Phenyl-1,3,5-trithienyl-diketopyrrolopyrrole: A molecular backbone potentially affording high efficiency for solution-processed small-molecule organic solar cells through judicious molecular design

Article abstract of DOI:10.1002/asia.201300371

Finding new molecular backbones is necessary for further advances in solution-processed small-molecule organic solar cells (SM-OSCs). Increasing molecular π conjugation generally enhances the light-harvesting ability, and the resulting strong π-π-stacking interactions improve the charge-carrier transport ability; both increase the efficiency. In this study, we focus on the phenyl-1,3,5-trithienyl (3T-P) backbone because of its C₃ symmetry, planarity, and particularly high conjugation between the three arms through the core phenyl unit. When the three arms were functionalized with diketopyrrolopyrrole (DPP) units to afford 3D-T-P, only modest efficiency was achieved (1.16 %). Introduction of 4,8-bis(2-(2-ethylhexylthienyl)) benzodithiophene (BDT) between the 3T-P and DPP units to give 3D-B-T-P enhanced the light-harvesting ability, and particularly improved the hole mobility by 1.5 orders of magnitude (5.91×10^-2 versus 1.05×10 ^-3 cm² V^-1 s^-1). When using PC71BM as the acceptor material, 3D-B-T-P gave the best power conversion efficiency (PCE) of 2.27 %, which is about 1.9 times higher than the best efficiency from 3D-T-P (≈1.16 %). The efficiency can be improved up to 3.60 % with 3 % (v/v) of 1,8-diiodooctane (DIO) as the cosolvent and thermal annealing at 100 °C for 10 min. This PCE is, to the best of our knowledge, the highest efficiency reported to date among the phenyl-1,3,5-based C₃-symmetric molecules. Removing one DPP unit from 3D-T-P to form 2D-T-P, or from 3D-B-T-P to form 2D-B-T-P both decreased the light-harvesting ability and the hole mobility, thereby affording lower efficiency. Taken together, our results demonstrate that the planar phenyl-1,3,5-trithienyl-based C₃-symmetric structure can be a promising backbone, and enhancing the conjugation of the 3D-T-P backbone can effectively improve the device performance.

Full text of DOI:10.1002/asia.201300371

FULL PAPER
DOI: 10.1002/asia.201300371
Phenyl-1,3,5-Trithienyl-Diketopyrrolopyrrole: A Molecular Backbone
Potentially Affording High Efficiency for Solution-Processed Small-Molecule
Organic Solar Cells through Judicious Molecular Design
[
a, b]
[a]
[a]
[a]
[a]
Shanlin Zhang,
Bo Jiang, Chuanlang Zhan,* Jianhua Huang, Xin Zhang,
[a] [a] [a] [a]
Hui Jia, Ailing Tang, Lili Chen, and Jiannian Yao*
Dedicated to Professor Chunli Bai on the occasion of his 60th birthday
Abstract: Finding new molecular back-
bones is necessary for further advances
in solution-processed small-molecule
organic solar cells (SM-OSCs). Increas-
ing molecular p conjugation generally
enhances the light-harvesting ability,
and the resulting strong p–p-stacking
interactions improve the charge-carrier
transport ability; both increase the effi-
ciency. In this study, we focus on the
phenyl-1,3,5-trithienyl (3T-P) backbone
ethylhexylthienyl)) benzodithiophene
(BDT) between the 3T-P and DPP
units to give 3D-B-T-P enhanced the
light-harvesting ability, and particularly
improved the hole mobility by 1.5
3.60% with 3% (v/v) of 1,8-diiodooc-
tane (DIO) as the cosolvent and ther-
mal annealing at 1008C for 10 min.
This PCE is, to the best of our knowl-
edge, the highest efficiency reported to
date among the phenyl-1,3,5-based C3-
symmetric molecules. Removing one
DPP unit from 3D-T-P to form 2D-T-P,
or from 3D-B-T-P to form 2D-B-T-P
both decreased the light-harvesting
ability and the hole mobility, thereby
affording lower efficiency. Taken to-
gether, our results demonstrate that
the planar phenyl-1,3,5-trithienyl-based
À2
orders of magnitude (5.91ꢀ10 versus
À3
2
À1 À1
1.05ꢀ10 cm V s ). When using
PC71BM as the acceptor material, 3D-
B-T-P gave the best power conversion
efficiency (PCE) of 2.27%, which is
about 1.9 times higher than the best ef-
ficiency from 3D-T-P (ꢀ1.16%). The
efficiency can be improved up to
because of its C symmetry, planarity,
3
and particularly high conjugation be-
tween the three arms through the core
phenyl unit. When the three arms were
functionalized with diketopyrrolopyr-
role (DPP) units to afford 3D-T-P, only
C -symmetric structure can be a promis-
3
Keywords: donor–acceptor
systems · heterocycles · molecular
devices · small molecules · solar
cells
ing backbone, and enhancing the con-
jugation of the 3D-T-P backbone can
effectively improve the device perfor-
mance.
modest
efficiency
was
achieved
(
1.16%). Introduction of 4,8-bis(2-(2-
Introduction
acid methyl ester (PC61BM or PC71BM) as the acceptor
material, because of their advantages of low cost, light
weight, flexibility, and the potential to afford green
In recent years, intensive research efforts have focused on
solution-processed bulk-heterojunction polymer solar cells
[1–6]
energy.
On account of the great efforts devoted to the
(
BHJ PSCs), which usually consist of a conjugated polymer
material design and device optimization, impressive power
conversion efficiencies (PCEs) of PSCs of 7–10% have been
as the donor material and [6,6]phenyl-C61 (or C71)-butyric
[2,7–11]
frequently reported in the literature.
However, from
the material point of view, polymeric materials usually bear
several defects, such as broad molecular-weight distributions,
+
+
[
a] S. Zhang, B. Jiang, Prof. C. Zhan, J. Huang, X. Zhang, H. Jia,
A. Tang, L. Chen, Prof. J. Yao
[3–5]
difficult purification, and batch-to-batch variations.
In
Beijing National Laboratory of Molecular Science
CAS Key Laboratory of Photochemistry
Institute of Chemistry, Chinese Academy of Sciences
Beijing, 100190 (P.R. China)
Fax : (+86)10-82616517
E-mail: clzhan@iccas.ac.cn
this respect, solution-processed small molecules display their
merits, including well-defined structures, higher purity, in-
creased order, reduced batch-to-batch variations, and repro-
[12–19]
ducible device performances.
To date, although a large
amount of small molecules have been reported to fabricate
small-molecule organic solar cells (SM-OSCs), the typical
backbones that can afford high efficiency over 4% are
rather few, including 1) bow-shaped molecules based on
jnyao@iccas.ac.cn
+
[
b] S. Zhang
University of Chinese Academy of Sciences
Beijing 100039 (P.R. China)
[
20,21]
+
silole and pyridyl
A
H
U
G
R
N
U
G
2) star-shaped mole-
[
] These two authors contributed equally.
[
22,23]
cules;
capped with electron-deficient units;
Supporting information for this article is available on the WWW
under http://dx.doi.org/10.1002/asia.201300371.
[24–26]
and 4) dye mole-
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C. Zhan, J. Yao et al.
[27]
cules based on Squaraine di-
[28–31]
ketopyrrolopyrrole (DPP).
Finding new molecular back-
bones is necessary for the fur-
ther advances of SM-OSCs.
Among those excellent back-
bones that can afford high pho-
tovoltaic efficiencies, triphenyl-
amine (TPA) is a promising
building block on account of its
C -symmetric structure, which
3
can offer good solubility, well-
defined film-forming properties,
and enhanced charge-transport
[22,23,32–38]
ability,
and TPA-based
molecules with high efficiencies
of 3–4% have been reported
[
22,23,36–38]
recently.
central
However, the
nitrogen
3
sp -hybrid
atom breaks the possible conju-
gation between the p electrons
[23]
of three arms.
Compared to
the TPA core, a substituted
phenyl at the 1,3,5-positions
can be an interesting core that
can offer not only a C -symmet-
3
ric structure but also stronger
Scheme 1. Chemical structures of the five molecules.
