The influence of electron deficient unit and interdigitated packing shape of new polythiophene derivatives on organic thin-film transistors and photovoltaic cells

Article abstract of DOI:10.1002/pola.24724

A series of new polythiophene derivatives containing a thiazole ring as an electron deficient unit were successfully synthesized via Stille coupling reactions. Synthesized polymers were classified into two types (H-shape packing and A-shape packing) based on their interdigitated packing structure induced by different side chain configurations. The thiophene derivatives that contained a thiazole unit (PT50Tz50, PTz100, and PTTz) exhibited much better thermal stability than did the full thiophene polymers (PT100 and PTT). The polymers containing the thiazole unit (PTz100 and PTTz) showed a red-shifted absorption spectrum with clear vibronic structure. In addition, the XRD and AFM results showed that the polymers containing the thiazole unit and interdigitated H-shape exhibited much better ordered and connected intermolecular structures than did other polymers. The improved intermolecular ordering and surface morphologies directly facilitated charge carrier transport in thin film transistor (TFT) devices, without introducing charge traps, and yielded higher solar cell performance. Among these polymers, the PTTz copolymer exhibited the best TFT performance (μ = 0.050 cm² V^-1 s^-1, on/off ratio = 10⁶, and V_th = -2 V) and solar cell performance (PCE = 1.39%, J_sc = 6.58 mA cm^-2, and V_oc = 0.58 V).

Full text of DOI:10.1002/pola.24724

The Influence of Electron Deficient Unit and Interdigitated Packing Shape
of New Polythiophene Derivatives on Organic Thin-Film Transistors and
Photovoltaic Cells
1
2
3
4
1
1
1
HOYOUL KONG, * SHINUK CHO, DONG HOON LEE, NAM SUNG CHO, MOO-JIN PARK, IN HWAN JUNG, JONG-HWA PARK,
3
1
CHAN EON PARK, HONG-KU SHIM
1
Department of Chemistry, Korea Advanced Institute of Science and Technology (KAIST), Daejeon 305-701, South Korea
2
3
Department of Physics and EHSRC, University of Ulsan, Ulsan 680-749, South Korea
Department of Chemical Engineering, Polymer Research Institute, Pohang University of Science and Technology, Pohang 790-
784, South Korea
4
LG Display Co., Ltd., 1007 Deogeun-ri, Wollong-myeon, Paju-si, Gyeonggi-do 413-811, South Korea
Received 7 February 2011; accepted 9 April 2011
DOI: 10.1002/pola.24724
Published online 2 May 2011 in Wiley Online Library (wileyonlinelibrary.com).
ABSTRACT: A series of new polythiophene derivatives contain-
ing a thiazole ring as an electron deficient unit were success-
fully synthesized via Stille coupling reactions. Synthesized
polymers were classified into two types (H-shape packing and
A-shape packing) based on their interdigitated packing struc-
ture induced by different side chain configurations. The thio-
phene derivatives that contained a thiazole unit (PT50Tz50,
PTz100, and PTTz) exhibited much better thermal stability than
did the full thiophene polymers (PT100 and PTT). The polymers
containing the thiazole unit (PTz100 and PTTz) showed a red-
shifted absorption spectrum with clear vibronic structure. In
addition, the XRD and AFM results showed that the polymers
containing the thiazole unit and interdigitated H-shape exhib-
ited much better ordered and connected intermolecular
structures than did other polymers. The improved intermolecu-
lar ordering and surface morphologies directly facilitated charge
carrier transport in thin film transistor (TFT) devices, without
introducing charge traps, and yielded higher solar cell perform-
ance. Among these polymers, the PTTz copolymer exhibited the
2
ꢀ1 ꢀ1
6
best TFT performance (l ¼ 0.050 cm V
s
, on/off ratio ¼ 10 ,
and Vth ¼ ꢀ2 V) and solar cell performance (PCE ¼ 1.39%,
ꢀ2
J
sc ¼ 6.58 mA cm , and Voc ¼ 0.58 V). VC 2011 Wiley Periodicals,
Inc. J Polym Sci Part A: Polym Chem 49: 2886–2898, 2011
KEYWORDS: conjugated polymers; crystallization; photovoltaic
cells; thin-films; transistors
INTRODUCTION Organic semiconductors have attracted
extensive scientific interest for applications in organic elec-
tronics and optoelectronics, including organic thin film tran-
ever, P3HT electronic devices fabricated in air generally
exhibited much lower performances due to oxygen and
water sensitivities that arose from the relatively high-lying
1
–16
3,4
sistors (OTFTs) and organic photovoltaic cells (OPVs).
highest occupied molecular orbital (HOMO) level. To over-
Polymer semiconductors, in particular, have been studied for
their advantages, which include chemical tunability, compati-
bility with plastic substrates, structural flexibility, mechanical
come this problem, some groups have developed polythio-
phene derivatives with low-lying HOMO levels by curtailing
the effective conjugation length of the polymer main chain.
1
7,18
000
stability, and processability.
Ong and coworkers reported the synthesis of poly(3,3 -
2
ꢀ1
didodecylquaterthiophene) (PQT-12), with l ¼ 0.14 cm V
To date, a large number of semiconducting polymers have
been generated and characterized. Among them, polythio-
phene derivatives with regioregular alkyl side chains have
been the most extensively studied materials due to good
crystallinity induced by strong intermolecular alignment. For
example, regioregular head-to-tail poly(3-hexyl thiophene)
ꢀ
1
4
s
and good oxidative doping stability. McCulloch and co-
workers
reported
poly(2,5-bis(3-alkylthiophene-2-yl)th-
ieno[3,2-b]thiophene) (PBTTT), which incorporated
a
thieno[2,3-b]thiophene moiety. TFTs fabricated with PBTTT
have yielded the highest mobilities reported to date, l ¼
2
ꢀ1 ꢀ1 5
1
,2
0.6–1.0 cm V
s .
(
cm
P3HT) exhibits a high charge carrier mobility (up to 0.3
2
ꢀ1 ꢀ1
V
s
) in OTFTs and a high power conversion effi-
In addition to these full thiophene polymers, thiophene-
based copolymers that incorporate a fused thiazolothiazole
ciency (PCE) in bulk heterojunction (BHJ) solar cells. How-
*
Present address: Department of Materials Science and Engineering, Johns Hopkins University, Baltimore, Maryland 21218.
Correspondence to: S. Cho (E-mail: sucho@ulsan.ac.kr) or C. E. Park (E-mail: cep@postech.ac.kr) or H.-K. Shim (E-mail: hkshim@kaist.ac.kr))
Journal of Polymer Science Part A: Polymer Chemistry, Vol. 49, 2886–2898 (2011) V
2011 Wiley Periodicals, Inc.
C
2886
WILEYONLINELIBRARY.COM/JOURNAL/JPOLA

ARTICLE
unit, for example, poly(2,5-bis(3-dodecyl-5-(3-dodecylthio-
phen-2-yl)thiophene-2-yl)thiazolo[5,4-d]thiazole) (PTzQT-12)
and its derivatives, have been described as an active material
2
ꢀ1
ꢀ1
for OTFTs (l ¼ 0.14–0.3 cm
V
s ). These donor–
acceptor (D–A) copolymers showed highly extended p-elec-
tron systems and strong p-stacking. In addition, these
copolymers showed improved solubility by the juxtaposition
of additional long alkyl thiophenes next to the basic repeat-
ing unit of poly(2,5-bis(3-dodecylthiophene-2-yl)thiazolo[5,4-
d]thiazole). Recently, many D–A copolymers composed of
combinations of thiophene (as an electron donor) and elec-
tron deficient aromatic rings, such as thiazolothiazole, bithia-
zole, and benzothiadiazole (as an electron acceptor) have
7
–10
been reported.
