Dithienocyclopentathieno[3,2-b]thiophene hexacyclic arene for solution-processed organic field-effect transistors and photovoltaic applications

Article abstract of DOI:10.1002/asia.201100979

We have developed a ladder-type dithienocyclopentathieno[3,2-b]thiophene (DTCTT) hexacyclic unit in which the central thieno[3,2-b]thiophene ring was covalently fastened to two adjacent thiophene rings through carbon bridges, thereby forming two connected cyclopentadithiophene (CPDT) units in a hexacyclic coplanar structure. This stannylated Sn-DTCTT building block was copolymerized with three electron-deficient acceptors, dibromo-thieno[3,4-c]pyrrole-4,6-dione (TPD), dibromo-benzothiadiazole (BT), and dibromo-phenanthrenequinoxaline (PQX), by Stille polymerization, thereby furnishing a new class of alternating donor-acceptor copolymers: PDTCTTTPD, PDTCTTBT, and PDTCTTPQX, respectively. Field-effect transistors based on PDTCTTPQX and PDTCTTBT yielded high hole mobilities of 0.017 and 0.053 cm² V^-1 s^-1, respectively, which are among the highest performances among amorphous donor-acceptor copolymers. A bulk heterojunction solar cell that incorporated PDTCTTTPD with the lower-lying HOMO energy level delivered a higher V _oc value of 0.72 V and a power conversion efficiency (PCE) value of 2.59 %.

Full text of DOI:10.1002/asia.201100979

FULL PAPERS
DOI: 10.1002/asia.201100979
DithienocyclopentathienoACTHNUGRTNEUNG[3,2-b]thiophene Hexacyclic Arene for Solution-
Processed Organic Field-Effect Transistors and Photovoltaic Applications
Yen-Ju Cheng,* Chiu-Hsiang Chen, Tai-Yen Lin, and Chain-Shu Hsu*[a]
Abstract: We have developed a ladder-
type dithienocyclopentathieno[3,2-
b]thiophene (DTCTT) hexacyclic unit
in which the central thieno[3,2-b]thio-
phene ring was covalently fastened to
two adjacent thiophene rings through
carbon bridges, thereby forming two
(TPD),
dibromo-benzothiadiazole
PDTCTTPQX and PDTCTTBT yield-
ed high hole mobilities of 0.017 and
0.053 cm2 VÀ1 sÀ1, respectively, which
are among the highest performances
among amorphous donor–acceptor co-
polymers. A bulk heterojunction solar
cell that incorporated PDTCTTTPD
with the lower-lying HOMO energy
level delivered a higher Voc value of
0.72 V and a power conversion efficien-
cy (PCE) value of 2.59%.
G
(BT), and dibromo-phenanthrenequi-
noxaline (PQX), by Stille polymeri-
zation, thereby furnishing a new class
of alternating donor–acceptor copoly-
mers: PDTCTTTPD, PDTCTTBT, and
PDTCTTPQX, respectively. Field-
AHCTUNGTRENNUNG
connected
cyclopentadithiophene
effect
transistors
based
on
(CPDT) units in a hexacyclic coplanar
structure. This stannylated Sn-DTCTT
building block was copolymerized with
three electron-deficient acceptors, di-
Keywords: copolymerization
field-effect transistors · photovol-
taics · polymers · solar cells
·
bromo-thienoACHTUNGTRENNUNG[3,4-c]pyrrole-4,6-dione
Introduction
energy, which can enhance the intrinsic charge mobility.[5]
4H-cyclopenta[2,1-b:3,4-b’]dithiophene (CPDT)[6] is a tricy-
clic coplanar thiophene-based unit that has been widely em-
ployed as a building block for producing LBG polymers.
Polymer-based organic photovoltaics (OPVs) have attracted
considerable interest in the formation of low-cost, light-
weight, large-area, and flexible photovoltaic devices.[1] To
achieve high efficiencies of these OPVs, the most-difficult
challenge is to develop p-type conjugated polymers that si-
multaneously possess low band-gaps (LBGs), to capture
more solar photons, and high hole mobilities for efficient
charge-transport. The most-powerful way to prepare a LBG
polymer is to link electron-rich-donor- and electron-defi-
cient-acceptor units along the conjugated polymer back-
bone.[2] Based on this molecular strategy, a large amount of
research has been directed towards developing new elec-
tron-rich donor segments for p-type materials.[3] Multifused
arenes with forced structural planarity have been a common
structural feature in donor segments of successful LBG
polymers.[3] Forced planarization by covalently fastening ad-
jacent aromatic units into the polymeric backbone provides
an effective way to reduce the band-gap, because parallel p-
orbital interactions can facilitate p-electron delocalization
and elongate the effective conjugation length.[4] Further-
more, rigidification prevents the rotational disorder around
interannular single bonds to lower the reorganization
PolyACHUTGTNREN[UNG 2,6-ACTHUNGTRENNNUG
thiophene)-alt-4,7-(2,1,3-benzothiadiazole)]
which uses CPDT as the donor and BT as the acceptor, was
one of the first successful LBG polymers to be used in
OPVs,[7] and showed very high short-circuit currents (Jsc).
