Acceptor-acceptor conjugated copolymers based on perylenediimide and benzothiadiazole for all-polymer solar cells

Article abstract of DOI:10.1002/pola.27108

Donor-acceptor (D-A) conjugated copolymers are one of known classes of organic optoelectronic materials and have been well developed. However, less attention has been paid on acceptor-acceptor (A-A) conjugated analogs. In this work, two types of A-A conjugated copolymers, namely P1-Cn and P2-Cn (n is the carbon number of their alkyl side chains), were designed and synthesized based on perylenediimide (PDI) and 2,1,3-benzothiadiazole (BT). Different from P1-Cn, P2-Cn polymers have additional acetylene π-spacers between PDI and BT and thus hold a more planar backbone configuration. Property studies revealed that P2-Cn polymers possess a much red-extended UV-vis absorption spectrum, stronger π-π interchain interactions, and one-order larger electron mobility in their neat film state than P1-Cn. However, all-polymer solar cells using P1-Cn as acceptor component and poly(3-hexyl thiophene) or poly(2,7-(9,9-didodecyl- fluoene)-alt-5,5′-(4,7-dithienyl-2-yl-2,1,3-benzothiadiazole) as donor component exhibited much better performance than those based on P2-Cn. Apart from their backbone chemical structure, the side chains were found to have little influence on the photophysical, electrochemical, and photovoltaic properties for both P1-Cn and P2-Cn polymers. 2014 Wiley Periodicals, Inc. J. Polym. Sci., Part A: Polym. Chem. 2014, 52, 1200-1215 Two types of acceptor-acceptor conjugated copolymers are designed and synthesized based on perylenediimide (PDI) and benzothiadiazole (BT) with and without acetylene π-spacers between PDI and BT units in their backbones. Their basic properties and photovoltaic performance as acceptor components for all-polymer solar cells are investigated and compared. Copyright

Full text of DOI:10.1002/pola.27108

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Acceptor–Acceptor Conjugated Copolymers Based on Perylenediimide
and Benzothiadiazole for All-Polymer Solar Cells
1
,2
2
3
2
2
2
Cong-Wu Ge, Chong-Yu Mei, Jun Ling, Jin-Tu Wang, Fu-Gang Zhao, Long Liang,
2
1
2
Hong-Jiao Li, Yong-Shu Xie, Wei-Shi Li
1
Key Laboratory for Advanced Materials and Institute of Fine Chemicals, East China University of Science and Technology,
Shanghai 200237, China
2
Laboratory of Organic Functional Materials and Chemistry, Shanghai Institute of Organic Chemistry, Chinese Academy of
Sciences, Shanghai 200032, China
3
Department of Polymer Science and Engineering, Zhejiang University, Hangzhou 310027, China
Correspondence to: Y.-S. Xie (E-mail: yshxie@ecust.edu.cn) or W.-S. Li (E-mail: liws@mail.sioc.ac.cn)
Received 13 November 2013; accepted 8 January 2014; published online 6 February 2014
DOI: 10.1002/pola.27108
ABSTRACT: Donor–acceptor (D–A) conjugated copolymers are
one of known classes of organic optoelectronic materials and
have been well developed. However, less attention has been
paid on acceptor–acceptor (A–A) conjugated analogs. In this
work, two types of A–A conjugated copolymers, namely P1-Cn
and P2-Cn (n is the carbon number of their alkyl side chains),
were designed and synthesized based on perylenediimide (PDI)
and 2,1,3-benzothiadiazole (BT). Different from P1-Cn, P2-Cn
polymers have additional acetylene p-spacers between PDI and
BT and thus hold a more planar backbone configuration. Prop-
erty studies revealed that P2-Cn polymers possess a much red-
extended UV–vis absorption spectrum, stronger p–p interchain
interactions, and one-order larger electron mobility in their
neat film state than P1-Cn. However, all-polymer solar cells
using P1-Cn as acceptor component and poly(3-hexyl thiophene)
0
or
poly(2,7-(9,9-didodecyl-fluoene)-alt25,5 -(4,7-dithienyl-2-yl-
2,1,3-benzothiadiazole) as donor component exhibited much
better performance than those based on P2-Cn. Apart from their
backbone chemical structure, the side chains were found to have
little influence on the photophysical, electrochemical, and photo-
voltaic properties for both P1-Cn and P2-Cn polymers. V
2014
C
Wiley Periodicals, Inc. J. Polym. Sci., Part A: Polym. Chem. 2014,
52, 1200–1215
KEYWORDS: conjugated polymers; conducting polymers;
organic solar cells; perylenediimides; structure-property
relations
INTRODUCTION Conjugated polymers possess
dimensional p-extended backbone, which endows them out-
a
one-
and easy of synthesis. Especially for the latter type, intramo-
lecular charge transfer (ICT) interactions generally occur
between electron-rich and electron-deficient units, where
electron (partially) transfers from the former to the latter.
Thus, the electron-rich unit behaves as an electron donor
(D), while the electron-deficient unit as an electron acceptor
(A), and the copolymer is referred as a donor–acceptor (D–
A) conjugated copolymer. This kind of copolymers usually
standing optic and electronic properties and a wide range of
1
applications in light-emitting diodes (LED), field effect tran-
2
3
4
5
sistors (FET), photovoltaics (PV), sensors, and so on.
Thanks for the invention of efficient palladium-mediated C–C
6
7
cross-coupling reactions including Stille, Suzuki, and Sono-
8
gashira types, alternative copolymers composed of at least
3
two different kinds of optoelectronic moieties have become
one of important classes in conjugated polymers besides
homopolymers. The flexible choice of composing units and
their organization styles benefits researchers to tailor the
material properties and functions adaptable to specific appli-
cations. To date, a large number of such alternative conju-
has a small band gap and a wide light absorption spectrum,
with some extreme cases the onset absorption wavelength
9
longer than 1000 nm. Furthermore, the combination of D
and A units makes it easy to tune the energy levels of the
resultant material. As a result, D–A copolymers are wel-
comed by a variety of applications. For example, organic pho-
tovoltaics (OPVs) have achieved a big progress in the past
1
–5
gated copolymers have been designed and synthesized.
3
However, for the most cases, the backbone adopted alterna-
tive two different electron-rich units or one electron-rich and
one electron-deficient unit owing to their robust properties
decade, where the power conversion efficiency (PCE) has
1
0
been raised from 3 to 5% before 2005 to nowadays over
1
1
9%. One important reason for such achievements is the
Additional Supporting Information may be found in the online version of this article.
2014 Wiley Periodicals, Inc.
V
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SCHEME 1 (a) Synthesis of P1-Cn and P2-Cn polymers. (b) Chemical structures of P3HT and PFDTBT.
1
7
development of a number of high performance D–A low
bandgap copolymers as donor component for the bulk heter-
such as quinoxaline and benzobisthiadiazole. The produced
A–A copolymers showed a best efficiency of 0.40% for their
OPV devices with P3HT. Zhan and coworkers synthesized A–
A copolymer based on perylenediimide (PDI) and fluorenone
3
,12
ojunction (BHJ) active layer of OPVs.
In addition to donor
material, D–A copolymers have also succeeded in application
as acceptor materials in place of fullerene derivatives for
1
8
and found it is a good air-stable n-type semiconductor.
Reynolds and coworkers reported the homopolymer of isoin-
digo and its copolymer with BT. Only homopolymer was
tested as electron acceptor for OPV devices with a best effi-
ciency of 0.47% in the work.
3
(c),3(d),13
OPVs.
Besides photovoltaics, D–A copolymers having
1
9
high performance FET properties with either p-type, n-type,
and ambipolar charge transportation nature have also been
2
,14
reported.
However, for alternative conjugated copolymers
composed of two different electron-deficient units (A–A
copolymers), the number of reported examples is very lim-
ited. Ober and coworkers synthesized an A–A copolymer
based on 2-alkylbenzotriazole and 2,1,3-benzothiadiazole
Here, we report two new types of A–A copolymers based on
PDI and BT (Scheme 1). PDI is a typical electron-deficient
unit with exceptional photochemical and thermal stability,
low LUMO energy level, and good electron transportation
2
21
(
BT) and demonstrated an electron mobility of 0.02 cm V
21
15
20
s
for its OFET devices. In a subsequent work, this A–A
properties. Its applications in optoelectronic devices can be
copolymer was applied as electron acceptor to combine with
poly(3-hexylthiophene) (P3HT) for all-polymer solar cells.
traced back to 1986 when Tang reported the first bilayer
OPV device. Later, a variety of small molecular PDI deriva-
1
6
21
However, the efficiency was not satisfied. Later, benzotriazole
unit was used to couple with other electron-deficient units,
tives and polymers bearing PDI moieties in the side chains
or in the backbone were explored as n-channel
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0
semiconductors and acceptor materials for OPVs.
The
spectroscopy was performed on a Hitachi U-3310 spectropho-
tometer at room temperature. Fluorescence spectroscopy was
performed on a Hitachi F4600 fluorophotometer. Cyclic vol-
tammetry (CV) was performed with both solution and film
samples on a CHI 660C instrument using a three-electrode cell
with a glassy carbon as working electrode, a platinum wire as
2
21 21
reported FET electron mobility surpasses 1 cm
V
s
,
while the OPV efficiency record over 3%. It is valuable to
point out that PDI has been used to combine with a number
of electron-donating units, such as dithienothiophene, oligo-
thiophene, carbazole, dithienopyrrole, and dibenzosilole, for
2
2,23
the construction of D–A conjugated copolymers.
All-
counter electrode, and Ag/AgNO as reference electrode. The
3
polymer PV cells using these PDI-based D–A copolymers as
acceptor component displayed promising performance with
an efficiency up to 2.23%. But for A–A type copolymers, only
one example (as mentioned in the above) has been
reported. This PDI-based A–A copolymer was investigated
only as n-type transistors for FET, not for PV application.
solution samples were prepared in CH Cl with a concentra-
2
2
21
tion of 0.1 mM, and measured under a scan rate of 100 mV s
in the presence of 0.1 M Bu NPF . The film samples were pre-
4
6
pared by casting their CHCl3 solutions onto a glass carbon
1
8
electrode, and then measured in CH CN in the presence of 0.1
3
21
M Bu NPF with a scan rate of 100 mV s . Thermogravimet-
4 6
ric analysis (TGA) was performed on a TGA Q500 instrument
BT is another popular electron-deficient building block for D–
ꢀ
21
under a nitrogen flow with a heating rate of 10 C min . Dif-
ferential scanning calorimetry (DSC) was performed using a
Q200 DSC instrument under a nitrogen atmosphere with heat-
3
A conjugated copolymers. The first photovoltaic D–A copoly-
2
4
mer was composed of pyrrole, thiophene, and BT. In 2003, a
0
famous D–A copolymer, poly(2,7-(9,9-dialkyl-fluoene)-alt-5,5 -
ꢀ
21
ing and cooling rate of 10 C min . Atomic force microscopy
AFM) was performed on a Veeco Nanoscope IIIa multimode
(
4,7-dithienyl-2-yl-2,1,3-benzothiadiazole) (PFDTBT), was
(
reported and displayed an impressing large open-circuit volt-
apparatus by a tapping mode with a silicon tip.
