Conjugated side-chain-isolated D-A copolymers based on benzo[1,2-b:4,5-b']dithiophene-alt-dithienylbenzotriazole: Synthesis and photovoltaic properties

Article abstract of DOI:10.1021/cm3017006

Conjugated side-chain-isolated D-A copolymers, based on the donor unit of benzodithiophene (BDT) with a thiophene-conjugated side chain, thiophene π bridge, and the acceptor unit of benzotriazole (BTA) with or without fluorine substitution (PBDT-FBTA and PBDT-HBTA), were designed and synthesized for elucidating their structure-property relationships. The copolymer films demonstrated well-defined absorption peaks with steep absorption edges, consistent with their rigid and ordered structures in the solid films. The substitution of a thiophene-conjugated side chain on the BDT unit in the copolymers aroused 15-nm red-shifted absorption in comparison with its polymer analogues with alkoxy side chains on the BDT unit. Compared to PBDT-HBTA, PBDT-FBTA with two-fluorine-atom substitution on the BTA unit demonstrated a lower highest occupied molecular orbital energy level, higher hole mobility, and significantly better photovoltaic performance. A polymer solar cell (PSC) based on PBDT-FBTA/PC₇₀BM (1:2, w/w) with a 5% 1,8-diiodooctane additive displayed a power conversion efficiency (PCE) of 6.0% with a J_sc of 11.9 mA cm^-2, a V_OC of 0.75 V, and a fill factor of 67.2%, under the illumination of AM1.5G, 100 mW cm^-2. Even at a thicker active layer of 400 nm, the PSC still demonstrated a higher PCE of 4.74%. The results indicate that PBDT-FBTA is a promising polymer donor material for future application of large-area PSCs.

Full text of DOI:10.1021/cm3017006

Subscriber access provided by Columbia Univ Libraries
Article
Conjugated Sidechain Isolated Donor-Acceptor
Copolymers based on Benzo[1,2-b:4,5-b']dithiophene-alt-
dithienylbenzotriazole: Synthesis and Photovoltaic Properties
Jie Min, Zhi-guo Zhang, Siyuan Zhang, and Yongfang Li
Chem. Mater., Just Accepted Manuscript • DOI: 10.1021/cm3017006 • Publication Date (Web): 30 Jul 2012
Downloaded from http://pubs.acs.org on July 31, 2012
Just Accepted
“Just Accepted” manuscripts have been peer-reviewed and accepted for publication. They are posted
online prior to technical editing, formatting for publication and author proofing. The American Chemical
Society provides “Just Accepted” as a free service to the research community to expedite the
dissemination of scientific material as soon as possible after acceptance. “Just Accepted” manuscripts
appear in full in PDF format accompanied by an HTML abstract. “Just Accepted” manuscripts have been
fully peer reviewed, but should not be considered the official version of record. They are accessible to all
readers and citable by the Digital Object Identifier (DOI®). “Just Accepted” is an optional service offered
to authors. Therefore, the “Just Accepted” Web site may not include all articles that will be published
in the journal. After a manuscript is technically edited and formatted, it will be removed from the “Just
Accepted” Web site and published as an ASAP article. Note that technical editing may introduce minor
changes to the manuscript text and/or graphics which could affect content, and all legal disclaimers
and ethical guidelines that apply to the journal pertain. ACS cannot be held responsible for errors
or consequences arising from the use of information contained in these “Just Accepted” manuscripts.
Chemistry of Materials is published by the American Chemical Society. 1155
Sixteenth Street N.W., Washington, DC 20036
Published by American Chemical Society. Copyright © American Chemical Society.
However, no copyright claim is made to original U.S. Government works, or works
produced by employees of any Commonwealth realm Crown government in the
course of their duties.

Page 1 of 26
Chemistry of Materials
1
2
3
4
5
6
Conjugated Sidechain Isolated D-A Copolymers Based on
Benzo[1,2-b:4,5-b']dithiophene-alt-dithienylbenzotriazole: Synthesis and Photovoltaic
Properties
7
8
9
Jie Min, Zhi-Guo Zhang*, Siyuan Zhang, and Yongfang Li*
10
11
12
13
14
15
16
17
18
19
20
21
22
23
24
25
26
27
28
29
30
31
32
33
34
35
36
37
38
39
40
41
42
43
44
45
46
47
48
49
50
51
52
53
54
55
56
57
58
59
60
Beijing National Laboratory for Molecular Sciences, CAS Key Laboratory of Organic Solids,
Institute of Chemistry, Chinese Academy of Sciences, Beijing 100190 (China)
E-mail: liyf@iccas.ac.cn (Y. Li), zgzhangwhu@iccas.ac.cn (Z. Zhang)
Abstract
Conjugated sidechain isolated D-A copolymers, based on the donor unit of
benzodithiophene (BDT) with thiophene conjugated side chain, thiophene pi-bridge and the
acceptor unit of benzotriazole (BTA) with or without fluorine substitution (PBDT-FBTA and
PBDT-HBTA), were designed and synthesized for elucidating their structure–property
relationships. The copolymer films demonstrated well defined absorption peaks with steep
absorption edges, consistent with their rigid and ordered structures in the solid films. The
substitution of thiophene conjugated side chain on the BDT unit in the copolymers aroused 15
nm red-shifted absorption in comparison with its polymer analogues with alkoxy side chains on
BDT unit. Compared to PBDT-HBTA, PBDT-FBTA with two fluorine atoms substitution on
BTA unit demonstrated lower HOMO energy level, higher hole mobility and significantly
better photovoltaic performance. The PSC based on PBDT-FBTA/ PC70BM (1:2, w/w) with
5% DIO additive displayed a power conversion efficiency of 6.0% with a Jsc of 11.9 mA/cm2, a
VOC of 0.75 V and a FF of 67.2%, under the illumination of AM1.5G, 100 mW/cm2. Even at a
thicker active layer of 400 nm, the PSC still demonstrated a higher PCE of 4.74%. The results
indicate that PBDT-FBTA is a promising polymer donor material for future application of large
area PSCs.
Keywords: polymer solar cells, two-dimension-conjugated polymers, side chain isolation, D−A
copolymers
1
ACS Paragon Plus Environment

Chemistry of Materials
Page 2 of 26
1
2
3
4
5
1. Introduction
6
7
8
9
Bulk heterojunction (BHJ) polymer solar cells (PSCs)[1] based on p−type conjugated
polymers as donor[2-9] and n−type fullerene derivatives[10] as acceptor have been intensively
studied in recent years for the generation of affordable, clean, and renewable energy.
Advantages of the BHJ PSCs include low−cost fabrication of large−area devices, light
weight, mechanical flexibility, and easy tunability of chemical properties of the photovoltaic
materials.
10
11
12
13
14
15
16
17
18
19
20
21
22
23
24
25
26
27
28
29
30
31
32
33
34
35
36
37
38
39
40
41
42
43
44
45
46
47
48
49
50
51
52
53
54
55
56
57
58
59
60
It has been realized that an ideal polymer donor in PSCs should exhibit broad absorption
with high absorption coefficient in the visible region, high hole mobility, suitable electronic
energy levels matching to the fullerene acceptor, and appropriate compatibility with fullerene
acceptor to form nanoscale bicontinuous network.[2-9] These specific design criteria can offer
high values of short circuit current (Jsc), open circuit voltage (Voc) and fill factor (FF) of the
PSCs, which are related to the power conversion efficiency (PCE) of the PSCs by the following
equation: PCE = (Jsc×Voc×FF)/Pin, where Pin is the input light power.
For broadening the absorption, the two-dimension-conjugated (2-D-conjugated) polymers
with conjugated side chain (see Type 1 in Figure 1) were designed and synthesized in our
group.[11] The 2-D-conjugated polymers possess higher hole mobility thanks to the
2-D-conjugated structure, and broader absorption deriving from both the main chains and
conjugated side chains. Thus this family of 2-D-conjugated polythiophenes demonstrated good
device performances in PSCs[11a] and organic field−effect transistors (OFETs).[12] Now this
strategy has been successfully extended to develp high efficiency polymers. Copolymers
(PBDTTT) of benzodithiophene (BDT) and thieno[3,4−b]−thiophene (TT) is one of the most
2
ACS Paragon Plus Environment