On the other hand, thieno
tive unit in the fused-thiophene family. The incorporation of
symmetrical and coplanar thieno[3,2-b]thiophene units into
ACHTUNGTRENN[UNG 3,2-b]thiophene is another attrac-
AHCTUNGTRENNUNG
conjugated polymers has been shown to facilitate strong in-
terchain interactions for ordered packing. In addition,
thienoACHTNUTRGNE[NUG 3,2-b]thiophene-based conjugated polymers have
shown lower-lying HOMO energy levels, which is an impor-
tant prerequisite for acquiring open-circuit voltage (Voc)
values.[8] To improve the solubility of the resulting polymers,
it is usually necessary to introduce alkyl chains into the b-
positions of the thienoACHTNUTGRNEUNG
[3,2-b]thiophene unit.[8] However, this
substitution also has a negative effect on the effective conju-
gation owing to severe steric-hindrance-induced twisting be-
tween neighboring units.[9] By taking these aforementioned
points into account, it is of great interest to integrate CPDT
and thienoACTHNUTRGNEUG[N 3,2-b]thiophene units into a molecular entity
with forced rigidification, to simultaneously extend the con-
jugation, whilst maintaining the coplanarity. Herein, we
[a] Prof. Dr. Y.-J. Cheng, C.-H. Chen, T.-Y. Lin, Prof. Dr. C.-S. Hsu
Department of Applied Chemistry
National Chiao Tung University
1001 Ta Hsueh Road, Hsin-Chu, 30010 (Taiwan)
E-mail: yjcheng@mail.nctu.edu.tw
report
a ladder-type dithienocyclopentathienoAHCTUTGNENRNUG
phene (DTCTT) unit where the central thienoACHTUNGTRENNUNG
phene ring is covalently fastened to two adjacent thiophene
rings through carbon bridges. In views of structural composi-
tion, this hexacyclic arene consists of two CPDT rings that
cshsu@mail.nctu.edu.tw
Supporting information for this article is available on the WWW
under http://dx.doi.org/10.1002/asia.201100979.
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Chem. Asian J. 2012, 7, 818 – 825

mal, optical, and electrochemical properties have been care-
fully characterized. These polymers showed promise for ap-
plications in solution-processed field-effect transistors and in
solar-cell devices.
Results and Discussion
Synthesis
Scheme 1. The chemical structures of the bicyclic (TT), tricyclic (CPDT),
and hexacyclic (DTCTT) units.
The synthesis of the DTCTT monomer is shown in
Scheme 3. 2,5-Bis(trimethylstannyl)thienoACTHNUGRTENUNG[3,2-b]thiophene
are connected through
(Scheme 1).
a
thieno
[3,2-b]thiophene ring
(1)[10] was treated with ethyl-2-bromothiophene-3-carboxyl-
ate (2) by Stille coupling to obtain compound 3. Double nu-
cleophilic addition of freshly prepared 4-(octyloxy)phenyl-
magnesium bromide to the ester groups of compound 3 led
to the formation of benzylic alcohol 4, which was subjected
to intramolecular annulation through an acid-mediated Frie-
del–Crafts reaction to furnish the fused nonacyclic arene,
DTCTT.[11] The Friedel–Crafts cyclization between two adja-
cent thiophene units was more challenging than for its bi-
phenyl-based analogue, presumably owing to the higher
ring-strain. The octyloxy side-chains at the para position of
the phenyl rings could stabilize the formation of the carbon
cation in the intermediate, thus promoting the intramolecu-
lar Friedel–Crafts cyclization. DTCTT was efficiently lithiat-
ed by tert-butyllithium followed by quenching with trime-
thyltin chloride to afford the distannyl Sn-DTCTT in moder-
ate yield (65%). The donor (Sn-DTCTT) was copolymer-
ized with TPD, BT, and PQX units by Stille coupling poly-
merization to afford PDTCTTTPD (Mn =18 kDa, PDI=
2.44), PDTCTTBT (Mn =20 kDa, PDI=1.55), and
PDTCTTPQX (Mn =10 kDa, PDI=1.41), respectively
(Scheme 4). All of the polymerization reactions were carried
out under microwave-assisted conditions in only 45 min
(Table 1). All of the intermediates, monomers, and corre-
sponding copolymers were fully characterized by 1H and
13C NMR spectroscopy (see the Supporting Information).