D–A systems enhance charge carrier
transport and broaden the UV-vis absorption spectrum as a
result of the intermolecular interactions (especially p–p
stacking), increased ionization potential (IP), and longer
effective conjugation length. Currently, several research
groups are attempting to develop D–A copolymers for OTFTs
and OPVs.
Here we describe a series of new solution-processable semi-
0
0
0
conducting polythiophenes, poly(5,5 -bis(3 ,4-didodecyl-2,2 -
0
bithiophen-5-yl)-2,2 -bithiophene) (PT100), random copoly-
mer that incorporate repeating units of PT100 and PTz100
0 0 0
PT50Tz50), poly(5,5 -bis(3 ,4-didodecyl-2,2 -bithiophen-5-
yl)-2,2 -bithiazole) (PTz100), poly(5,5 -bis(2,5 -(thiophene-
(
0
0
0
0
2
and
,5-diyl)bis(3-dodecylthiophene)-5-yl)-2,2 -bithiophene) (PTT),
0
0
poly(5,5 -bis(2,5 -(thiophene-2,5-diyl)bis(3-dodecylthio-
0
phene)-5-yl)-2,2 -bithiazole) (PTTz), containing different quan-
tities of the thiazole ring as an electron deficient unit in both
types of alkyl chain packing systems. These polymers were
designed with consideration for several structural features.
First, polymers with different content ratios of the thiazole
unit were designed to characterize the effects of D–A composi-
tion on the effective conjugation length, band gap, and struc-
tural ordering. Second, two types of alkyl chain packing sys-
tems (A- and H-shaped) were applied to these polymers (Fig.
FIGURE 1 Schematic representations of two types of interdigi-
tated packing structures: (a) A-shaped packing (PT100,
PT50Tz50, PTz100) and (b) H-shaped packing (PTT, PTTz).
[
Color figure can be viewed in the online issue, which is avail-
able at wileyonlinelibrary.com.]
1
). Generally, H-shaped packing polymers (such as PQT-12 and
RESULTS AND DISCUSSION
4
,5
PBTTT) show higher intermolecular ordering and TFT per-
formance than A-shaped packing polymers (such as poly(3,3 -
didodecyl-2,2 :5 ,2 -terthiophene) and poly(2,5-bis(3-dodecylth-
iophen-2-yl)-thieno[2,3-b]thiophene) (PBTCT)).
Synthesis and Thermal Properties
Scheme 1 shows the syntheses of PT100, PT50Tz50,
00
0
0
00
0
0
1
1,12
PTz100, PTT, and PTTz. The monomers 5,5 -bis(3-dode-
0
0
cylthiophen-2-yl)-2,2 -bithiophene (4) and 5,5 -bis(3-dode-
To obtain the H-shaped packing polymers, the unsubstituted
thiophene ring was incorporated between dodecylthiophenes
of the A-shaped packing polymers. Finally, to improve poly-
mer solubility, we incorporated additional dodecylthiophene
rings next to repeating units of 4 or 6 thiophenes. These
polymers exhibited UV-vis, cyclic voltammetry (CV), X-ray
diffraction (XRD), and atomic force microscopy (AFM) char-
acteristics that depended on the thiazole content and the
alkyl chain packing geometry. These design factors directly
affected the TFT and OPV performances. Among these poly-
mers, PTTz, which contained an electron deficient ring in an
H-shaped interdigitated packing system, exhibited the high-
cylthiophen-2-yl)-2,2 -bithiazole (5) were synthesized via
0
0
Stille coupling using 5,5 -dibromo-2,2 -bithiophene (1) and
0
0
5
,5 -dibromo-2,2 -bithiazole (2) with the monomer tribu-
tyl(3-dodecylthiophen-2-yl)stannane (3) in relatively high
yields, 77% and 73%, respectively. The final monomers 5,5 -
0
0
bis(5-bromo-3-dodecylthiophen-2-yl)-2,2 -bithiophene
(6)
0
0
and 5,5 -bis(5-bromo-3-dodecylthiophen-2-yl)-2,2 -bithiazole
(7) were easily prepared by N-bromosuccinimde (NBS) bro-
mination from 4 and 5, respectively, with high yields. Other
0
0
0
final monomers, (4,4 -didodecyl-2,2 -bithiophene-5,5 -diyl)-
0
0
0
bis(trim ethylstannane) (9) and (2,2 -(4,4 -didodecyl-2,2 -
0
bithiophene-5,5 -diyl)dithiophene)bis(trimethylstannane) (12),
2
ꢀ1 ꢀ1
6
est TFT (l ¼ 0.050 cm
V
s
, on/off ¼ 10 ) and solar
were prepared by stannylation, and these final mono-
mers were used for polymerization without further
purification.
ꢀ
2
cell performances (PCE ¼ 1.39%, Jsc ¼ 6.58 mA cm , and
V
oc
¼ 0.58 V).
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JOURNAL OF POLYMER SCIENCE PART A: POLYMER CHEMISTRY DOI 10.1002/POLA
SCHEME 1 Synthetic routes for PT100, PT50Tz50, PTz100, PTT, and PTTz.
The syntheses of the polymers were carried out using Stille
coupling in the presence of tris(dibenzylideneacetone) dipal-
ladium (0) (Pd (dba) ) and tri(o-tolyl)phosphine (P(o-tolyl) )
PT100, PT50Tz50, PTz100, PTT, and PTTz were found to
exhibit very good thermal stabilities, losing less than 5% of
ꢁ
their weight upon heating to about from 390 to 443 C, as
2
3
3
as the catalyst and ligand, respectively. We additionally syn-
thesized the random copolymer PT50Tz50 with a 1:1 ratio
of 6 to 7 to investigate closely the effect of the content of
the thiazole ring as an electron deficient unit. The polymers
were purified by reprecipitation and Soxhlet extraction with
methanol and acetone. Their chemical structures were veri-
determined by TGA under nitrogen (Table 1). The polymers
containing thiazole units, such as PT50Tz50, PTz100, and
PTTz, exhibited much better thermal stabilities than did
PT100 or PTT. The DSC (Fig. 2 and Table 1) thermograms
for the polymers showed two discrete endotherms upon
ꢁ
heating between 37–60 C (the first transition temperature)
1
ꢁ
fied by H NMR and elemental analysis. The number-average
and 103–204 C (the second transition temperature), similar
molecular weights (M ) of PT100, PT50Tz50, PTz100, PTT,
to the DSC patterns of other thiophene-based copolymer sys-
tems. In addition, PT50Tz50, PTz100, and PTTz, which con-
tained the thiazole unit, exhibited much higher second tran-
sition temperatures than did PT100 or PTT as a result of
the rigid polymer backbone attributed to the thiophene–thia-
n
and PTTz were determined by gel permeation chromatogra-
phy (GPC) by using a polystyrene standard and were found
to be 11,200 (M /M ¼ 2.31), 10,600 (M /M ¼ 2.42),
w
n
w
n
1
3,200 (M /M ¼ 2.38), 12,100 (M /M ¼ 2.39), and
w
n
w
n
6
13,800 (M /M ¼ 2.33), respectively.
zole (D–A) effect.
w
n
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ARTICLE
TABLE 1 Thermal, Optical, and Electrochemical Properties of the Polymers
Absorption kmax (nm)
f
opt
g
elec
g
PDI
T
5d
T
1
T
2
E
E
IP
(eV)
a
b
ꢁ
c
ꢁ
d
ꢁ
e
g
h
i
Polymer
M
n
(M
w
/M
n
)
( C)
( C)
( C)
Warm Solution
R.T. Solution
Thin Film
(eV)
(eV)
PT100
PT50Tz50
PTz100
PTT
11,200
10,600
13,200
12,100
13,800
2.31
2.42
2.38
2.39
2.33
390
438
428
394
443
54, 103
58, 116
60, 204
44, 117
37, 189
39
89
454
465
472
467
478
459
517
1.91
1.87
1.87
1.96
1.92
2.48
2.37
2.38
2.46
2.38
5.11
5.12
5.22
5.09
5.15
474, 627
501, 613
475
530, 610
549, 609
533
90, 224
77
PTTz
202
503, 552, 604
546, 599
a
g
Number-average molecular weight determined with GPC using
polystyrene.