2
5
age (VOC) around 1 V. To date, BT was coupled with a vari-
3
26
27
ety of donor units, including carbazole, dibenzosilole,
Materials
2
8
29
30
germafluorene, dithienopyrrole, C- or Si-bridged dithio-
Unless indicated, all commercial reagents were used as
received. Reaction solvents were dehydrated following com-
mon methods, tetrahydrofuran (THF), toluene, triethylamine
(TEA), and diisopropylamine (DIPA) refluxed over a mixture
of sodium and benzophenone, while dichloromethane (DCM)
3
1
32
33
phenes, oligothiophene, and ladder-type moieties, for D–A
photovoltaic copolymers. Some of them exhibited promising
photovoltaic performance with a PCE record over 6%.
Considering high electron affinity for both PDI and BT units,
the combination of these two units to form A–A copolymers
is expected to produce interesting materials with exceptional
optoelectronic properties. With this motivation, we recently
designed and synthesized polymer P1-Cn and P2-Cn based
on PDI and BT (Scheme 1, n is the carbon number of the
side chain, R). As compared with P1-Cn, the structure of P2-
Cn has additional acetylene p-spacers between PDI and BT
units. Such design would relieve the steric hindrance
between PDI and BT, and thus may enable a better conjuga-
tion along the backbone. Both polymers were tested as elec-
tron acceptor component to couple with P3HT and PFDTBT
dried over CaH
use. Alkylamines (RNH
-hexyldecyl, 2-octyldodecyl, and 2-decyltetradecyl), 4,7-
bis(4,4,5,5-tetramethyl-1,3,2-dioxabrolan-2-yl) benzothiadia-
zole (BT2B), and 4,7-diethynylbenzothiadiazole (BT2ace)
were synthesized according to literature procedures. Polymer
2
under argon, and freshly distilled prior to
2
, R 5 3,7-dimethyloctyl, 2-butyloctyl,
34
2
35
36
PFDTBT with n-dodecyl side chains was prepared following
25
the reported method and was determined to have weight-
average molecular weight of 21.1 kDa and a PDI of 2.10.
P3HT was purchased from Lumtech (LT-S909).
0
N,N -Bis(2-Ethylhexyl)-3,4,9,10-Perylene Diimide (PDI-C8)
(
with n-dodecyl side chains, Scheme 1) donor materials for
A mixture of 3,4,9,10-perylenetetracarboxylic dianhydride
(2.35 g, 6 mmol), 2-ethylhexylamine (3.10 g, 24 mmol), zinc
acetate (0.88 g, 4.8 mmol), and imidazole (80 g) was stirred
at 160 C for 5 h under Ar atmosphere. After cool to room
temperature, the reaction mixture was added with HCl aque-
fabrication of OPV devices. Although P1-Cn polymers have a
poorer p-conjugation along the backbone, a wider bandgap,
and a lower electron mobility in neat film state than P2-Cn,
their OPV cells displayed better photovoltaic performance.
ꢀ
ous solution (2 M, 50 mL), followed by extraction with CH Cl2
2
EXPERIMENTAL
several times. The combined organic phases were dried over
Na SO . After filtration, the filtrate was concentrated and the
1
2
4
H NMR spectra were recorded on a Varian Mercury 300 or
residue was subjected to silica gel column chromatography
using CH Cl as an eluent. The product PDI-C8 (3.65 g) was
400 MHz spectrometer using CDCl3 or C D Cl as a solvent
2 2 4
2
2
and tetramethyl silane as an internal reference. Matrix-
assisted laser deionization time-of-flight (MALDI-TOF) mass
spectroscopy was performed on a Shimadzu Biotech Axima
Performance Mass Spectrometer using dithranol or a-cyano-
isolated as a deep red solid in a yield of 99%.
1
H NMR (300 MHz, CDCl , ppm): d 8.60 (d, J 5 7.8 Hz, 4H),
3
8.51 (d, J 5 8.4 Hz, 4H), 4.14 (d, J 5 7.5 Hz, 4H), 1.91 (m,
4-hydroxycinnamic acid (CHCA) as a matrix. Gel permeation
2H), 1.45–1.29 (m, 16H), 0.94 (m, 12H).
chromatography (GPC) was performed on a Waters 1515
HPLC instrument equipped with a Waters 2489 UV detector,
using CHCl3 as an eluent. The weight-average molecular
0
N,N -Bis(3,7-Dimethyloctyl)-3,4,9,10-Perylene Diimide
(PDI-C10)
weight (M ) and its polydispersity index (PDI) were calcu-
lated based on polystyrene standards. UV–vis absorption
PDI-C10 (1.71 g) was synthesized as deep red solid from
3,4,9,10-perylenetetracarboxylic dianhydride (1.02 g, 2.6
w
1
202
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mmol), 3,7-dimethyl-1-octylamine (1.64 g, 10.4 mmol), zinc
acetate (0.38 g, 2.08 mmol), and imidazole (45 g) following
a similar method as PDI-C8. Yield: 98%.
closed vial for 72 h. After cool to room temperature, the
reaction mixture was bubbling with Ar to remove the excess
bromine, and then concentrated under vacuum. The residue
was subjected to silica gel column chromatography, using
hexane/CHCl3 (1/10, v/v) as an eluent, affording 3.01 g
PDI2Br-C8 as deep red solid in a yield of 78%.
1
H NMR (300 MHz, CDCl , ppm): d 8.59 (d, J 5 8.1 Hz, 4H),
3
8
1
.48 (d, J 5 8.1 Hz, 4H), 4.19 (d, J 5 7.2 Hz, 4H), 1.75 (m, 2H),
.42–1.16 (m, 16H), 1.05 (m, 4H), 0.88 (d, J 5 6.6 Hz, 9H).
1
H NMR (300 MHz, CDCl , ppm): d 9.49 (d, J 5 8.4 Hz, 2H),
3
0
N,N -Bis(2-Butyloctyl)-3,4,9,10-Perylene Diimide
8.93 (s, 2H), 8.71 (d, J 5 8.4 Hz, 2H), 4.16 (d, J 5 6.6 Hz, 4H),
(
PDI-C12)
PDI-C12 (1.87 g) was synthesized as deep red solid from
,4,9,10-perylenetetracarboxylic dianhydride (1.02 g, 2.6
mmol), 2-butyloctylamine (1.91 g, 10.4 mmol), zinc acetate
0.38 g, 2.08 mmol), and imidazole (45 g) following a similar
1
.96 (m, 2H), 1.47–1.24 (m, 16H), 0.94 (m, 12H). MALDI-TOF
1
MS for C H Br N O : calcd 772.1; found: 772.8 (M ).
4
0
40
2 2 4
3
0
N,N -Bis(3,7-Dimethyloctyl)-1,7-Dibromo-3,4,9,10-Perylene
Diimide (PDI2Br-C10)
PDI2Br-C10 (1.48 g) was synthesized as deep red solid
from PDI-C10 (1.71 g, 2.55 mmol), bromine (24.45 g, 153
mmol), and CH Cl2 (80 mL) following a similar method as
PDI2Br-C8. Yield: 70%.
(
method as PDI-C8. Yield: 99%.
1
H NMR (300 MHz, CDCl , ppm): d 8.65 (d, J 5 8.1 Hz, 4H),
3
2
8
2
.57 (d, J 5 8.1 Hz, 4H), 4.14 (d, J 5 7.2 Hz, 4H), 2.01 (m,
H), 1.41–1.22 (m, 32H), 0.87 (m, 12H).
1
H NMR (300 MHz, CDCl , ppm): d 9.48 (d, J 5 8.1 Hz, 2H),
3
0
N,N -Bis(2-Hexyldecyl)-3,4,9,10-Perylene Diimide
(
8
1
0
.92 (s, 2H), 8.70 (d, J 5 8.1 Hz, 2H), 4.24 (d, J 5 8.4 Hz, 4H),
.74 (m, 2H), 1.37–1.16 (m, 16H), 1.04 (d, J 5 6.3 Hz, 6H),
.87 (d, J 5 6.6 Hz, 12H). MALDI-TOF MS for C H Br N O :
PDI-C16)
PDI-C16 (2.16 g) was synthesized as deep red solid from
,4,9,10-perylenetetracarboxylic dianhydride (1.02 g, 2.6
mmol), 2-hexyldecylamine (2.51 g, 10.4 mmol), zinc acetate
0.38 g, 2.08 mmol), and imidazole (45 g) following a similar
4
4
48
2 2 4
3
1
calcd 828.2; found: 828.5 (M ).
(
0
N,N -Bis(2-Butyloctyl)-1,7-Dibromo-3,4,9,10-Perylene
Diimide (PDI2Br-C12)
method as PDI-C8. Yield: 99%.
1
PDI2Br-C12 (1.65 g) was synthesized as deep red solid
from PDI-C12 (1.85 g, 2.55 mmol), bromine (24.45 g, 153
H NMR (300 MHz, CDCl , ppm): d 8.62 (d, J 5 8.1 Hz, 4H),
.53 (d, J 5 8.4 Hz, 4H), 4.15 (d, J 5 7.2 Hz, 4H), 2.00 (m,
H), 1.42–1.16 (m, 48H), 0.85 (m, 12H).
3
8
2
mmol), and CH Cl2 (80 mL) following a similar method as
2
PDI2Br-C8. Yield: 70%.
0
N,N -Bis(2-octyldodecyl)-3,4,9,10-Perylene Diimide
(
1
H NMR (300 MHz, CDCl , ppm): d 9.49 (d, J 5 8.4 Hz, 2H),
.92 (s, 2H), 8.70 (d, J 5 8.4 Hz, 2H), 4.14 (d, J 5 7.2 Hz, 4H),
3
PDI-C20)
PDI-C20 (2.42 g) was synthesized as deep red solid from
,4,9,10-perylenetetracarboxylic dianhydride (1.02 g, 2.6
mmol), 2-octyldodecylamine (3.09 g, 10.4 mmol), zinc ace-
tate (0.38 g, 2.08 mmol), and imidazole (45 g) following a
similar method as PDI-C8. Yield: 98%.
8
2
.00 (m, 2H), 1.52–1.07 (m, 32H), 0.88 (m, 12H). MALDI-TOF
3
1
MS for C48
H
56Br
2
N
2
O
4
: calcd 884.3; found: 886.0 ([M 1 H] ).
0
N,N -Bis(2-Hexyldecyl)-1,7-Dibromo-3,4,9,10-Perylene
Diimide (PDI2Br-C16)
PDI2Br-C16 (1.83 g) was synthesized as deep red solid
from PDI-C16 (2.13 g, 2.55 mmol), bromine (24.45 g, 153
1
H NMR (300 MHz, CDCl , ppm): d 8.59 (d, J 5 8.1 Hz, 4H),
.48 (d, J 5 8.1 Hz, 4H), 4.12 (d, J 5 6.9 Hz, 4H), 2.00 (m,
3
8
2H), 1.37–1.19 (m, 60H), 0.84 (m, 12H).
mmol), and CH Cl (80 mL) following a similar method as
2 2
PDI2Br-C8. Yield: 72%.
0
N,N -Bis(2-Decyltetradecyl)-3,4,9,10-Perylene Diimide
(
1
H NMR (300 MHz, CDCl , ppm): d 9.47 (d, J 5 8.1 Hz, 2H),
PDI-C24)
PDI-C24 (2.74 g) was synthesized as deep red solid from
,4,9,10-perylenetetracarboxylic dianhydride (1.02 g, 2.6
mmol), 2-decyltetradecylamine (3.68 g, 10.4 mmol), zinc ace-
tate (0.38 g, 2.08 mmol), and imidazole (45 g) following a
similar method as PDI-C8. Yield: 99%.