The resulting copolymers showed excellent solubilities in
common organic solvents, such as CHCl3, toluene, chloro-
benzene, and 1,2-dichlorobenzene.
Functionalization at the bridging carbon allows for the in-
troduction of four highly solubilizing side-chains on the two
CP moieties, thereby making DTCTT derivatives highly
soluble. Herein, we report the synthesis of a Sn-DTCTT mo-
nomer that was copolymerized with 1,3-dibromo-5-
octylthienoACHTUNGTRENNUNG[3,4-c]pyrrole-4,6-dione (TPD), 2,7-dibromo-
2,1,3-benzothiadiazole (BT), and 5,8-dibromophenanthrene-
quinoxaline (PQX) acceptors to afford a new class of conju-
gated D–A alternating copolymers (Scheme 2). Their ther-
Scheme 2. The chemical structures of polymers PDTCTTTPD,
PDTCTTBT, and PDTCTTPQX.
Thermal Properties
Thermal properties of these
polymers were analyzed by dif-
ferential scanning calorimetry
(DSC) and thermal gravimet-
ric analysis (TGA; Table 1).
The decomposition tempera-
tures (Td) of the polymers
were in the range 419–4278C
(Figure 1), thus suggesting
their sufficient thermal stabili-
ties for OPV applications.
From the DSC measurements,
neither glass-transition temper-
atures nor melting points were
Scheme 3. The synthesis of monomer Sn-DTCTT.
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Y.-J. Cheng, C.-S. Hsu et al.
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band at shorter wavelengths
(400–550 nm) was due to local-
À
ized p p* transitions (LT) and
the other band at longer wave-
lengths (550–00 nm) was attrib-
uted to intramolecular charge
transfer (ICT) between elec-
tron-rich donors and electron-
deficient acceptors. However,
the LT and ICT bands of
PDTCTTTPD overlapped into
a
single broad band, which
covered the whole visible
region (400–750 nm), thereby
indicating that the accepting
strength of TPD was weaker
than that of the BT and PQX
units. The absorption spectra
Scheme 4. Stille reactions to afford polymers PDTCTTTPD, PDTCTTBT, and PDTCTTPQX.
Table 1. Molecular weights, polydispersity index and thermal properties
of the DTCTT-based polymers.
[a]
[a]
Copolymer
Mw
Mn
PDI[a]
Td [8C][b]
PDTCTTTPD
PDTCTTBT
PDTCTTPQX
44000
31000
14400
18000
20000
10200
2.44
1.55
1.41
427
419
420
[a] Molecular weight and polydispersity were determined by gel-permea-
tion chromatography (GPC) in THF. [b] Decomposition temperature
(5% weight loss) measured by TGA.
Figure 2. Normalized absorption spectra of the polymers in CHCl3.
Figure 1. Thermal gravimetric analysis (TGA) measurements of the poly-
mers; ramping rate: 108CminÀ1
.
observed for all of the polymers, thus suggesting that these
copolymers were amorphous.
Figure 3. Normalized absorption spectra of the polymers in thin films.
Optical Properties
The absorption spectra of these polymers were measured in
both dilute CHCl3 (Figure 2) and as thin films (Figure 3);
the correlated optical parameters are summarized in
Table 2. Copolymers PDTCTTBT and PDTCTTPQX exhib-
ited two distinct bands in their absorption spectra. One
of all of the polymers shifted towards longer wavelengths
from the solution state to the solid state, thus indicating that
the planar structure of DTCTT was capable of inducing
À
stronger interchain p p interactions. The optical band gaps
(Egopt) deduced from the absorption edges of thin-film spec-
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Chem. Asian J. 2012, 7, 818 – 825

Thiophene-Based Donor–Acceptor Polymers
Table 2. Optical properties of the copolymers in the chloroform solution and in the
thin film.
Organic Field-Effect Transistors (OFETs) and
Photovoltaic Characteristics
Polymer
Solution in CHCl3
lmax [nm] lonset [nm] Eg [eV] lmax [nm] lonset [nm] Eg [eV]
Thin film
opt
opt
The solution-processed OFET devices were fabri-
cated using a bottom-gate, top-contact configura-
tion with evaporated-gold-source/drain-electrodes
and an octadecyltrichlorosilane-modified SiO2-gate
dielectric on an n-doped silicon-wafer surface. The
PDTCTTTPD 619, 671
PDTCTTBT 451, 714
PDTCTTPQX 483, 719
712
793
829
1.74
1.56
1.50
651, 671
455, 729
477, 703
721
821
838
1.72
1.51
1.48
tra were in the following order: PDTCTTPQX (1.48 eV)<
PDTCTTBT (1.51 eV)<PDTCTTTPD (1.72 eV).