[39–42]
conjugation.
Despite those
strong points, photovoltaic per-
formances of the conjugated C -symmetric structure based
moving a DPP from 3D-T-P and 3D-B-T-P, respectively.
3
on the solution-processed 1,3,5-substituted phenyl are still
After various characterizations, we found that the C -sym-
metric molecules exhibited more favorable optoelectronic
properties (e.g., stronger light-harvesting ability, higher hole
3
[41]
poor, with its highest efficiency only reaching 1.12%,
which is far away from the excellent structures that offer
[20,24–27,31,34,43]
high efficiencies of up to 5–7%.
How can this
mobilities) than those of C -symmetric molecules. Similarly,
2
core give improved photovoltaic performances?
the BDT-bridged molecules also exhibited better optoelec-
tronic properties than their counterparts without the BDT
bridge. Finally, the best molecule afforded an enhanced
PCE of 3.60%, which is the highest efficiency reported to
The efficiency of SM-OSCs is deeply related to their
light-harvesting ability, exciton diffusion, exciton separation
efficiency, and carrier transporting ability, all of which can
be adjusted by the molecular structures and device optimi-
zation. As such, to shed light on the 1,3,5-substituted phenyl
core, herein we utilize the 1,3,5-substituted phenyl as an
electron-donor core, the widely reported unit of diketopyr-
date among phenyl-based C -symmetric molecules and
3
makes the C -symmetric phenyl-1,3,5-trithienyl-DPP a new
3
backbone that could potentially afford high photovoltaic ef-
ficiency.
[28–33]
rolopyrrole (DPP)
as the electron-acceptor unit, and
thiophene and two-dimensional benzodithiophene (2D-
[
24,25,31,44,45]
BDT)
as alternative units to adjust the molecular
Results and Discussion
configuration and conjugation, thereby obtaining a series of
C - or C -symmetric molecules, as shown in Scheme 1. First-
Synthesis
3
2
ly, we selected the phenyl-1,3,5-trithienyl (3T-P) core to co-
valently bridge three-armed diketopyrrolopyrrole (DPP)
The synthetic routes to the five molecules are shown in
Scheme 2. 3T-P (3a) was synthesized according to the litera-
[46]
units, thus forming a C -symmetric conjugated phenyl-1,3,5-
ture method.
3HT-P (3b) was obtained by Suzuki cou-
3
trithienyl-DPP backbone (3D-T-P). Then, an n-hexyl side
chain was introduced to the 3-position of the bridged thio-
phene to obtain 3D-HT-P. Finally, 4,8-bis(2-(2-ethylhexylth-
ienyl)) benzodithiophene (BDT) was introduced between
pling reaction (Scheme 2i) as a colorless oil in 75% yield.
Stille coupling reaction of the tristannyl compounds 4a or
4b with 5 (Scheme 2iii) afforded 3D-T-P, 3D-HT-P, and 2D-
T-P in a yield of 55, 30, and 49%, respectively. Bromination
of 3a with N-bromosuccinimide (NBS; Scheme 2iv) afforded
3Br-T-P (6) in a 95% yield. 3B-T-P (9) was obtained as
a yellow oil with a yield of 51% by means of a two-step pro-
3T-P and DPP units, thus leading to 3D-B-T-P. For compari-
son, two C -symmetric dendrimers, 2D-T-P and 2D-B-T-P,
2
were also synthesized, both of which were designed by re-
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C. Zhan, J. Yao et al.
Scheme 2. Synthetic routes to 3D-T-P, 3D-T-P, 3D-B-T-P, 2D-T-P, and 2D-B-T-P. Reaction conditions: a) [Pd
A
H
U
G
R
N
U
(PPh
3
)
4
], K
2
CO
3
, toluene/H
2
O, 1108C, 12 h;
b) nBuLi, À788C, 1 h; then (CH)
3 3 4 3
SnCl, RT, 2 h; c) [Pd ACHTNUGTNERNUG( PPh ) ], toluene, 1108C, 24 h; d) NBS, CHCl , RT. 24 h. EH=2-ethylhexyl.
Table 1. Thermal and optoelectronic properties of the five molecules.
soln
[b]
film
max
film
edge
opt
cv
l
[nm]/emax
fwhm [nm]
sol
l
l
Eg
E
[V]
red
E
[V]
ox
HOMO
[eV]
LUMO
[eV]
Eg
T
d
[8C]
max
5
À1
À1 [a]
[c]
[d]
[e]
[f]
[
ꢀ10 m cm
]
film
[nm]
[nm]
[eV]
[eV]
3
3
3
2
2
D-T-P
582 (1.5)
581 (1.5)
594 (2.2)
580 (0.3)
590 (1.3)
102
99
108
101
109
155
139
172
162
153
582, 627
567, 610
587, 643
581, 627
600, 650
684
670
697
681
701
1.81
1.85
1.77
1.82
1.76
À0.87
À0.80
À0.83
À0.80
À0.80
0.78
0.73
0.73
0.75
0.74
À5.18
À5.13
À5.13
À5.15
À5.14
À3.53
À3.60
À3.57
À3.60
À3.60
1.65
1.53
1.56
1.55
1.54
407.2
391.8
399.0
410.6
381.1
D-HT-P
D-B-T-P
D-T-P
D-B-T-P
[
[
a] Molar extinction coefficient at lmax in solution. [b] Full width of the solution spectrum at half-maximum. [c] The onset of the film absorption edge.
film
d] Optical bandgap estimated from the formula of 1240/l . [e] Electrochemical bandgap estimated from the cyclic voltammetry data. [f] Decomposi-
edge
d
tion temperature (T ; 5% weight loss).
cess in which the first involved a 2D-BDT stannation reac-
tion (Scheme 2ii) to obtain 8, subsequently followed by
a Stille coupling reaction of 8 and 6 (Scheme 2iii). 3D-B-T-P
and 2D-B-T-P were obtained by a similar stannation reac-
tion to obtain 10, and a Stille coupling reaction of 10 and 5,
with modest one-step yields of 28 and 20%, respectively.
We have to point out that 2D-T-P and 2D-B-T-P were ob-
tained as coproducts with their C -symmetric counterparts
3
of 3D-T-P and 3D-B-T-P in one reaction batch, respectively.
Thermal Stability
The thermal stability of the five molecules was investigated
by thermogravimetric analysis (TGA). As shown in
Figure 1. TGA curves of the five molecules.
Figure 1, the decomposition temperature (T ; 5% weight
d
loss) was observed to be 407.2, 391.8, 399.0, 410.6, and
optical data are summarized in Table 1. Figure 2a shows the
solution absorption spectrum. All five molecules display two
absorption bands in chloroform, with one band located at
350–450 nm, which corresponds to the p–p* transitions of
the backbones, and the other band emerging at 450–750 nm,
which can be ascribed to the intramolecular charge-transfer
381.18C for 3D-T-P, 3D-HT-P, 3D-B-T-P, 2D-T-P, and 2D-B-
T-P, respectively (Figure 1 and Table 1), all of which are
thermally stable enough for further characterizations and
device fabrications.
[47]
transition between the BDT-T-Ph moiety and DPP unit.
Optical Properties
With respect to 3D-T-P, 3D-HT-P shows a slightly blueshift-
soln
max
Figure 2 shows the absorption spectrum of the five mole-
ed absorption band (l =582 versus 581 nm) and a smaller
À6
cules in chloroform (1ꢀ10 m) and in solid thin films. The
full width at half-maximum (fwhm=99 versus 102 nm), thus
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C. Zhan, J. Yao et al.
Figure 2b shows the normalized absorption of the five
molecules in the solid state. 3D-HT-P exhibits a blueshifted
film absorption and a relatively weaker absorbance from
3
00 to 450 nm than 3D-T-P, probably due to the introduction
of hexyl, which causes the poor planarity of 3D-HT-P. Simi-
lar to the solution absorption, after introducing 2D-BDT,
both the C -symmetric 3D-B-T-P and C -symmetric 2D-B-T-
3
2
P show redshifted film absorption and a relatively stronger
absorbance from 300 to 450 nm relative to their counter-
parts without 2D-BDT, thus indicating that 2D-BDT can in-
crease the conjugation and enhance the film absorption. The
optical bandgaps calculated from the film absorption edge
of 3D-T-P, 3D-HT-P, 3D-B-T-P, 2D-T-P, and 2D-B-T-P are
1
.81, 1.85, 1.77, 1.82, and 1.76 eV, respectively.
