Intermolecular Arrangement of Fullerene Acceptors Proximal to Semiconducting Polymers in Mixed Bulk Heterojunctions

Article abstract of DOI:10.1002/anie.201801173

Precise control of the molecular arrangements at the interface between the electron donor and acceptor in mixed bulk heterojunctions (BHJs) remains challenging, despite the correlation between structural characteristics and efficiency in organic photovoltaics (OPVs). This study reveals that the substitution patterns of linear and branched alkyl side chains on electron-donating/-accepting alternating copolymers can control the positions of an acceptor molecule (C₆₀) around the π-conjugated main chains in mixed BHJs. Two-dimensional solid-state NMR demonstrates a marked difference in the location of C₆₀ in the blend films. A copolymer with an electron-accepting unit positioned in close proximity to C₆₀ demonstrated higher OPV performance in combination with various fullerene derivatives. This molecular design offers precise control over the interfacial molecular structure, thereby paving the way for overcoming the current limitations of OPVs comprising mixed BHJs.

Full text of DOI:10.1002/anie.201801173

A Journal of the Gesellschaft Deutscher Chemiker
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Accepted Article
Title: Intermolecular Arrangement of Fullerene Acceptors around
Semiconducting Polymers in Mixed Bulk Heterojunctions
Authors: Chao Wang, Kyohei Nakano, Hsiao Fang Lee, Yujiao Chen,
You-lee Hong, Yusuke Nishiyama, and Keisuke Tajima
This manuscript has been accepted after peer review and appears as an
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To be cited as: Angew. Chem. Int. Ed. 10.1002/anie.201801173
Angew. Chem. 10.1002/ange.201801173
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Angewandte Chemie International Edition
10.1002/anie.201801173
COMMUNICATION
Intermolecular Arrangement of Fullerene Acceptors around
Semiconducting Polymers in Mixed Bulk Heterojunctions
[
a]
[a]
[a]
[a]
[b]
Chao Wang , Kyohei Nakano , Hsiao Fang Lee , Yujiao Chen , You-lee Hong , Yusuke
Nishiyama[b,c], and Keisuke Tajima*[a]
Abstract: Precise control of the molecular arrangements at the
interface between the electron donor and acceptor in mixed bulk
heterojunctions (BHJs) remains challenging, despite its vital
importance for achieving high efficiency in organic photovoltaics
to improving the performance of OPVs further. The interfacial
structures of mixed BHJs, however, are difficult to analyze at the
molecular scale due to the limitations of analytical methods.
Controlling the interfacial structures is even more challenging in
BHJs.
27
(OPVs). Here, we report that substitution patterns of linear and
branched alkyl side chains on electron-donating/-accepting
alternating copolymers can control the positions of an acceptor
molecule (C60) around the π-conjugated main chains in mixed BHJs.
Two-dimensional solid-state NMR showed a marked difference in the
location of C60 in the blend films. The copolymer that allowed C60 to
be close to its electron-accepting unit showed higher OPV
performance in combinations with various fullerene derivatives. This
molecular design paves the way for controlling the interfacial
molecular structure precisely, and for overcoming the current limits of
OPVs based on mixed BHJs.
Systematic studies of the polymer synthesis have suggested
that the structures of the π-conjugated main chains are not the
only factor that affects the mixed BHJ structure and the OPV
performance. Alkyl side chains, the primary function of which is to
make the polymer soluble, can affect the OPV performance,
sometimes substantially. The length, size, and shape of the alkyl
chains on the main chains affect intermolecular packing,
orientation, and morphology in the mixed BHJ films, which are
28-31
important factors in OPV performance.
Graham et al.
hypothesized that the bulkiness of the alkyl side chains in D-A
copolymers may also affect the position of the acceptor molecules
32
around the polymers. In the excited state, the electron density
of the polymers would be higher in the A unit; thus, the
arrangement of the acceptor molecules being close to the A unit
can improve the charge transfer from the polymer to the acceptor.
A meta-analysis of the reported performance of OPVs with D-A
copolymers supports this hypothesis, although there are notable
exceptions. They also synthesized a D-A structure as an
experimental model system to investigate the effect of the
bulkiness on the OPV performance. However, the differences in
OPV performance cannot be attributed solely to the
intermolecular arrangement of the acceptors because the change
in the alkyl side chains in the D-A system would result in
substantial differences in the polymer properties such as the
This decade has witnessed the remarkable development of
organic photovoltaics (OPVs) as a promising renewable energy
source owing to their potential use in lightweight, flexible, and
1-3
large-area devices.