Electrochemical Properties
Cyclic voltammetry (CV) was used to examine the electro-
chemical properties and evaluate the HOMO and LUMO
levels of the polymers (Table 3, Figure 4). All of the poly-
mers showed stable and reversible p-doping and n-doping
processes, which are important prerequisites for p-type semi-
conductor materials. The HOMO energy levels for
PDTCTTTPD, PDTCTTBT, and PDTCTTPQX were esti-
mated to be À5.30, À5.08, and À5.04 eV, respectively
(Figure 5), which was consistent with the observation that
TPD-based conjugated polymers generally exhibit lower-
lying HOMO energy levels.[12] According to the HOMO–
LUMO energy differences, the band-gaps (Egel; el=electro-
chemical) obtained from CV measurements were greater
than their corresponding optical band-gaps (Egopt), which
was consistent with other literature reports.[13]
Figure 5. Energy diagram of HOMO–LUMO levels for DTCTT-based
polymers and PC71BM.
output and transfer characteristics of typical devi-
Table 3. Electrochemical onset potentials and electronic energy levels of the poly-
mers.
ces of PDTCTTBT and PDTCTTPQX that were
annealed at 1508C are shown in Figure 6, and the
corresponding device parameters are shown in
Table 4. The hole mobilities of the polymers were
calculated from the transport characteristics of the
FETs by plotting IDS versus VGS. Polymers
PDTCTTBT and PDTCTTPQX showed impres-
sive saturated field-effect mobilities of 0.053 and
0.017 cm2 VÀ1 sÀ1 and on/off ratios of 2ꢁ105 and 3ꢁ
106, respectively. These values are among the high-
est FET mobilities for amorphous conjugated polymers. Pre-
sumably, the rigid and coplanar DTCTT unit plays an impor-
tant role in achieving the high-charge mobility. Nevertheless,
onset
onset
el
Copolymer
Eox
[V]
Ered
[V]
HOMO
[eV]
LUMOel
[eV]
LUMOopt[a]
[eV]
Eg
[eV]
PDTCTTTPD 0.50
PDTCTTBT 0.28
PDTCTTPQX 0.24
À1.67
À1.42
À1.34
À5.30
À5.08
À5.04
À3.13
À3.38
À3.46
À3.58
À3.57
À3.56
2.17
1.70
1.58
[a] LUMO levels of the polymers were obtained from the equation LUMO=HO-
opt
MO+Eg
.
PDTCTTTPD showed
a
lower mobility of 2.5ꢁ
10À4 cm2 VÀ1 sÀ1 with an on/off ratio of 6ꢁ102.
Bulk heterojunction OPVs were also fabricated on the
basis of the ITO/PEDOT:PSS/polymer:PC71BM/Ca/Al con-
figuration and their performances were measured under
100 mWcmÀ2 AM 1.5 illumination. The characterization
data and the optimal blending ratios of the active layers are
summarized in Table 5 and the J–V curves of these devices
are shown in Figure 7. The device based on the
PDTCTTPQX/PC71BM (1:3, w/w) blend exhibited Voc =
0.62 V, Jsc =7.33 mAcmÀ2, FF=42%, and PCE=1.91%.
The poorer efficiency may come from the relatively lower
molecular weight of PDTCTTPQX and the unfavorable
Figure 4. Cyclic voltammograms of the polymers in thin films; scan rate:
80 mVsÀ1
.
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Y.-J. Cheng, C.-S. Hsu et al.
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Figure 6. Typical output characteristics of OFETs device of a) PDTCTTBT, b) PDTCTTPQX, c) PDTCTTTPD annealed at 1508C, and their corre-
sponding transfer characteristics (d–f, respectively).
Table 4. OFET device characteristics.
highest hole mobility for PDTCTTBT was responsible for
Copolymer
Tannealing
[8C]
mhole
cm2 VÀ1 sÀ1
Ion/Ioff for
holes
6ꢁ102
2ꢁ105
3ꢁ106
Vth, hole
[V]
the higher photocurrent of the devices. Furthermore, the
device based on the PDTCTTTPD/PC71BM (1:2, w/w)
blend delivered a Voc value of 0.72 V, a higher Jsc value
(8.35 mAcmÀ2), and an FF value of 43%, thereby producing
the highest PCE value of 2.59%. This enhancement of Voc
was ascribed to the lowest-lying HOMO energy level of the
PDTCTTTPD polymer.
]
PDTCTTTPD
PDTCTTBT
PDTCTTPQX
150
150
150
2.5ꢁ10À4
5.3ꢁ10À2
1.7ꢁ10À2
0.61
À6.5
3.45
Table 5. Photovoltaic characteristics.