Page 3 of 26
Chemistry of Materials
1
2
3
4
5
6
7
8
9
efficient photovoltaic materials in the PSCs[6]. Huo et. al successfully applied the 2-D
conjugation concept to PBDTTT structure by thienyl-substitution on the BDT unit. [5b] The 2-D
conjugated polymer exhibit better thermal stabilities, red-shifted absorption spectra, lower
HOMO levels, significantly higher hole mobility, and greatly improved photovoltaic properties,
in comparison with the corresponding alkoxy substituted copolymers. [5b]
10
11
12
13
14
15
16
17
18
19
20
21
22
23
24
25
26
27
28
29
30
31
32
33
34
35
36
37
38
39
40
41
42
43
44
45
46
47
48
49
50
51
52
53
54
55
56
57
58
59
60
To overcome the steric hindrance induced by the large conjugated side chain and improve
the planarity and optical properties, we recently proposed a “side-chain-isolation” concept and
developed the 2-D-conjugated polythiophenes with unsubstituted thienyl spacer (Type 2 in
Figure 1).[13] In such polymers, due to the proper side chain distance and the improved
planarity of polymer backbone, these polymers demonstrated red−shifted and enhanced
absorption thus improved photovoltaic properties. Considering the diverse molecular
engineering approach under this side chain isolated photovoltaic materials, such as changing the
nature of side chain and spacer as well as introducing donor−acceptor (D−A) concept in the
conjugated side chain,[14-16] the side chain isolated photovoltaic materials could open a new way
for developing high performance polymer solar cells.
Figure 1. Three typical molecular architectures of 2-D-conjugated polymers. (Here d represents
the distance between the conjugated side chains, and the alkyl chain group attached on the
acceptor unit was omitted for clarity due to its negligible effect on the planarity.)
3
ACS Paragon Plus Environment

Chemistry of Materials
Page 4 of 26
1
2
3
4
5
6
7
8
To further extend the absorption and modulate the energy levels, here we introduce D−A
concept by changing the side chain isolation spacer partly with the acceptor unit of
benzotriazole (BTA) [17] or fluorinated BTA,[18] and synthesized two new 2-D-conjugated and
side-chain-isolated D−A copolymers (Type 3 in Figure 1) of PBDT-HBTA and PBDT-FBTA
(see Scheme 1). The incorporation of Fluorine atom in the two-dimension architecture is
inspired by its unique features as demonstrated by You et al., such as strong inter- and
intramolecular interactions and smallest electron-withdrawing group in size.[18-19] In the
copolymers, the benzodithiophene (BDT) unit with thiophene conjugated side chain[20] was
used as donor unit to form the 2-D-conjugated polymers, in considering the good planarity and
symmetric structure of BDT unit and the high photovoltaic efficiency of the copolymers based
on the thiophene-substituted BDT unit.[5a,20,21] The 2-D-conjugated and sidechain-isolated D−A
copolymers combine the advantages of broader absorption and higher hole mobility of the
2-D-conjugation, less steric hindrance of the sidechain-isolation, and the broad absorption and
lower HOMO energy level of the D-A copolymerization. As a result, the two dimensional
character is clearly demonstrated in the as-developed polymers. For example, in comparison
with the linear copolymer analogues with alkoxy side chains on BDT unit[17a] and that with
alkyl side chain on BDT unit,[18] the absorption spectra with thiophene conjugated side chain is
red-shifted by ca. 15 nm. Among these two copolymers, the fluorinated copolymer
PBDT−FBTA demonstrated promising photovoltaic properties. The PSC based on
PBDT−FBTA as donor and PC70BM as acceptor showed a power conversion efficiency of
6.0% with an open circuit voltage of 0.75 V, under the illumination of AM1.5G, 100 mW/cm2.
9
10
11
12
13
14
15
16
17
18
19
20
21
22
23
24
25
26
27
28
29
30
31
32
33
34
35
36
37
38
39
40
41
42
43
44
45
46
47
48
49
50
51
52
53
54
55
56
57
58
59
60
4
ACS Paragon Plus Environment

Page 5 of 26
Chemistry of Materials
1
2
3
4
5
2. Results and Discussion
6
7
2.1. Synthesis of Monomers and Polymers
8
9
The synthetic routes of fluorinated dithienylbenzotriazole (FBTA) and the D-A copolymers are
respectively depicted in Schemes 1 and 2. The fluorine atom substituted dithienylbenzotriazole
was firstly described by You et al but with low yield[18]. Here an easier synthesis procedure
with higher overall yield was explored in detail. The reduction of 4,5-difluoro-2-nitroaniline
with tin powder in 12 N HCl gave 4,5-difluoro-1,2-phenylenediamine (1), which was treated
with NaNO2 to afford compound 2. Alkylation of compound 2 was carried out in methanol with
potassium tert-butoxide and 1-bromooctane in a good yield. The position of the alkyl group in
10
11
12
13
14
15
16
17
18
19
20
21
22
23
24
25
26
27
28
29
30
31
32
33
34
35
36
37
38
39
40
41
42
43
44
45
46
47
48
49
50
51
52
53
54
55
56
57
58
59
60
1
compound 3 was confirmed by H NMR. The bromination of benzotriazole (3) was finished
firstly by activation of the benzotriazole ring with trimethylsilyl group and subsequently
electrophilic substitution with bromine. The fluorinated dithienylbenzotriazole (FTBA) was
obtained by a stille coupling followed by an N-bromosuccinimide (NBS) bromination.
C8H17
C8H17
N
N
N
N
N
H2N
NO2
N
F
NH
F
H2N
NH2
N
F
N
F
NaNO2
AcOH
Sn
1-BrC8H17
t-BuOK
LDA
Si
Si
HCl
(Me)3SiCl
F
F
F
F
F
F
2
1
3
4
C8H17
C8H17
N
C8H17
N
N
N
N
F
N
N
N
N
F
Sn(Bu)3
S
S
Br2
S
S
NBS
S
Br
Br
Br
Br
Pd(PPh3)4
F
F
F
F
5
6
FBTA
Scheme 1. Synthetic route of the fluorinated monomer (FBTA)
5
ACS Paragon Plus Environment