3
8.91 (s, 2H), 8.68 (d, J 5 8.1 Hz, 2H), 4.14 (d, J 5 7.2 Hz, 4H),
1.99 (m, 2H), 1.54–1.04 (m, 48H), 0.84 (m, 12H). MALDI-TOF
3
1
MS for C H Br N O : calcd 996.4; found: 998.1 ([M 1 H] ).
56 72
2 2 4
0
N,N -Bis(2-Octyldodecyl)-1,7-Dibromo-3,4,9,10-Perylene
Diimide (PDI2Br-C20)
1
H NMR (300 MHz, CDCl , ppm): d 8.65 (d, J 5 8.1 Hz, 4H),
.57 (d, J 5 8.1 Hz, 4H), 4.14 (d, J 5 7.5 Hz, 4H), 2.01 (m,
PDI2Br-C20 (2.12 g) was synthesized as deep red solid
from PDI-C20 (2.42 g, 2.55 mmol), bromine (24.45 g, 153
3
8
2H), 1.39–1.20 (m, 80H), 0.85 (m, 12H).
mmol), and CH Cl2 (80 mL) following a similar method as
2
PDI2Br-C8. Yield: 75%.
0
N,N -Bis(2-Ethylhexyl)-1,7-Dibromo-3,4,9,10-Perylene
Diimide (PDI2Br-C8)
1
H NMR (300 MHz, CDCl , ppm): d 9.39 (d, J 5 8.4 Hz, 2H),
3
A mixture of PDI-C8 (3.07 g, 5 mmol) and bromine (47.94 g,
8.94 (s, 2H), 8.61 (d, J 5 8.1 Hz, 2H), 4.12 (d, J 5 6.9 Hz, 4H),
1.98 (m, 2H), 1.34–1.18 (m, 64H), 0.84 (m, 12H). MALDI-TOF
ꢀ
3
00 mmol) in 100 mL CH Cl was stirred at 60 C in a
2
2
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MS for C H Br N O : calcd 1109.5; found: 1110.3
(br, 32H), 0.83 (br, 12H). Anal. Calcd for (C H N O S) : C,
54 58 4 4 n
75.49; H, 6.80; N, 6.52. Found: C, 74.54; H, 6.73; N, 5.96.
6
4
88
2
2
4
1
(
[M 1 H] ).
0
N,N -Bis(2-Decyltetradecyl)-1,7-Dibromo-3,4,9,10-Perylene
Diimide (PDI2Br-C24)
P1-C16
Yield: 61%. M
: 13.3 kDa, PDI: 1.58.
w
PDI2Br-C24 (2.49 g) was synthesized as deep red solid
from PDI-C24 (2.71 g, 2.55 mmol), bromine (24.45 g, 153
1
ꢀ
H NMR (400 MHz, C
2
D
2
Cl
4
, 110 C, ppm): d 8.93 (br, 2H),
8
(
.40 (br, 4H), 7.79 (br, 2H), 4.28 (br, 4H), 2.20 (br, 2H), 1.35
br, 48H), 0.84 (br, 12H). Anal. Calcd for (C H N O S) : C,
mmol), and CH Cl2 (80 mL) following a similar method as
2
6
2
74
4
4
n
PDI2Br-C8. Yield: 80%.
7
6.66; H, 7.68; N, 5.77. Found: C, 75.72; H, 7.54; N, 5.40.
1
3
H NMR (300 MHz, CDCl , ppm): d 9.39 (d, J 5 8.1 Hz, 2H), 8.83
P1-C20
(s, 2H), 8.60 (d, J 5 8.1 Hz, 2H), 4.12 (d, J 5 6.9 Hz, 4H), 1.98
Yield: 57%. M : 7.76 kDa, PDI: 1.43.
w
(
m, 2H), 1.32–1.19 (m, 80H), 0.85 (m, 12H). MALDI-TOF MS for
1
C H Br N O : calcd 1121.6; found: 1122.2 ([M 1 H] ).
1
7
2
104
2
2
4
ꢀ
H NMR (400 MHz, C D Cl , 110 C, ppm): d 8.84 (br, 2H),
2
2
4
8
.31 (br, 4H), 7.83 (br, 2H), 4.23 (br, 4H), 2.09 (br, 2H), 1.20
S) : C,
7.59; H, 8.37; N, 5.17. Found: C, 76.30; H, 8.05; N, 4.90.
General Procedure for Synthesis of P1-Cn (n 5 8, 10, 12,
6, 20, and 24)
A mixture of dibromo-monomer (PDI2Br-Cn, n 5 8, 10, 12,
6, 20, or 24, 0.6 mmol), BT2B (0.23 g, 0.6 mmol), tetrakis-
triphenylphosphine)-palladium (13.50 mg, 12 mmol), aque-
ous KOAc solution (2 M, 20 mL), aliquat 336 (two to three
drops), and toluene (20 mL) was subjected to degas thor-
oughly by freeze–pump–thaw cycling three times, and then
(
br, 64H), 0.78 (br, 12H). Anal. Calcd for (C70
H
90
N
4
O
4
n
1
7
1
(
P1-C24
w
Yield: 59%. M : 6.98 kDa, PDI: 1.48.
1
ꢀ
H NMR (400 MHz, C D Cl , 110 C, ppm): d 8.97 (br, 2H),
2
2
4
8.50 (br, 4H), 7.83 (br, 2H), 4.20 (br, 4H), 2.10 (br, 2H), 1.30
(br, 66H), 0.79 (br, 12H). Anal. Calcd for (C H N O S) : C,
78.35; H, 8.93; N, 4.69. Found: C, 77.54; H, 8.67; N, 4.42.
ꢀ
stirred at 95 C for 72 h under argon. Afterward, phenylbor-
7
8
106
4
4
n
21
onic acid in toluene solution (100 mg mL , 1 mL) was added.
After the reaction mixture was stirred at 95 C for 4 h, bromo-
ꢀ
General Procedure for Synthesis of P2-Cn
benzene (1 mL) was added and the reaction mixture was
stirred for another 4 h to complete the end-capping proce-
dure. The whole mixture was cooled to room temperature
(
n 5 12 and 20)
A mixture of dibromo-monomer (PDI2Br-C12 or PDI2Br-C20,
.187 mmol), BT2ace (31.40 mg, 0.17 mmol), tetrakis(triphe-
nylphosphine) palladium (6.50 mg, 5 lmol), copper iodide
2.14 mg, 10 lmol), diisopropylamine (10 mL), and toluene (20
0
and poured into CH OH (300 mL) to precipitate the product.
3
3
After filtration, the crude product was washed with CH OH,
(
dried in vacuum, and subjected to Soxhlet extraction with a
sequence of CH OH, acetone, hexane, and CHCl . Finally, the
mL) was subjected to degas thoroughly by freeze–pump–thaw
3
3
ꢀ
cycling three times, and then stirred at 70 C for 10 h under
CHCl fraction was concentrated, filtered through a 0.20 mm
3
argon. Afterward, phenylacetylene (0.1 mL) was added and the
Nylon filter to remove the insoluble impurities, and further
subjected to size exclusion chromatography with Bio-Beads
SX1 (Bio-Rad) column using chloroform as an eluent. The P1-
Cn polymers were obtained as atropurpureus solid.
ꢀ
reaction mixture was stirred at 70 C for 2 h to complete the
end-capping procedure. The whole reaction mixture was cooled
to room temperature and poured into CH OH (200 mL) to pre-
3
cipitate the product. After filtration, the crude polymer was
P1-C8
washed with CH OH, dried in vacuum, and subjected to Soxhlet
3
Yield: 55%. M : 12.8 kDa, PDI: 1.89.
extraction with a sequence of CH OH, acetone, hexane, and
w
3
CHCl . Finally, the CHCl3 fraction was concentrated, filtered
3
1
ꢀ
H NMR (400 MHz, C D Cl , 110 C, ppm): d 8.81 (br, 2H),
2
2
4
through a 0.20 lm Nylon filter to remove the insoluble impur-
ities, and further subjected to size exclusion chromatography
with a Bio-Beads SX1 (Bio-Rad) column using chloroform as an
eluent. The P2-Cn polymers were obtained as black solid.
8
.35 (br, 4H), 7.66 (br, 2H), 4.25 (br, 4H), 2.07 (br, 2H), 1.36
(
br, 16H), 0.88 (br, 12H). Anal. Calcd for (C H N O S) : C,
46 42 4 4 n
7
3.97; H, 5.67; N, 7.50. Found: C, 72.82; H, 5.76; N, 6.94.
P1-C10
Yield: 64%. M : 20.4 kDa, PDI: 2.26.
P2-C12
w
Yield: 76%. M : 38.7 kDa, PDI: 5.71.
w
1
ꢀ
H NMR (400 MHz, C D Cl , 110 C, ppm): d 8.84 (br, 2H),
1
ꢀ
H NMR (400 MHz, C D Cl , 110 C, ppm): d 8.75 (br, 2H),
2 2 4
.49 (br, 4H), 7.79 (br, 2H), 4.21 (br, 4H), 2.06 (br, 2H), 1.32
2
2
4
8
.40 (br, 4H), 7.80 (br, 2H), 4.21 (br, 4H), 2.10 (br, 2H), 1.31
8
(
br, 20H), 0.81 (br, 18H). Anal. Calcd for (C H N O S) : C,
50 50 4 4 n
(br, 32H), 0.86 (br, 12H). Anal. Calcd for (C H N O S) : C,
58 58 4 4 n
7
7
4.78; H, 6.28; N, 6.98. Found: C, 73.58; H, 6.38; N, 6.47.
6.79; H, 6.44; N, 6.18. Found: C, 75.83; H, 6.37; N, 6.38.
P1-C12
P2-C20
Yield: 71%. M : 11.9 kDa, PDI: 1.69.
Yield: 83%. M : 223.0 kDa, PDI: 5.44.
w
w
1
ꢀ
1
ꢀ
H NMR (400 MHz, C D Cl , 110 C, ppm): d 8.77 (br, 2H),
2 2 4
H NMR (400 MHz, C D Cl , 110 C, ppm): d 8.91 (br, 2H),
2
2
4
8.58 (br, 4H), 7.81 (br, 2H), 4.26 (br, 4H), 2.17 (br, 2H), 1.36
8.56 (br, 4H), 7.83 (br, 2H), 4.31 (br, 4H), 2.10 (br, 2H), 1.37
1
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(
7
br, 64H), 0.88 (br, 12H). Anal. Calcd for (C H N O S) : C,
8.54; H, 8.02; N, 4.95. Found: C, 78.25; H, 7.97; N, 4.77.