Copolymer
Ratio of copolymer/ Hole mobility Voc
Jsc
FF PCE
[%] [%]
PC71BM [wt.%]
[cm2 VÀ1 sÀ1
]
[V] [mAcmÀ2
]
PDTCTTTPD
PDTCTTBT
PDTCTTPQX
1:2
1:4
1:3
2.5ꢁ10À4
5.3ꢁ10À2
1.7ꢁ10À2
0.72
0.64
0.62
8.35
8.03
7.33
43
50
42
2.59
2.57
1.91
Conclusions
We have synthesized
a
ladder-type hexacyclic
DTCTT unit, which contained two CPDT moieties
that were connected through a central thieno
b]thiophene unit. The stannylated Sn-DTCTT
building block was copolymerized with three electron-defi-
cient acceptors, 1,3-dibromo-5-octyl-thieno[3,4-c]pyrrole-4,6-
ACHTUNGTRENNUNG[3,2-
morphology. The PDTCTTBT/PC71BM (1:4, w/w)-based
device showed higher Jsc and FF values (8.03 mAcmÀ2 and
50%, respectively), thereby leading to a PCE of 2.57%. The
AHCTUNGTRENNUNG
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Thiophene-Based Donor–Acceptor Polymers
solution was filtrated through a 0.45 mm filter and the substrates were
transferred into a glove box. The photoactive layer was then spin-coated
at different speeds to tune its thickness. After drying, the samples were
annealed for 15 min. The processing parameters (spin-coating speed, an-
nealing temperature) were as follows: PDTCTTTPD/PC71BM (900 rpm;
1508C), PDTCTTBT/PC71BM (800 rpm; 1508C), PDTCTTPQX/PC71BM
(600 rpm; 1508C). The cathode made of calcium (35 nm thick) and alumi-
num (100 nm thick) was evaporated through a shadow mask under high
vacuum (<10À6 torr). Each device was constituted of 4 pixels and defined
by an active area of 0.04 cm2. Finally, the devices were encapsulated and
I–V curves were measured in air.
Electrical Characterization under Illumination
The devices were characterized under 100 mWcmÀ2 AM 1.5 simulated
light measurement (Yamashita Denso solar simulator). Current-density-
voltage (J–V) characteristics of the PSC devices were obtained by a
Keithley 2400 SMU. Solar illumination conforming the JIS Class AAA
was provided by a SAN-EI 300W solar simulator equipped with an AM
1.5G filter. The light intensity was calibrated with a Hamamatsu S1336–
5BK silicon photodiode. The performances presented herein were the
average of the 4 pixels of each device.
Figure 7. J–V characteristics of ITO/PEDOT:PSS/polymer:PC71BM/Ca/Al
under illumination of AM 1.5, 100 mWcmÀ2
.
dione (TPD), 2,7-dibromo-2,1,3-benzothiadiazole (BT), and
5,8-dibromo-phenanthrenequinoxaline (PQX), by Stille
polymerization. The performance of devices based on
PDTCTTTPD/PC71BM and PDTCTTPQX/PC71BM blends
exhibited PCE values of 2.59% and 1.91%, respectively. In
addition, PDTCTTBT not only showed promising hole mo-
bility (0.053 cm2 VÀ1 sÀ1) in bottom-gate OEFTs device, but
also exhibited a good PCE value of 2.57% in a polymer
solar cell using PDTCTTBT/PC71BM (1:4, w/w) as the
active layer. This result indicates that the incorporation of
coplanar DTCTT arenes into conjugated polymers has
promise in both OFET and OPV applications.
OFET Fabrication and Characterization
Bottom-gate/top-contact (BG/TC) OFETs were fabricated to investigate
the charge-transport properties of the polymers. For the BGTC devices,
the semiconductor layers were deposited by spin-coating a 5 mgmLÀ1
polymer solution in ODCB under a N2 atmosphere onto OTS-treated, n-
doped Si wafers that had a 300 nm SiO2 dielectric layer. The capacitance
of the 300 nm SiO2 gate insulator was 11 nFcmÀ2. The devices were sub-
sequently annealed for 10 min at 1508C in a glove box under a N2 atmos-
phere. Electrical measurement of the OFET devices was carried out at
room temperature in air by using a 4156C, Agilent Technologies. The
field-effect mobility was calculated in the saturation regime by using the
equation IDS =(mWCi/2L)ACHTGNUTRENNUNG
m is the field-effect mobility, W is the channel width (100 mm), L is the
channel length (1 mm), Ci is the capacitance per unit area of the gate die-
lectric layer (11 nF/cm2), and VG is the gate voltage.