This progress has been driven by the
synthesis of novel semiconducting polymers whose optical and
electronic properties are carefully tuned by the design of π-
conjugated structures. Donor-acceptor (D-A) alternating
copolymers consisting of electron-donating (D) and electron-
accepting (A) units have been widely used as a key method for
4-9
tuning the electronic properties. The photoactive layers of highly
efficient OPVs are mixed bulk heterojunction (BHJ) structures
typically composed of a blend of a semiconducting copolymer as
the electron donor and fullerene derivatives as the electron
33,
electronic structure, crystallinity, and morphology in BHJ films.
34
1
0,11
Although this hypothesis could provide important design
acceptor.
1
Recently, the performance of OPVs reached over
12
principles for semiconducting polymers in OPVs, it is not yet clear
how effective this simple approach is to control the intermolecular
arrangements.
1% based on BHJs of polymers and fullerene derivatives.
There have been substantial advances in understanding the
mechanism of OPVs. It has been shown that the properties of the
organic interfaces strongly affect the charge separation and
In this work, we developed a molecular design to clarify the
effects of the alkyl chains on the arrangement of the acceptors in
mixed BHJ films and the OPV performance. We synthesized two
new D-A copolymers based on 4,8-dimethoxybenzo[1,2-b:4,5-
13
recombination processes. The charge-transfer state at the
14-19
interface has a strong correlation with the OPV performance.
Therefore, the spatial arrangement of the donor and acceptor can
strongly affect the photophysical and electronic processes in
b']dithiophene (DMBDT; the
D unit) and benzo[1,2-b:4,5-
OPVs, as suggested by theoretical calculations2
0-22
b']dithiophene-4,8-dione (BDTQ; the A unit) with thiophenes as
the π-conjugated bridge (Scheme 1). Either linear (C12) or
and
experimental studies using planar heterojunctions as model
23-26
branched (C12
to the D and A units. BDTP-1 has C12 and C12
C
8
) alkyl chains are attached to the thiophenes next
chains at the
systems.
Taken together, these studies suggest that precise
C
8
control of the BHJ structure at the molecular level could be crucial
thiophene units next to DMBDT and BDTQ, respectively, whereas
BDTP-2 has the alkyl chains in the opposite positions. We
expected that the two types of side chain would create certain
steric environments around the D and A units to control the
access of fullerenes. Importantly, because the DMBDT and BDTQ
units have similar structures, we showed that switching the
alkylation patterns between BDTP-1 and BDTP-2 has little effect
on the polymer properties in the pristine films and the mixed BHJ
films. Two-dimensional (2D) solid-state (SS)-NMR measurements
provided direct structural information about the mixed BHJ from
the correlation between the methoxy group on the DMBDT units
and the fullerene. The effects of the molecular arrangements on
the OPV performance were also investigated.
[
[
[
a]
b]
c]
Dr. C. Wang, Dr. K. Nakano, Dr. H. F. Lee, Y. Chen, Dr. K. Tajima
RIKEN Center for Emergent Matter Science (CEMS)
2-1 Hirosawa, Wako, Saitama 351-0198, Japan
E-mail: keisuke.tajima@riken.jp
Dr. Y.-L. Hong, Dr. Y. Nishiyama
RIKEN CLST-JEOL Collaboration Center
1-7-22 Suehiro-cho, Tsurumi-ku, Yokohama, Kanagawa 230-0045,
Japan
Dr. Y. Nishiyama
JEOL RESONANCE Inc.
Musashino, Akishima, Tokyo 196-8558, Japan
Supporting information for this article is given via a link at the end of
the document.
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Angewandte Chemie International Edition
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COMMUNICATION
O
1. n-BuLi
O
O
R
series of fullerene derivatives (C60, PC61BM, PC71BM, ICBA, and
bisPCBM; see Figure S3 for the structures) was also investigated.
The weight ratio of the polymer to the fullerenes was fixed as 1:2
for all the combinations because it was optimal for the OPVs (see
below). The absorption spectra of the BHJ films were also
indistinguishable for BDTP-1 and BDTP-2 for each fullerene
derivative (Figure 1b for C60 and Figure S4 for the other
derivatives). The identical absorption spectra indicated that
changing the alkyl substitution patterns does not affect the
electronic structures and the intermolecular interactions in the thin
films.