The optical band gap was determined from the UV-vis absorption
onset in the solid state.
h
b
Polydispersity index (PDI).
Decomposition temperature determined by TGA based on 5% weight
The electrochemical band gap was determined by CV.
The IP value of each polymer film was determined from the onset volt-
c
i
loss.
age of the first oxidation potential with ferrocene at ꢀ4.8 eV.
d
Endotherms and
e
f
ꢁ
Exotherms on heating at 10 C/min.
Warm solution: dilute chloroform solution at 50 C; R.T. solution:
ꢁ
dilute chloroform solution at room temperature; film: thin film spin
coated from the chloroform solution.
Optical and Electrochemical Properties
exhibited smaller optical band gaps than those composed
only of thiophene units due to the D–A effect (A-shaped:
PT100 > PT50Tz50 * PTTz and H-shaped: PTT > PTTz)
(Table 1). This trend was consistent with the electrochemical
band gaps.
The UV-vis absorption spectra of the polymers in dilute chlo-
roform solution as well as in spin-coated thin films were
recorded (Fig. 3). The UV-vis absorption maxima of the poly-
mers were found to be 454–478 nm without observation of
shoulder peaks in the warm solution (Table 1). Although the
overall shapes of the absorption spectra obtained from the
warm solutions were quite similar, the UV-vis absorption
spectra of the polymers containing thiazole units (PTz100
and PTTz) were slightly red-shifted. This red-shift of the
absorption in PTz100 and PTTz was more significant when
the warm solutions were cooled to room temperature. In
addition, well-defined vibronic structures were clearly visible
at 552 and 604–627 nm in the room temperature solutions.
The appearance of vibronic peaks indicated a transition from
disordered molecular ordering to well-ordered molecular
packing at room temperature. These results also indicated
that the molecular structures that contained more electron
deficient units of polythiophene produced longer effective
conjugation lengths and better ordered intermolecular pack-
ing (stronger p–p interactions, in particular, which resulted
from the D–A effects). The absorption maxima obtained from
thin films were red-shifted by 40–60 nm with respect to the
peaks obtained from solution, again implying well-organized
intermolecular ordering in the solid states.
CV measurements of the polymer were conducted to deter-
mine the polymers’ IPs (Fig. 4). These measurements were
performed in an electrolyte solution of 0.1 M tetrabutylam-
monium tetrafluoroborate (TBABF ) in anhydrous acetoni-
4
trile at room temperature under nitrogen with a scan rate of
50 mV/s. To convert the measured redox behavior into IPs,
we used an empirical relationship based on the detailed
comparison of valence effective Hamiltonian calculations and
experimental electrochemical measurements, assuming that
the energy level of ferrocene/ferrocenium was 4.8 eV below
the vacuum level. The IPs of the polymers were found to
vary from 5.09 to 5.22 eV. These IP values were higher than
those of general polythiophenes, which implied better resist-
ance against oxidative doping and a high open-circuit voltage
(Voc) in the case of the solar cell device. In addition, as the
thiazole content increased, higher IP values were found.
XRD and Structural Properties
XRD analyses of thin films were carried out investigate the
structural ordering. Thin films (thickness of 70–80 nm)
were spin-cast onto octyltrichlorosilane (OTS-8) modified Si/
The absorption spectra obtained from the thin films were
very broad and covered the visible region, which indicated
that these polymers may be adapted to OPV applications.
Note that the optical properties did not depend on packing
type in a straightforward manner. However, the influence of
packing type on the electrical properties explored using
TFTs was quite obvious.
ꢁ
SiO2 substrates and annealed at 120 C for 10 min. (100)
peaks were observed for PT100, PT50Tz50, PTz100, PTT,
ꢁ
ꢁ
ꢁ
ꢁ
ꢁ
and PTTz at 2y ¼ 4.21 , 4.32 , 4.42 , 3.75 , and 4.34 ,
respectively, which corresponded to d-spacings (the inter-
layer distance) of 21.0, 20.4, 19.9, 23.5, and 20.3 Å, respec-
tively (Fig. 5). In the cases of both A- and H-shaped inter-
layer packing structures, as the thiazole content increased,
the thin films showed smaller lamellar distances (A-shaped:
PT100 > PT50Tz50 > PTz100 and H-shaped: PTT >
PTTz), and enhanced (100) and (200) peaks. These results
were consistent with the optical and electrochemical results.
In addition, the increased thiazole content led to significantly
The optical band gaps of the polymers were determined
from the UV-vis absorption onsets in the solid state (E
g
¼
1240/konset eV). On the whole, the polymers exhibited low
optical band gaps of 1.87–1.96 eV. In both A- and H-shaped
packing systems, the polymers containing thiazole units
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JOURNAL OF POLYMER SCIENCE PART A: POLYMER CHEMISTRY DOI 10.1002/POLA
TFT Properties
OTFTs based on PT100, PT50Tz50, PTz100, PTT, and PTTz
were fabricated by solution processing. Top-contact OTFTs
were fabricated on a highly n-doped silicon wafer with a
2
00 nm thick thermally grown SiO dielectric layer. The sur-
2
face of the substrate was modified with OTS-8. The
FIGURE 2 DSC thermograms of (a) PT100, (b) PT50Tz50, (c)
ꢁ
PTz100, (d) PTT, and (e) PTTz at a temperature ramp of 10 C/
2
min under N .
improved p–p interactions (010) and a newly formed sharp
ꢁ
p–p peak 2y ¼ 24.7 (d-spacing ¼ 3.6 Å), corresponding to
the general p–p interactions of the only thiophene-based
polymers and the interactions between relatively electron
6
(b)
rich and deficient units, respectively.
This feature implied
greatly improved p–p intermolecular stacking. The H-shaped
packing polymers exhibited smaller p–p distances (4.2 Å)
than did the A-shaped packing polymers (4.5–4.6 Å). The
improved structural characteristics directly affected the TFT
properties.
Film Morphologies
Figure 6 shows tapping mode AFM images of PT100,
PT50Tz50, PTz50, PTT, and PTTz on the OTS-8 modified
ꢁ
silicon wafer substrates after annealing at 120 C for 10
min. The AFM images of the A-shaped packing polymer thin
films showed rough crystalline domains and disconnected
surface images between the domains. In contrast, the H-
shaped packing polymers showed much smoother and better
connected surface images. Thiazole-containing polymers that
assumed either packing system showed smooth and well-
connected surface images. Smoother and better-connected
surfaces can facilitate charge carrier transport in TFT devices
FIGURE 3 UV-vis absorption spectra of PT100, PT50Tz50, Tz50,
PTT, and PTTz in (a) warm and (b) room temperature chloro-
form solution, and (c) film. [Color figure can be viewed in the
online issue, which is available at wileyonlinelibrary.
com.]
6
by reducing the number of charge traps.