Chemistry of Materials
Page 6 of 26
1
2
3
4
5
6
7
8
9
PBDT-HBTA and PBDT-FBTA were synthesized by Stille coupling reaction,[6] as shown in
Scheme 2. The two copolymers are soluble in chlorinated solvents, such as chloroform,
chlorobenzene and dichlorobenzene. The number-average molecular weight (Mn) of the
polymers is 31.2K for PBDT-HBTA and 114.5K for PBDT-FBTA, with polydispersity index
(PDI) of 2.60 and 2.77 respectively. Thermal stability of the polymers was investigated with
thermogravimetric analysis (TGA) as shown in Figure S1 in Supporting Information (SI). The
onset temperatures with 5% weight-loss (Td) of PBDT-HBTA and PBDT-FBTA are 327 °C and
364 °C, respectively. This indicates that the copolymers are stable enough for the applications
in optoelectronic devices. The data of molecular weight and Td of the two copolymers were
listed in Table 1 for a clear comparison. DSC thermogram of PBDT-FBTA (see Figure S2 in SI)
shows a small endothermic peak at 110 °C, while there are no endothermic or exothermic peaks
in the DSC thermogram of PBDT-HBTA in the temperature range of 30~300oC. The results
indicate there could be some morphology transformation at ca. 110 °C for PBDT-FBTA with
fluorine atoms substitution.
10
11
12
13
14
15
16
17
18
19
20
21
22
23
24
25
26
27
28
29
30
31
32
33
34
35
36
37
38
39
40
41
42
43
44
45
46
47
48
49
50
51
52
53
54
55
56
57
58
59
60
Table 1. Molecular weights, thermal properties and physicochemical properties of the
copolymers.
a
b
opt
Mn
PDI
Td
λ edg Eg
HOMO LUMO Mobility
(eV)
(eV) (cm2·V-1s-1)
Polymers
(g/mol) (Mw/Mn) (˚C) ( nm) (eV)
PBDT-HBTA 81.3K
PBDT-FBTA 317.1K
2.60
2.77
327
364
659 1.88 -5.13
649 1.91 -5.26
-3.16
-3.08
1.8×10-3
2.4×10-3
[a] 5% weight loss temperature measured by TGA under N2.
[b] For the polymer films.
6
ACS Paragon Plus Environment

Page 7 of 26
Chemistry of Materials
1
2
3
4
5
6
7
8
9
10
11
12
13
14
15
16
17
18
19
20
21
22
23
24
25
26
27
28
29
30
31
32
33
34
35
36
37
38
39
40
41
42
43
44
45
46
47
48
49
50
51
52
53
54
55
56
57
58
59
60
Scheme 2. Synthetic routes to the side chain isolated D-A copolymers.
2.2. Optical and Electrochemical Properties.
Figure 2 shows the absorption spectra of the polymer solutions in chloroform and films on
quartz plate, and the absorption data were also listed in Table 1 for comparison. The solution
and film absorptions of the two copolymers display similar absorption band with well defined
peaks and steep absorption edges. In comparison with the analogue copolymer with alkoxy side
chains on BDT unit[17a] and that with alkyl side chain on BDT unit[18], the absorption spectrum
of PBDT-HBTA with thiophene conjugated side chain is red-shifted by ca. 15 nm. The
absorption edges of the polymer films are at 659 nm for PBDT−HBTA and 649 nm for
PBDT−FBTA, corresponding to optical bandgaps of 1.88 eV and 1.91 eV, respectively.
Moreover, the two copolymer films show well−defined absorption spectra, indicating the
ordered polymer chains and densely packed side chains in the polymer film, which should be
beneficial to higher hole mobility and photovoltaic performance. The absorption of
PBDT−FBTA film is only red-shifted a little than that of its solution, which reveals strong
7
ACS Paragon Plus Environment

Chemistry of Materials
Page 8 of 26
1
2
3
4
5
6
7
8
9
aggregation existed in the solution for the fluorinated polymer.[19] When the polymer solutions
were heated to 80 °C, the absorption peaks blue shifted in some extent, as shown in Figure 2a
and 2b, and the shoulder peak at ca. 600 nm weakened, implying partial dis-aggregation of the
polymer backbone at the high temperature.
10
11
12
13
14
15
16
17
18
19
20
21
22
23
24
25
26
27
28
29
30
31
32
33
34
35
36
37
38
39
40
41
42
43
44
45
46
47
48
49
50
51
52
53
54
55
56
57
58
59
60
Figure 2. The dichlorobenzene solution and film absorption spectra of (a) PDTS-HBTA and (b)
PDTS-FBTA. (c) Cyclic voltammograms of the polymer films on glassy carbon electrode in a
0.1 mol/L n−Bu4NPF6 acetonitrile solution at a sweep rate of 100 mV/s.
2.3. X-ray Diffraction and Hole Mobility.
The X-ray diffraction patterns of the two polymers, as shown in Figure S3 in SI, display a
(100) diffraction peak at ca. 2θ = 3.70°, corresponding to an interchain d–spacing of 23.68 Å.
This value is greater than that of P3HT (16.4 Å)[22] due to the bulky side chain on the polymers.
The (010) diffraction peaks with broad feature located at ca. 2θ = 24.8°, corresponding to a
facial π-π stacking distance of 3.67 Å. These results indicate that the substitution of the
hydrogen with fluorine on the benzotriazole group has no effect on the interchain d–spacing and
π-π stacking distance. While, the difference in their solid structure is revealed by their second
order or third order diffraction peaks, which is properly related to the inter- and intramolecular
8
ACS Paragon Plus Environment

Page 9 of 26
Chemistry of Materials
1
2
3
4
5
6
interactions through C-F···H and F···S interactions. The crystalline characteristics of these two
polymers appeared to be favorable for charge transport in PSCs.
7
8
9
To measure the hole mobilities of the polymers, organic field-effect transistors were
fabricated in a top contact geometry using Au as the source and drain electrode. Figure S5 and
Figure S6 in SI show the output and transfer curves of the OTFT devices based on
PBDT-HBTA and PBDT-FBTA respectively. The calculated hole mobilities were 1.8×10-3
10
11
12
13
14
15
16
17
18
19
20
21
22
23
24
25
26
27
28
29
30
31
32
33
34
35
36
37
38
39
40
41
42
43
44
45
46
47
48
49
50
51
52
53
54
55
56
57
58
59
60
cm2/Vs for PBDT–HBTA and 2.4×10-3 cm2/Vs for PBDT–FBTA (see Table 1), confirming
the relatively higher hole mobility of these two copolymers.
2.4. Electrochemical Properties
The highest occupied molecular orbital (HOMO) and the lowest unoccupied molecular
orbital (LUMO) energy levels of the copolymers were measured by electrochemical cyclic
voltammetry, and were calculated from the onset oxidation potential (φox) and onset reduction
potential (φred) obtained from the cyclic voltammograms of the polymers according to the
following equations[23]: EHOMO = –e(φox＋4.71) (eV) and ELUMO = – e(φred＋4.71), where the
unit of potential is V vs. Ag/Ag+. Figure 2c shows the cyclic voltammograms of the two
polymers. The φox and φred of PBDT-HBTA are 0.42 V and −1.55 V vs. Ag/Ag+ respectively,
corresponding to HOMO level of −5.13 eV and LUMO level of −3.16 eV. After introducing
fluorine atom in PBDT-FBTA, its HOMO energy level is down–shifted to –5.26 eV. The
HOMO and LUMO energy levels of the polymers were also shown in Table 1. The lower
HOMO energy levels of PBDT-FBTA can provide better air stability in ambient condition and
higher open circuit voltage (Voc) of the PSCs with PBDT-FBTA as donor materials, because the
Voc is usually proportional to the difference between the LUMO level of the acceptor and the
HOMO level of the donor.
2.5. Photovoltaic Properties.
9
ACS Paragon Plus Environment

