loss of the chain transfer agent during the homopolymeri-
zation. This caused bimodal distributions during the block
copolymer formation. By altering the temperature and solvent
polarity the side reaction could be minimized and thus the ratio
of unreactive homopolymer reduced. After hydrolysis of the
sulfonate protection groups the block copolymer formed
uniform and stable micelles in aqueous solutions. The highly
charged sulfonate groups are strong coordinating groups espe-
cially for electrostatic interaction with charged nanoparticles.
Ideal semiconductors for this approach are CdSe nanorods. They
combine both good absorption in the visible spectrum of light
and high electron mobility. By exchanging the typical phosphine
ligands with a positive charged aminoethanethiol the particles
can be attached to our hole conductor micelles. In consequence
we created semiconductor colloids including both a donor
material and an acceptor. The domain sizes are defined by the
micelle core and the nanoparticle size, which can be adjusted in
individual reactions. As the system is based on an aqueous
dispersion no hazardous solvents are necessary for processing
enabling large scale industrial fabrication. The strong electro-
static interaction of the sulfonate polymer allows high loading
capacities while maintaining the good solubility. In combination
Fig. 12 General scheme for the preparation of a donor–acceptor (D–A)
microstructure from hybrid colloidal nanocomposites.
the literature the HOMO and LUMO levels of PDMTPA are at
5.0 eV and 1.8 eV respectively.6 CdSe nanoparticles of similar
shape typically have a conduction band edge at 6.2 eV and a
valence band edge at 4.4 eV.44 Thus this system fulfil the
requirements for charge transfer.
Transmission electron micrographs show uniformly distrib-
uted CdSe nanoparticles with an average diameter of 5 nm and
length of 21 nm (Fig. S8 in the ESI†). The positively charged
AET ligands not only convey the water solubility, but also yield a
strong coulombic interaction between the nanoparticles and the
negatively charged sulfonate groups. By mixing both solutions
the nanocrystals immediately attach to the negative charged
micelles. The strong driving force is attributed to the enthalpy
benefit from the release of multiple counterions by exchanging
with a single particle. These strong interactions enable a high
loading capacity in comparison to uncharged polymers like
polyvinylpyridine, while maintaining the stability of the disper-
sions.28 Composites of the CdSe nanoparticles and the
PDMTPA-b-PBu4N+SS micelles are shown in the transmission
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18 S.-W. Yeh, K.-H. Wei, Y.-S. Sun, U.-S. Jeng and K. S. Liang,
Macromolecules, 2005, 38, 6559.
19 A. Haryono and W. H. Binder, Small, 2006, 2, 600.
20 Y. Lin, V. K. Daga, E. R. Anderson, S. P. Gido and J. J. Watkins, J.
Am. Chem. Soc., 2011, 133, 6513.
21 Q. Zhang, S. Gupta, T. Emrick and T. P. Russell, J. Am. Chem. Soc.,
2006, 128, 3898.
22 M. C. Lechmann, S. A. L. Weber, J. Geserick, N. Husing, R. Berger
and J. S. Gutmann, J. Mater. Chem., 2011, 21, 7765.
23 S. Maria, A. S. Susha, M. Sommer, D. V. Talapin, A. L. Rogach and
M. Thelakkat, Macromolecules, 2008, 41, 6081.
with other polymerization techniques all kind of functional
polymers such as polythiophenes or low band-gap polymers can
be integrated into this environmentally benign processing of
devices from water. Furthermore various inorganic semi-
conductors such as TiO2 or CuInS2 are interesting alternatives
which can easily be incorporated. In conclusion this approach
opens a promising pathway towards defined donor–acceptor
hybrid systems using semiconductor amphiphilic block
copolymers.
€
24 S. Huttner, M. Sommer, U. Steiner and M. Thelakkat, Appl. Phys.
Lett., 2010, 96, 073503.
€
25 E. M. Barea, G. Garcia-Belmonte, M. Sommer, S. Huttner,
Acknowledgements
H. J. Bolink and M. Thelakkat, Thin Solid Films, 2010, 518, 3351.
26 J. C. Brendel, Y. Lu and M. Thelakkat, J. Mater. Chem., 2010, 20,
7255.
€
Financial support from SFB 840 and Bayerische Eliteforderung
€
is kindly acknowledged. Furthermore we thank Melanie Fortsch
27 Y. Lu, M. Hoffmann, R. S. Yelamanchili, A. Terrenoire,
€
and Katharina Neumann for the TEM and MALDI measure-
ments respectively.
M. Schrinner, M. Drechsler, M. W. Moller, J. Breu and
M. Ballauff, Macromol. Chem. Phys., 2009, 210, 377.
28 R. S. Yelamanchili, Y. Lu, T. Lunkenbein, N. Miyajima, L.-T. Yan,
M. Ballauff and J. Breu, Small, 2009, 5, 1326.
29 H. Okamura, Y. Takatori, M. Tsunooka and M. Shirai, Polymer,
2002, 43, 3155.
30 S. C. Miller, J. Org. Chem., 2010, 75, 4632.
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