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ARTICLE
Among these polymers, the PTTz polymer that contained an
electron deficient ring and interdigitated H-shape exhibited
ꢁ
the best TFT performance. After annealing at 120 C, the
TFT device composed of PTTz exhibited the highest mobility,
2
ꢀ1 ꢀ1
l ¼ 0.050 cm
V
s
, which was similar to the average
2
ꢀ1 ꢀ1
value (l ¼ 0.039 cm
V
s ) obtained from the 16 unit
cells. In addition, the device showed a high on/off ratio of
6
1
0 . This high on/off value was attributed to a low-lying IP
value (5.15 eV) of PTTz preventing the oxygen doping. The
TFT results were certainly the consequence of more ordered
intermolecular (lamellar and p–p) packing and longer
FIGURE 4 Cyclic voltammograms of PT100, PT50Tz50, Tz50,
PTT, and PTTz.
semiconducting layer (thickness 40 nm) was spin-cast onto
the substrate at 2500 rpm for 60 s from a 0.5 wt % chloro-
benzene solution. Au source and drain electrodes were de-
posited through a shadow mask on top of active layer. The
channel length (L) was 50 lm and the channel width (W)
was 1500 lm.
Figure 7 shows the transfer characteristics of the polymers
for the effects of the two alkyl-chain packing systems (A-
and H- shaped) and the contents of the electron deficient
unit. The mobilities, on/off ratios, and threshold voltages of
the OTFTs obtained from these polymers are listed in Table
2. The TFT mobilities were calculated in the saturation re-
gime using the following equation: I ¼ (W/2L) lC (V
–
gs
ds
i
2
V ), where I is the drain-source current in the saturated
th
ds
region, l is the field-effect mobility, C is the capacitance per
i
unit area of the insulation layer, and Vgs and Vth are the gate
and threshold voltages, respectively.
In the cases of both A- and H-shaped interdigitated packing
systems, as the thiazole content increased, the carrier mobili-
ties were significantly improved [Fig. 7(a,b)]. In addition,
polymers with the interdigitated H-shape (PTT and PTTz)
showed very good Vth values (ꢀ1 through ꢀ2) and turn-on
voltages that were independent of the thiazole content,
whereas the Vth and turn-on voltages of the polymers with
the interdigitated A-shape (PT100, PT50Tz50, and PTz100)
shifted sharply to lower voltages as the thiazole content
increased. The trends in Vth (which indicated the presence of
charge traps) were consistent with expectations from the
AFM images. The polymers with lower Vth showed smoother
and better-connected film morphologies. In both polythio-
phenes (PT100 and PTT) and D–A polythiophenes (PTz100
and PTTz) with thiazole rings as the electron deficient unit,
H-shaped packing polymers showed much higher charge car-
rier mobilities than A-shaped packing polymers [Fig. 7(c,d)].
FIGURE 5 Out-of-plane (left) and in-plane (right) XRD patterns
of (a) PT100, (b) PT50Tz50, (c) PTz100, (d) PTT, and (e) PTTz.
[Color figure can be viewed in the online issue, which is avail-
able at wileyonlinelibrary.com.]
Figure 8 shows the transfer curves and the mobility plot for
PTTz as-cast and annealed devices at various temperatures.
INFLUENCE OF ELECTRON DEFICIENT UNIT, KONG ET AL.
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JOURNAL OF POLYMER SCIENCE PART A: POLYMER CHEMISTRY DOI 10.1002/POLA
FIGURE 6 Topography (upper) and phase (lower) AFM images of (a) PT100, (b) PT50Tz50, (c) PTz100, (d) PTT, and (e) PTTz. [Color
figure can be viewed in the online issue, which is available at wileyonlinelibrary.com.]
FIGURE 7 Transfer characteristics of PT100, PT50Tz50, Tz50, PTT, and PTTz depending on ((a) and (b)) the thiazole content, as
electron accepting unit, and ((c) and (d)) different types of interdigitated packing structures. [Color figure can be viewed in the
online issue, which is available at wileyonlinelibrary.com.]
2892
WILEYONLINELIBRARY.COM/JOURNAL/JPOLA

ARTICLE
TABLE 2 The Performance of TFTs and Solar Cells Based on the Polymers
2
ꢀ1 ꢀ1 a
s )
Mobility (cm V
Threshold
On/Off
Ratio
V
oc
J
sc
PCE
(%)
ꢀ
2
Polymer
Max
Average
Voltage (Vth
)
FF
(V)
(mA cm )
6.5 ꢂ 10ꢀ
0.0017
0.0054
0.0051
0.050
5
5.0 ꢂ 10
0.0014
0.0044
0.0042
0.039
ꢀ5
ꢀ10
ꢀ9
ꢀ5
ꢀ1
ꢀ2
10
3
PT100
PT50Tz50
PTz100
PTT
4
10
5
10
0.31
0.36
0.51
0.58
4.45
6.58
0.71
1.39
5
10
6
PTTz
10
a
Evaluated from the saturation regime at V
D
¼ ꢀ60 V.
ꢁ
effective conjugation length, consistent with the UV, CV, AFM,
and XRD results. In addition, the transfer curve measured for
the PTTz device annealed at 120 C exhibited a very small
heated at 80 C for 10 min in air. Then, an aluminum (Al,
100nm) electrode was deposited by thermal evaporation in a
ꢁ
ꢀ7
vacuum of 5 ꢂ 10 Torr. All thermal annealing processes
Vth of ꢀ2 and a near-zero turn-on voltage, which implied a
significant reduction in the number of charge traps in the
active layer. When the devices were annealed at a higher
were carried out on a calibrated and stabilized heat stage
(HCS600V, INSTEC) for 15 min under N2 atmosphere. After
annealing, the devices were placed on a metal plate at room
temperature to cool down. Current density–voltage (J–V)
characteristics of the devices were measured using a Keith-
ley 236 Source Measure Unit. Solar cell performance utilized
an Air Mass 1.5 Global (AM 1.5 G) solar simulator with an
ꢁ
temperature than 140 C, they showed decreased mobilities
probably due to the movement of polymer main-backbone
deviated from the well ordered intermolecular packing.
Photovoltaic Cell Properties
ꢀ
2
irradiation intensity of 1000 W m
.
A representative polymer from either of the two alkyl chain
packing systems (PTz100 and PTTz), both containing the
electron deficient unit, was selected for testing in solar cell
devices. BHJ solar cells were fabricated with the following
structure: ITO-coated glass substrate/PEDOT:PSS/PTz100 or
Figure 9 shows the J–V characteristics for photovoltaic devi-
ces and the incident photon to converted current efficiency
(IPCE) curves of PTz100 and PTTz. The power conversion
efficiency (PCE), short-circuit current (Jsc), open-circuit volt-
age (Voc), and fill factor (FF) of photovoltaic devices for
PTz100 and PTTz are listed in Table 2. The PTTz:PC70BM
device exhibited a better solar cell performance (PCE of
PTTz:PC70BM (1:4 w/w)/titanium sub-oxide (TiO )/Al.
x
PEDOT:PSS (Baytron PH) was spin-cast from aqueous solu-
tion to form a film of 40 nm thickness. The substrate was
ꢁ
ꢀ2
dried at 140 C for 10 min in air, and then transferred into a
1.39% with Jsc ¼ 6.58 mA cm , Voc ¼ 0.58 V, and FF ¼
glove box to spin-cast the active layer. A solution containing
a mixture of PTz100 or PTTz:PC70BM (1:4, w/w) in dichlor-
obenzene with a concentration of 35 mg/mL was then spin-
36%) than did the PTz100:PC70BM device (PCE of 0.71%
ꢀ
2
with Jsc ¼ 4.45 mA cm , Voc ¼ 0.51 V, and FF ¼ 31%). The
V
oc and FF of the PTTz:PC70BM device presented only slight
cast on top of the PEDOT/PSS layer. The TiO precursor solu-
tion was spin-cast in air on top of the PTz100 or
improvements over the properties of the PTz100:PC70BM
device. However, the Jsc of the PTTz:PC70BM device was
much higher than that of the PTz100:PC70BM device, which
x
PTTz:PC70BM layer. After TiO deposition, the sample was
x
FIGURE 8 (a) Transfer characteristics, and (b) mobility plot of PTTz in the saturation regime at a constant source-drain voltage of
60 for various annealing temperatures. [Color figure can be viewed in the online issue, which is available at
ꢀ
V
wileyonlinelibrary.com.]