TABLE 1 Molecular Weight, PDI, Yield, and Thermal Decompo-
sition Temperature of P1-Cn and P2-Cn
7
4
90
4
4
n
ꢀ
d
T ( C)
a
Polymer
Yield (%)
M
w
(kDa)
PDI
Device Fabrication and Characterization
The OPV cells were fabricated with a structure of ITO/
PEDOT:PSS/active layer/Ca/Al. First, indium tin oxide (ITO)-
P1-C8
55
64
71
61
57
59
76
83
12.8
20.4
11.9
13.3
7.76
6.98
38.7
1.89
2.26
1.69
1.58
1.43
1.48
5.71
5.44
445
439
432
428
424
421
254
255
P1-C10
P1-C12
P1-C16
P1-C20
P1-C24
P2-C12
P2-C20
21
coated glass substrates with sheet resistance ꢁ10 X sq
were cleaned successively by ultrasonication in detergent,
deionized water, acetone, and isopropyl alcohol, and then
subjected to UV/ozone cleaning for 20 min. Second,
poly(3,4-ethylenedioxythiophene):poly(styrenesulfonate)
(
PEDOT:PSS, Heraeus Clevios P VP. Al 4083) was spin-coated
on the top of ITO layer from its aqueous solution and baked
223.0
ꢀ
at 150 C for 10 min, giving a thickness about 30 nm. The
a
active layer was the blend film of the test polymer (P1-Cn
or P2-Cn) with P3HT or PFDTBT in a weight ratio of 1:1.
The film was prepared by spin-coating from an o-dichloro-
benzene (ODCB) solution with a total weight concentration
d
The decomposition temperature T was taken at 5% of weight loss.
referred to polystyrene standards (Table 1). In contrast, P2-
Cn polymers have a larger molecular weight up to 223 kDa,
but with a very broad polydispersity. This fact implies that
the integration of acetylene p-spacers and the change of
palladium-mediated C–C coupling reaction type made the
polymerization more smoothly.
21
of 20 mg mL at a speed rate of 2000 rpm for 60 s in a
nitrogen-filled glovebox. For the P3HT-based cells, the plates
ꢀ
were annealed at 120 C for 15 min, while the PFDTBT-
ꢀ
based cells were annealed at 110 C for 15 min. Finally, 10
nm-thick Ca layer and a 100 nm-thick Al layer were subse-
quently thermally deposited on the top of the active layer
All the synthesized polymers have good solubility in com-
mon organic solvents, such as chloroform, toluene, chloro-
benzene, and THF. Thermogravimetric analysis (TGA)
2
6
under a high vacuum (10 mbar) through a shadow mask.
2
The effective area was 7 mm for each cell. The layer thick-
ness was measured with a Veeco Dektak 150 profilometer.
Current density–voltage (J–V) curves were recorded on a
Keithley 2420 source meter. Photocurrent was acquired
upon irradiation using an AAA solar simulator (Oriel
revealed that P1-Cn polymers have good thermal stability
ꢀ
with a 5%-weight-loss temperature (T
) higher than 400 C
d
(Table 1 and Supporting Information Fig. S21). The insertion
of acetylene p-spacers in the backbone lowered the thermal
9
4043A, 450 W) with AM 1.5G filter. The intensity was
stability. The T
d
for polymer P2-C12 and P2-C20 decreases
2
2
ꢀ
adjusted to be 100 mW cm
under the calibration with a
to 254 and 255 C, respectively. Differential scanning calo-
NREL-certified standard silicon cell (Orial reference cell
1150). External quantum efficiency (EQE) was detected
with a 75 W Xe lamp, Oriel monochromator 74125, optical
chopper, lock-in amplifier, and a NREL-calibrated crystalline
silicon cell. All measurements were performed in a nitrogen-
filled glovebox at room temperature.
rimetry (DSC) showed that P1-C12 and P1-C20 have a
ꢀ
9
phase transition temperature around 163 C in the heating
ꢀ
process while 117 C in cooling process (Supporting Infor-
mation Fig. S22). Optical microscopy confirmed that these
ꢀ
two polymers does not melt over 250 C upon heating, sug-
gesting such DSC enthalpy peaks are due to some kind of
solid-to-solid phase transition. In contrast, no phase transi-
tion was observed in the DSC traces of P2-C12 and P2-C20
RESULTS AND DISCUSSION
ꢀ
in the temperature range of 0–200 C.
Synthesis and Thermal Properties
The syntheses of the monomers and polymers are outlined
in Scheme 1. The key monomers, PDI2Br-Cn (n 5 8, 10, 12,
Solution Properties
The spectroscopy in dilute solution generally reflects inher-
ent properties of a single molecule or a single strand of poly-
mers. Figure 1 displays UV–vis absorption spectra of P1-C20
and P2-C20 in CHCl3 solution with a concentration of 0.01
mM at room temperature. For the comparison purpose, the
spectra of their component compounds, PDI-C20, BT, and
BT2ace, are also shown. All the data are summarized in
Table 2. In the range of 250–800 nm, polymer P1-C20 exhib-
its three main absorption peaks 277, 395, and 486 nm, and
a shoulder around 550 nm. These peaks are different from
those of BT (305 and 312 nm) and PDI-C20 (262, 459, 490,
and 526 nm). Although the apex of the longest absorption
peak of P1-C20 (486 nm) locates in the blue region to that
of PDI-C20 (526 nm), its absorption onset (593 nm) has lon-
ger wavelength than that of PDI-C20 (547 nm). These
16, 20, and 24), were prepared from perylenetetracarboxylic
dianhydride first by amidation with the corresponding alkyl
3
7
amine, followed by bromination with bromine. The total
yields for the two steps were higher and the reaction condi-
tions were milder than another popular method in litera-
3
8
tures, in which the above two steps were reverse. After
Suzuki coupling of PDI2Br-Cn with BT2B, polymer P1-Cn
(n 5 8, 10, 12, 16, 20, and 24) were produced in a moderate
yield in the range of 55–71% (Table 1). Meanwhile,
Sonogashira-coupling polymerization between PDI2Br-Cn
and BT2ace afforded polymer P2-Cn (n 5 12 and 20) having
acetylene p-spacers in the backbone. The so prepared P1-Cn
polymers have a weight-average molecular weight (M ) in
w
the range of 6.98–20.4 kDa with a PDI of 1.48–2.26, as
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absorption peak is as large as 114 nm, suggesting the back-
bone of polymer P2-C20 is in good p-conjugation. It is not
clear at this stage the above red shift is due to the presence
of an ICT band between BT and PDI units or not. As ICT
3
bands are often observed with D–A copolymers, but not yet
with A–A type copolymers, the further study on the origina-
tion of the above band transitions of P2-C20 would be
meaningful and is now in progress.
The further comparison was performed between P1-C20 and
P2-C20. Obviously, P2-C20 has a wider absorption spectrum,
which extends up to 700 nm. In contrast, the absorption
spectrum of P1-C20 is limited to 600 nm. Calculated from
their absorption onset, the optical band gaps (Eg,opt) of poly-
mer P1-C20 and P2-C20 are 2.09 eV and 1.76 eV, respec-
tively (Table 2). The latter is 0.33 eV lower than the former,
demonstrating the better p-conjugation in P2-C20 than in
P1-C20. These results illustrate that the acetylene p-spacers
between BT and PDI units have great effect on the backbone
p-conjugation and thus photophysical properties of the
polymers.
FIGURE 1 UV–vis absorption spectra of P1-C20 and P2-C20
polymers, and their component compounds, BT, BT2ace, and
The side chains of P1-Cn have little effect on their UV–vis
absorption properties, as all these polymers showed nearly
3
PDI-C20 in CHCl with a concentration of 0.01 mM at room
temperature. [Color figure can be viewed in the online issue,
which is available at wileyonlinelibrary.com.]
identical spectra in CHCl (Supporting Information Fig. S23).
3
However, compared with P2-C12, P2-C20 displays a red-
shifted absorption spectrum (kmax: 460 nm vs. 434 nm). As
P2-C20 has a quite larger molecular weight than P2-C12
observations indicate p-electron conjugation does occur
between BT and PDI moieties in P1-C20 polymer backbone
but with a limited extent. In contrast, polymer P2-C20 dis-
plays a broad and intense absorption plateau from 400 to
(
Table 1), the observed spectral difference may be caused by
large difference in molecular weight of the polymers. For all
polymers, the molar absorption coefficients are in the range
700 nm, together with two peaks at 284 and 319 nm. The
4
21
21
of 10
M
cm , suggesting the effective light-acquisition
presence of such plateau is owing to the overlap of a couple
of absorption peaks, including 460, 589, and 640 nm. As
compared with PDI-C20 and BT2ace (the longest absorption
peak at 366 nm), polymer P2-C20 displays an obvious red-
extended absorption spectrum. The red shift for the longest
capabilities in their light-responsive spectra (Table 2).
The redox properties of polymer P1-C20 and P2-C20 and
their component compounds were measured by CV in
CH Cl2 solution [Fig. 2(a) and Table 2]. Polymer P1-C20
2
TABLE 2 Optical and Electrochemical Properties of PDI-C20, BT, BT2ace, and Polymer P1-Cn and P2-Cn in Solution
k
onset
E
ox,onset
E
red,onset
E
HOMO
b
E
LUMO
c
E
g,opt
d
E
g,CV
a
e
Sample
k
max (nm)
(nm)
(V)
(V)
(eV)
(eV)
(eV)
(eV)
PDI-C20
BT
262 (5.8), 459 (2.1), 490 (5.0), 526 (8.1)
305 (9.9), 312 (10.0)
547
350
407
600
603
604
600
593
600
671
704
0.91
0.99
0.99
0.91
0.92
0.92
0.92
0.91
0.91
0.92
0.91
20.77
21.01
20.87
20.76
20.78
20.79
20.77
20.77
20.79
20.67
20.69
25.63
25.71
25.71
25.63
25.64
25.64
25.64
25.63
25.63
25.64
25.63
23.95
23.71
23.85
23.96
23.94
23.93
23.95
23.95
23.93
24.05
24.03
2.27
3.54
3.05
2.07
2.06
2.05
2.07
2.09
2.07
1.85
1.76
1.68
2.00
1.86
1.67
1.70
1.71
1.69
1.68
1.70
1.59
1.60
BT2ace
P1-C8
265 (8.1), 310 (4.6), 323 (6.0), 366 (3.6)
278 (8.8), 399 (3.9), 492 (2.7)
278 (9.3), 399 (4.5), 488 (3.1)
278 (8.0), 400 (4.1), 491 (2.9)
278 (7.1), 400 (4.0), 487(2.8)
277 (7.2), 395 (3.9), 486 (2.8)
277 (7.4), 392 (3.3), 493 (2.7)
284 (5.5), 434 (3.2), 530 (2.6)
284 (5.8), 319 (5.6), 460 (4.6), 640 (2.9)
P1-C10
P1-C12
P1-C16
P1-C20
P1-C24
P2-C12
P2-C20
a
c
Data in parentheses are molar absorption coefficients (e) in solution in
Calculated by 2(4.8 2 EFc/Fc1 1 Ered,onset).
4
21
21
d
e
a unit of 10
b
M
cm
.
Calculated by 1,240/konset
.
Calculated by 2(4.8 2 EFc/Fc1 1 Eox,onset).
Calculated by ELUMO 2 EHOMO
.
1
206
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FIGURE 2 (a) CV profiles and (b) energy diagram of PDI-C20, BT, BT2ace, and polymer P1-C20 and P2-C20 in CH
Cl
2 2
. [Color figure
can be viewed in the online issue, which is available at wileyonlinelibrary.com.]
displayed reduction peaks during 20.5 to 21.5 V and oxida-
tion peaks in 0.9–1.3 V, with onset potentials of 20.77 V and
slightly higher than BT2ace (25.71 eV), whereas its LUMO
(24.03 eV) is lower than both PDI-C20 (23.95 eV) and
BT2ace (23.85 eV). These energy level diagrams are out-
lined in Figure 2(b). However, for their side chains, the influ-
ence on the redox properties in solution is negligible (Table
2 and Supporting Information Fig. S24).