Chemistry of Materials
Page 10 of 26
1
2
3
4
5
6
7
8
9
Polymer solar cells were fabricated from PBDT-HBTA or PBDT-FBTA as donor and
(6,6)-phenyl-C70-butyric acid methyl ester (PC70BM) as acceptor with a general device structure
(see the inset of Figure 3) of ITO/PEDOT:PSS/Polymer:PC70BM/Ca(20 nm)/Al(90 nm). The
active layers were spin-coated from chlorobenzene (CB) solution of the donor and acceptor,
1,8-diiodooctane (DIO) was used as processing additive to optimize the morphology, and
pre-thermal annealing at 110 °C for 10 min was performed before deposition of the metal top
electrode.
10
11
12
13
14
15
16
17
18
19
20
21
22
23
24
25
26
27
28
29
30
31
32
33
34
35
36
37
38
39
40
41
42
43
44
45
46
47
48
49
50
51
52
53
54
55
56
57
58
59
60
Table 2. The comparison of the photovoltaic properties of the PSCs based on polymer/PC70BM
(1:1, w/w) without or with DIO additive under the illumination of AM1.5G, 100 mW/cm2.
Voc
Jsc
FF PCE Thickness
Polymers
DIO
( V) (mAcm-2) (%) (%)
(nm)
No 0.60
Yes 0.58
No 0.72
5.38
7.41
5.68
7.61
10.94
52.8 1.70
80 nm
PBDT−HBTA
56.5 2.43 110 nm
57.2 2.34
62.1 3.45
80 nm
86 nn
PBDT−FBTA Yes 0.73
Yes 0.76
53.8 4.47 202 nm
10
ACS Paragon Plus Environment

Page 11 of 26
Chemistry of Materials
1
2
3
4
5
6
7
8
9
10
11
12
13
14
15
16
17
18
19
20
21
22
23
24
25
26
27
28
29
30
31
32
33
34
35
36
37
38
39
40
41
42
43
44
45
46
47
48
49
50
51
52
53
54
55
56
57
58
59
60
Figure 3. Current density−voltage curves of the PSCs based on polymer/PC70BM (1:1, w/w)
with and without DIO as a processing additive, under the illumination of AM1.5G, 100
mW/cm2. The inset shows the schematic diagram of the device.
Figure 3 shows the J-V curves of the PSCs based on the copolymer/PC70BM (1:1, w/w)
with and without DIO processing additive, under the illumination of AM1.5G, 100 mW/cm2,
and the photovoltaic parameters of the devices are summarized in Table 2. In the absence of the
additive, the PSC devices based on polymer/PC70BM (1:1, w/w) exhibit relatively poor
performance with a PCE of only 1.53% for PDBT-HBTA and 2.34% for PDBT-FBTA. The
fluorinated polymer PDBT-FBTA exhibited a VOC of 0.73 V, 0.1 V higher than that of
PDBT-HBTA, which is benefitted from its lower-lying HOMO energy level. The higher hole
mobility of PDBT-FBTA is expected to contribute in part to the higher photocurrents, higher
fill factors and better device performance. The addition of 5% DIO to the blend solution
11
ACS Paragon Plus Environment

Chemistry of Materials
Page 12 of 26
1
2
3
4
5
6
7
8
9
dramatically improved the photovoltaic performance of the devices. As shown in the J−V
curves of the PSCs based on polymer/PC70BM (1:1, w/w) with DIO additive, both polymers
show improved efficiency than that without the additive, due mainly to significantly increased
currents. The device based on PBDT-FBDA/PC70BM (1:1, w/w) with 5% DIO additive
demonstrated a PCE of 4.47% with a high JSC of 10.96 mA/cm2, a high VOC of 0.76 V and a FF
of 53.8%.
10
11
12
13
14
15
16
17
18
19
20
21
22
23
24
25
26
27
28
29
30
31
32
33
34
35
36
37
38
39
40
41
42
43
44
45
46
47
48
49
50
51
52
53
54
55
56
57
58
59
60
Table 3. The effect of the active layer thickness on the photovoltaic performance of the PSCs
based on a PDTS-FBTA/PC70BM (1: 2, w/w) with DIO additive, under the illumination of
AM1.5G, 100 mW/cm2.
Active Layer Thickness Voc
Jsc
FF PCE
(nm)
( V) (mAcm-2) (%) (%)
400 nm
190 nm
102 nm
0.75
0.75
0.77
10.82
11.90
10.03
58.4 4.74
67.2 6.00
71.6 5.53
12
ACS Paragon Plus Environment

Page 13 of 26
Chemistry of Materials
1
2
3
4
5
6
7
8
9
10
11
12
13
14
15
16
17
18
19
20
21
22
23
24
25
26
27
28
29
30
31
32
33
34
35
36
37
38
39
40
41
42
43
44
45
46
47
48
49
50
51
52
53
54
55
56
57
58
59
60
Figure 4. (a) Current density−voltage curves of the PSCs based on PBDT-FBTA/PC70BM (1:2,
w/w) with DIO as additive and with different active layer thickness, under the illumination of
AM1.5G, 100 mW/cm2; (b) Incident-photon-to-converted−current efficiency (IPCE) spectra of
the PSCs based on PBDT-FBTA/PC70BM (1:2, w/w) blend film with DIO as additive. The
inset of Figure 4b shows transmission spectrum of the active layer.
13
ACS Paragon Plus Environment

Chemistry of Materials
Page 14 of 26
1
2
3
4
5
6
7
8
9
Considering the promising photovoltaic properties of the fluorinated polymer
PBDT-FBTA, device optimization was further performed by changing the weight ratios of
PBDT-FBTA donor and PC70BM acceptor and the thickness of the active layers. The optimized
weight ratio of PBDT-FBTA: PC70BM is 1:2. Figure 4(a) shows the J-V curves of the PSCs
based on PBDT-FBTA/PC70BM (1:2, w/w) with DIO processing additive and with different
active layer thickness, under the illumination of AM1.5G, 100 mW/cm2, and the photovoltaic
parameters of the devices are summarized in Table 3. The IPCE and transmission spectra based
on the various blends are shown in Figure 4b. From the transmission spectrum of the active
layer (see the inset of Figure 4b), we can see that thicker active layer can ensure better
light-harvesting ability, and ca. 90% light was absorbed in the wavelength range of 300-620 nm
for the film at 190 nm. At an active layer thickness of 102 nm, a PCE of 5.53% was obtained
together with a notable FF of 71.6% and a JSC of 10.03 mA/cm2. The FF of 71.6% is the highest
value in the PSCs with the 2-D-conjugated polymers as donor, which indicates that the charge
flow in the device is well-balanced and no significant recombination loss occurs within the
active layer under this condition. Under an optimal active layer thickness of 190 nm, the device
exhibits a high Jsc of 11.90 mA cm-2 with a broad and high IPCE over 70% in the wavelength
range of 450-630 nm (see Figure 4(b)). Together with a VOC of 0.75 V and a fill factor of
67.2%, a further improved PCE of 6.0% was achieved. Interestingly, even at a thicker active
layer of 400 nm, the PSC still demonstrated a higher PCE of 4.74%. The insensitivity of the
photovoltaic performance of the PSCs on the active layer thickness should be benefitted from
10
11
12
13
14
15
16
17
18
19
20
21
22
23
24
25
26
27
28
29
30
31
32
33
34
35
36
37
38
39
40
41
42
43
44
45
46
47
48
49
50
51
52
53
54
55
56
57
58
59
60
14
ACS Paragon Plus Environment