R
Me Sn
3
S
S
S
S
2
. Me SnCl
3
S
S
S
S
SnMe3
R
R
O
DMBDT-T1: R =
DMBDT-T2: R =
C12H25
M1: R =
M2: R =
12 25
C H
C
8
H
17
8 17
C H
C10H21
C10H21
(
NH ) [Ce(NO ) ]
4
2
3
6
O
O
O
O
R
R
Br
NBS
S
S
S
S
S
S
S
S
Br
R
R
M3: R =
M4: R =
12 25
C H
BDTQ-T1: R =
BDTQ-T2: R =
C
12 25
H
C H
C
8
H
17
8
17
C H
10 21
C10H21
C
10
H
21
8 17
C H
O
Pd
P(o-tol)
2
(dba)
3
,
12 25
C H
O
S
S
S
3
S
M1
+
M4
S
S
n
S
S
O
8 17
C H
O
C12H25
10 21
C H
Figure 1. UV-vis absorption spectra of BDTP-1 and BDTP-2 (a) in the pristine
polymer films and (b) the mixed BHJ films with C60 (polymer:C60 = 1:2 by weight).
BDTP-1
C10H21
C12H25
S
O
C H
8
17
O
Pd (dba) ,
S
2
3
S
S
S
P(o-tol)
n
3
S
M2
+
M3
S
S
O
X-ray diffraction (XRD) was carried out on the pristine
polymer films and the BHJ films. The peak positions and the
intensities in the out-of-plane XRD patterns were identical for
L
C12H25
O
C H
8
17
10 21
C H
BDTP-2
BDTP-1 and BDTP-2 with lamellar d-spacing (d ) of 22.3 Å
(Figure 2a). The XRD patterns were also identical for the BHJ
films of BDTP-1 and BDTP-2 with all the fullerene derivatives
(Figure 2b for C60 and Figure S5 for the other derivatives). Grazing
incident wide-angle X-ray scattering (GIWAXS) measurements
were conducted to investigate the intermolecular stacking and the
orientation further. The pristine polymer films and the BHJ films
with the fullerene derivatives showed indistinguishable GIWAXS
patterns for BDTP-1 and BDTP-2 in terms of intensity and
anisotropy (Figure 3 for the pristine films and the mixed BHJ films
with C60 and Figure S6 for the other BHJs). The patterns showed
weak edge-on orientations of the polymer chains both in the
pristine films and the BHJ films. By taking the line profiles along
the qxy axes (in-plane) of the GIWAXS images, the π-stacking
Scheme 1. Synthetic routes for monomers and polymers. The polymers have
the same DMBDT (blue) and BDTQ (red) main chain structure, but different
substitution patterns of the linear and branched alkyl chains on the thiophenes.
Scheme 1 shows the synthetic routes for monomers and
polymers. Detailed synthetic procedures including the preparation
of precursors DMBDT-T1 and DMBDT-T2 are shown in the
Supporting Information. BDTQ-T1 and BDTQ-T2 were prepared
directly by one-step oxidation of DMBDT-T1 and DMBDT-T2
using cerium ammonium nitrate, respectively. Monomers M1 and
M2 were prepared by stannylation of DMBDT-T1 and DMBDT-T2,
respectively. Meanwhile, brominations of BDTQ-T1 and BDTQ-
T2 using NBS gave monomers M3 and M4, respectively. Both
BDTP-1 and BDTP-2 were synthesized via the Stille coupling
distances (d
BDTP-1 and BDTP-2 showed d
of the same values in the blend films in the range of 3.53–3.56
Å depending on the acceptor (Table S1). The d values were
π
) of the polymers were calculated (Figure S7). Both
π
of 3.53 Å in the pristine films and
d
π
π
reaction with Pd
These two polymers had comparable molecular weights (M
2.7 and 22.9 kDa, respectively, with the same polydispersity
2
(dba)
3
and P(o-tol)
3
as the catalyst system.
small for the semiconducting polymers, indicating that the
polymers had strong interchain interactions in the films. Figures 4
and S8 show the atomic force microscopy (AFM) height images
for the BHJ films. The morphologies of the blend films with the
fullerene derivatives were indistinguishable for BDTP-1 and
BDTP-2 for each fullerene derivative. Transmission electron
microscopy (TEM) of BDTP-1:C60 and BDTP-2:C60 films also
showed very similar images without any clear features of phase
separation, suggesting that the blend morphology is similar to
each other in mesoscale (Figure S9).
n
) of
2
index of 2.0. Differential scanning calorimetry did not show any
clear phase transitions for either polymer. Thermogravimetric
analysis demonstrated the good thermal stability of the polymers
with the same thermolysis onset temperature at 385 °C (Figure
S1).