0
.91 V, respectively. Based on the experimental fact that fer-
1
rocene/ferrocenium (Fc/Fc ) redox potential (its standard
3
9
energy level is 4.8 eV as relative to vacuum ) was measured
to be 0.08 V under the same conditions, the lowest unoccu-
pied molecular orbital (LUMO) and the highest occupied
molecular orbital (HOMO) energy levels of P1-C20 were cal-
culated to be 23.95 eV and 25.63 eV, respectively. Mean-
while, the LUMO and HOMO energy levels of its component
compounds were measured to be 23.95 eV and 25.63 eV
for PDI-C20, while 23.71 eV and 25.71 eV for BT, respec-
tively. The data indicate polymer P1-C20 has a same HOMO
and LUMO level as that of PDI-C20, and a slightly higher
HOMO level and a deeper LUMO than BT. Under the same
way, we also found that the HOMO energy level of polymer
P2-C20 (25.63 eV) is the same as PDI-C20 (25.63 eV) but
To penetrate the backbone geometry and theoretically under-
stand the origination of their molecular orbitals, density
4
0
functional theory (DFT) studies were performed at the
4
1
B3LYP /6–31G** level with a Gaussian 03 program pack-
4
2
age. For both polymer families, trimers with methyl side
chains were used as model compounds. Their optimized
molecular geometries and the electron wave functions of the
HOMO and LUMO orbitals are displayed in Figure 3.
It is clear that the backbone of P1-Cn is in vastly twisted
state. The PDI units are not planar with twisting angles
FIGURE 3 Optimized molecular geometries and electron wave functions of HOMO and LUMO orbitals of the trimer models for P1-
Cn and P2-Cn via DFT calculation. [Color figure can be viewed in the online issue, which is available at wileyonlinelibrary.com.]
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HOMO of polymer P1-Cn, electron density is delocalized
through both PDI and BT units, suggesting the p-conjugation
between them. However, in its LUMO orbital, electron density
mainly localizes on PDI units. In the case of P2-Cn, electron
density resides in PDI and BT units for both HOMO and
LUMO orbitals, implying a good p-conjugation. The calculated
HOMO and LUMO energy levels are 26.22 and 24.01 eV for
P1-Cn, and 26.01 and 24.13 eV for P2-Cn, respectively.
Thus, the calculated energy gap of P1-Cn is 2.22 eV, whereas
that of P2-Cn is 1.88 eV. The results show that P2-Cn has a
low-lying LUMO and a smaller energy gap than P1-Cn, coin-
ciding with electrochemical observations.
Film Properties
Film properties are vitally important for those materials
used in film devices. They are not only determined by the
material chemical composition but also intimately governed
by the molecular/chain packing structure in the film and
specific intermolecular/interchain interactions. Figure 4 com-
pares the UV–vis absorption spectra of P1-C12, P1-C20, P2-
C12, and P2-C20 films (solid lines) with their solution ones
FIGURE 4 UV–vis absorption spectra of P1-C12, P1-C20, P2-
3
C12, and P2-C20 in film state. Their spectra in CHCl solution
(
dot lines). For polymer P1-C12 and P1-C20, the film spec-
are shown as dot curves for comparison. [Color figure can be
viewed in the online issue, which is available at wileyonlineli-
brary.com.]
tra displayed quite similar shape but with slightly red-
shifted apex positions (6–11 nm). When the side chain of
P1-Cn becomes larger, the relative intensity of the longest
peak (ꢂ500 nm) as referred to the second one (ꢂ400 nm)
decreases gradually (Fig. 4 and Supporting Information Fig.
S25). This implies that interchain interaction becomes
weaker in the polymer with larger side chains. In the cases
of P2-Cn, P2-C12 exhibits an apex at 444 nm, slightly red-
shifted from that in solution (10 nm). Interestingly, P2-C20
displays a more extended absorption plateau up to 674 nm
and increases the relative absorption intensity in the longer
wavelength region in the film state. These spectral changes
suggest the occurrence of intense interchain interactions in
the polymer P2-C20 film, which would be good for its pho-
tovoltaic application. From their onset absorption points, the
optical energy gaps (Eg,opt) were evaluated (Table 3). For
between two naphthalene moieties being in the range of
ꢀ
2
0.1–22.0 . The dihedral angles between BT and the con-
ꢀ
nected naphthalene moiety are as large as 50.5–55.6 , imply-
ing their p-conjugation is poor. In contrast, the backbone of
P2-Cn is much planar. The twisting angles between the two
naphthalene moieties of the PDI units decrease to 14.1–
ꢀ
1
4.5 . More importantly, the dihedral angles between BT and
ꢀ
PDI units become 11.6–15.0 , much smaller than those for
P1-Cn. These results indicate the insertion of acetylene
spacers effectively releases the steric hindrance between BT
and PDI and enables a better p-conjugation, which is consist-
ent with the observations in UV–vis spectroscopy. In the
TABLE 3 Optical and Electrochemical Properties of Polymer P1-Cn and P2-Cn in Film State
2
5
2
k
onset
E
ox,onset
E
red,onset
E
HOMO
b
E
LUMO
c
E
g,opt
d
E
g,CV
e
m
V
e
(10 cm
21 21
a
Polymer
k
max (nm)
(nm)
(V)
(V)
(eV)
(eV)
(eV)
(eV)
s
)
P1-C8
278 (5.9), 406 (5.1), 482 (4.1)
278 (6.7), 406 (5.5), 478 (4.1)
278 (8.4), 406 (6.8), 478 (5.4)
278 (8.2), 406 (7.4), 475 (5.5)
278 (7.5), 406 (6.1), 476 (4.6)
278 (6.1), 404 (5.1), 476 (4.2)
314 (5.7), 444 (5.1)
627
632
622
619
617
618
704
725
0.93
0.95
0.93
0.92
0.87
0.86
20.70
20.68
20.71
20.72
20.80
20.80
20.65
20.73
25.65
25.67
25.65
25.64
25.59
25.58
–
24.02
24.03
24.01
24.00
23.92
23.92
24.07
23.99
1.98
1.96
1.99
2.00
2.01
2.01
1.76
1.71
1.63
1.64
1.64
1.64
1.67
1.66
–
3.5 6 0.3
8.1 6 0.7
4.8 6 0.2
4.6 6 0.6
5.4 6 0.7
3.1 6 0.1
11.1 6 1.0
20.3 6 2.6
P1-C10
P1-C12
P1-C16
P1-C20
P1-C24
P2-C12
P2-C20
f
–
f
326 (6.8), 466 (7.0), 674 (5.2)
–
–
–
a
d
Data in paratheses are absorption coefficients of the films in a unit of
Calculated by 1,240/konset.
Calculated by ELUMO 2 EHOMO
No oxidation peak was found.
6
21
e
f
1
b
0
cm , estimated from dividing the absorbance by film thickness.
.
Calculated by 2(4.8 2 EFc/Fc1 1 Eox,onset).
Calculated by 2(4.8 2 EFc/Fc1 1 Ered,onset).
c
1
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semiconductors is electron mobility. In this work, we used
space-charge-limited current (SCLC) method with a device
configuration of glass/Al/polymer/Al to measure electron
4
3
mobility. According to Mott–Gurney law, SCLC theory can
be described by
2
9
ðVa2VbiÞ
J5 e0erl
;
3
8
d
where J is current density, e is permittivity of vacuum, e is
0
r
a
relative permittivity of the material, m is mobility, V is
applied voltage, Vbi is built-in voltage, and d is the thickness
of the active film. The measurements show that P1-Cn poly-
2
5
2
21
mers have electron mobility in the order of 10
s
(
cm
, whereas P2-Cn polymers have one-order higher values
Table 3 and Supporting Information Fig. S26). A more pla-
V
21
nar backbone, intense interchain interactions, and slightly
regular packing structure in film state may account for this
better electron mobility observed for P2-Cn. However, the
side chains have little influence on electron transport for
both P1-Cn and P2-Cn.
Photovoltaic Properties
As A–A copolymers have great potential to be used as elec-
tron acceptors in OPVs, we evaluated this aspect properties
of P1-Cn and P2-Cn with a device structure of glass/ITO/
PEDOT:PSS/active layer/Ca/Al. In this work, two donor poly-
mers, P3HT and PFDTBT, were chosen to couple with P1-Cn
or P2-Cn for the fabrication of the BHJ active layer. Such
consideration is owing to P3HT represents a typical donor
material in the field while PFDTBT possesses a narrower
FIGURE 5 CV profiles of P1-Cn (n 5 8, 10, 12, 16, 20, and 24)
and P2-Cn (n 5 12 and 20) polymer films. [Color figure can be
viewed in the online issue, which is available at wileyonlineli-
brary.com.]
both P1-Cn and P2-Cn, the data slightly decrease as referred
to their solution values (Table 2).
25
bandgap and low-lying HOMO and LUMO energy levels.
For evaluating the photovoltaic performance of the polymers
as acceptor material for all-polymer solar cells, the device
Figure 5 displays CV profiles of P1-Cn and P2-Cn polymers
measured in film states. The onset potentials for their first
oxidation and reduction, and the calculated HOMO and
LUMO energy levels are listed in Table 3. As compared with
those in solution (Table 2), these electrochemical data do
not alter significantly.
To reveal polymer chain packing structure in film state, X-
ray diffraction (XRD) was performed on P1-C20 and P2-C20
films (Fig. 6). For P1-C20 film, only a broad peak was
ꢀ
observed in the range of 15–25 , indicating an amorphous
structure. However, the P2-C20 film showed an additional
ꢀ
broad diffraction peak during 5–8 , suggesting a slightly reg-
ular packing among its polymer chains. In another set of
experiments, we found P1-C12 and P2-C12 films had amor-
phous structure similar to those of P1-C20 and P2-C20
(
Supporting Information Fig. S29), suggesting little influence
of the side chain on their film structure for both P1-Cn and
ꢀ
P2-Cn. Furthermore, annealing at 120 C for 10 min did not
change the film structure.
As all the polymers have a relatively low-lying LUMO level
(
around 24.00 eV), they are generally n-type organic semi-
FIGURE 6 XRD profiles of P1-C20 and P2-C20 films casting
from their CHCl3 solutions. [Color figure can be viewed in the
online issue, which is available at wileyonlinelibrary.com.]
conductors and have potential to be used as electron accept-
ors in OPVs. One of important properties of n-type
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fabrication conditions were first subjected to optimization
using one polymer to represent its class (Supporting Infor-
mation Tables S1–S7). For P1-Cn/P3HT-based all-polymer
solar cells, the optimization was performed with P1-C10 and
found the best conditions were donor/acceptor weight ratio
to be 1:1, using o-dichlorobenzene (ODCB) as a processing
ꢀ
solvent, spin-coated at 2000 rpm, and annealed at 120
C
for 15 min. For all-polymer solar cells based on P2-Cn/
P3HT, optimization with P2-C20 gave the best conditions
similar to those for P1-C10/P3HT cells. In the case of
PFDTBT as donor material, the optimization was only car-
ried with P1-C10, and found the suitable conditions for the
device fabrication were donor/acceptor weight ratio to be
1
:1, using ODCB as a processing solvent, spin-coated at 800
ꢀ
rpm, and annealed at 110 C for 15 min.