Electrochemical Properties
Figure 3a shows the cyclic voltammogram of the five mole-
cules with Ag/AgCl as the reference electrode. The empiri-
cal equation of EHOMO/LUMO =À
A
T
N
T
N
U
G
+4.40) eV was ap-
(ox/red)
onset
A
H
U
G
R
N
U
G
plied to estimate the HOMO and LUMO energy levels by
Figure 2. a) UV/Vis absorption spectrum of the five molecules in chloro-
À6
form with a concentration of 1ꢀ10 m and b) in thin films.
indicating that the introduction of n-hexyl slightly weakens
the conjugation between the phenyl core and the terminal
DPP unit. Interestingly, when 2D-BDT was introduced, 3D-
B-T-P displays a significantly improved light-harvesting abil-
ity relative to 3D-T-P in chloroform, including a redshifted
soln
max
l
of 594 nm, an enhanced maximum molar extinction co-
5
À1
À1
efficient (emax) of 2.2ꢀ10 m cm , and an enlarged fwhm of
08 nm. That improvement can be ascribed to the enlarged
1
conjugation offered by 2D-BDT. The enhanced light-har-
vesting ability is essential to the promoted photocurrent
when applied in photovoltaic devices. It is worth noting that
the C -symmetric 2D-T-P and 2D-B-T-P exhibit weaker
3
light-harvesting ability in solution relative to their C -sym-
3
metric counterparts of 2D-T-P and 2D-B-T-P, which involves
soln
max
a slightly blueshifted l
(580 versus 582 nm and 590 versus
5
5
94 nm) and an obviously decreased e
.5ꢀ10 m cm and 1.3ꢀ10 versus 2.2ꢀ10 m cm ), thus
(0.3ꢀ10 versus
max
5
À1
À1
5
5
À1
À1
1
indicating that three symmetric arms are necessary for
strong light-harvesting ability. We noted that the emax is de-
creased 5-fold when removing one DPP unit from 3D-T-P,
whereas it is decreased only 1.7-fold after one DPP unit is
removed from 3D-B-T-P, thereby suggesting that 2D-BDT,
which is localized at the arm free of DPP, does contribute to
Figure 3. a) Cyclic voltammograms of the five molecules in CHCl
3
/0.1m
À1
Bu
4
NBF
6
at 100 mVs and b) energy levels of different components in
a photovoltaic device.
[
48,49]
using the onset of oxidation/reduction potentials.
The
the phenyl core. We also have to point out that compared to
electrochemical parameters are summarized in Figure 3b
and Table 1. All five molecules show similar energy levels
with HOMOs in the range of À5.13 to À5.18 eV and
LUMOs in the range of À3.53 to À3.60 eV, which match
soln
2D-T-P, 2D-B-T-P still exhibits redshifted lmax, enhanced
emax, and enlarged fwhm, once again demonstrating the im-
portance of introducing 2D-BDT to enlarge conjugation and
strengthen absorption.
[50]
well with the acceptor material of PC71BM, as shown in
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C. Zhan, J. Yao et al.
Figure 3b. We have to note that either the introduction of
D-BDT or the transformation from a C - to C -symmetric
2
2
3
structure does not alter the energy levels of those molecules.
CV
The electrochemical bandgaps (Eg ) of all five molecules
are approximately 1.53–1.65 eV, a 0.2 eV mismatch with the
optical bandgaps (ꢀ1.76–1.85 eV).
Charge-Transport Properties
The hole mobilities of those five molecules blended with
PC71BM were tested by using the space-charge limited cur-
[47,51–53]
rent (SCLC) model
with a device configuration of tin-
doped indium oxide (ITO)/poly(3,4-ethylenedioxythio-
phene)/poly(styrene sulfonate) (PEDOT:PSS)/active layer/
Au. 3D-T-P, 3D-HT-P, and 2D-T-P display similar hole mo-
À3
À3
À3
2
À1 À1
bilities of 1.05ꢀ10 , 1.75ꢀ10 , and 0.44ꢀ10 cm V s ,
respectively, which indicates that the C - or C -symmetric
2
3
structure makes no difference in hole mobilities. Relative to
the hole mobilities of those molecules without a BDT unit,
3
D-B-T-P and 2D-B-T-P exhibit hole mobilities of 1.79ꢀ
À2
À2
2
À1 À1
10
and 5.91ꢀ10 cm V s , which is one order of magni-
tude larger than 3D-T-P, 3D-HT-P, and 2D-T-P (Table 2 and
the Supporting Information). The improvement of hole mo-
bility can be ascribed to the increased conjugation offered
by the BDT unit. On the other hand, it is also consistent
with the favorable film morphology of 3D-B-T-P/PC71BM
and 2D-B-T-P/PC71BM.
Figure 4. a) Current density–voltage characteristics (under AM 1.5 G,
100 mWcm illumination) and b) EQE spectra of OSC devices. The
device structures are ITO/PEDOT:PSS/compounds: PC71BM/Ca/Al.
2
medium photovoltaic perfor-
Table 2. Photovoltaic performances based on the five molecules blended with PC71BM.
mance with a V of 0.68 V, a Jsc
oc
Active layer
D/A ratios)
V
[V]
oc
J
sc
FF
[%]
PCE
Mobility
À2
À2
2
À1 À1
of 4.80 mAcm , an FF of 33%,
(
A
H
N
T
E
U
[mAcm
]
A
T
G
R
N
U
G
[cm V
s
]
and a PCE of 1.16% when the
D/A ratio is 1:4. When n-hexyl
was introduced, 3D-HT-P gave
À3
3
3
2
2
3
3
3
D-T-P/PC71BM (1:4)
D-HT-P/PC71BM (1:5)
D-T-P/PC71BM (1:2)
D-B-T-P/PC71BM (2:1)
D-B-T-P/PC71BM (1:1)
0.68
0.84
0.70
0.74
0.83
0.72
0.77
4.80
4.45
3.87
5.57
6.78
9.11
7.69
33.0
33.0
29.9
45.3
40.3
47.7
59.0
1.16 (1.12)
1.24 (1.20)
0.81 (0.75)
1.86 (1.81)
2.27 (2.20)
3.13 (3.04)
3.60 (3.41)
1.05ꢀ10
1.75ꢀ10
0.44ꢀ10
1.79ꢀ10
5.91ꢀ10
–
À3
À3
À2
À2
a
4
slightly decreased Jsc of
.4 mAcm , presumably due to
À2
[
a]
b]
D-B-T-P/PC71BM (1:1)
D-B-T-P/PC71BM (1:1)
the poor light-harvesting ability
of 3D-HT-P compared to 3D-T-
P, as discussed in the section on
[
À2
4.24ꢀ10
[
1
a] Adding 3% (v/v) DIO as cosolvent. [b] Adding 3% (v/v) DIO as cosolvent and thermal annealing at
008C.
UV/Vis absorption. However,
the Voc of 3D-HT-P was clearly
improved to 0.84 V with respect
to that value of 3D-T-P, which can be ascribed to the large
Photovoltaic Properties
To evaluate the photovoltaic performances of various mole-
cules, OSCs were fabricated by using them as the donor ma-
terial and PC71BM as the acceptor material with the tradi-
tional architecture of ITO/PEDOT:PSS/blends/Ca/Al. The
blends were prepared from solutions in ortho-dichloroben-
shunt resistance (R ) of devices fabricated from 3D-HT-P/
sh
PC71BM. Accordingly, the efficiency of 3D-HT-P was
slightly improved to 1.24%. When 2D-BDT was introduced
between the 3T-P and DPP units, 3D-B-T-P displayed a sig-
À2
nificantly improved Jsc of 6.78 mAcm , an enhanced FF of
À1
zene (o-DCB) with a total concentration of 40 mgmL .