INFLUENCE OF ELECTRON DEFICIENT UNIT, KONG ET AL.
2893

JOURNAL OF POLYMER SCIENCE PART A: POLYMER CHEMISTRY DOI 10.1002/POLA
FIGURE 9 (a) J–V characteristics of a device with the structure ITO/PEDOT: PSS/polymer (PTz100 or PTTz):PC70BM (1:4, w/w)/TiOx/
2
Al under 100 mW/cm AM 1.5 solar irradiation, and (b) incident photon conversion efficiencies (IPCE) of these devices. [Color
figure can be viewed in the online issue, which is available at wileyonlinelibrary.com.]
resulted from a higher charge carrier mobility of PTTz than
of PTz100. Thus, the improved Jsc of the PTTz: PC70BM de-
vice directly affected the PCE. In addition, the PTTz:
PC70BM device showed more effective light absorption and
photoinduced charge transport to the electrodes than did the
PTz100: PC70BM device. Based on these preliminary solar
cell results, we can confirm the PTTz derivatives have the
potential for use in OPV applications.
The UV-vis spectra were recorded using a Jasco V-530 UV-vis
spectrometer and the photoluminescence (PL) spectra were
recorded using
a Spex Fluorolog-3 spectrofluorometer
(model FL3-11). CV was performed using an AUTOLAB/PG-
STAT12 system with a three-electrode cell in a 0.10 M solu-
tion of Bu NBF in acetonitrile at a scan rate of 50 mV/s. A
4
4
film of each polymer was coated onto a Pt wire electrode by
dipping the electrode into a solution containing the polymer.
Synchrotron X-ray diffraction analysis of the polymer films
was performed at the 10C1 beamline (wavelength z 1.54 Å)
at the Pohang Accelerator Laboratory (PAL). An AFM (Multi-
mode IIIa, Digital Instruments) operating in tapping-mode
was used to image the surface morphologies of the
semiconductors.
EXPERIMENTAL
Materials
n-Butyllithium, 1.0 M solution of trimethyltin chloride in tet-
rahydrofuran (THF), 2-bromothiophene, anhydrous toluene,
0
anhydrous chlorobenzene, [1.1 -bis(diphenylphosphino)-fer-
rocene]dichloropalladium (II) (Pd(dppf)Cl ), and tri(o-tolyl)-
The electrical characteristics of the TFTs were determined
using a Keithley 4200 semiconductor parametric analyzer. In
all measurements, the channel length (L) was 50 lm and the
channel width (W) was 1500 lm. The field-effect mobilities
were extracted in the saturation regime for each polymer
from the slope of the source-drain current. Current density–
voltage (J–V) characteristics of the solar cell devices were
measured using a Keithley 236 Source Measure Unit. Solar
cell performance measurements were conducted using an
Air Mass 1.5 Global (AM 1.5 G) solar simulator with an irra-
2
phosphine were purchased from Aldrich Chemical. Tris(di-
benzylideneacetone)dipalladium (0) was purchased from
STREM Chemicals. Magnesium (purum for Grignard reac-
tions) was purchased from Fluka. N-bromosuccinimde (NBS)
was purchased from Acros. Chloroform, methylene chloride,
tetrahydrofuran (THF), and toluene were purchased from
Junsei Chemical. All reagents and solvents were purchased
commercially, were of analytical-grade quality, and were
used without further purification.
ꢀ
2
diation intensity of 1000 Wm
.
Measurements
1
13
Synthesis of Materials
5
bithiazole (2)
These compounds were synthesized according to procedures
outlined in the literature.
The H and C NMR spectra were recorded using a Bruker
AVANCE 400 spectrometer, with tetramethylsilane as an in-
ternal reference. Elemental analysis was performed using an
EA 1110 Fisons analyzer. The number- and weight-average
molecular weights of the polymers were determined by gel
permeation chromatography (GPC) using a Viscotek T60A
instrument with polystyrene as the standard. Thermogravi-
metric analysis (TGA) was carried out using a TA Q500 ana-
0 0 0 0
,5 -Dibromo-2,2 -bithiophene (1) and 5,5 -Dibromo-2,2 -
1
9
Tributyl(3-dodecylthiophen-2-yl)stannane (3)
This compound was prepared in accordance with the litera-
2
0 1
ture methods.
H NMR (CDCl , 400 MHz, d): 7.54 (d, 1H),
3
ꢁ
lyzer with a heating rate of 10 C/min under a nitrogen
atmosphere. Differential scanning calorimetry (DSC) meas-
urements were performed using a TA Q100 instrument
7.12 (d, 1H), 2.62 (t, 2H), 1.58 (m, 8H), 1.38 (m, 24H), 1.14
(m, 6H), 0.91 (m, 12H); C NMR (CDCl , 100 MHz, d):
150.71, 130.75, 130.59, 129.05, 32.93, 32.22, 31.95, 29.79,
29.70, 29.67, 29.64, 29.38, 29.06, 28.96, 27.31, 22.71, 14.11,
1
3
3
ꢁ
under a nitrogen atmosphere at a heating rate of 10 C/min.
2894
WILEYONLINELIBRARY.COM/JOURNAL/JPOLA

ARTICLE
þ
1
C
3.63, 10.86; EIMS (m/z) 541 [M ]; Anal. calcd for
54SSn: C 62.10, H 10.05, S 5.92; found: C 62.04, H 10.01,
110.82, 31.94, 30.49, 29.68, 29.65, 29.55, 29.50, 29.48,
29.40, 29.34, 29.25, 22.66, 14.01; MS (MALDI-TOF) 824
28
H
þ
S 5.79.
[M ]; Anal. calcd for C H Br S : C 58.24, H 6.84, S 15.55;
4
0
56
2 4
found: C 58.02, H 6.79, S 15.41.
0
0
5
,5 -Bis(3-dodecylthiophen-2-yl)-2,2 -bithiophene (4)
0
0
A 150 mL flask was charged with compound 1 (1.0 g, 3.09
mmol), compound 3 (3.68 g, 6.79 mmol), tris(dibenzylide-
neacetone) dipalladium (0) (0.06 g, 0.06 mmol), tri(o-tolyl)-
phosphine (0.08 g, 0.25 mmol), and anhydrous toluene (25
mL). The solution was refluxed with vigorous stirring at 125
5,5 -Bis(5-bromo-3-dodecylthiophen-2-yl)-2,2 -
bithiazole (7)
The compound was synthesized using the method described
for the preparation of compound 6, starting with compound
5 (2.2 g, 3.29 mmol), NBS (1.29 g, 7.24 mmol), and chloro-
form (55 mL).
ꢁ
C for 24 h under a nitrogen atmosphere. The mixture was
added to water (100 mL) and extracted with chloroform.
The extract was then successively washed with water and
1
Yield: 1.96 g (72%). H NMR (CDCl
3
, 400 MHz, d): 7.77 (s,
2
0
1
2
H), 6.92 (s, 2H), 2.68 (t, 4H), 1.60 (m, 4H), 1.24 (m, 36H),
.86 (t, 6H); C NMR (CDCl , 100 MHz, d): 160.64, 142.72,
41.89, 132.92, 132.35, 127.56, 112.52, 31.92, 30.41, 29.68,
9.64, 29.61, 29.51, 29.48, 29.43, 29.39, 29.31, 22.65, 14.00;
MS (MALDI-TOF) 826 [M ]; Anal. calcd for C H Br N S : C
5.19, H 6.58, N 3.39, S 15.51; found: C 54.86, H 6.37, N
brine. After drying over anhydrous MgSO
4
, the solvent was
13
3
evaporated. The residue was purified by column chromatog-
raphy on silica gel with 1:1 hexane/di-chloromethane as the
eluent. The product was recrystallized from dichlorome-
thane/methanol to afford compound 4.