As for P2-Cn series only P2-C12 and P2-C20 were synthe-
sized, we compared photovoltaic performance of P1-Cn and
P2-Cn among P1-C12, P1-C20, P2-C12, and P2-C20. Eight
all-polymer solar cells based P1-C12, P1-C20, P2-C12, or
P2-C20 as acceptor while P3HT or PFDTBT as donor mate-
rial were fabricated following the above optimized condi-
tions. Their current–voltage (J–V) curves are displayed in
Figure 7(a) and device parameters are summarized in Table
4. From these data, it is clear that P1-Cn showed a better
photovoltaic performance than P2-Cn, while the influences
from their side chains were small. For example, in the cases
of P3HT as donor material, the cell based on P1-C20 exhib-
ited a V of 0.54 V, a short-circuit current (J ) of 0.69 mA
OC
SC
2
2
cm , and a fill factor (FF) of 41.5%, giving a PCE of 0.15%.
The P1-C12-based solar cell displayed similar device per-
formance, with a PCE of 0.14%. However, when the acceptor
component was changed to P2-C12 or P2-C20, VOC
decreased to be 0.35–0.38 V, while J reduced to around
SC
2
2
0
.50 mA cm , resulting in a much poor PCE (0.06%). Inter-
estingly, in the cases of PFDTBT as donor component, all the
devices raised their VOC values (0.88 V for P1-Cn-based and
around 0.75 V for P2-Cn-based cells). These improvements
may originate from the deeper HOMO level of PFDTBT over
FIGURE 7 (a) J–V curves and (b) EQE spectra of OPV devices
based on P3HT or PFDTBT as donor component and P1-Cn
2
5(b)
44
P3HT (25.5 eV
P1-Cn-based cells enhanced to over 1.30 mA cm . Conse-
quently, the PCE for P1-Cn-based cells increased to near
vs. 25.1 eV ). In addition, the J of
SC
2
2
(
n 5 12 and 20) or P2-Cn (n 5 12 and 20) as acceptor compo-
nent. [Color figure can be viewed in the online issue, which is
available at wileyonlinelibrary.com.]
0.30%. Meanwhile, the devices based on P2-Cn and PFDTBT
showed a slightly improvement than those based on P2-Cn
and P3HT.
improved their photocurrent significantly with the largest
EQE value near 19%. Consequently, these cells finally
improved their performance.
The different performance for the checked cells can be
explained by their external quantum efficiency (EQE) spectra
[
Fig. 7(b)]. The devices based on P1-Cn with either P3HT or
PFDTBT as donor component showed photovoltaic response
in the range of 300–650 nm, while those based on P2-Cn in
the range of 300–700 nm. These are consistent with their
absorption spectra. However, in the cases of P3HT as donor
component, the EQE values of the devices are all below 7%,
resulting in poor cell performance. Compared with the P2-
Cn-based cells, P1-Cn-based cells displayed a slightly larger
photocurrent in the whole spectral range. When the donor
component was changed to PFDTBT, the P1-Cn-based cells
The above device studies reveal that both P1-Cn and P2-Cn
are not a good acceptor component in combination with
P3HT or PFDTBT for OPVs. To penetrate the detail factors
responsible to such poor photovoltaic performance, photo-
luminescent quenching experiments were first performed. As
shown in Figure 8, all the films of pure materials, including
P1-C20, P2-C20, P3HT, and PFDTBT, luminesced intensely
in the range of 600–750 nm upon excitation at 550 nm.
However, the blend films made of P1-C20 or P2-C20 as one
1
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TABLE 4 Device Parameters of OPV Cells Based on P3HT or PFDTBT as Donor Component and P1-Cn (n 5 12 and 20) or P2-Cn
n 5 12 and 20) as Acceptor Component
(
22
25
2
21 21
s
25
2
21 21
s
Active layer
V
OC (V)
JSC (mA cm
)
FF (%)
PCE (%)
m
h
(10 cm V
)
m
e
(10 cm V
)
P3HT/P1-C12
0.52
0.54
0.35
0.38
0.88
0.88
0.75
0.76
0.68
0.69
0.48
0.51
1.30
1.36
0.39
0.42
40.9
41.5
35.2
39.1
25.7
25.7
27.0
27.4
0.14
0.15
0.06
0.07
0.29
0.31
0.08
0.09
1.3 6 0.1
1.9 6 0.2
1.1 6 0.1
1.4 6 0.1
1.1 6 0.1
1.2 6 0.1
0.15 6 0.01
0.23 6 0.01
1.5 6 0.4
2.4 6 0.5
0.9 6 0.1
1.6 6 0.4
1.2 6 0.1
1.7 6 0.3
1.2 6 0.3
2.6 6 0.5
P3HT/P1-C20
P3HT/P2-C12
P3HT/P2-C20
PFDTBT/P1-C12
PFDTBT/P1-C20
PFDTBT/P2-C12
PFDTBT/P2-C20
component and P3HT or PFDTBT as another component in
a weight ratio of 1:1, showed strongly reduced fluorescence.
The quenching extent for the most cases was near 90%.
These observations suggest that the charge separation pro-
cess takes place efficiently between the two components
after they capture the light photon. However, if getting a
closer look, one can find that the luminescent quenching
happened more strongly for the blend films based on P1-
C20 than those based on P2-C20. The fact implies that the
charge-separation may occur more efficiently in the P1-C20-
based films. This may be one of the reasons for the larger
photocurrent observed with P1-Cn-based cells.
and 20) slightly decreased. But the values still kept in the
same order range. However, the blend films based on P2-Cn
(n 5 12 and 20) significantly reduced their electron mobility
to a one-order lower level. Conversely, the P3HT-based blend
films either with P1-Cn or P2-Cn as acceptor component
25
2
21 21
displayed hole mobility in the order of 10
cm
V
s
.
However, for PFDTBT-based blend films, those with P1-Cn
as acceptor component kept hole mobility in the order of
2
5
2
21 21
10 cm V
s
, whereas those with P2-Cn dropped their
2
6
2
21 21
hole mobility into the order of 10 cm V
s
.
To understand the polymer chain packing structures in blend
films that influence the charge transportation, XRD analysis
was performed (Fig. 9). It was found that an intense diffrac-
Second, the carrier mobility for both hole and electron was
measured for the blend films via SCLC method with hole-
only (ITO/PEDOT:PSS/blend film/Au) and electron-only (Al/
blend film/Al) devices (Table 4, Supporting Information Figs.
S27 and S28). Compared with those of the neat films, the
electron mobility of the blend films based on P1-Cn (n 5 12
ꢀ
ꢀ
tion peak at 5.35 and a weak peak at 10.7 with d-spacing
of 1.65 nm and 0.83 nm, respectively, appeared in the XRD
profile of the blend film based on P3HT and P1-C20. These
peaks are consistent with the reported P3HT lamellar pack-
4
5
ing structure, suggesting that P3HT forms crystalline in
FIGURE 8 Photo luminescent spectra of the polymer films
upon excitation at 550 nm at room temperature. [Color figure
can be viewed in the online issue, which is available at
wileyonlinelibrary.com.]
FIGURE 9 XRD profiles of the blend films based on P3HT or
PFDTBT as donor component and P1-C20 and P2-C20 as
acceptor component. [Color figure can be viewed in the online
issue, which is available at wileyonlinelibrary.com.]
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2
FIGURE 10 AFM topographical height (a–d) and phase (e–h) images (5 3 5 mm ) of the blend films based on P3HT/P1-C20 (a, e),
PFDTBT/P1-C20 (b, f), P3HT/P2-C20 (c, g), and PFDTBT/P2-C20 (d, h) with a weight ratio of 1:1. [Color figure can be viewed in the
online issue, which is available at wileyonlinelibrary.com.]
the blend film. Another set of experiments revealed that heat
annealing promotes the crystallization of P3HT in the film
similar worm-like structures together with several black
dots. However, the PFDTBT/P2–20 film appeared rougher,
suggesting a poorer morphology.
(
Supporting Information Fig. S30). When the acceptor com-
ponent was replaced with P2-C20, the intensity of such dif-
fraction peaks drops significantly (Fig. 9). This implies less
P3HT crystalline in the blend film. Furthermore, annealing
had no effect in promoting the crystallization of P3HT in this
blend film (Supporting Information Fig. S30). However, in
the case of PFDTBT, both blend films with P1-C20 or P2-
C20 are amorphous as no sharp peak besides halo diffrac-
From the above analysis, one may understand why P1-Cn
polymers are superior than P2-Cn as acceptor component
for all-polymer solar cells although the latter possess a much
planar backbone and better p-conjugation, a wider absorp-
tion spectrum, a larger electron mobility, and a more regular
packing structure in the neat film state. The main reasons
come from the following aspects: (1) P1-Cn polymers have a
slight high-lying LUMO energy level, thus providing a larger
ꢀ
tion in the range of 15–25 appeared in their XRD patterns
(
Fig. 9). But if taking a closer look, one may find that the
PFDTBT/P1-C20 blend film showed a weak and broad dif-
fraction peak around 5 , whereas the PFDTBT/P2-C20 film
did not. The fact suggests a slightly more regular packing
structure for the PFDTBT/P1-C20 film than that based on
PFDTBT/P2-C20. Furthermore, annealing treatment did not
change the film structure (Supporting Information Fig. S31).
VOC; (2) the photo-induced charge-separation may occur
ꢀ
more efficiently in P1-Cn-based blend films; (3) the P1-Cn-
based blend films showed better or at least comparable
charge transportation for both hole and electron carriers; (4)
a much better chain-packing structure and film morphology
were observed with P1-Cn-based blend films.
The morphology of the blend films was studied by atomic
force microscopy (AFM). As shown in Supporting Informa-
tion Figure 10, clear differences were observed for the
checked blend films. Worm-like structures with a diameter
in the range of tens to hundreds nanometers appeared in
the AFM of P3HT/P1-C20 film, suggesting the occurrence of
micro-phase separation between P3HT and P1-C20. Such
worm-like structure may be assignable to P3HT crystalline
phase. The film was rather smooth with a root-mean-square
For all-polymer solar cells, the successful acceptor materials
developed so far include four types of polymers, which are
2
2,23
all D–A structure based on perylenediimide,
naphthalene
4
6
47
48
diimide, cyano-substituted, or benzothiadiazole unit. By
combining with suitable donor polymers, these acceptor
polymers could produce good PSCs having PCE in the range
4
6(e)
of 1–3%, with the best record of 3.3%.
Compared with
these known polymeric acceptor materials, A–A type conju-
gated polymers have not yet exhibited satisfied performance.
However, considering the good electron affinity for all com-
posed moieties, A–A type copolymers would potentially be a
kind of promising acceptor materials for all-polymer solar
cells. From the study in this work, one may learn some
important principles for the molecular design of A–A conju-
gated copolymers. First, A–A copolymers should possess suit-
able energy levels as they not only provide a large VOC for
(RMS) roughness of 0.47 nm. However, when the acceptor
was changed to P2-C20, the film became rougher, with a
RMS roughness of 1.48 nm. More importantly, the presence
of many big black dots suggests the morphology is far from
ideal for the photo-to-electric conversion, thus resulting in a
rather poor device performance. In the cases of PFDTBT as
donor component, the blend film based on P1-C20 displayed
1
212
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the device but also ensure efficient photo-generation of
charge carriers by photo-induced charge separation. Second,
A–A copolymers with high performance should have a just
right miscibility and microphase-separation with donor
material in their blend films. In the ideal case, the A–A
copolymer itself has strong p–p interchain interactions for
good charge transportation and forms nanosize level bicon-
tinuous microphase separation structure with donor poly-
1, 409–419; (e) M. Helgesen, R. Sondergaard, F. C. Krebs, J.