40.3%, and an increased PCE of 2.27%. The improved Jsc
of 3D-B-T-P relative to 3D-T-P and 3D-HT-P can be attrib-
uted to the stronger light-harvesting ability, the higher hole
mobility, and the favorable film morphology, as will be dis-
cussed in the sections on AFM and TEM. When adding 3%
(v/v) 1,8-diiodooctane (DIO) as cosolvent, the efficiency
After optimizing the ratio of donor and acceptor (see the
Supporting Information), the best device results of each
molecule are summarized in Table 2. The optimum ratio of
donor/PC71BM is dependent on the mass absorptivity (see
the Supporting Information). The current density versus
voltage (J–V) curves are shown in Figure 4a; see also the
Supporting Information. Compound 3D-T-P exhibits
could be further increased to 3.13% with a promising J of
sc
À2
9.11 mAcm and an FF of 47.7%. When the above devices
Chem. Asian J. 2013, 00, 0 – 0
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C. Zhan, J. Yao et al.
were thermally annealed at 1008C, the efficiency could ulti-
mately be enhanced to 3.60%. This PCE is, to the best of
our knowledge, the highest efficiency reported to date
(Figure 4b). Among these EQE values, 3D-B-T-P blended
with PC71BM shows the highest value (over 40%), which
indicates that the photoresponse of this molecule is very ef-
ficient in the bulk heterojunction (BHJ) devices. The Jsc
values calculated from the integral of EQE curves are con-
among the phenyl-based C -symmetric molecules. More im-
3
portantly, our results demonstrate that the planar phenyl-
based C -symmetric structure can be a promising backbone
sistent with the J values obtained from the J–V curves.
3
sc
that is equal to the nonplanar triphenylamine (TPA) back-
bone, which affords high photovoltaic efficiency. For com-
Morphologies
parison, the C -symmetric 2D-T-P and 2D-B-T-P were also
2
used to prepare SM-OSCs. Both 2D-T-P and 2D-B-T-P ex-
The surface morphology of the blended films was studied by
tapping-mode atomic force microscopy (AFM). The Sup-
porting Information shows the height images collected from
the device films. The root-mean-square (rms) roughness of
the blend films were 0.204 (3D-T-P/PC71BM), 0.582 (3D-
HT-P/PC71BM), 0.254 (3D-B-T-P/PC71BM), 1.170 (3D-B-
T-P/PC71BM with 3% DIO and annealing), 0.217 (2D-T-P/
PC71BM), and 1.160 nm (2D-B-T-P/PC71BM=2:1), respec-
tively. Phase images of the six films show different features,
as shown in Figure 5. The 3D-T-P/PC71BM, 3D-T-P/
PC71BM, 2D-T-P/PC71BM, 3D-B-T-P/PC71BM with 3%
DIO and annealing, and 2D-B-T-P/PC71BM films show iso-
lated spherical domains with sizes of approximately 8–13, 8–
15, 10–15, 20–27, 25–30, and 15–25 nm, respectively. When
the BDT unit was introduced, the domain sizes were clearly
increased from 8–15 (3D-T-P, 3D-HT-P, and 2D-T-P) to 15–
30 nm (3D-B-T-P and 2D-B-T-P), which approaches the ex-
hibited inferior PCE with respect to their C -symmetric
3
counterparts of 3D-T-P (0.81 versus 1.16%) and 3D-B-T-P
(
1.86 versus 2.27%), which implies that the three symmetric
arms are necessary to retain the light-harvesting ability.
Compound 2D-B-T-P also gives higher efficiency than 2D-
T-P, which mainly results from the improved hole mobility
of 2D-B-T-P, as shown in Table 2, thus indicating that the in-
troduction of BDT is necessary to improve the hole mobility
of those molecules. Herein, two basic principles that concern
the material design for those C -symmetric molecules can be
3
drawn from the results discussed above: 1) Three symmetric
arms should be linked to ensure strong light-harvesting abili-
ty, and 2) a large conjugation in each arm should be avail-
able to retain the high hole mobility.
The external quantum efficiency (EQE) curves of the op-
timized devices were tested, as shown in Figure 4b and the
Supporting Information. All seven curves exhibit a broad re-
sponse from 350 to 700 nm and are consistent with their re-
spective UV/Vis absorption profile (see the Supporting In-
formation), thus indicating that the absorbed photons con-
tribute to the photovoltaic conversion. The maximum mono-
chromatic EQE values are 31, 28, 40, 27, and 33% for the
devices prepared from the blends of 3D-T-P/PC71BM=1:4,
[54]
citon diffusion length in organic materials.
As a result,
3D-B-T-P- and 2D-B-T-P-based OSC devices exhibit rela-
tively high FF values.
TEM was used to study the influence of the addition of
DIO as the cosolvent and thermal annealing at 1008C for
10 min on the bulk phase separation of the 3D-B-T-P/
PC71BM films. As shown in the Supporting Information,
the bright regions can be attributed to the 3D-B-T-P do-
mains, whereas the dark regions can be attributed to the
3D-HT-P/PC71BM=1:5, 3D-B-T-P/PC71BM=1:1, 2D-T-P/
PC71BM=1:2, and 2D-B-T-P/PC71BM=2:1, respectively
Figure 5. AFM phase images (500ꢀ500 nm) of the a) 3D-T-P/PC71BM, b) 3D-HT-P/PC71BM, c) 3D-B-T-P/PC71BM, d) 3D-B-T-P/PC71BM (3% DIO
and thermal annealing), e) 2D-T-P/PC71BM, and f) 2D-B-T-P/PC71BM, respectively.
&
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C. Zhan, J. Yao et al.
PC71BM domains due to its high electron-scattering densi-
Table 3. The diffraction angles and the corresponding stacking distance
of the five molecules and their blended films with PC71BM.
[
55]
ty. Phase separation in the bulk of the ODCB spin-coated
film was ambiguous (see the Supporting Information),
whereas the ODCB-DIO (3%) spin-coated film exhibited
two distinct feature types (see the Supporting Information).
It indicated that the addition of DIO as cosolvent and an-
nealing helps the self-organization of the active layer and
produces continuous interpenetrating network films, which
is essential for the exciton separation and charge transport.
It is worth noting that the ODCB-DIO (3%) spin-coated
film exhibits continuous nanoscale phase separation about
2
q [8]/d [ꢂ]
2q [8]/d [ꢂ]
3D-T-P
5.50/16.1
5.10/17.3
3.58/24.7
6.08/14.5
4.23/20.9
3D-T-P/PC71BM (1:4)
3D-T-P/PC71BM (1:5)
3D-B-T-P/PC71BM (1:1)
2D-T-P/PC71BM (1:2)
2D-B-T-P/PC71BM (2:1)
–
–
3
3
2
2
D-HT-P
D-B-T-P
D-T-P
5.68/15.5
6.10/14.5
4.10/21.5
D-B-T-P
ing distance of the conjugated arms according to the formu-
la of 2dsinq=l (herein, l=1.5418 ꢂ). In the pristine 3D-T-
P film, the arm stacking distance was calculated to be
10–25 nm, which is consistent with AFM results, and en-
hanced PCE.
1
6.1 ꢂ. After introducing n-hexyl, 3D-HT-P exhibits a simi-
lar distance of 17.3 ꢂ, probably because the hexyl is not lo-
cated in the stacking direction of the conjugated arms.
Moreover, when the conjugated 2D-BDT was incorporated
into the conjugated arms, 3D-B-T-P exhibited a significantly
enhanced stacking distance of 24.7 ꢂ in the direction of the
conjugated arms. Similar results can also be observed when
comparing the stacking distance of 2D-T-P and 2D-B-T-P,
thus indicating that the introduction of 2D-BDT into the
conjugated arms not only increases the conjugation but also
increases the stacking distance in the arm direction. After
blending with PC71BM, as shown in Figure 6b, the stacking
patterns of 3D-T-P and 3D-HT-P disappear, thus indicating
the disruption of the molecular order of the donor domain
by PC71BM. However, 3D-B-T-P and 2D-B-T-P retain
some degree of stacking order in the arm directions with
weak diffraction peaks at 2q=4.1–6.18, presumably due to
the 2D-BDT enhancing the molecular aggregation. The
stronger molecular aggregation of 3D-B-T-P and 2D-B-T-P
is very consistent with the AFM images, as shown in Fig-
ure 5c,f, which show a larger domain size than other films.