Experimental Section
Synthesis of Compound 3
General Measurement and Characterization
To
15.6 mmol), ethyl 2-bromothiophene-3-carboxylate (2; 8.10 g, 34.5 mmol),
[Pd(PPh3)4] (0.91 g, 0.78 mmol), and degassed toluene (156 mL). The
a 50 mL round-bottomed flask was added compound 1 (7.30 g,
All chemicals were purchased from Aldrich or Acros and used as re-
ceived unless otherwise stated. 1H and 13C NMR spectra were measured
by using a Varian 300 MHz spectrometer. The molecular weights of the
polymers were measured by GPC (Viscotek VE2001GPC), and polystyr-
ene was used as the standard (eluent: THF). Differential scanning calo-
rimeter (DSC) was measured on a TA Q200 Instrument and thermal
gravimetric analysis (TGA) was recorded on a Perkin–Elmer Pyris under
a nitrogen atmosphere at a heating rate of 108CminÀ1. Absorption spec-
tra were recorded on a HP8453 UV/Vis spectrophotometer. Cyclic vol-
tammetry was conducted on a Bioanalytical Systems Inc. analyzer. A
glassy carbon coated with a thin polymer film was used as the working
electrode and Ag/AgCl as the reference electrode; electrolyte: 0.1m tet-
rabutylammonium hexafluorophosphate (TBAPF6) in MeCN. CV curves
were calibrated by using ferrocence as the standard, the HOMO of which
was set to À4.8 eV with respect to the zero-vacuum level. The HOMO
energy levels were obtained from the equation HOMO=
AHCTUNGTRENNUNG
mixture was heated to reflux under a N2 atmosphere for 24 h. After re-
moval of toluene under reduced pressure, the residue was purified by
column chromatography on silica gel (n-hexane /EtOAc, 20:1 v/v) and
then recrystallized from THF to give an orange solid (5.48 g, 83%).
1H NMR (CDCl3, 300 MHz): d=7.67 (s, 2H), 7.52 (d, J=5.4 Hz, 2H),
7.23 (d, J=5.4 Hz, 2H), 4.32 (q, J=7.2 Hz, 4H), 1.33 ppm (t, J=7.2 Hz,
6H); 13C NMR ([D8]THF, 75 MHz): d=163.3, 143.5, 141.5, 137.4, 131.6,
129.6, 125.7, 122.4, 61.3, 14.6 ppm; MS (EI): m/z calcd for C20H16O4S4:
448.60; found: 448.
Synthesis of Compound 4
A Grignard reagent was prepared according to the following procedure.
To a suspension of magnesium turnings (1.46 g, 61.0 mmol) and 1,2-dibro-
moethane (3–4 drops) in dry THF (61 mL) was slowly added 1-bromo-4-
(octyloxy)benzene (17.36 g, 61.0 mmol) dropwise and the mixture was
stirred for 1 h. To a solution of compound 3 (2.18 g, 4.86 mmol) in dry
THF (55 mL) under a N2 atmosphere was added 4-(octyloxy)benzene-1-
magnesium bromide (48.6 mL, 48.6 mmol) dropwise at room tempera-
ture. The resulting mixture was heated to reflux for 16 h. The reaction
mixture was extracted with EtOAc (3ꢁ400 mL) and water (150 mL). The
combined organic layer was dried over MgSO4. After removal of the sol-
vent under reduced pressure, the residue was purified by column chroma-
tography on silica gel (n-hexane /EtOAc, 20:1 v/v) to give a brown oil
(3.94 g, 69%). 1H NMR (CDCl3, 300 MHz): d=7.20–7.10 (m, 10H), 6.80
(d, J=6.9 Hz, 8H), 6.75 (s, 2H), 6.43 (d, J=5.4 Hz, 2H), 3.94 (t, J=
6.5 Hz, 8H), 3.25 (br s, 2H), 1.90–1.70 (m, 8H), 1.50–1.20 (m, 40H),
onset
À(Eox ÀEferroceneonset+4.8). The LUMO levels of the polymers were ob-
onset
tained from the equation LUMO=À(Ered ÀEferroceneonset+4.8).
Fabrication and Characterization of the BHJ Device
ITO/glass substrates were ultrasonically cleaned sequentially in deter-
gent, water, acetone, and isopropyl alcohol. Then, the substrates were
covered by a 30 nm thick layer of PEDOT:PSS (Clevios P, provided by
H. C. Stark) by spin-coating. After annealing in air at 1508C over 30 min,
the samples were cooled to room temperature. The polymers were dis-
solved in ortho-dichlorobenzene (ODCB, 0.47 wt%) and PC71BM (pur-
chased from Nano-C) was added to reach the desired ratio. The solution
was then heated at 1108C and stirred overnight. Prior to deposition, the
Chem. Asian J. 2012, 7, 818 – 825
ꢀ 2012 Wiley-VCH Verlag GmbH & Co. KGaA, Weinheim
www.chemasianj.org
823

Y.-J. Cheng, C.-S. Hsu et al.