Mater. Chem. 2010, 20, 36–60; (f) H. Zhou, L. Yang, W. You,
Macromolecules 2012, 45, 6072632; (g) H. Ye, W. Li, W. Li,
Chin. J. Org. Chem. 2012, 32, 266–283; (h) G. Li, R. Zhu, Y.
Yang, Nat. Photonics 2012, 6, 153–161.
4
2
(a) S. W. Thomas, G. D. Joly, T. M. Swager, Chem. Rev.
007, 107, 1339–1386; (b) X. Feng, L. Liu, S. Wang, D. Zhu,
Chem. Soc. Rev. 2010, 39, 2411–2419; (c) H. N. Kim, Z. Guo, W.
Zhu, J. Yoon, H. Tian, Chem. Soc. Rev. 2011, 40, 79–93.
3
,49
mers in their blend films.
5 F. Hide, M. A. D. Garcia, B. J. Schwartz, A. J. Heeger, Acc.
Chem. Res. 1997, 30, 430–436.
CONCLUSIONS
6 (a) J. K. Stille, Angew. Chem., Int. Ed. 1986, 25, 508–524; (b)
B. Carsten, F. He, H. J. Son, T. Xu, L. Yu, Chem. Rev. 2011, 111,
Two A–A type conjugated polymers, P1-Cn and P2-Cn, were
designed and synthesized based on perylenediimide and
1
7
8
9
493–1528.
N. Miyaura, A. Suzuki, Chem. Rev. 1995, 95, 2457–2483.
K. Sonogashira, J. Organomet. Chem. 2002, 653, 46–49.
(a) E. Zhou, S. Yamakawa, K. Tajima, C. Yang, K. Hashimoto,
2,1,3-benzothiadiazole units. Owing to the steric hindrance
between the directly connected PDI and BT units, the back-
bone of P1-Cn is not planar at all. The insertion of acetylene
p-spacers in P2-Cn effectively releases such steric hindrance
and makes the backbone much planar and in good p-
conjugation. Consequently, P2-Cn polymers display a much
broader absorption spectrum, a lower LUMO level, stronger
interchain interactions, and larger electron mobility for their
films than P1-Cn. However, in all-polymer solar cells using
these two types of the polymers as acceptor component and
P3HT or PFDTBT as donor component, the performance of
P1-Cn devices surpassed those based on P2-Cn, with larger
Chem. Mater. 2009, 21, 4055–4061; (b) E. Zhou, Q. Wei, S.
Yamakawa, Y. Zhang, K. Tajima, C. Yang, K. Hashimoto, Mac-
romolecules 2010, 43, 8212826; (c) E. Zhou, J. Cong, K.
Hashimoto, K. Tajima, Energy Environ. Sci. 2012, 5, 9756–9759.
10 (a) G. Li, V. Shrotriya, J. Huang, Y. Yao, T. Moriarty, K.
Emery, Y. Yang, Nat. Mater. 2005, 4, 864–868; (b) W. Ma, C.
Yang, X. Gong, K. Lee, A. J. Heeger, Adv. Funct. Mater. 2005,
1
5, 1617–1622.
1
1 (a) Z. He, C. Zhong, S. Su, M. Xu, H. Wu, Y. Cao, Nat. Pho-
tonics 2012, 6, 591–595; (b) S.-H. Liao, H.-J. Huo, Y.-S. Cheng,
S.-A. Chen, Adv. Mater. 2013, 25, 4766–4771; (c) J. You, L. Dou,
K. Yoshimura, T. Kato, K. Ohya, T. Moriarty, K. Emery, C.-C.
Chen, J. Gao, G. Li, Y. Yang, Nat. Commun. 2013, 4, 1446; (d)
K. Li, Z. Li, K. Feng, X. Xu, L. Wang, Q. Peng, J. Am. Chem.
Soc. 2013, 135, 13549–13557.
VOC and J . A higher LUMO energy level, more efficient
SC
charge-separation between donor and acceptor polymers in
the blend film, and a better morphology may account for the
better photovoltaic performance of P1-Cn. Apart from the
chemical structure of the backbone, the side chains have
been found to have little influence on the optical, electro-
chemical, and final photovoltaic properties. Although the
best PCE achieved was only 0.31%, this work has demon-
strated the potential to use A–A type conjugated copolymers
as acceptor component for organic solar cells. The basic
understanding of this kind of polymers and the exploration
of new materials with good performance are the topics wor-
thy further study.
12 P.-L. T. Boudreault, A. Najari, M. Leclerc, Chem. Mater.
2
011, 23, 456–469.
1
2
3 C. L. Chochos, N. Tagmatarchis, V. G. Gregoriou, RSC Adv.
013, 3, 7160–7181.
1
4 (a) S. Cho, J. Lee, M. H. Tong, J. H. Seo, C. Yang, Adv.
Funct. Mater. 2011, 21, 1910–1916; (b) X. Guo, F. S. Kim, M. J.
Seger, J. S. A. Enekhe, M. D. Watson, Chem. Mater. 2012, 24,
1
434–1442; (c) Z. Chen, M. J. Lee, R. S. Ashraf, Y. Gu, S. Albert-
Seifried, M. M. Nielsen, B. Schroeder, T. D. Anthopoulos, M.
Heeney, I. McCulloch, H. Sirringhaus, Adv. Mater. 2012, 24,
6
47–652.
1
5 J. K. Lee, M. C. Gwinner, R. Berger, C. Newby, R. Zentel, R.
ACKNOWLEDGMENTS
H. Friend, H. Sirringhaus, C. K. Ober, J. Am. Chem. Soc. 2011,
33, 9949–9951.
1
This work was supported by National Science Foundation of
China (Nos. 20974119, 90922019, and 21074147), Shanghai
Science and Technology Commission (No. 13JC1407000), and
Chinese Academy of Sciences.
16 M. C. Gwinner, T. J. K. Brenner, J.-K. Lee, C. Newby, C. K.
Ober, C. R. McNeill, H. Sirringhaus, J. Mater. Chem. 2012, 22,
4
436–4439.
1
7 J. L. Banal, J. Subbiah, H. Graham, J. K. Lee, K. P.
Ghiggino, W. W. Wong, Polym. Chem. 2013, 4, 1077–1083.
REFERENCES AND NOTES
1
8 X. Zhao, Y. Wen, L. Ren, L. Ma, Y. Liu, X. Zhan, J. Polym.
Sci., Part A: Polym. Chem. 2012, 50, 4266–4271.
1
(a) A. C. Grimsdale, K. L. Chan, R. E. Martin, P. G. Jokisz, A.
B. Holmes, Chem. Rev. 2009, 109, 897–1091; (b) K. T. Kamtekar,
A. P. Monkman, M. R. Bryce, Adv. Mater. 2010, 22, 572–582; (c)
S. Gong, C. Yang, J. Qin, Chem. Soc. Rev. 2012, 41, 4797–4807.
19 R. Stalder, J. G. Mei, J. Subbiah, C. Grand, L. A. Estrada, F.
So, J. R. Reynolds, Macromolecules 2011, 44, 6303–6310.
2
0 (a) X. Zhan, A. Facchetti, S. Barlow, T. J. Marks, M. A.
2
2
7
(a) C. Wang, H. Dong, W. Hu, Y. Liu, D. Zhu, Chem. Rev.
009, 109, 5868–5923; (b) A. Facchetti, Chem. Mater. 2011, 23,
33–758.
Ratner, M. R. Wasielewski, S. R. Marder, Adv. Mater. 2011, 23,
268–284; (b) B. J. Jung, N. J. Tremblay, M.-L. Yeh, H. E. Katz,
Chem. Mater. 2011, 23, 568–582; (c) C. Huang, S. Barlow, S. R.
Marder, J. Org. Chem. 2011, 76, 2386–2407; (d) C. Li, H.
Wonneberger, Adv. Mater. 2012, 24, 613–636; (e) E. Kozma, M.
Catellani, Dyes Pigments 2013, 98, 160–179.
3
(a) B. C. Thompson, J. M. J. Fr eꢀ chet, Angew. Chem. Int. Ed.
2008, 47, 58–77; (b) J. Chen, Y. Cao, Acc. Chem. Res. 2009, 42,
1709–1718; (c) Y. J. Cheng, S. H. Yang, C. S. Hsu, Chem. Rev.
2009, 109, 5868–5923; (d) X. Zhan, D. Zhu, Polym. Chem. 2010,
21 C. W. Tang, Appl. Phys. Lett. 1986, 48, 183–185.
WWW.MATERIALSVIEWS.COM
JOURNAL OF POLYMER SCIENCE, PART A: POLYMER CHEMISTRY 2014, 52, 1200–1215
1213

JOURNAL OF
POLYMER SCIENCE
ARTICLE
WWW.POLYMERCHEMISTRY.ORG
2
2 (a) X. Zhan, Z. Tan, B. Domercq, Z. An, X. Zhang, S. Barlow,
Y. Li, D. Zhu, B. Kippelen, S. R. Marder, J. Am. Chem. Soc.
007, 129, 7246–7247; (b) Z. Tan, E. Zhou, X. Zhan, X. Wang, Y.
Li, S. Barlow, S. R. Marder, Appl. Phys. Lett. 2008, 93, 073309;
c) X. Zhan, Z. Tan, E. Zhou, Y. Li, R. Misra, A. Grant, B.
J. Hagan, E. W. V. Stryland, J.-L. Br eꢀ das, H. L. Anderson, M. R.
Wasielewski, S. R. Marder, J. Phys. Chem. A 2009, 113, 10826–
10832; (b) E. Kozma, F. Munno, D. Kotowski, F. Bertini, S.
Luzzati, M. Catellani, Synth. Met. 2010, 160, 996–1001.
2
(
3
8 (a) F. Wurthner, V. Stepanenko, Z. Chen, C. R. Saha-Moller,
Domercq, X.-H. Zhang, Z. An, X. Zhang, S. Barlow, B. Kippelen,
S. R. Marder, J. Mater. Chem. 2009, 19, 5794–5803.
N. Kocher, D. Stalke, J. Org. Chem. 2004, 69, 7933–7939; (b) M.
J. Ahrens, M. J. Tauber, M. R. Wasielewski, J. Org. Chem.
2006, 71, 2107–2114; (c) Z. H. Chen, Y. Zheng, H. Yan, A.
Facchetti, J. Am. Chem. Soc. 2009, 131, 8–9.
2
3 (a) E. Zhou, K. Tajima, C. Yang, K. Hashimoto, J. Mater.
Chem. 2010, 20, 2362–2368; (b) E. Zhou, J. Cong, Q. Wei, K.
Tajima, C. Yang, K. Hashimoto, Angew. Chem., Int. Ed. 2011,
5
3
9 J. Zhang, W. Cai, F. Huang, E. Wang, C. Zhong, S. Liu, M.
0, 2799–2803.