These results indicate that the introduction of 2D-BDT in-
creases the conjugation, enhances the molecular aggrega-
tion, and more importantly, improves the hole mobilities of
blending films, as discussed in the section on charge-trans-
port properties. We have to point out that both pristine and
blended film of 2D-T-P exhibits sharp diffraction peaks at
XRD Patterns
To investigate the molecular stacking in the solid state,
XRD patterns of the five molecular films and their blended
films with PC71BM were tested on a silica substrate.
Figure 6 shows the XRD patterns of 3D-T-P, 3D-HT-P, 3D-
B-T-P, 2D-T-P, and 2D-B-T-P and their blended films on
silica by drop-casting. As shown in Figure 6a, all five mole-
cules show clear diffraction peaks at 2q=3.5–6.18, which can
be ascribed to the periodical order of the conjugated arms
in the C - or C -symmetric molecules. The diffraction pat-
2
3
terns at 2q=15–208, which can be attributed to the p–p
stacking pattern, are weak for those molecules. Table 3
shows the diffraction angles and their corresponding stack-
2
qꢀ6.18, which can be explained by its relatively small mo-
lecular shape and fewer alkyl chains, which offers its stack-
ing order in the directions of the conjugated arms.
Conclusion
A series of solution-processed C - or C -symmetric small
2
3
molecules based on a phenyl core with conjugated thio-
phene (T), DPP, and BDT attached at the ortho, para, and
meta positions on the core (designated 3D-T-P, 3D-HT-P,
3
D-B-T-P, 2D-T-P, and 2D-B-T-P) were synthesized. The C3-
symmetric 3D-T-P and 3D-B-T-P show stronger light-har-
vesting ability than their C -symmetric counterparts 2D-T-P
2
and 2D-B-T-P. Moreover, the higher conjugated 3D-B-T-P
and 2D-B-T-P, which have the two-dimensional benzodithio-
phene (2D-BDT) as bridge, exhibit stronger light-harvesting
Figure 6. a) XRD patterns of the five molecules and b) their blended
films on silica.
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C. Zhan, J. Yao et al.
ability and higher hole mobilities than the less conjugated
D-T-P and 2D-T-P. Finally, two material design principles
1,3,5-Tris[2-(5-diketopyrrolopyrrole)thiophene]benzene (3D-T-P)
3
Under protection of argon at À708C, a 1.6m solution of n-butyllithium in
hexanes (0.6 mL, 0.96 mmol) was added dropwise to 3T-Ph (90 mg,
that are essential to the C -symmetric materials can be de-
3
0
.28 mmol) dissolved in THF (15 mL). The solution was warmed to room
temperature for 1 h, and then 1.0m trimethyltin chloride in THF (1.3 mL,
.3 mmol) was added and stirred for 30 min. The reaction mixture was
rived from these results: 1) three symmetric arms should be
linked, and 2) a large conjugation in each arm should be
available. According to those design motifs, we have ob-
tained a promising planar 1,3,5-phenyl-substituted molecule,
1
poured into water (50 mL) and extracted with EtOAc (50 mL). The or-
ganic phase was evaporated to afford a white oil (approximately 210 mg),
which was used for the next step without further purification. Following
the representative general procedure for a Stille coupling reaction, 5
3
D-B-T-P, which demonstrates a PCE of 3.60%, with a V
oc
À2
of 0.77 V, a Jsc of 7.69 mAcm , and an FF of 59%. This
(
325 mg, 0.54 mmol) was treated with the white oil (210 mg) in the pres-
PCE is, to the best of our knowledge, the highest efficiency
ence of [Pd(PPh ] (25 mg) and toluene (15 mL). After heating the mix-
ture to reflux for 6 h, the mixture was poured into water (50 mL) and ex-
tracted with CH Cl (50 mL). The organic layer was dried over anhydrous
A
H
U
G
R
N
U
G
3 4
)
reported to date among the phenyl-based C -symmetric mol-
3
ecules. More importantly, our results demonstrate that the
2
2
sodium sulfate and removed under reduced pressure. The crude product
was purified by column chromatography on silica gel with chloroform/
hexane/MeOH to give a dark solid (3D-T-P; 70 mg, 49%). H NMR
planar phenyl-based C -symmetric structure can be a promis-
3
ing backbone that is equal to the frequently reported non-
planar triphenylamine backbone, thereby affording high
photovoltaic efficiency.
1
(
7
(
400 MHz, CDCl
.73 (s, 3H), 7.62 (d, J=4.0 Hz, 3H), 7.42 (d, J=4.0 Hz, 3H), 7.34–7.37
m, J=4.0 Hz, 6H), 7.24 (t, J=8.0 Hz, 3H), 4.04 (t, J=8.0 Hz, 12H),
.86–2.10 (d, J=8.0 Hz, 6H), 1.24–1.44 (m, 48H), 0.88–0.95 ppm (m,
3
): d=8.95 (d, J=4.0 Hz, 3H), 8.90 (d, J=4.0 Hz, 3H),
1
3
1
1
3
1
1
6
1
3
3
6H); C NMR (600 MHz, CDCl ): d=161.61, 161.48, 143.43, 142.41,
Experimental Section
39.84, 139.64, 136.95, 136.37, 135.50, 135.01, 130.49, 130.04, 128.52,
28.44, 125.98, 124.95, 124.84, 121.39, 108.20, 108.12, 46.06, 39.47, 39.25,
0.62, 30.40, 28.85, 28.55, 28.51, 23.89, 23.73, 23.39, 23.29, 14.42, 14.234,
Materials
All of the starting materials and solvents were purchased from Sigma Al-
drich or Alfa Aesar and were used without further purification unless
otherwise stated. THF and toluene were distilled from sodium benzophe-
none ketyl under nitrogen before use. The starting material of 2,6-bis(tri-
methyltin)-4,8-bis(octyloxyl)benzo[1,2-b;4,5-b’] bithiophene (7) was pur-
chased from Solarmer, and 3-(5-bromothiophen-2-yl)-2,5-bis(2-ethylhex-
0.77, 10.70 ppm; MALDI-TOF MS: m/z calcd for
C
108
H
126
N
6
O
6
S
9
:
890.7; found: 1891.8; elemental analysis calcd (%) for C108
8.53, H 6.71, N 4.44; found: C 68.58, H 6.67, N 4.42.
H
126
N
6
O
6
S
9
: C
From this reaction, we also obtained a dark solid called 6,6’-{5’,5’’’-[5-(thi-
ophen-2-yl)-1,3-phenylene]bis([2,2’-bithiophene]-5’,5-diyl)}bis{2,5-bis(2-
ethylhexyl)-3-(thiophen-2-yl)pyrrolo[3,4-c]pyrrole-1,4(2H,5H)-dione}
2D-T-P; 50 mg) as coproduct in one batch. H NMR (400 MHz, CDCl
d=8.95 (d, J=4.0 Hz, 2H), 8.90 (d, J=4.0 Hz, 2H), 7.71 (s, 2H), 7.67 (s,
AHCTUNGTRENNUNG
A
H
U
G
R
N
N
ACHTUNGTRENNUNG
yl)-6-(thiophen-2-yl)pyrrolo
chased from Suna Tech, Inc. 1,3,5-Phenyltriboronic acid, tri
was purchased from Combi-Block, Inc. Compound 3T-P (3a) was synthe-
A
H
U
G
R
N
U
G
A
H
U
G
R
N
U
1
(
3
):
AHCTUNGTRENNUNG
1
3
2
H), 7.61 (d, J=4.0 Hz, 2H), 7.44 (d, J=4.0 Hz, 1H), 7.36 (d, J=4.0 Hz,
H), 7.34 (d, J=4.0 Hz, 2H), 7.31 (d, J=4.0 Hz, 2H), 7.25 (d, J=4.0 Hz,
[
46]
sized according to a literature method.