Page 15 of 26
Chemistry of Materials
1
2
3
4
5
6
7
the higher hole mobility of the polymer, and it is of crucial importance for large area fabrication
of the device in future commercial applications.
8
9
10
11
12
13
14
15
16
17
18
19
20
21
22
23
24
25
26
27
28
29
30
31
32
33
34
35
36
37
38
39
40
41
42
43
44
45
46
47
48
49
50
51
52
53
54
55
56
57
58
59
60
Figure 5. Tapping mode AFM (a) topography image and (b) phase image of the blend film of
PBDT-FBTA/PC70BM (1: 2, w/w) without DIO; (c) topography image and (d) phase image of
the blend film of PBDT-FBTA/PC70BM (1: 2, w/w) with DIO.
The effect of DIO additive is most clearly visualized from atomic force microscopy (AFM)
images of PBDT-FBTA/PC70BM (1: 2, w/w) blend film with or without DIO additive, as
15
ACS Paragon Plus Environment

Chemistry of Materials
Page 16 of 26
1
2
3
4
5
6
7
8
9
shown in Figure 5. Without DIO, the composite film exhibits micro-scale phase separation,
suggesting poor dispersion of PC70BM in the polymer matrix (Figure 5a and 5b). In contrast,
nano–morphology with 20–30 nm domain size is clearly visible for the film with 5% DIO
additive. The bicontinuous network with nano–scale phase separation improved the exciton
dissociation and carrier collection efficiency, thus leading to an increase in short-circuit current
density as well as the device efficiency. The GIXRD measurement of the polymer/PCBM blend
film with and without DIO can provide further evidence on the change of the blend film
structures (see Figure S4 in SI). For the blend film, the decreased peak intensity of the blend
film with 5% DIO, compared to blend film without DIO, indicates the crystalline domain size
within the film is decreased. This result is consistent with the morphology change.
10
11
12
13
14
15
16
17
18
19
20
21
22
23
24
25
26
27
28
29
30
31
32
33
34
35
36
37
38
39
40
41
42
43
44
45
46
47
48
49
50
51
52
53
54
55
56
57
58
59
60
3. Conclusions
In conclusion, we synthesized two new 2-D-conjugated and side-chain-isolated D-A
copolymers, PBDT-HBTA and PBDT-FBTA, based on thiophene-substituted BDT donor unit,
BTA acceptor unit without or with fluorine substitution, and thiophene π-bridges between the
donor and acceptor units, for the studies on the relationship of molecular structure and
photovoltaic properties of the polymer photovoltaic materials. The copolymer films
demonstrated well defined absorption peaks with steep absorption edges, consistent with their
rigid and ordered structures in the solid films. The substitution of thiophene conjugated side
chain on the BDT unit in the copolymers aroused 15 nm red-shifted absorption in comparison
with its polymer analogues with alkoxy side chains on BDT unit. Compared to PBDT-HBTA,
PBDT-FBTA with two fluorine atoms substitution on BTA unit demonstrated lower HOMO
energy level, higher hole mobility and significantly better photovoltaic performance. The PSC
16
ACS Paragon Plus Environment

Page 17 of 26
Chemistry of Materials
1
2
3
4
5
6
7
8
9
based on PBDT-FBTA/ PC70BM (1:2, w/w) with 5% DIO additive displayed a power
conversion efficiency of 6.0% with a Jsc of 11.9 mA/cm2, a VOC of 0.75 V and a FF of 67.2%,
under the illumination of AM1.5G, 100 mW/cm2. Even at a thicker active layer of 400 nm, the
PSC still demonstrated a higher PCE of 4.74%. The results indicate that PBDT-FBTA is a
promising polymer donor material for future application of large area PSCs.
10
11
12
13
14
15
16
17
18
19
20
21
22
23
24
25
26
27
28
29
30
31
32
33
34
35
36
37
38
39
40
41
42
43
44
45
46
47
48
49
50
51
52
53
54
55
56
57
58
59
60
4. Experimental Section
1
Instrumentation. H NMR spectra were measured on a Bruker DMX–400 spectrometer with
d–chloroform as the solvent and trimethylsilane as the internal reference. UV−visible
absorption spectra were measured on a Hitachi U–3010 UV−vis spectrophotometer. Mass
spectra were recorded on a Shimadzu spectrometer. Elemental analyses were carried out on a
flash EA 1112 elemental analyzer. Thermogravimetric analysis (TGA) was conducted on a
Perkin–Elmer TGA–7 thermogravimetric analyzer at a heating rate of 20 °C/min and under a
nitrogen flow rate of 100 mL/min. Molecular weight of the polymer was measured by Gel
permeation chromatography (GPC), using polystyrene as standard and THF as the eluent. The
electrochemical cyclic voltammetry was performed on a Zahner IM6e Electrochemical
Workstation, in an acetonitrile solution of 0.1 mol/L n-Bu4NPF6 at a potential scan rate of 100
mV/s with an Ag/Ag+ reference electrode and a platinum wire counter electrode. The film
morphology was measured using an atomic force microscope (AFM, SPA-400) using the
tapping mode. X-ray diffraction patterns of the pristine polymer thin films were measured using
a Rigaku D/ MAX 2500V/ PC diffractometer operated in grazing incidence mode.
Materails: All chemicals and reagents were purchased from commercial sources and used
without further purification.
17
ACS Paragon Plus Environment

Chemistry of Materials
Page 18 of 26
1
2
3
4
5
6
7
8
9
4,5-difluorobenzene-1,2-diamine (1): 4,5-difluoro-2-nitroaniline (10 g, 38 mmol) and 12 M
HCl (311 mL) were put into a two-neck flask under the protection of Argon atmosphere. After
cooling the mixture to 0 °C, Then tin power (33 g) was added slowly, while the reaction
temperature was maintained at 25-30 °C. Continue to reaction when the tin power completely
depleted after one hour at the same temperature, and then put it in the refrigerator overnight.
The reaction mixture was put into 500 mL water, and then use 4 M NaOH to adjust the pH
value to pH10. Meanwhile, the reaction mixture was extracted three times with ethyl acetate.
The organic layer was washed with water, dried (MgSO4) and then concentrated under reduced
10
11
12
13
14
15
16
17
18
19
20
21
22
23
24
25
26
27
28
29
30
31
32
33
34
35
36
37
38
39
40
41
42
43
44
45
46
47
48
49
50
51
52
53
54
55
56
57
58
59
60
pressure.
The
crude
product
was
recrystallized with
methanol
to
obtain
1
4,5-difluorobenzene-1,2-diamine with a 80% yield. H NMR (400 MHz, CDCl3, ppm): 7.94 (t,
2H), 4.57 (m, 4H). Ms, m/z (%): 144. Calculated for C6H6N2F2: C, 50.00; H, 4.17; N, 19.44;
found: C, 50.09; H, 4.12; N, 19.23.
5,6-difluoro-1H-benzo[d][1,2,3]triazole (2): Compound 1 (14 g, 0.1 mol) was dissolved in
AcOH (12 ml, 0.2 mol) and 500 ml of water on heating. The reaction mixture was cooled, and a
solution of NaNO2 (8 g, 0.11 mol) in 200 ml of water was added at 5 °C. The reaction mixture
became immediately dark-green, and it was stirred at room temperature for 1 h. The precipitate
obtained after cooling was filtered off, dried in air and recrystallised from water. Yield, 81%;
1H NMR (400 MHz, CDCl3, ppm): 15.81 (s, 1H), 7.89 (t, 2H). Ms, m/z (%): 155. Calculated for
C6H3N3F2: C, 46.45; H, 1.93; N, 27.10; found: C, 46.73; H, 1.92; N, 27.03.
2-(2-octyl)-5,6-difluoro-2H-benzo[d][1,2,3]triazole (3): Compound 2 (12 g, 80 mmol),
potassium tert-butoxide (30 g, 200 mmol) and 1-bromooctane (29 g, 150 mmol) were dissolved
in methanol (200 mL). The reaction mixture was refluxed for 24 h and monitored by TLC. The
18
ACS Paragon Plus Environment