þ
3
8
54
2 2 4
5
1
Yield: 1.58 g (77%). H NMR (CDCl , 400 MHz, d): 7.16 (d,
3.19, S 15.43.
3
2
1
1
1
2
6
H), 7.11 (d, 2H), 7.01 (d, 2H), 6.92 (d, 2H), 2.76 (t, 4H),
0
0
4
,4 -Didodecyl-2,2 -bithiophene (8)
1
3
.63 (m, 4H), 1.23 (m, 36H), 0.85 (t, 6H); C NMR (CDCl3,
00 MHz, d): 139.84, 136.75, 135.27, 130.27, 130.07, 126.47,
23.82, 123.78, 31.91, 30.65, 29.66, 29.59, 29.51, 29.50,
9.48, 29.44, 29.35, 29.24, 22.68, 14.12; MS (MALDI-TOF)
The compound was synthesized according to the previously
published procedure. H NMR (400 MHz, CDCl , d): 6.96 (s,
H), 6.74 (s, 2H), 2.54 (t, 4H), 1.59 (m, 4H), 1.28 (m, 36H),
.86 (t, 6H); C NMR (100 MHz, CDCl , d): 143.97, 137.36,
6 1
3
2
0
1
2
13
þ
3
67 [M ]; Anal. calcd for C H S : C 72.01, H 8.76, S 19.23;
4
0 58 4
24.80, 118.68, 31.92, 30.52, 30.38, 29.67, 29.66, 29.64,
found: C 71.89, H 8.68, S 18.99.
9.59, 29.45, 29.35, 29.30, 22.69, 14.11; EIMS (m/z) 502
þ
0
0
5
,5 -Bis(3-dodecylthiophen-2-yl)-2,2 -bithiazole (5)
[M ]; Anal. calcd for C32
H
S
54
2
: C 76.43, H 10.82, S 12.75;
The compound was synthesized using the method described
found: C 76.38, H 10.76, S 12.58.
for the preparation of compound 4, starting with compound
0
0
0
(
4,4 -Didodecyl-2,2 -bithiophene-5,5 -diyl)bis(trimethyl
2
(1.5 g, 4.60 mmol), compound 3 (5.48 g, 10.12 mmol),
stannane) (9)
tris(dibenzylideneacetone)dipalladium (0) (0.09 g, 0.09
mmol), tri(o-tolyl)phosphine (0.12 g, 0.37 mmol), and anhy-
drous toluene (40 mL).
The compound was synthesized according to the previously
published procedure. H NMR (400 MHz, CDCl , d): 7.09 (s,
3
H), 2.53 (t, 4H), 1.55 (m, 4H), 1.25 (m, 36H), 0.86 (t, 6H),
0.36 (s, 18H); C NMR (100 MHz, CDCl , d): 151.62, 143.01,
3
6 1
2
1
13
Yield: 2.23 g (73%). H NMR (CDCl
3
, 400 MHz, d): 7.84 (s,
2
1
1
3
2
H), 7.25 (d, 2H), 6.96 (d, 2H), 2.76 (t, 4H), 1.64 (m, 4H),
130.87, 125.97, 32.67, 32.16, 31.89, 30.57, 30.40, 29.66,
1
3
.22 (m, 36H), 0.86 (t, 6H); C NMR (CDCl , 100 MHz, d):
29.60, 29.48, 22.69, 14.10; MS (MALDI-TOF) (m/z) 828
3
þ
60.50, 142.04, 141.57, 133.57, 130.20, 126.23, 125.35,
1.93, 30.56, 29.65, 29.62, 29.56, 29.50, 29.49, 29.46, 29.31,
[M ]; Anal. calcd for C38
H
70
S
2
Sn : C 55.09, H 8.52, S 7.74;
2
found: C 56.38, H 8.59, S 7.97.
þ
9.24, 22.65, 13.98; MS (MALDI-TOF) 669 [M ]; Anal. calcd
0
0
0
5
,5 -Dibromo-4,4 -didodecyl-2,2 -bithiophene (10)
for C H N S : C 68.21, H 8.44, N 4.19, S 19.17; found: C
3
8 56 2 4
The compound was synthesized according to the previously
68.15, H 8.23, N 4.08, S 18.91.
2
1 1
published procedure.
H NMR (400 MHz, CDCl , d): 6.75 (s,
3
0 0
,5 -Bis(5-bromo-3-dodecylthiophen-2-yl)-2,2 -
5
2H), 2.50 (t, 4H), 1.56 (m, 4H), 1.29 (m, 36H), 0.87 (t, 6H);
1
3
bithiophene (6)
C NMR (100 MHz, CDCl , d): 142.9, 136.2, 124.4, 107.9,
3
To a stirred solution of compound 4 (1.06 g, 1.59 mmol) in
chloroform (25 mL), N-bromosuccinimde (NBS) (0.61 g, 3.42
mmol) was added. The mixture was stirred at RT for 3 h,
then added to water (100 mL) and extracted with dichloro-
methane. The extract was successively washed with water.
31.9, 29.67, 29.64, 29.61, 29.5, 29.4, 29.3, 29.2, 22.7, 14.1; MS
þ
(MALDI-TOF) (m/z) 660 [M ]; Anal. calcd for C32
H
52Br
S
: C
2
2
58.17, H 7.93, S 9.71; found: C 58.56, H 7.65, S 9.86.
0
0
0
0
2
,2 -(4,4 -Didodecyl-2,2 -bithiophene-5,5 -diyl)dithiophene
(11)
After drying over anhydrous MgSO , the solvent was re-
4
A solution of 2-bromothiophene (2.37 g, 14.53 mmol) in 15
mL anhydrous tetrahydrofuran (THF) was added dropwise
to magnesium (0.47 g, 19.38 mmol) in anhydrous THF (10
moved by rotary evaporation, and the residue was purified
by recrystallization from dichloromethane/methanol to
obtain compound 6.
ꢁ
mL), and the mixture was refluxed for 2 h at 60 C under
1
Yield: 0.98 g (75%). H NMR (CDCl
3
, 400 MHz, d): 7.08 (d,
nitrogen gas. The resulting mixture was added slowly to a
solution containing compound 10 (3.20 g, 4.84 mmol) and
2
1
1
H), 6.94 (d, 2H), 6.87 (s, 2H), 2.69 (t, 4H), 1.60 (m, 4H),
1
3
0
.25 (m, 36H), 0.87 (t, 6H); C NMR (CDCl , 100 MHz, d):
[1.1 -bis(diphenylphosphino)-ferrocene]dichloropalladium (II)
3
40.72, 137.26, 134.30, 132.74, 131.86, 127.08, 124.05,
(Pd(dppf)Cl2) (0.08 g, 0.097 mmol) in anhydrous THF
INFLUENCE OF ELECTRON DEFICIENT UNIT, KONG ET AL.