FULL PAPERS
1.00–0.80 ppm (m, 12H); 13C NMR (CDCl3, 75 MHz): d=158.3, 146.2,
139.9, 139.6, 137.0, 131.6, 131.5, 128.7, 123.9, 120.6, 113.7, 80.1, 67.9, 31.8,
29.4, 29.3, 29.2, 26.0, 22.6, 14.1 ppm; MS (FAB): m/z calcd for
C72H92O6S4: 1181.76; found: 1182.
270 Watt. Finally, 2-bromothiophene (9.3 mg, 0.057 mmol) was added and
the mixture was reacted for 10 min at 270 Watt. The solution was added
dropwise into MeOH. The precipitate was collected by filtration and
washed by Soxhlet extraction sequentially with acetone, n-hexane , and
CHCl3 for 1 week. Pd–thiol gel (Silicycle Inc.) and Pd–TAAcOH were
added to the CHCl3 solution to remove the residual Pd catalyst and Sn
metal. After filtration and removal of the solvent, the polymer was re-
dissolved in CHCl3 and added into MeOH to force re-precipitation. The
purified polymer was collected by filtration and dried under vacuum for
Synthesis of DTCTT
To a solution of compound 4 (3.35 g, 2.83 mmol) in boiling acetic acid
(450 mL) was added a drop of conc. sulfuric acid and the resulting solu-
tion was stirred for 3 h at 958C. After removal of the acetic acid under
reduced pressure, the residue was purified by column chromatography on
silica gel (n-hexane /EtOAc, 100:1 v/v) to give a yellow oil (0.74 g, 23%).
1H NMR (CDCl3, 300 MHz): d=7.20–7.10 (m, 10H), 7.03 (s, 2H), 6.78
(d, J=8.7 Hz, 8H), 3.88 (t, J=6.6 Hz, 8H), 1.80–1.60 (m, 8H), 1.50–1.10
(m, 40H), 0.95–0.80 ppm (m, 12H); 13C NMR (CDCl3, 75 MHz): d=
158.2, 157.4, 148.8, 136.8, 136.6, 134.7, 134.4, 128.9, 125.3, 123.0, 122.2,
114.3, 67.8, 61.1, 31.8, 29.3, 29.24, 29.20, 26.0, 22.6, 14.1 ppm; MS (FAB):
m/z calcd for C72H88O4S4: 1145.73; found: 1145.
1 day to give
a black solid (114 mg, 85%, Mn =20000, PDI=1.55).
1H NMR (CDCl3, 300 MHz): d=8.20–8.00 (m, 2H), 7.80–7.60 (m, 1H),
7.30–7.00 (m, 9H), 6.90–6.60 (m, 8H), 4.10–3.70 (m, 8H), 1.90–1.60 (m,
8H), 1.50–1.10 (m, 40H), 1.00–0.80 ppm (m, 12H).
Synthesis of PDTCTTPQX
To
0.088 mmol), 5,8-dibromo-phenanthrenequinoxaline (PQX; 38.71 mg,
0.088 mmol), [Pd2A(dba)3] (3.24 mg, 0.0035 mmol), tri(o-tolyl)phosphine
a 15 mL round-bottomed flask was added Sn-DTCTT (130 mg,
C
ACHTUNGTRENNUNG
Synthesis of Monomer Sn-DTCTT
(8.61 mg, 0.028 mmol), and dry chlorobenzene (3.8 mL). The mixture was
degassed by bubbling through N2 gas for 10 min at room temperature.
The flask was placed into a microwave reactor and reacted for 45 min at
270 Watt. Then, tributyl(thiophen-2-yl)stannane (16.5 mg, 0.044 mmol)
was added and the mixture was reacted for 10 min at 270 Watt. Finally, 2-
bromothiophene (7.78 mg, 0.048 mmol) was added and the mixture was
reacted for 10 min at 270 Watt. The solution was added dropwise into
MeOH. The precipitate was collected by filtration and washed by Soxhlet
extraction sequentially with acetone, n-hexane , and CHCl3 for 1 week.
Pd–thiol gel (Silicycle Inc.) and Pd–TAAcOH were added to the CHCl3
solution to remove the residual Pd catalyst and Sn metal. After filtration
and removal of the solvent, the polymer was re-dissolved in CHCl3 and
added into MeOH to force re-precipitation. The purified polymer was
collected by filtration and dried under vacuum for 1 day to give a black
solid (90.3 mg, 72%, Mn =10200, PDI=1.41). 1H NMR (CDCl3,
300 MHz): d=9.60–9.30 (m, 2H), 8.70–8.40 (m, 2H), 8.20–7.60 (m, 8H),
7.50–7.30 (m, 8H), 7.00–6.70 (m, 8H), 4.10–3.70 (m, 8H), 1.85–1.60 (m,
8H), 1.50–1.00 (m, 40H), 0.90–0.70 ppm (m, 12H).