The UV-vis absorption spectra of BDTP-1 and BDTP-2 were
identical, including the absorption coefficient in films (Figure 1a).
The films showed the absorption maxima at 503 and 526 nm
along with a shoulder at around 610 nm. The optical bandgaps
(
E
g
) of the polymers were estimated to be 1.62 eV from the
absorption onset in the film spectra. The HOMO energy levels
HOMO) of BDTP-1 and BDTP-2 evaluated by photoelectron
(E
spectroscopy in air were both −5.22 eV (Figure S2). The UV-vis
absorption of the mixed BHJ films of BDTP-1 and BDTP-2 with a
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V−1 s−1, respectively. The BHJ films with the fullerene derivatives
showed similar μSCLC values between BDTP-1 and BDTP-2, which
varied in the range of 1.55 × 10− to 1.37 × 10 cm
6
−5
2
V
−1 −1
s ,
depending on the fullerene derivative used. For instance, μSCLC of
the BDTP-1:C60 and BDTP-2:C60 films were 2.62 × 10−6 and 2.66
−
6
2
−1 −1
×
10 cm V s , respectively, differing by less than 2%.
To obtain atomic-level information on the structures in mixed
films of the polymers and fullerene derivatives, SS-NMR
measurements were conducted with C60 as a model for the
fullerenes. The BHJ powder samples for the SS-NMR
measurements were prepared from the spin-coated films in a
Figure 2. XRD patterns of BDTP-1 and BDTP-2 in (a) the pristine polymer films
and (b) the mixed BHJ films with C60 (polymer:C60 = 1:2 by weight).
13
similar way to those for the other measurements with C-enriched
60 (see Supporting Information for details). One-dimensional
C
1
13
(1D) H and C single-pulse magic angle spinning (MAS) SS-
NMR spectra of the BHJ samples showed almost identical
patterns for BDTP-1 and BDTP-2 with well-resolved NMR signals
1
(Figure S11a and b). The peaks at 1.5 and 3.8 ppm in 1D
H
spectra were assigned to the protons on the alkyl side chains and
the methoxy group of the DMBDT unit, respectively. The peaks at
5.9 and 7 ppm may be assigned to the protons on the π-
conjugated main chain in crystalline and amorphous domains,
35
13
respectively. 1D C spectra showed a major peak at 143.3 ppm
and a minor peak at 143.9 ppm (Figure S11b), both of which can
13
be assigned to the carbons in C60 because of the C enrichment
in C60 (90%) and the large C60 content (polymer:C60 = 1:2). The
small peak was assigned to C60 molecules interacting with
36
molecular oxygen, as reported previously. The peak positions
13
were identical with those in the 1D C SS-NMR spectrum of pure
13
C-enriched C60 (Figure S11c).
D 1H- C heteronuclear correlation (HETCOR) SS-NMR
13
2
spectra are shown in Figures 5a and b for BDTP-1:C60 and BDTP-
1
3
2
1
:C60, respectively. A clear correlation between the C peak at
1
43.3 ppm and H peak at 3.8 ppm was observed for BDTP-2:C60,
which was assigned to C60 and the methoxy group of the DMBDT
unit in the polymer, respectively (Figure 5b, circled). This
correlation provided direct evidence for the close proximity
between C60 and the DMBDT unit of BDTP-2 at the interface of
the BHJ (Figure 5d). In contrast, the correlation was absent for
BDTP-1:C60, indicating that the C60 was farther from the DMBDT
unit than in BDTP-2:C60. Because the numbers and lengths of the
alkyl side chains were identical and only the positions were
swapped in BDTP-1 and BDTP-2, the available vacant volumes
around the polymer chains were expected to be identical.
Therefore, we assumed that the C60 groups were positioned close
to the BDTQ unit in BDTP-1:C60 (Figure 5c). The branched alkyl
chains close to the BDTQ unit could hinder the access of C60 to
the neighboring DMBDT unit. This result proves that precise
control of the fullerene arrangements around the polymer chains
is possible in mixed BHJs through designing the steric
environment by using the side chains.
Figure 3. GIWAXS patterns of BDTP-1 and BDTP-2 in (a, b) the pristine
polymer films and (c, d) the mixed BHJ films with C60 (polymer:C60 = 1:2 by
weight).