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JOURNAL OF POLYMER SCIENCE PART A: POLYMER CHEMISTRY DOI 10.1002/POLA
ꢁ
ꢁ
(
25 mL) at 0 C. The mixture was refluxed for 12 h at 60 C,
(0.013 g 0.014 mmol), tri(o-tolyl)phosphine (0.017 g, 0.055
after which HCl solution (10%) was added. The mixture was
washed with ethyl acetate, NaOH (10%), NaHCO3 (1 M), and
water. After drying over anhydrous MgSO4, the solvent was
evaporated. Purification on a silica column with 1:1 hexane/
ethyl acetate as eluent, followed by recrystallization from
dichloromethane/methanol gave compound 11.
mmol), and anhydrous chlorobenzene (23 mL) were used in
this polymerization. H NMR (TCE, 400 MHz, d): aromatic;
1
7.19–7.02 (m, 8H), aliphatic; 2.82 (b, 8H), 1.72 (b, 8H),
1.45–1.31 (b, 72H), 0.91–0.90 (b, 12H); Anal. calcd for
C H S : C 74.04, H 9.49, S 16.47; found: C 74.15, H 9.53,
7
2 110 6
ꢁ
S 16.51; Solubility: 5.0 mg/1.0 mL chlorobenzene at 25 C.
1
0
0
0
0
Yield: 2.37 g (74%). H NMR (CDCl3, 400 MHz, d): 7.28 (d,
Poly(5,5 -bis(3 ,4-didodecyl-2,2 -bithiophen-5-yl)-2,2 -
bithiazole) (PTz100)
2
H), 7.11 (d, 2H), 7.05 (t, 2H), 6.97 (s, 2H), 2.70 (t, 4H), 1.62
m, 4H), 1.25 (m, 36H), 0.87 (t, 6H); C NMR (CDCl3, 400
1
3
(
Compound 7 (0.575 g, 0.695 mmol), Compound 9 (0.576 g,
MHz, d): 140.33, 135.96, 134.87, 129.52, 127.40, 126.35,
0.695 mmol), tris(dibenzylideneacetone)dipalladium (0)
125.77, 125.28, 31.91, 30.52, 29.67, 29.64, 29.57, 29.54,
29.53, 29.52, 29.44, 29.35, 22.69, 14.12; MS (MALDI-TOF)
666 [Mþ]; Anal. calcd for C40H58S4: C 72.01, H 8.76, S
19.23; found: C 72.15, H 8.87, S 18.98.
(
0.013 g 0.014 mmol), tri(o-tolyl)phosphine (0.017 g, 0.055
mmol), and anhydrous chlorobenzene (23 mL) were used in
this polymerization.
1
1
H NMR (TCE, 400 MHz, d): H NMR (CDCl , 400 MHz, d):
3
0 0 0 0
2,2 -(4,4 -Didodecyl-2,2 -bithiophene-5,5 -diyl)
dithiophene)bis(trimethylstannane) (12)
To a solution of compound 11 (2.0 g, 3.0 mmol) in 80 mL
THF, a 2.5 M solution of n-butyllithium in hexane (3.0 mL,
aromatic; 7.94 (b, 2H), 7.06–7.02 (b, 4H), aliphatic; 2.81 (b,
(
8
1
1
H), 1.74–1.72 (b, 8H), 1.46–1.31 (b, 72H), 0.93–0.89 (b,
2H); Anal. calcd for C H N S : C 71.86, H 9.30, N 2.39, S
70 108 2 6
6.44; found: C 71.95, H 9.46, N 2.51, S 16.47; Solubility: 5.0
ꢁ
ꢁ
mg/1.0 mL chlorobenzene at 38 C.
7
.5 mmol) was added dropwise at ꢀ78 C. The solution was
ꢁ
stirred at ꢀ78 C for 30 min then stirred at room tempera-
Random copolymer using repeat units of PT100 and
PTz100 (PT50Tz50)
Compound 6 (0.293 g, 0.355 mmol), Compound 7 (0.293 g,
ꢁ
ture for another 1 h. The solution was cooled to ꢀ78 C and
a 1.0 M solution of trimethyltin chloride in THF (9.0 mL, 9.0
mmol) was added in one portion. The solution was warmed
to room temperature and stirred at RT for 24 h. The reaction
mixture was quenched with water, extracted in dichlorome-
thane, and washed several times with water. The organic
0.355 mmol), Compound 9 (0.588 g, 0.710 mmol), tris(di-
benzylideneacetone)dipalladium (0) (0.013 g 0.014 mmol),
tri(o-tolyl)phosphine (0.018 g, 0.056 mmol), and anhydrous
chlorobenzene (23 mL) were used in this polymerization.
layer was dried over MgSO , and the solvent was evaporated
4
1
H NMR (TCE, 400 MHz, d): aromatic; 7.94 (b, 2H), 7.19–
under reduced pressure to yield 12. The product was used
7.03 (b, 12H), aliphatic; 2.81 (b, 16H), 1.73–1.71 (b, 16H),
without further purification.
1
1
.46–1.30 (b, 144H), 0.92–0.89 (b, 24H); Solubility: 1.0 mg/
.0 mL chlorobenzene at 33 C.
1
Yield: 2.35 g (79%). H NMR (CDCl
3
, 400 MHz, d): 7.23 (d,
ꢁ
2
1
1
1
2
9
1
H), 7.14 (d, 2H), 6.98 (s, 2H), 2.74 (t, 4H), 1.65 (m, 4H),
1
3
0
0
.32 (m, 36H), 0.88 (t, 6H), 0.40 (s, 18); C NMR (CDCl3,
00 MHz, d): 141.71, 139.82, 138.02, 135.46, 134.66, 129.79,
26.73, 126.26, 31.92, 30.46, 29.68, 29.67, 29.66, 29.60,
9.53, 29.45, 29.39, 29.36, 22.69, 14.13; MS (MALDI-TOF)
92 [M ]; Anal. calcd for C H S Sn : C 55.65, H 7.51, S
2.92; found: C 55.57, H 7.39, S 12.84.
Poly(5,5 -bis(2,5 -(thiophene-2,5-diyl)bis(3-dodecylthio-
phene)-5-yl)-2,2 -bithiophene) (PTT)
0
Compound 6 (0.565 g, 0.685 mmol), Compound 12 (0.680 g,
0.685 mmol), tris(dibenzylideneacetone)dipalladium (0)
(0.013 g 0.014 mmol), tri(o-tolyl)phosphine (0.017 g, 0.055
mmol), and anhydrous chlorobenzene (23 mL) were used in
this polymerization.
þ
4
6
74
4
2
General Polymerization Procedure
1
H NMR (TCE, 400 MHz, d): aromatic; 7.18–7.05 (m, 12H),
A 100 mL flask was charged with the dibromo compound,
the distannane compound, tris(dibenzylideneacetone)dipalla-
dium (0), tri(o-tolyl)phosphine, and anhydrous chloroben-
zene. The solution was refluxed with vigorous stirring at 140
aliphatic; 2.81 (b, 8H), 1.72 (b, 8H), 1.45–1.30 (b, 72H),
0
8
.93–0.90 (b, 12H); Anal. calcd for C H114S8: C 72.12, H
80
.62, S 19.25; found: C 72.27, H 8.69, S 19.35; Solubility: 1.0
ꢁ
ꢁ
ꢁ
mg/1.0 mL chlorobenzene at 27 C.
C for 3 days. After cooling to 50 C the reaction solution
was poured into 200 mL methanol containing 5 mL hydro-
chloric acid and stirred for 5 h. The precipitated solid was
then subjected to sequential Soxhlet extraction with metha-
nol and acetone to remove the low molecular weight fraction
of the material and the catalyst residues. The residue was
extracted with chlorobenzene to give the product after
removing chlorobenzene and drying in vacuo.