Page 19 of 26
Chemistry of Materials
1
2
3
4
5
6
7
8
9
reaction mixture was then poured into saturated NH4Cl solution, and extracted with CHCl3 and
washed with water twice. The organic extraction was dried over anhydrous MgSO4 and the
solvent was evaporated under reduced pressure. Column chromatography on silica gel was
10
11
12
13
14
15
16
17
18
19
20
21
22
23
24
25
26
27
28
29
30
31
32
33
34
35
36
37
38
39
40
41
42
43
44
45
46
47
48
49
50
51
52
53
54
55
56
57
58
59
60
1
performed to obtain 4,5-difluoro-2-octylbenzotriazole as a colorless oil with a 45% yield. H
NMR (400 MHz, CDCl3, ppm): 7.91 (t, 2H), 4.67 (d, 2H), 2.21 (m, 2H), 1.52-1.18 (m, 10H),
0.89 (t, 3H). Ms, m/z (%): 267. Calculated for C14H19N3F2: C, 62.92; H, 7.12; N, 15.73; found:
C, 62.98; H, 7.11; N, 15.65.
4,7-di(trimethylsilyl)-2-(2-octyl)-5,6-difluoro-2H-benzo[d][1,2,3]triazole (4): 2.0 M Lithium
diisopropylamide (LDA) (33 mL, 66 mmol) was added dropwise over 10 min to a solution of
compound 3 (8 g, 30 mmol) and dry THF (100 mL) under argon at -78 °C. The solution was
stirred for 30 min, and then trimethylsilyl chloride (7.6 g, 70 mmol) was added dropwise over
10 minutes at -78 °C. The temperature was maintained while reaction was stirred for 3h, and
then the reaction was quenched with 10 mL of saturated NH4Cl. The reaction was warmed to
room temperature and poured into saturated NH4Cl. The mixture was extracted with CHCl3,
washed with water twice. The organic extraction was dried over anhydrous MgSO4 and the
solvent was evaporated under reduced pressure. Column chromatography on silica gel was
performed to obtain 4,7-di(trimethylsilyl)-5,6-difluoro-2-octylbenzotriazole as a colorless oil
with a 75% yield. 1H NMR (400 MHz, CDCl3, ppm): 4.63 (d, 2H), 2.19 (m, 2H), 1.52-1.18 (m,
10H), 0.28-0.35 (t, 21H). Ms, m/z (%): 411. Calculated for C14H30N3F2Si2: C, 40.87; H, 7.30; N,
10.22; found: C, 40.98; H, 7.21; N, 10.09.
4,7-dibromo-2-(2-octyl)-5,6-difluoro-2H-benzo[d][1,2,3]triazole (5): Monomer 4 (8.22 g, 20
mmol) was dissolved into CHCl3 (100 mL), and bromine (9.5 g, 60 mmol) was added in one
19
ACS Paragon Plus Environment

Chemistry of Materials
Page 20 of 26
1
2
3
4
5
6
7
8
9
portion, and the reaction was stirred for 24 h at 60 °C, shielded from light. After cooling the
mixture to room temperature, a NaOH aqueous solution was added and the aqueous layer was
extracted with CHCl3. The organic layer was dried over anhydrous MgSO4 and the solvent was
evaporated under reduced pressure. Compound 5 was obtained as a light yellow oil by column
chromatography in a 85% yield. 1H NMR (400 MHz, CDCl3, ppm): 4.66 (d, 2H), 2.27 (m, 2H),
1.48-1.13 (m, 10H), 0.87 (t, 3H). Ms, m/z (%): 425. Calculated for C14H17N3F2Br2: C, 39.53; H,
4.00; N, 9.88; found: C, 39.98; H, 4.11; N, 9.67.
10
11
12
13
14
15
16
17
18
19
20
21
22
23
24
25
26
27
28
29
30
31
32
33
34
35
36
37
38
39
40
41
42
43
44
45
46
47
48
49
50
51
52
53
54
55
56
57
58
59
60
2-(2-octyl)-5,6-difluoro-4,7-di(thiophen-2-yl)-2H-benzo[d][1,2,3]triazole (6): Monomer 5
(6.8 g, 16 mmol), tributyl(2-thienyl)tin (18.7 g, 50 mmol), and Pd(PPh3)4 (416 mg, 0.36 mmol)
were dissolved in 150 mL of dry THF. The reaction mixture was then heated to reflux, and
stirred for 48 h under a nitrogen atmosphere. After cooling, the reaction solution was extracted
three times with ethyl acetate. The organic layer was washed with water, dried over anhydrous
MgSO4, and then concentrated under reduced pressure. Further purification was performed
using silica gel column chromatography (petroleum ether/methylene = 4:1 as eluent),
1
yellow-green crystals was obtained. The yield was 90%. H NMR (400 MHz, CDCl3, ppm):
8.23 (d, 2H), 7.51 (d, 2H), 7.23 (m, 2H), 4.76 (d, 2H), 2.57 (m, 2H), 1.58-1.18 (m, 10H), 0.91 (t,
3H). Ms, m/z (%): 433. Calculated for C22H23N3F2S2: C, 60.97; H, 5.31; N, 9.70; found: C,
70.01; H, 5.37; N, 9.58.
4,7-bis(5-bromothiophen-2-yl)-2-(2-butyloctyl)-5,6-difluoro-2H-benzo[d][1,2,3]triazole
(FBTA): Under the darkness, compound 6 (2.6 g, 6 mmol) was dissolved in the mixture of
CHCl3 (60 mL) and acetic acid (60 mL). After cooling the mixture to 0 °C, NBS (2.35 g, 13.2
mmol) was added in portions. After 12 h, the reaction mixture was extracted with CHCl3 and
20
ACS Paragon Plus Environment

Page 21 of 26
Chemistry of Materials
1
2
3
4
5
6
7
8
9
washed by water twice and dried (MgSO4). The organic solvent was evaporated. The crude
product was purified by column chromatography on silica gel using 10:1 petroleum ether:
methylene chloride as the eluent. Yellow crystals were obtained with 72% yield. 1H NMR (400
MHz, CDCl3, ppm): 7.93 (d, 2H), 7.15 (m, 2H), 4.71 (d, 2H), 2.33 (m, 2H), 1.44-1.12 (m, 10H),
0.88 (t, 3H). Ms, m/z (%): 591. Calculated for C22H21N3F2S2Br2: C, 44.67; H, 3.55; N, 7.11;
found: C, 44.77; H, 3.47; N, 7.08.
10
11
12
13
14
15
16
17
18
19
20
21
22
23
24
25
26
27
28
29
30
31
32
33
34
35
36
37
38
39
40
41
42
43
44
45
46
47
48
49
50
51
52
53
54
55
56
57
58
59
60
Synthesis of PBDT-HBTA. Under the protection of Argon atmosphere, 0.5 mmol of the
2,6-Bis(trimethyltin)-4,8-bis(5-(2-ethylhexyl)thiophen-2-yl)benzo[1,2-b:4,5-b’]
dithiophene
[24]
(monomer BDT)
was put into a two-neck flask. Then 12 ml of degassed toluene and 0.5
mmol of 2-octyl-4,7-di(5-bromo-thiophen-2-yl)-2H-benzo[1,2,3] triazole (monomer HBTA)[17a]
were added to the mixture. The solution was flushed with argon for 10 min, and then 25 mg of
Pd(PPh3)4 was added. After another flushing with argon for 20 min, the reactant was heated to
reflux for 12 h. Then the reactant was cooled to room temperature and the polymer was
precipitated by adding 200 ml of methanol, filtered through a Soxhlet thimble, and then
subjected to Soxhlet extraction with methanol, hexane, and chloroform. The polymer was
recovered as solid from the chloroform fraction by rotary evaporation. The solid was dried
under vacuum for 12 h. The yield of the polymerization reaction was about 47%. GPC: Mw =
1
81.3 kg/mol, Mn= 31.2 kg/mol, Mw/Mn = 2.60. H NMR (400 MHz, CDCl3), δ(ppm): 7.39 (m,
2H), 7.19 (m, 2H), 2.76 (m, 4H), 1.72-1.20(m, 50H), 0.79-0.90 (m, 21H).
Synthesis of PBDT-FBTA. The polymerization process was the same as that for PBDT-HBTA,
except that monomer FBTA[18] was used instead of monomer HBTA and the reactant was
1
refluxed for 12h. Yield: 63%. GPC: Mw = 43.0 kg/mol, Mn= 32.0 kg/mol, Mw/Mn = 1.35. H
21
ACS Paragon Plus Environment