1
2
H), 7.34 (d, J=4.0 Hz, 2H), 7.14 (t, J =4.0 Hz, J =4.0 Hz, 1H), 4.03 (t,
Synthesis and Characterizations
1
2
J =4.0 Hz, J =8.0 Hz, 8H), 1.86–1.93 (d, J=8.0 Hz, 4H), 1.25–1.41 (m,
The synthesis routes to 3D-T-P, 3D-HT-P, 2D-T-P, 3D-B-T-P, and 2D-B-
T-P are shown in Scheme 2. The detailed synthetic processes are as fol-
lows.
13
3
1
1
1
3
3
2H), 0.84–0.94 ppm (m, 24H); C NMR (600 MHz, CDCl ): d=161.68,
61.52 143.74, 142.98, 142.44, 139.82, 139.74, 136.89, 136.05, 135.96,
35.31, 134.93, 130.42, 129.94, 128.44, 128.25, 125.99, 125.66, 124.89,
24.76, 124.11, 122.41, 121.39, 108.17, 108.13, 45.94, 39.36, 39.14, 30.46,
0.26, 29.74, 28.68, 28.39, 23.74, 23.58, 23.22, 23.13, 14.23, 14.08, 10.62,
1
,3,5-Tris[2-
ACHTUNGTRENNUNG( 5-bromo)thiophene]benzene (3Br-T-P)
NBS (300 mg, 1.69 mmol) was added to a solution of 3T-P (100 mg,
10.55 ppm; MALDI-TOF MS: m/z calcd for
C
78
H
88
N
4
O
4
S
7
:
1368.5;
0
.31 mmol) in chloroform (40 mL). The solution was stirred overnight in
found: 1370.1; elemental analysis calcd (%) for C78
H
88
N
4
O
4
S
7
: C 68.38, H
the dark. Then the solution was diluted with additional chloroform and
washed with water. After the solvent had been evaporated under reduced
pressure, the crude product was purified by column chromatography on
6.47, N 4.09; found: C 68.36, H 6.47, N 4.14.
1
,3,5-Tris[2-(5-diketopyrrolopyrrole)(3-hexylthiophene)]benzene (3D-HT-
P)
silica gel with chloroform/hexane to yield 3Br-T-P as a white solid
1
(
160 mg, 93%). H NMR (400 MHz, CDCl
3
): d=7.08 (d, J=4.0 Hz, 3H),
Following the reaction steps of 3D-T-P, 3DPP-HT-P was obtained as
7
.12 (d, J=4.0 Hz, 3H), 7.52 ppm (s, 3H); MALDI-TOF MS: m/z calcd
1
a dark solid (100 mg, 63%). H NMR (400 MHz, CD
2
Cl
2
): d=8.91 (d, J=
for C18 Br : 557.7; found: 558.3.
H
9
3 3
S
4
3
8
.0 Hz, 3H), 8.83 (d, J=4.0 Hz, 3H), 7.66 (d, J=4.0 Hz, 3H), 7.53 (s,
1
H), 7.34 (d, J=4.0 Hz, 3H), 7.25–7.30 (m, J=4.0 Hz, 6H), 4.00 (t, J =
1
,3,5-Tris[2-(3-hexyl)thiophene]benzene (3HT-P)
ACHTUNGTRENNUNG
2
1
2
.0 Hz, J =8.0 Hz, 12H), 2.75 (t, J =4.0 Hz, J =4.0 Hz, 6H), 1.81–1.91
Following the representative general procedure for Suzuki cross-coupling,
(m, 6H), 1.62–1.70 (m, 6H) 1.24–1.35 (m, 66H), 0.82–0.91 ppm (m,
1
3
2
-bromo-3-hexylthiophene (500 mg, 2 mmol) was treated with 1,3,5-phe-
nyltriboronic acid, tri(pinacol)ester (166 mg, 0.4 mmol) in the presence of
Pd(PPh ] (25 mg), toluene (15 mL), and aqueous K CO (2m, 5 mL).
After heating the mixture to reflux for 20 h, the mixture was poured in
water (50 mL) and extracted with CH Cl (50 mL). The organic layer was
45H); C NMR (600 MHz, CDCl ): d=162.04, 143.09, 140.92, 140.23,
3
A
C
H
T
U
N
G
T
R
E
N
N
U
N
G
139.58, 138.29, 137.08, 136.81, 136.09, 135.43, 134.92, 130.66, 130.17,
[
A
C
H
T
U
N
G
T
R
E
N
N
U
N
G
3
)
4
2
3
129.97, 129.38, 128.68, 128.22, 128.05, 124.81, 108.44, 46.16, 39.51, 39.35,
31.93, 31.18, 30.61, 30.46, 29.45, 29.22, 29.08, 28.86, 28.60, 23.92, 23.79,
23.39, 22.87, 14.38, 10.80 ppm; MALDI-TOF MS: m/z calcd for
C126H162N O S : 2143.0; found: 2142.1; elemental analysis calcd (%) for
2
2
dried over anhydrous sodium sulfate and removed under reduced pres-
sure. The crude product was purified by column chromatography on
6
6 9
C126H162N O S : C 70.54, H 7.61, N 3.92; found: C 70.51, H 7.65, N 3.88.
6
6
9
silica gel with chloroform/hexane to give a colorless oil (92 mg, 49%).
1
H NMR (400 MHz, CD
.00 (d, J=4.0 Hz, 3H), 2.72 (t, J =8.0 Hz, J =8.0 Hz, 6H), 1.61 (quint,
J=8.0 Hz, 6H), 1.20–1.30 (m, 18H), 7.00 ppm (m, 9H); MALDI-TOF
MS: m/z calcd for C36 : 576.3; found: 577.0.
2
Cl
2
): d=7.45 (s, 3H), 7.24 (d, J=4.0 Hz, 3H),
1,3,5-Tris(5- AHCTUNETGRNNUN{G 4,8-bis[5-(2-ethylhexyl)thiophen-2-yl]benzo[1,2-b:4,5-
b’]dithiophen-2-yl}thiophen-2-yl)benzene (3B-T-P)
1
2
7
Under protection of argon at À708C, a 1.6m solution of n-butyllithium in
hexanes (0.6 mL, 1 mmol) was added dropwise to BDT (578 mg, 1 mmol)
dissolved in THF (25 mL). The solution was warmed to room tempera-
ture for 1 h, and then a 1.0m solution of trimethyltin chloride in THF
48 3
H S
&
&
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C. Zhan, J. Yao et al.
(
1.3 mL, 1.3 mmol) was added. The reaction mixture was poured into
[6] S. Gꢃnes, H. Neugebauer, N. S. Sariciftci, Chem. Rev. 2007, 107,
1324.
[7] H. Y. Chen, J. H. Hou, S. Q. Zhang, Y. Y. Liang, G. W. Yang, Y.
Yang, L. P. Yu, Y. Wu, G. Li, Nat. Photonics 2009, 3, 649.
[8] L. T. Dou, J. B. You, J. Yang, C. C. Chen, Y. J. He, S. Murase, T.
Moriarty, K. Emery, G. Li, Y. Yang, Nat. Photonics 2012, 6, 180.
water (50 mL) and extracted with EtOAc (50 mL). The organic phase
was evaporated to afford a yellow oil (approximately 700 mg), which was
used for the next step without further purification. Following the repre-
sentative general procedure for the Stille coupling reaction, 3Br-T-P
(
56 mg, 0.1 mmol) was treated with the yellow oil (350 mg) in the pres-
ence of [Pd(PPh ] (25 mg) and toluene (20 mL). After heating the mix-
ture to reflux for 12 h, the mixture was poured in water (50 mL) and ex-
tracted with CH Cl (50 mL). The organic layer was dried over anhydrous
A
C
H
T
U
N
G
T
R
E
N
N
U
N
G
3 4
)
[
9] W. Li, A. Furlan, K. H. Hendriks, M. M. Wienk, R. A. J. Janssen, J.
Am. Chem. Soc. 2013, DOI: 10.1021/ja401434x.