0
0
0
Poly(5,5 -bis(2,5 -(thiophene-2,5-diyl)bis(3-dodecylthio-
phene)-5-yl)-2,2 -bithiazole) (PTTz)
Compound 7 (0.554 g, 0.670 mmol), Compound 12 (0.665 g,
.670 mmol), tris(dibenzylideneacetone)dipalladium (0)
0.013 g 0.014 mmol), tri(o-tolyl)phosphine (0.017 g, 0.054
mmol), and anhydrous chlorobenzene (23 mL) were used in
this polymerization.
0
(
0
0
0
0
1
Poly(5,5 -bis(3 ,4-didodecyl-2,2 -bithiophen-5-yl)-2,2 -
bithiophene) (PT100)
H NMR (TCE, 400 MHz, d): aromatic; 7.93 (s, 2H), 7.20–
7.04 (m, 8H), aliphatic; 2.80 (b, 8H), 1.71 (b, 8H), 1.44–1.30
(b, 72H), 0.91–0.89 (b, 12H); Anal. calcd for C H N S : C
Compound 6 (0.563 g, 0.682 mmol), Compound 9 (0.565 g,
7
8 112 2 8
0.682 mmol), tris(dibenzylideneacetone)dipalladium (0)
70.21, H 8.46, N 2.10, S 19.23; found: C 70.31, H 8.61, N
2896
WILEYONLINELIBRARY.COM/JOURNAL/JPOLA

ARTICLE
2
4
.38, S 19.36; Solubility: 1.0 mg/1.0 mL chlorobenzene at
2 C.
Soc 1995, 117, 233–244; (c) Cho, S.; Lee, K.; Yuen, J.; Wang, G.;
Moses, D.; Heeger, A. J.; Surin, M.; Lazzaroni, R. J Appl Phys
ꢁ
2
006, 100, 114503.
3
Bao, Z.; Dodabalapur, A.; Lovinger, A. J Appl Phys Lett 1996,
9, 4108–4110.
CONCLUSIONS
6
We have successfully synthesized a series of new organic
semiconducting polythiophene derivatives that contained
varying thiazole ring contents, as an electron deficient unit,
in the two alkyl-chain packing geometries (A- and H-
shaped). The polymers were prepared via a Stille coupling
reaction, and the electronic and optoelectronic properties
were investigated. The copolymers that contained the thia-
zole unit exhibited much better thermal stabilities than did
the full thiophene polymers. As the thiazole content
increased, the UV-vis absorption spectra became more red-
shifted and showed better-defined vibronic structures, indi-
cating a longer effective conjugation length and better order-
ing in the intermolecular packing.
4
(a) Ong, B. S.; Wu, L. Y.; Liu, P.; Gardner, S. J Am Chem Soc
2
004, 126, 3378–3379; (b) Liu, P.; Li, Y.; Ong, B. S.; Zhu, S. J
Am Chem Soc 2006, 128, 4554–4555.
5
(a) McCulloch, I.; Heeney, M.; Bailey, C.; Genevicius, K.; Mac-
ronald, I.; Shkunov, M.; Sparrowe, D.; Tierney, S.; Wagner, R.;
Zhang, W.; Chabinyc, M. L.; Kline, R. J.; Mcgehee, M. D.;
Toney, M. F. Nat Mater 2006, 5, 328–333; (b) Hamadani, B. H.;
Gundlach, D. J.; McCulloch, I.; Heeney, M. Appl Phys Lett 2007,
9
1, 243512.
6
(a) Osaka, I.; Sauv e´ , G.; Zhang, R.; Kowalewski, T.; McCul-
lough, R. D. Adv Mater 2007, 19, 4160–4165; (b) Osaka, I.;
Zhang, R.; Sauv e´ , G.; Smilgies, D.-M.; Kowalewski, T.; McCul-
lough, R. D. J Am Chem Soc 2009, 131, 2521–2529.
These trends were consistent with the XRD and AFM results.
The polymers containing the thiazole unit and assuming the
interdigitated H-shape exhibited much better ordered (espe-
cially p–p stacking) and connected intermolecular structures
between domains than did other polymers. Improved inter-
molecular ordering and surface morphologies directly facili-
tated charge carrier transport in TFT devices without charge
traps and higher solar cell performances. Among these poly-
mers, the copolymers that contained high thiazole content
and an interdigitated H-shape exhibited much better elec-
tronic and optoelectronic device performances. As a result,
the devices fabricated using PTTz exhibited the highest TFT
7
(a) Shaheen, S. E.; Vangeneugden, D.; Kiebooms, R.; Van-
derzande, D.; Fromherz, T.; Padinger, F.; Brabec, P. C. J.; Sari-
ciftci, N. S. Synth Met 2001, 121, 1583–1584; (b)
Vangeneugden, D. L.; Vanderzande, D. J. M.; Salbeck, J.; van
Hal, P. A.; Janssen, R. A. J.; Hummelen, J. C.; Brabec, C. J.;
Shaheen, S. E.; Sariciftci, N. S. J Phys Chem B 2001, 105,
1
1106–11113; (c) Lee, T. W.; Kang, N. S.; Yu, J. W.; Hoang, M.
H.; Kim, K. H.; Jin, J.-I.; Choi, D. H. J Polym Sci Part A: Polym
Chem 2010, 48, 5921–5929; (d) Patra, D.; Sahu, D.; Padhy, H.;
Kekuda, D.; Chu, C.-W.; Lin, H.-C. J Polym Sci Part A: Polym
Chem 2010, 48, 5479–5489.
8
(a) Zhang, M.; Tsao, H. N.; Pisula, W.; Yang, C.; Mishra, A.
2
ꢀ1 ꢀ1
6
mobility, l ¼ 0.050 cm V
s , with a high on/off of 10
K.; M u¨ llen, K. J Am Chem Soc 2007, 129, 3472–3473; (b) Lee,
J.-Y.; Choi M.-H.; Song, H.-J.; Moon, D.-K. J Polym Sci Part A:
Polym Chem 2010, 48, 4875–4883.
(
attributed to the low-lying IP value (5.15 eV)), a Vth of ꢀ2,
and better solar cell performance, PCE ¼ 1.39%, J ¼ 6.58
sc
ꢀ
2
mA cm , and V ¼ 0.58 V. Thus, PTTz and its derivatives
oc
9
(a) Moul e´ , A. J.; Tsami, A.; B u¨ nnagel, T. W.; Forster, M.; Kro-
may be promising semiconductors for use in high perform-
ance OTFTs and OPVs.
nenberg, N. M.; Scharber, M.; Koppe, M.; Morana, M.; Brabec,
C. J.; Meerholz, K.; Scherf, U. Chem Mater 2008, 20, 4045–4050;
(b) Hou, J.; Chen, T. L.; Zhang, S.; Chen, H.-Y.; Yang, Y. J Phys
Chem C 2009, 113, 1601–1605; (c) Hou, J.; Park, M. H.; Zhang,
S.; Yao, Y.; Chen, L. M.; Li, J. H.; Yang, Y. Macromolecules
2008, 41, 6012–6018; (d) Leenen, M. A. M.; Meyer, T.; Cucinotta,
F.; Thiem, H.; Anselmann, R.; Cola, L. D. J Polym Sci Part A:
Polym Chem 2010, 48, 1973–1978.
This work was supported by KISCO and a grant (F0004011-
2
2
009-32) from the Information Display R&D Center, one of the
1st Century Frontier R&D Programs funded by the Ministry of
Commerce, Industry, and Energy of the Korean Government.
This work at University of Ulsan was supported by Priority
Research Centers Program through the National Research
Foundation of Korea (NRF) funded by the Minstery of Educa-
tion, Science and Technology (2009-0093818).
1
0
(a) Bundgaard, E.; Krebs, F. C. Macromolecules 2006, 39,
2
823–2831; (b) Bundgaard, E.; Krebs, F. C. Sol Energy Mater
Sol Cells 2007, 91, 1019–1025.
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