Figure 4. AFM height images of the mixed BHJ films with C60 and (a) BDTP-1
and (b) BDTP-2 (polymer:C60 = 1:2 by weight).
To elucidate the electric conduction properties of the films,
the current density (J)-voltage (V) curves were measured for the
hole-only devices based on the pristine polymer films and the BHJ
films (Figure S10). The hole mobilities (μSCLC) were calculated
from the space-charge-limited region of the curves (Table S2).
The devices based on the pristine BDTP-1 and BDTP-2 films
afforded similar μSCLC values of 1.30 × 10− and 1.32 × 10 cm
6
−6
2
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COMMUNICATION
BDTP-2:
PC71BM
0
0
0
0
.81 ± 0.01
.92 ± 0.01
.92 ± 0.02
.89 ± 0.02
5.7 ± 0.2
0.93 ± 0.02
0.59 ± 0.02
0.51 ± 0.02
0.47 ± 0.01
0.47 ± 0.01
2.4 ± 0.2
0.40 ± 0.01
0.26 ± 0.01
BDTP-1:
ICBA
BDTP-2:
ICBA
BDTP-1:
bisPCBM
1.3 ± 0.1
1.0 ± 0.1
0.46 ± 0.03
0.42 ± 0.02
0.51 ± 0.03
0.37 ± 0.03
BDTP-2:
0.88 ± 0.01
bisPCBM
OPVs based on mixed BHJs of BDTP-1 and BDTP-2 with the
fullerene derivatives were fabricated with a device architecture of
ITO/PEDOT:PSS/polymer:fullerene (1:2 by weight)/Ca/Al. The
films with BDTP-1 and BDTP-2 were prepared under the same
conditions at the same time, so that they had the same thickness
and light absorption in the OPVs (Figures 1b and S4). Figure 6
compares the photovoltaic performances of BDTP-1:C60 and
BDTP-2:C60. The OPV based on BDTP-1:C60 shows a 19% higher
short circuit current density (JSC) under simulated solar irradiation
and 18% higher external quantum efficiency (EQE) over the whole
absorbing region. The same trend was observed for all the OPVs
with different fullerene derivatives and a different content of C60
Figure 5. 2D H-13C HETCOR SS-NMR spectra for the mixed BHJ samples with
C
1
60 and (a) BDTP-1 and (b) BDTP-2 (polymer:C60 = 1:2 by weight). The
measurements are conducted with CP contact time of 15 ms. Schematic
representation of the C60 arrangement around the polymer main chain for (c)
BDTP-1 and (d) BDTP-2.
(polymer:C60 = 1:6 by weight) (Tables 1 and S3 and Figures S19-
21); the OPVs with BDTP-1 showed JSC values 14–58% higher
than those with BDTP-2 in the BHJ devices for all the fullerene
acceptors. The largest difference in JSC between BDTP-1 and
BDTP-2 was in the polymer:ICBA devices (higher by 58%).
The charge generation process in OPVs can be divided into
more primary processes of (1) light absorption and exciton
generation, (2) exciton migration, (3) exciton dissociation into a
charge pair at D/A interface, (4) dissociation of the charge pair
into free charges and (5) charge transport to the electrodes. Since
the macroscopic analyses (UV-vis absorption, XRD, GIWAXS,
AFM, TEM and space-charge-limited current) indicated that
BDTP-1 and BDTP-2 had identical electronic and electric
properties and similar mesoscopic structures in the BHJ films, the
similar efficiencies of the processes 1, 2, and 5 are expected.
Therefore, the differences in OPV performance, mainly JSC, can
be attributed to the difference of the efficiencies in the processes
of 3 and 4 which is induced by the local molecular arrangement
of the fullerenes around the polymer chains. In principle, the
electronic coupling between the excited states and the CT state
and the Coulombic binding energy of the CT state are important
for the processes 3 and 4, respectively, both of which can depend
on the molecular arrangement due to the D-A nature of the
polymers. The excited state of the D-A polymers have more
electron density localized on the A units, which facilitate the
process 3 if the A units are close to the electron acceptor.