2
2
[
[
[
10] Y. Liang, Z. Xu, J. Xia, S.-T. Tsai, Y. Wu, G. Li, C. Ray, L. Yu, Adv.
Mater. 2010, 22, E135.
11] C. E. Small, S. Chen, J. Subbiah, C. M. Amb, S.-W. Tsang, T.-H. Lai,
J. R. Reynolds, F. So, Nat. Photonics 2012, 6, 115.
12] M. Singh, R. Kurchania, J. A. Mikroyannidis, S. S. Sharma, G. D.
Sharma, J. Mater. Chem. A 2013, 1, 2297.
13] Y. Lin, Y. F. Li, X. W. Zhan, Chem. Soc. Rev. 2012, 41, 4245.
14] A. Mishra, P. Bꢄuerle, Angew. Chem. 2012, 124, 2060; Angew.
Chem. Int. Ed. 2012, 51, 2020.
sodium sulfate and removed under reduced pressure. The crude product
was purified by column chromatography on silica gel with chloroform/
hexane to give a yellow oil (3B-T-P; 140 mg, 70%). H NMR (400 MHz,
1
CD
2 2
Cl ): d=7.69 (s, 3H), 7.66 (s, 3H), 7.59 (d, J=8.0 Hz, 3H), 7.45 (d,
J=4.0 Hz, 3H), 7.30–7.34 (quartet, J=4.0 Hz, 6H), 7.28 (d, J=4.0 Hz,
3
3
0
H), 7.24 (d, J=4.0 Hz, 3H), 6.94 (d, J=4.0 Hz, 3H), 6.92 (d, J=4.0 Hz,
H), 2.88 (d, J=4.0 Hz, 12H), 1.70 (m, 6H), 1.31–1.45 (m, 48H), 0.85–
[
[
.96 ppm (m, 36H); MALDI-TOF MS: m/z calcd for C120
132
H S15: 2052.6;
found: 2053.0.
[
15] B. Walker, C. Kim, T.-Q. Nguyen, Chem. Mater. 2011, 23, 470.
Compounds 3D-B-T-P and 2D-B-T-P
[16] J. E. Anthony, Chem. Mater. 2011, 23, 583.
[
17] Y. W. Li, Q. Guo, Z. Li, J. Pei, W. Tian, Energy Environ. Sci. 2010,
, 1427.
18] J. Roncali, Acc. Chem. Res. 2009, 42, 1719.
19] F. Wꢃrthner, K. Meerholz, Chem. Eur. J. 2010, 16, 9366.
20] Y. M. Sun, G. C. Welch, W. L. Leong, C. J. Takacs, G. C. Bazan, A. J.
Heeger, Nat. Mater. 2012, 11, 44.
21] T. S. Van der Poll, J. A. Love, T.-Q. Nguyen, G. C. Bazan, Adv.
Mater. 2012, 24, 3646.
Following the reaction of 3D-T-P and 2D-T-P, 3D-B-T-P was obtained as
3
a black solid (50 mg, 28%) and 2D-B-T-P as a dark solid (35 mg, 20%).
[
[
[
1
Data for 3D-B-T-P: H NMR (400 MHz, CDCl
3
): d=9.00 (s, 3H), 8.90 (s,
3
1
9
1
1
1
1
1
2
1
H), 7.58 (s, 3H), 7.30–7.44 (m, 15H), 7.14–7.19 (m, 6H), 6.98–7.03 (m,
2H), 3.92 (s, 12H), 2.96 (s, 12H), 1.80–1.84 (m, 12H), 1.25–1.50 (m,
1
3
3
6H), 0.86–0.98 ppm (m, 72H); C NMR (600 MHz, CDCl ): d=161.61,
[
[
61.23, 146.14, 145.96, 143.03, 142.74, 142.63, 139.59, 139.41, 138.99,
38.66, 137.93, 137.31, 137.05, 136.90, 136.19, 135.49, 134.86, 130.29,
30.04, 128.80, 128.48, 128.26, 125.97, 125.73, 124.41, 124.32, 123.66,
23.60, 123.25, 121.21, 120.70, 120.52, 119.17, 119.03, 108.22, 108.08,
00.16, 46.14, 45.94, 41.68, 39.60, 39.40, 34.80, 34.76, 32.89, 30.64, 30.43,
9.98, 29.24, 28.76, 28.54, 26.02, 23.97, 23.71, 23.448, 14.57, 14.36, 11.26,
1.22, 10.90, 10.76 ppm; MALDI-TOF MS: m/z calcd for
22] H. Shang, H. Fan, Y. Liu, W. Hu, Y. F. Li, X. W. Zhan, Adv. Mater.
2
011, 23, 1554.
[
[
23] S. Paek, N. Cho, S. Cho, J. K. Lee, J. Ko, Org. Lett. 2012, 14, 6326.
24] J. Zhou, X. Wan, Y. Liu, Y. Zuo, Z. Li, G. He, G. Long, W. Ni, C.
Li, X. Su, Y. Chen, J. Am. Chem. Soc. 2012, 134, 16345.
25] Y. Liu, X. Wan, F. Wang, J. Zhou, G. Long, J. Tian, Y. Chen, Adv.
Mater. 2011, 23, 5387.
[
C
C
210
H
H
246
N
N
6
O
O
6
S
S
21: 3619.0; found: 3616.0; elemental analysis calcd (%) for
210
246
6
6
21: C 69.61, H 6.84, N 2.32; found: C 69.64, H 6.80, N 2.37.
1
[26] R. Fitzner, E. Mena-Osteritz, A. Mishra, G. Schulz, E. Reinold, M.
Weil, C. Kçrner, H. Ziehlke, C. Elschner, K. Leo, M. Riede, M.
Pfeiffer, C. Uhrich, P. Bꢄuerle, J. Am. Chem. Soc. 2012, 134, 11064.
[27] X. Xiao, G. D. Wei, S. Y. Wang, J. D. Zimmerman, C. K. Renshaw,
M. E. Thompson, S. R. Forrest, Adv. Mater. 2012, 24, 1956.
[28] Y. Zhang, X.-D. Dang, C. Kim, T.-Q. Nguyen, Adv. Energy Mater.
2011, 1, 610.
Data for 2D-B-T-P: H NMR (400 MHz, CD
2
Cl
3
): d=8.83–9.03 (m, 4H),
6
1
.86–7.69 (m, 34H), 3.75–4.05 (m, 8H), 2.85–3.05 (s, 12H), 1.75–1.95 (m,
1
3
0H), 1.15–1.65 (m, 80H), 0.70–1.15 ppm (m, 60H); C NMR (600 MHz,
): d=161.22, 160.89, 145.70, 145.61, 143.04, 142.43, 142.16, 139.27,
39.21, 139.04, 138.57, 138.26, 137.95, 137.58, 137.46, 137.35, 137.17,
CDCl
3
1
1
1
1
1
4
2
1
36.89, 136.87, 136.80, 136.59, 136.53, 136.47, 135.77, 134.98, 134.70,
34.45, 129.83, 129.57, 128.36, 128.03, 127.75, 127.68, 127.50, 125.92,
25.48, 125.27, 125.20, 124.80, 124.40, 123.88, 123.43, 123.29, 123.20,
22.81, 121.41, 120.21, 118.91, 118.63, 107.82, 107.68, 45.66, 45.51, 41.27,
1.20, 39.14, 38.91, 34.30, 34.12, 32.42, 32.31, 30.18, 29.97, 29.48, 28.76,
8.31, 28.08, 25.61, 25.56, 23.53, 23.26, 22.93, 22.86, 14.06, 14.00, 13.93,
3.83, 10.78, 10.72, 10.42, 10.27 ppm; MALDI-TOF MS: m/z calcd for
[29] S. Loser, C. J. Bruns, H. Miyauchi, R. P. Ortiz, A. Facchetti, S. I.
Stupp, T. J. Marks, J. Am. Chem. Soc. 2011, 133, 8142.
[30] B. Walker, A. B. Tamayo, X.-D. Dang, P. Zalar, J. H. Seo, A. Garcia,
Tantiwiwat, T.-Q. Nguyen, Adv. Funct. Mater. 2009, 19, 3063.