Chemistry of Materials
Page 22 of 26
1
2
3
4
5
6
7
NMR (400 MHz, CDCl3), δ（ppm）: 7.53-7.32 (m, 2H), 4.19 (m, 2H), 2.93 (m, 4H), 1.52-1.25(m,
50H), 0.79-0.95 (m, 21H).
8
9
Fabrication and Characterization of PSCs: The PSCs were fabricated with a configuration of
ITO/PEDOT:PSS (40 nm)/active layer/ Ca(20 nm)/Al(90 nm). A thin layer of PEDOT:PSS
(poly−(3,4−ethylenedioxythiophene): poly(styrene sulfonate)) was spin−cast on pre−cleaned
ITO−coated glass from a PEDOT:PSS aqueous solution (Baytron P VP AI 4083 from H. C.
Starck) at 2000 rpm and dried subsequently at 150 °C for 30 min in air, then the device was
transferred to a glove box, where the active layer of the blend of the polymer and fullerene
derivative was spin−coated onto the PEDOT:PSS layer. Finally, a Ca/Al metal top electrode
was deposited in vacuum onto the active layer at a pressure of ca. 5 × 10−5 Pa. The active area
of the device was 4 mm2. The thickness of the active layer was determined by an Ambios Tech.
XP−2 profilometer. The current density−voltage (J−V) characteristics were measured on a
computer−controlled Keithley 236 Source−Measure Unit. A xenon lamp coupled with AM 1.5
solar spectrum filter was used as the light source, and the optical power at the sample was 100
mW/cm2.
10
11
12
13
14
15
16
17
18
19
20
21
22
23
24
25
26
27
28
29
30
31
32
33
34
35
36
37
38
39
40
41
42
43
44
45
46
47
48
49
50
51
52
53
54
55
56
57
58
59
60
Supporting Information Available: TGA and DSC plots, X-ray diffraction patterns and the
OFET performance of the polymers. This information is available free of charge via the Internet
at http://pubs.acs.org/.
Acknowledgements This work was supported by NSFC (#51103164, 50933003 and 21021091),
The Ministry of Science and Technology of China (No: 2011AA050523 and 2010DFB63530)
and Chinese Academy of Sciences (No. KGCX2-YW-399+9-1 and GJHZ1124).
22
ACS Paragon Plus Environment

Page 23 of 26
Chemistry of Materials
1
2
3
4
References
5
6
7
8
9
[1] Yu, G.; Gao, J.; Hummelen, J. C.; Wudl, F.; Heeger, A. J. Science. 1995, 270, 1789.
[2] (a) Li, Y. F. Acc. Chem. Res. 2012, 45, 723. (b) Li, Y. F. Zou, Y. P. Adv. Mater. 2008, 20,
2952.
10
11
12
13
14
15
16
17
18
19
20
21
22
23
24
25
26
27
28
29
30
31
32
33
34
35
36
37
38
39
40
41
42
43
44
45
46
47
48
49
50
51
52
53
54
55
56
57
58
59
60
[3] Chen, J. W.; Cao, Y. Acc. Chem. Res. 2009, 42, 1709.
[4] (a) Cheng, Y.-J.; Yang, S.-H.; Hsu, C.-S. Chem. Rev. 2009, 109, 5868. (b) Chang, C.-Y.;
Cheng, Y.-J.; Hung, S.-H.; Wu, J.-S.; Kao, W.-S.; Lee, C.-H.; Hsu, C.-S. Adv. Mater. 2012,
24, 549.
[5] (a) Chen, H.-Y.; Hou, J. H.; Zhang, S. Q.; Liang, Y. Y.; Yang, G. W.; Yang, Y.; Yu, L. P.;
Wu, Y.; Li, G. Nature Photonics, 2009, 3, 649. (b) Huo, L. J.; Zhang, S. Q.; Guo, X.; Xu,
F.; Li, Y. F.; Hou, J. H. Angew. Chem. Int. Ed. 2011, 50, 9697.
[6] (a) Liang, Y.; Yu, L. Acc. Chem. Res. 2010, 43, 1227. (b) Liang, Y.; Xu, Z.; Xia, J.; Tsai,
S.-T.; Wu, Y.; Li, G.; Ray, C.; Yu, L. Adv. Mater. 2010, 22, E135.
[7] (a) Zhou, H.; Yang, L.; You, W. Macromolecules, 2012, 45, 607. (b) Chu, T.-Y.; Lu, J.;
Beaupré, S.; Zhang, Y.; Pouliot, J.-R.; Wakim, S.; Zhou, J.; Leclerc, M.; Li, Z.; Ding, J.;
Tao, Y. J. Am. Chem. Soc. 2011, 133, 4250. (c) Piliego, C.; Holcombe, T. W.; Douglas,
J. D.; Woo, C. H.; Beaujuge, P. M.; Fréchet, J. M. J. J. Am. Chem. Soc. 2010, 132, 7595. (d)
Bijleveld, J. C.; Zoombelt, A. P.; Mathijssen, S. G. J.; Wienk, M. M.; Turbiez, M.; Leeuw,
D. M. de; Janssen, R. A. J. J. Am. Chem. Soc. 2009, 131, 16616. (e) Zhou, N.; Guo, X.;
Ortiz, R. P.; Li, S.; Zhang, S.; Chang, R. P. H.; Facchetti, A.; Marks, T. J. Adv. Mater. 2012,
24, 2242. (f) Ong, K.-H.; Lim, S.-L.; Tan, H.-S.; Wong, H.-K.; Li, J.; Ma, Z.; Moh, L. C. H.;
Lim, S.-H.; de Mello, J. C.; Chen, Z.-K. Adv. Mater. 2011, 23, 1409. (e) Qin, R.; Li, W.;
Li, C.; Du, C.; Veit, C.; Schleiermacher, H.-F.; Andersson, M.; Bo, Z.; Liu, Z.; Inganas, O.;
Wuerfel, U.; Zhang, F. J. Am. Chem. Soc. 2009, 131, 14612. (g)Wang, E.; Hou, L.; Wang,
Z.; Hellström, S.; Zhang, F.; Inganäs, O.; Andersson, M. R. Adv. Mater. 2010, 22, 5240.
[8] (a) Jiang, J.-M.; Yang, P.-A.; Chen, H.-C.; Wei, K.-H. Chem. Commun. 2011, 47, 8877–8879.
(b) Yuan, M.-C.; Chiu, M.-Y.; Liu, S.-P. Chen, C.-M.; Wei, K.-H. Macromolecules. 2010,
43, 6936. (c) Su, M.-S.; Kuo, C.-Y.; Yuan, M.-C.; Jeng, U. S.; Su, C.-J.; Wei, K.-H. Adv.
23
ACS Paragon Plus Environment