Wang, C. Duan, T. Yang, Y. Cao, Macromolecules 2011, 44,
24 (a) J. K. J. van Duren, A. Dhanabalan, P. A. van Hal, R. A. J.
894–901.
Janssen, Synth. Met. 2001, 121, 1587–1588; (b) C. J. Brabec, C.
Winder, N. S. Sariciftci, J. C. Hummelen, A. Dhanabalan, P. A.
van Hal, R. A. J. Janssen, Adv. Funct. Mat. 2002, 12, 709–712.
4
0 (a) P. Hohenberg, W. Kohn, Phys. Rev. 1964, 136, B864–
B871; (b) W. Kohn, L. J. Sham, Phys. Rev. 1965, 140, A1133–
A1138.
2
5 (a) M. Svensson, F. Zhang, S. C. Veenstra, W. J. H. Verhees,
4
1 (a) A. D. Becke, J. Chem. Phys. 1993, 98, 5648–5652; (b) C.
Lee, W. Yang, R. G. Parr, Phys. Rev. 1988, B37, 785–789.
2 M. J. Frisch, G. W. Trucks, H. B. Schlegel, G. E. Scuseria, M.
J. C. Hummelen, J. M. Kroon, O. Inagan a€ s, M. R. Andersson,
Adv. Mat. 2003, 15, 988–991; (b) M.-H. Chen, J. Hou, Z. Hong,
G. Yang, S. Sista, L.-M. Chen, Y. Yang, Adv. Mater. 2009, 21,
4
A. Robb, J. R. Cheeseman, J. A. J. Montgomery, T. Vreven, K.
N. Kudin, J. C. Burant, J. M. Millam, S. S. Iyengar, J. Tomasi,
V. Barone, B. Mennucci, M. Cossi, G. Scalmani, N. Rega, G. A.
Petersson, H. Nakatsuji, M. Hada, M. Ehara, K. Toyota, R.
Fukuda, J. Hasegawa, M. Ishida, T. Nakajima, Y. Honda, O.
Kitao, H. Nakai, M. Klene, X. Li, J. E. Knox, H. P. Hratchian, J.
B. Cross, V. Bakken, C. Adamo, J. Jaramillo, R. Gomperts, R.
E. Stratmann, O. Yazyev, A. J. Austin, R. Cammi, C. Pomelli, J.
W. Ochterski, P. Y. Ayala, K. Morokuma, G. A. Voth, P.
Salvador, J. J. Dannenberg, V. G. Zakrzewski, S. Dapprich, A.
D. Daniels, M. C. Strain, O. Farkas, D. K. Malick, A. D. Rabuck,
K. Raghavachari, J. B. Foresman, J. V. Ortiz, Q. Cui, A. G.
Baboul, S. Clifford, J. Cioslowski, B. B. Stefanov, G. Liu, A.
Liashenko, P. Piskorz, I. Komaromi, R. L. Martin, D. J. Fox, T.
Keith, M. A. Al-Laham, C. Y. Peng, A. Nanayakkara, M.
Challacombe, P. M. W. Gill, B. Johnson, W. Chen, M. W.
Wong, C. Gonzalez, J. A. Pople, Gaussian 03; Gaussian, Inc.,
Wallingford, CT, 2004.
4
238–4242.
26 (a) N. Blouin, A. Michaud, M. Leclerc, Adv. Mat. 2007, 19,
2295–2300; (b) S. H. Park, A. Roy, S. Beaupre, S. Cho, N.
Coates, J. S. Moon, D. Moses, M. Leclerc, K. Lee, A. J. Heeger,
Nat. Photonics 2009, 3, 297–303.
2
7 (a) E. Wang, L. Wang, L. Lan, C. Luo, W. Zhuang, J. Peng, Y.
Cao, Appl. Phys. Lett. 2008, 92, 033307; (b) P.-L. T. Boudreault,
A. Michaud, M. Leclerc, Macromol. Rapid Commun. 2007, 28,
2
176–2179.
2
8 N. Allard, R. B. A €ı ch, D. Gendron, P.-L. T. Boudreault, C.
Tessier, S. Alem, S.-C. Tse, Y. Tao, M. Leclerc, Macromolecules
2010, 43, 2328–2333.
29 E. Zhou, M. Nakamura, T. Nishizawa, Y. Zhang, Q. Wei, K.
Tajima, C. Yang, K. Hashimoto, Macromolecules 2008, 41,
8302–8305.
30 (a) Z. Zhu, D. Waller, R. Gaudiana, M. Morana, D.
M u€ hlbacher, M. Scharber, C. Brabec, Macromolecules 2007, 40,
981–1986; (b) J. Peet, J. Y. Kim, N. E. Coates, W. L. Ma, D.
Moses, A. J. Heeger, G. C. Bazan, Nat. Mater. 2007, 6, 497–500.
1 (a) J. Hou, H.-Y. Chen, S. Zhang, G. Li, Y. Yang, J. Am.
4
3 (a) C. Goh, R. J. Kline, M. D. McGeheea, E. N. Kadnikova, J.
1
M. J. Fr eꢀ chet, Appl. Phys. Lett. 2005, 86, 122110; (b) G. Zhao, Y.
He, Z. Xu, J. Hou, M. Zhang, J. Min, H.-Y. Chen, M. Ye, Z.
Hong, Y. Yang, Y. Li, Adv. Funct. Mater. 2010, 20, 1480–1487.
3
Chem. Soc. 2008, 130, 16144–16145; (b) R. C. Coffin, J. Peet, J.
Rogers, G. C. Bazan, Nat. Chem. 2009, 1, 657–661.
4
4 M. C. Scharber, D. M u€ hlbacher, M. Koppe, P. Denk, C.
Waldauf, A. J. Heeger, C. J. Brabec, Adv. Mater. 2006, 18, 789–
32 (a) W. Yue, Y. Zhao, H. Tian, D. Song, Z. Xie, D. Yan, Y.
7
94.
Geng, F. Wang, Macromolecules 2009, 42, 6510–6518; (b) F.
Liang, J. Lu, J. Ding, R. Movileanu, Y. Tao, Macromolecules
4
5 W. Ma, C. Yang, X. Gong, K. Lee, A. J. Heeger, Adv. Funct.
Mater. 2005, 15, 1617–1622.
2009, 42, 6107–6114; (c) K.-H. Ong, S.-L. Lim, H.-S. Tan, H.-K.
Wong, J. Li, Z. Ma, L. C. H. Moh, S.-H. Lim, J. C. de Mello, Z.-
K. Chen, Adv. Mater. 2011, 23, 1409–1413; (d) J. Wang, H. Ye,
H. Li, C. Mei, J. Ling, W. Li, Z. Shen, Chin. J. Chem. 2013, 31,
ASAP, doi: 10.1002/cjoc.201300519.
46 (a) S. Fabiano, Z. Chen, S. Vahedi, A. Facchetti, B.
Pignataro, M. A. Loi, J. Mater. Chem. 2011, 21, 5891–5896; (b)
J. R. Moore, S. Albert-Seifried, A. Rao, S. Massip, B. Watts, D.
J. Morgan, R. H. Friend, C. R. McNeill, H. Sirringhaus, Adv.
Energy Mater. 2011, 1, 230–240; (c) T. W. Holcombe, J. E.
Norton, J. Rivnay, C. H. Woo, L. Goris, C. Piliego, G. Griffini, A.
Sellinger, J.-L. Bredas, A. Salleo, J. M. J. Fr eꢀ chet, J. Am.
Chem. Soc. 2011, 133, 12106–12114; (d) E. Zhou, J. Cong, M.
Zhao, L. Zhang, K. Hashimoto, K. Tajima, Chem. Commun.
33 (a) J. Lu, F. Liang, N. Drolet, J. Ding, Y. Tao, R. Movileanua,
Chem. Commun. 2008, 5315–5317; (b) Q. Zheng, B. J. Jung, J.
Sun, H. E. Katz, J. Am. Chem. Soc. 2010, 132, 5394–5404; (c) Y.-
C. Chen, C.-Y. Yu, Y.-L. Fan, L.-I. Hung, C.-P. Chen, C. Ting,
Chem. Commun. 2010, 46, 6503–6505; (d) C. Y. Chang, Y. J.
Cheng, S. H. Hung, J. S. Wu, W. S. Kao, C. H. Lee, C. S. Hsu,
Adv. Mater. 2012, 24, 549–553.
2
012, 48, 5283–5285; (e) T. Earmme, Y. J. Hwang, N. M. Murari,
S. Subramaniyan, S. A. Jenekhe, J. Am. Chem. Soc. 2013, 135,
1
4960–14963.
3
4 X. G. Guo, M. D. Watson, Org. Lett. 2008, 10, 5333–5336.
5 M. Zhang, H. N. Tsao, W. Pisula, C. Yang, A. K. Mishra, K.
4
7 (a) J. J. M. Halls, C. A. Walsh, N. C. Greenham, E. A.
3
Marseglia, R. H. Friend, S. C. Moratti, A. B. Holmes, Nature
995, 376, 498–500; (b) M. Granstr o€ m, K. Petritsch, A. C. Arias,
A. Lux, M. R. Andersson, R. H. Friend, Nature 1998, 395, 257–
60; (c) M. Magdalena Mandoc, W. Veurman, L. Jan Anton
M u€ llen, J. Am. Chem. Soc. 2007, 129, 3472–3473.
6 K. Lee, J. Lee, E. J. Jeong, A. Kronk, M. S. Lim, J. S. Kim,
Adv. Mater. 2012, 24, 2479–2484.
7 (a) S. A. Odom, R. F. Kelley, S. Ohira, T. R. Ensley, C.
1
3
2
3
Koster, B. de Boer, P. W. M. Blom, Adv. Funct. Mater. 2007, 17,
Huang, L. A. Padilha, S. Webster, V. Coropceanu, S. Barlow, D.
2167–2173.
1
214
JOURNAL OF POLYMER SCIENCE, PART A: POLYMER CHEMISTRY 2014, 52, 1200–1215

JOURNAL OF
POLYMER SCIENCE
WWW.POLYMERCHEMISTRY.ORG
ARTICLE
4
8 (a) C. R. McNeill, A. Abrusci, J. Zaumseil, R. Wilson, M. J.
Mater. Interfaces 2011, 3, 2924–2927; (d) D. Mori, H. Benten, H.
Ohkita, S. Ito, K. Miyake, ACS Appl. Mater. Interfaces 2012, 4,
3325–3329.
McKiernan, J. J. M. Halls, N. C. Greenham, R. H. Friend, Appl.
Phys. Lett. 2007, 90, 193506; (b) Y.-S. Huang, S. Westenhoff, I.
Avilov, P. Sreearunothai, J. M. Hodgkiss, C. Deleener, R. H.
Friend, D. Beljonne, Nat. Mater. 2008, 7, 483–489; (c) D. Mori,
H. Benten, J. Kosaka, H. Ohkita, S. Ito, K. Miyake, ACS Appl.
49 (a) X. Yang, J. Loos, Macromolecules 2007, 40, 1353–
1362; (b) L. Dong, W. Li, W.-S. Li, Nanoscale 2011, 3, 3447–
3461.
WWW.MATERIALSVIEWS.COM
JOURNAL OF POLYMER SCIENCE, PART A: POLYMER CHEMISTRY 2014, 52, 1200–1215
1215