[31] J. H. Huang, C. L. Zhan, X. Zhang, Y. Zhao, Z. H. Lu, H. Jia, B.
Jiang, J. Ye, S. L. Zhang, A. L. Tang, Y. Q. Liu, Q. B. Pei, J. N. Yao,
ACS Appl. Mater. Interfaces 2013, 5, 2033.
C
C
180
H
H
208
N
N
4
O
O
4
S
S
19: 3097.0; found: 3098.0; elemental analysis calcd (%) for
21: C 69.72, H 6.76, N 1.81; found: C 69.68, H 6.79, N 1.78.
210
246
6
6
[
32] A. L. Tang, L. J. Li, Z. H. Lu, J. H. Huang, H. Jia, C. L. Zhan, Z. A.
Tan, Y. F. Li, J. N. Yao, J. Mater. Chem. A 2013, 1, 5747.
[
33] O. P. Lee, A. T. Yiu, P. M. Beaujuge, C. H. Woo, T. W. Holcombe,
J. E. Millstone, J. D. Douglas, M. S. Chen, J. M. Frechet, Adv. Mater.
2
011, 23, 5359.
Acknowledgements
[
34] Y.-H. Chen, L.-Y. Lin, C.-W. Lu, F. Lin, Z.-Y. Huang, H.-W. Lin, P.-
H. Wang, Y.-H. Liu, K.-T. Wong, J. D. Wen, J. Miller, S. B. Darling,
J. Am. Chem. Soc. 2012, 134, 13616.
35] Q. Shi, P. Cheng, Y. F. Li, X. W. Zhan, Adv. Eng. Mater. 2012, 2, 63.
36] J. Zhang, D. Deng, C. He, Y. J. He, M. J. Zhang, Z.-G. Zhang, Z. J.
Zhang, Y. F. Li, Chem. Mater. 2011, 23, 817.
This work was financially supported by the NSFC (nos. 20973182,
1227112, and 21221002) and the Chinese Academy of Sciences, Project
73 (2011CB808400).
9
9
[
[
[
[
[
[
37] Y. Lin, Z. G. Zhang, H. Bai, Y. F. Li, X. W. Zhan, Chem. Commun.
[
[
1] O. Morton, Nature 2006, 443, 19.
2] Z. He, C. Zhong, X. Huang, W. Y. Wong, H. Wu, L. Chen, S. Su, Y.
Cao, Adv. Mater. 2011, 23, 4636.
2
012, 48, 9655.
38] Y. Lin, Z. G. Zhang, Y. F. Li, D. B. Zhu, X. W. Zhan, J. Mater.
Chem. A 2013, 1, 5128.
39] J. A. Mikroyannidis, S. S. Sharma, Y. K. Vijay, G. D. Sharma, ACS
Appl. Mater. Interfaces 2010, 2, 270.
40] R. de Bettignies, Y. Nicolas, P. Blanchard, E. Levillain, J. M. Nunzi,
J. Roncali, Adv. Mater. 2003, 15, 1939.
[
[
3] Y. J. Cheng, S. H. Yang, C. S. Hsu, Chem. Rev. 2009, 109, 5868.
4] C. Li, M. Liu, N. G. Pschirer, M. Baumgarten, K. Mꢃllen, Chem.
Rev. 2010, 110, 6817.
[
5] L. J. A. Koster, S. E. Shaheen, J. C. Hummelen, Adv. Engergy Mater.
2
012, 2, 1246.
Chem. Asian J. 2013, 00, 0 – 0
9
ꢁ 2013 Wiley-VCH Verlag GmbH & Co. KGaA, Weinheim
&
&
These are not the final page numbers! ÞÞ

www.chemasianj.org
C. Zhan, J. Yao et al.
[
41] W. L. Rance, B. L. Rupert, W. J. Mitchell, M. E. Kose, D. S. Ginley,
[49] Y. F. Li, Y. Cao, J. Gao, D. L. Wang, G. Yu, A. J. Heeger, Synth.
Met. 1999, 99, 243.
S. E. Shaheen, G. Rumbles, N. Kopidakis, J. Phys. Chem. C 2010,
1
14, 22269.
[50] Y. J. He, H. Y. Chen, J. H. Hou, Y. F. Li, J. Am. Chem. Soc. 2010,
132, 5532.
[51] J. Huang, Y. Zhao, W. He, H. Jia, Z. Lu, B. Jiang, C. Zhan, Q. Pei,
Y. Liu, J. Yao, Polym. Chem. 2012, 3, 2832.
[52] D. Natali, M. Sampietro, J. Appl. Phys. 2002, 92, 5310.
[53] G. G. Malliaras, J. R. Salem, P. J. Brock, C. Scott, Phys. Rev. B 1998,
58, R13411.
[54] G. Li, V. Shrotriya, J. S. Huang, Y. Yao, T. Moriarty, K. Emery, Y.
Yang, Nat. Mater. 2005, 4, 864.
[
42] M. E. Kçse, W. J. Mitchell, N. Kopidakis, C. H. Chang, S. E. Sha-
heen, K. Kim, G. Rumbles, J. Am. Chem. Soc. 2007, 129, 14257.
43] V. Steinmann, N. M. Kronenberg, M. R. Lenze, S. M. Graf, D.
Hertel, K. Meerholz, H. Bꢃrckstꢃmmer, E. V. Tulyakova, F. Wꢃrth-
ner, Adv. Eng. Mater. 2011, 1, 888.
44] P. Dutta, J. Kim, S. H. Eom, W.-H. Lee, I. N. Kang, S.-H. Lee, ACS
Appl. Mater. Interfaces 2012, 4, 6669.
45] L. Dou, J. Gao, E. Richard, J. You, C. C. Chen, K. C. Cha, Y. J. He,
G. Li, Y. Yang, J. Am. Chem. Soc. 2012, 134, 10071.
46] F. Cherioux, L. Guyard, Adv. Funct. Mater. 2001, 11, 305.
47] J. H. Huang, H. Jia, L. J. Li, Z. H. Lu, W. Q. Zhang, W. W. He, B.
Jiang, A. L. Tang, Z. A. Tan, C. L. Zhan, Y. F. Li, J. N. Yao, Phys.
Chem. Chem. Phys. 2012, 14, 14238.
48] S. Janietz, D. D. C. Bradley, M. Grell, C. Giebeler, M. Inbasekaran,
E. P. Woo, Appl. Phys. Lett. 1998, 73, 2453.
[
[
[
[55] X. N. Yang, J. Loos, S. C. Veenstra, W. J. H. Verhees, M. M. Wienk,
J. M. Kroon, M. A. J. Michels, R. A. J. Janssen, Nano Lett. 2005, 5,
579.
[
[
Received: March 20, 2013
Revised: April 17, 2013
Published online: && &&, 0000
[
&
&
Chem. Asian J. 2013, 00, 0 – 0
10
ꢁ 2013 Wiley-VCH Verlag GmbH & Co. KGaA, Weinheim
ÝÝ These are not the final page numbers!

FULL PAPER
Grow a backbone: A series of solu-
tion-processed C - or C -symmetric
Solar Cells
3
2
small molecules based on phenyl-1,3,5-
trithienyl-diketopyrrolopyrrole and
two-dimensional benzodithiophene as
an alternative bridge were synthesized.
Our results demonstrate that the
planar phenyl-1,3,5-substituted unit
can be a promising backbone for
highly efficient devices (see figure;
EH=2-ethylhexyl).
Shanlin Zhang, Bo Jiang,
Chuanlang Zhan,* Jianhua Huang,
Xin Zhang, Hui Jia, Ailing Tang,
Lili Chen, Jiannian Yao*
&&&& — &&&&
Phenyl-1,3,5-Trithienyl-Diketopyrrolo-
pyrrole: A Molecular Backbone Poten-
tially Affording High Efficiency for
Solution-Processed Small-Molecule
Organic Solar Cells through Judicious
Molecular Design
Chem. Asian J. 2013, 00, 0 – 0
11
ꢁ 2013 Wiley-VCH Verlag GmbH & Co. KGaA, Weinheim
&
&
These are not the final page numbers! ÞÞ