Chemistry of Materials
Page 24 of 26
1
2
3
4
5
6
Mater. 2011, 23, 3315. (d) Chen, Y.-C.; Yu, C.-Y.; Fan, Y.-L.; Hung, L.-I.; Chen, C.-P.;
Ting, C. Chem. Commun. 2010, 46, 6503.
7
[9] (a) Ahmed, E.; Subramaniyan, S.; Kim, F. S.; Xin, H.; Jenekhe, S. A. Macromolecules,
2011, 44, 7207. (b) Schroeder, B. C.; Huang, Z.; Ashraf, R. S.; Smith, J.; D'Angelo, P.;
Watkins, S. E.; Anthopoulos, T. D.; Durrant, J. R.; McCulloch, I. Adv. Funct. Mater. 2012,
8
9
10
11
12
13
14
15
16
17
18
19
20
21
22
23
24
25
26
27
28
29
30
31
32
33
34
35
36
37
38
39
40
41
42
43
44
45
46
47
48
49
50
51
52
53
54
55
56
57
58
59
60
22, 1663.(c)
Zhou, E.; Yamakawa, S.; Tajima, K.; Yang, C.; Hashimoto, K. Chem.
Mater. 2009, 21, 4055. (d) Zou, Y.; Najari, A.; Berrouard, P.; Beaupré, S.; Réda Aich, B.;
Tao, Y.; Leclerc, M. J. Am. Chem. Soc. 2010, 132, 5330.(e) Li, Z.; Ding, J.; Song, N.; Lu,
J.; Tao, Y. J. Am. Chem. Soc. 2010, 132, 13160. (f) Shi, Q.; Fan, H.; Liu, Y.; Hu, W.; Li, Y.;
Zhan, X. Macromolecules 2011, 44, 9173.
[10] He, Y. J.; Li, Y. F; Phys. Chem. Chem. Phys. 2011, 13, 1970.
[11] (a) Hou, J. H.; Tan, Z. A.; Yan, Y.; He, Y. J.; Yang, C. H.; Li, Y. F. J. Am. Chem. Soc.
2006, 128, 4911. (b) Hou, J. H.; Huo, L. J.; He, C.; Yang, C. H.; Li, Y. F. Macromolecules.
2006, 39, 594. (c) Zhou, E. J.; Tan, Z. A.; Huo, L. J.; He, Y. J.; Yang, C. H.; Li, Y. F. J.
Phys. Chem. B., 2006, 110, 26062.
[12] Zou, Y. P.; Wu, W. P.; Sang, G. Y.; Yang, Y.; Liu, Y. Q.; Li, Y. F.; Macromolecules. 2007,
40, 7231.
[13] (a) Zhang, Z.-G.; Zhang, S.; Min, J.; Cui, C.; Zhang, J.; Zhang, M.; Li, Y.; Macromolecules.
2012, 45, 113. (b) Zhang, Z.-G.; Zhang, S. Y.; Min, J.; Cui, C. H.; Geng, H.; Shuai, Z. G.;
Li, Y. F. Macromolecules. 2012, 45, 2312.
[14] Zhang, Z.-G.; Wang, J. Z.; J. Mater. Chem. 2012, 22, 4178.
[15] Huang, F.; Chen, K.-S.; Yip, H.-L.; Hau, S. K.; Acton, O.; Zhang, Y.; Luo, J.; Jen, A. K. Y.
J. Am. Chem. Soc. 2009, 131, 13886.
[16] (a) Zhang, Z.-G.; Liu, Y.-L.; Yang, Y.; Hou, K.; Peng, B.; Zhao, G.; Zhang, M.; Guo, X.;
Kang, E.-T.; Li, Y. F. Macromolecules. 2010, 43, 9376. (b) Zhang, Z.-G. Fan, H.; Min, J.;
Zhang, S.; Zhang, J.; Zhang, M.; Guo, X.; Zhan, X.; Li, Y. F. Polym. Chem. 2011, 2, 1678.
[17] (a) Zhang, Z. H.; Peng, B.; Liu, B.; Pan, C. Y.; Li, Y. F.; He, Y. H.; Zhou, K. C.; Zou, Y. P.
Polym. Chem. 2010, 1, 1441. (b) Min, J.; Zhang, Z.-G.; Zhang, S. Y.; Zhang, M. J.; Zhang,
J.; Li, Y.F. Macromolecules. 2011, 44, 7632.
24
ACS Paragon Plus Environment

Page 25 of 26
Chemistry of Materials
1
2
3
4
5
6
[18] Price, S. C.; Stuart, A. C.; Yang, L.; Zhou, H.; You, W. J. Am. Chem. Soc. 2011, 133,
4625.
7
8
9
[19] Zhou, H.; Yang, L.; Stuart, A. C.; Price, S. C.; Liu, S.; You, W.; Angew. Chem. Int. Ed.
2011, 50, 2995.
10
11
12
13
14
15
16
17
18
19
20
21
22
23
24
25
26
27
28
29
30
31
32
33
34
35
36
37
38
39
40
41
42
43
44
45
46
47
48
49
50
51
52
53
54
55
56
57
58
59
60
[20] Huo, L. J.; Hou, J. H.; Zhang, S. Q.; Chen, H.-Y.; Yang, Y. Angew. Chem. Int. Ed. 2010, 49,
1500.
[21] (a) Wang, M.; Hu, W.; Liu, P.; Li, W.; Gong, X.; Huang, F.; Cao, Y. J. Am. Chem. Soc. 2011,
133, 9638. (b) Peng, Q.; Liu, X.; Su, D.; Fu, G.; Xu, J.; Dai, L. Adv. Mater. 2011, 23,
4554.
[22] Ma, W.; Yang, C.; Gong, X.; Lee, K.; Heeger, A. J. Adv. Funct. Mater. 2005, 15, 1617
[23] Sun, Q.; Wang, H.; Yang, C.; Li, Y. F. J. Mater. Chem. 2003, 13, 800.
[24] Huo, L. J.; Guo, X.; Zhang, S. Q.; Li, Y. F.; Hou, J. H. Macromolecules. 2011, 44, 4035.
25
ACS Paragon Plus Environment

Chemistry of Materials
Page 26 of 26
1
2
3
4
5
For “Table of Content” use only
6
7
8
9
10
11
12
13
14
15
16
17
18
19
20
21
22
23
24
25
26
27
28
29
30
31
32
33
34
35
36
37
38
39
40
41
42
43
44
45
46
47
48
49
50
51
52
53
54
55
56
57
58
59
60
Title:
Conjugated
Sidechain
Isolated
D-A
Copolymers
Synthesis and
Based
Photovoltaic
on
Benzo[1,2-b:4,5-b']dithiophene-alt-dithienylbenzotriazole:
Properties
Authors: Jie Min, Zhi-Guo Zhang*, Siyuan Zhang, and Yongfang Li*
26
ACS Paragon Plus Environment