To a solution of DTCTT (1.20 g, 1.05 mmol) in dry THF (31 mL) was
added 1.6m solution of tBuLi in n-hexane (2.0 mL, 3.14 mmol) dropwise
at À788C. After stirring at À788C for 1 h, a solution of chlorotrimethyl-
stannane in THF (4.2 mL, 1.0m, 4.19 mmol) was added via syringe. The
mixture was quenched with water and extracted with n-hexane (3ꢁ
200 mL) and water (50 mL). The combined organic layers were dried
over MgSO4. After removal of the solvent under reduced pressure, the
residue was purified by recrystallizing from THF to give a yellow solid
(1.00 g, 65%). 1H NMR (CDCl3, 300 MHz): d=7.16 (d, J=8.7 Hz, 8H),
7.04 (s, 2H), 6.79 (d, J=8.7 Hz, 8H), 3.90 (t, J=6.5 Hz, 8H), 1.80–1.70
(m, 8H), 1.50–1.20 (m, 40H), 1.00–0.80 (m, 12H), 0.36 ppm (s, 18H);
13C NMR (CDCl3, 75 MHz): d=159.3, 158.1, 148.7, 142.7, 138.8, 136.7,
134.8, 134.6, 130.4, 129.0, 114.3, 67.9, 60.6, 31.8, 29.32, 29.28, 29.2, 26.1,
22.6, 14.1 ppm; MS (FAB): calcd for C78H104O4S4Sn2: 1471.34; found:
1471; elemental analysis (%) calcd for C78H104O4S4Sn2: C 63.67, H 7.12;
found: C 63.73, H 7.22.
Synthesis of PDTCTTTPD
To
0.105 mmol), 1,3-dibromo-5-octyl-thieno
44.6 mg, 0.105 mmol), [Pd2A(dba)3] (3.86 mg, 0.0042 mmol; dba=dibenzyli-
dene acetone), tri(o-tolyl)phosphine (10.26 mg, 0.032 mmol), and dry
a
15 mL round-bottomed flask was added Sn-DTCTT (155 mg,
AHCTUNGTRENNUNG
CTHUNGTRENNUNG
Acknowledgements
ACHTUNGTRENNUNG
chlorobenzene (4.5 mL). The mixture was degassed by bubbling through
N2 gas for 10 min at room temperature. The flask was placed into a mi-
crowave reactor and reacted for 45 min at 270 Watt. Then, tributyl(thio-
phen-2-yl)stannane (19.7 mg, 0.053 mmol) was added and the mixture
was reacted for 10 min at 270 Watt. Finally, 2-bromothiophene (9.3 mg,
0.057 mmol) was added and the solution was reacted for 10 min at
270 Watt. Next, the solution was added dropwise into MeOH. The pre-
cipitate was collected by filtration and washed by Soxhlet extraction se-
quentially with acetone and CHCl3 for 3 days. Pd–thiol gel (Silicycle Inc.)
and Pd–TAAcOH were added to the CHCl3 solution to remove the resid-
ual Pd catalyst and Sn metal. After filtration and removal of the solvent,
the polymer was re-dissolved in CHCl3 and added into MeOH to force
re-precipitation. The purified polymer was collected by filtration and
dried under vacuum for 1 day to give a dark-purple solid (129 mg, 87%,
Mn =18000, PDI=2.44). 1H NMR (CDCl3, 300 MHz): d=7.60–7.40 (m,
2H), 7.30–7.10 (m, 8H), 7.00–6.70 (m, 8H), 4.10–3.80 (m, 10H), 1.90–
1.60 (m, 8H), 1.50–0.95 (m, 55H), 0.90–0.70 ppm (m, 12H).
We thank the National Science Council and the “ATU Program” of the
Ministry of Education, Taiwan, for financial support.
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To
a 15 mL round-bottomed flask was added Sn-DTCTT (155 mg,
0.105 mmol),
4,7-dibromo-2,1,3-benzothiadiazole
(BT;
31.0 mg,
0.105 mmol), [Pd
N
ACHTUNGTREN(NUNG o-tolyl)phosphine
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45 min at 270 Watt. Then, tributyl(thiophen-2-yl)stannane (19.7 mg,
0.053 mmol) was added and the mixture was reacted for 10 min at
824
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Received: December 2, 2011
Published online: February 6, 2012
Chem. Asian J. 2012, 7, 818 – 825
ꢀ 2012 Wiley-VCH Verlag GmbH & Co. KGaA, Weinheim
www.chemasianj.org
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