Quantum chemical calculations based on density functional
theory (DFT) performed on a model polymer showed higher
electron density on the BDTQ units in the excited state (Figure
S24). Photoluminescence (PL) quenching measurements on
BDTP-1:C60 and BDTP-2:C60 films showed that the quenching
efficiency of BDTP-1 was slightly higher than that of BDTP-2
(Figure S22). Due to the low PL intensity, however, it was difficult
to quantitatively discuss the change in the efficiency of the
process 3 from the experiments. On the other hand, DFT
calculations on dyad models for the polymers/C60 interface
showed that the molecular arrangements around the polymer
chains can result in the significant difference of CT binding energy
Figure 6. (a) J-V curves under AM1.5 simulated solar light (100 mW cm–2
irradiation and (b) EQE spectra of OPVs with BDTP-1:C60 and BDTP-2:C60
BHJs films (polymer:C60 = 1:2 by weight).
)
Table 1. Summary of the performance of OPVs with BDTP-1 and BDTP-2
and various fullerene derivatives (polymer:C60 = 1:2 by weight). Each value
is the average of six devices with the standard deviation.
J
SC
BHJ layer
VOC (V)
–
FF
PCE (%)
2
(
mA cm )
BDTP-1:C60
BDTP-2:C60
0.65 ± 0.01
0.66 ± 0.02
3.7 ± 0.1
3.1 ± 0.1
0.39 ± 0.01
0.39 ± 0.01
0.95 ± 0.04
0.80 ± 0.03
BDTP-1:
PC61BM
0.79 ± 0.01
0.79 ± 0.02
0.80 ± 0.01
4.5 ± 0.2
3.9 ± 0.1
6.5 ± 0.1
0.54 ± 0.02
0.51 ± 0.02
0.56 ± 0.01
2.0 ± 0.1
1.6 ± 0.1
2.9 ± 0.1
BDTP-2:
PC61BM
BDTP-1:
PC71BM
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Angewandte Chemie International Edition
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and BDTP-1 could have a smaller binding energy than BDTP-2
[7]
[8]
[9]
S. Holliday, Y. Li, C. K. Luscombe, Prog. Polym. Sci. 2017, 70, 34-51.
X. Liu, H. Chen, S. Tan. Renew. Sust. Energ. Rev. 2015, 52, 1527-1538.
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2011, 123, 3051-3054; Angew. Chem. Int. Ed. 2011, 50, 2995-2998.
(see Supporting Information for the calculation details). At this
stage, we speculate that the molecular arrangement can affect
both the processes 3 and 4 simultaneously in OPVs.
[
[
[
10] M. Hiramoto, H. Fujiwara, M. Yokoyama, Appl. Phys. Lett. 1991, 58,
062-1064.
11] G. Yu, J. Gao, J. C. Hummelen, F. Wudl, A. J. Heeger, Science 1995,
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1
OPVs with BDTP-1 and BDTP-2 did not show a large
difference in the open circuit voltage (VOC) for each fullerene
derivative. Transient photovoltage measurement on OPVs
showed little difference in the carrier lifetime between the
polymers, indicating the similar recombination kinetics (Figure
S23). This may suggest that the position of fullerene relative to
2
2
[
[
13] R. A. Street., Adv. Mater. 2016, 28, 3814-3830.
14] T. M. Burke, S. Sweetnam, K. Vandewal, M. D. McGehee, Adv. Energy
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the D-A units has
a smaller effect on the bimolecular
recombination in BHJs than on the charge separation. The DFT
calculation of the model compound showed that the hole is quite
delocalized on the polymer chain (Figure S24c), which may
explain why the recombination was insensitive to the arrangement
of the fullerenes. Further investigation on the polymer design is
necessary to clarify their effects on the bimolecular recombination.
[
[
15] J. Lee, K. Vandewal, S. R. Yost, M. E. Bahlke, L. Goris, M. A. Baldo, J.
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Angewandte Chemie International Edition
10.1002/anie.201801173
COMMUNICATION
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COMMUNICATION
Carefully designed “polymer twins”,
BDTP-1 and BDTP-2, allowed us to
investigate the effects of alkyl side
chains on the molecular arrangement
around the semiconducting backbone
in the mixed bulk heterojunctions. 2D
solid-state NMR results show that the
positions of the fullerene can be
controlled by the side chain patterns,
which have correlation to the
performance of the OPVs.
Chao Wang, Kyohei Nakano, Hsiao
Fang Lee, Yujiao Chen, You-lee Hong,
Yusuke Nishiyama, and Keisuke Tajima*
Page No. – Page No.
Intermolecular arrangement of
fullerene acceptors around
semiconducting polymers in mixed
bulk heterojunctions
This article is protected by copyright. All rights reserved.