Solution-processed, indacenodithiophene-based, small-molecule organic field-effect transistors and solar cells

Article abstract of DOI:10.1039/c4tc00721b

Two indacenodithiophene-based molecules with different side chains, BTIDT-C6 and BTIDT-OC12, have been designed and synthesized for solution-processed, small-molecule organic solar cells (OSCs) donor materials. By optimizing the side chains, the hole mobility of the materials is modulated, which has been proven by the organic field-effect transistor (OFET) performances. Solar cells based on BTIDT-C6 show a power conversion efficiency (PCE) of 4.83%. To the best of our knowledge, this is the first report about indacenodithiophene-based, solution-processed, small-molecule OFETs, and it is also one of the highest PCE reports for the indacenodithiophene-based, solution-processed, small-molecule OSCs. This report makes indacenodithiophene- based small molecules the third type of high-efficiency (5% PCE), solution-processed, small-molecule OSCs donor materials, in addition to benzodithiophene (BDT) and dithienosilole (DTS). the Partner Organisations 2014.

Full text of DOI:10.1039/c4tc00721b

Journal of
Materials Chemistry C
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PAPER
Solution-processed, indacenodithiophene-based,
small-molecule organic field-effect transistors and
solar cells
Cite this: J. Mater. Chem. C, 2014, 2,
7523
Deyu Liu,ab Manjun Xiao,ac Zhengkun Du,a Yan Yan,d Liangliang Han,a V. A. L. Roy,d
bde
c
d
a
*
*
*
Mingliang Sun,
Weiguo Zhu, Chun Sing Lee and Renqiang Yang
Two indacenodithiophene-based molecules with different side chains, BTIDT-C6 and BTIDT-OC12, have
been designed and synthesized for solution-processed, small-molecule organic solar cells (OSCs) donor
materials. By optimizing the side chains, the hole mobility of the materials is modulated, which has been
proven by the organic field-effect transistor (OFET) performances. Solar cells based on BTIDT-C6 show a
power conversion efficiency (PCE) of 4.83%. To the best of our knowledge, this is the first report about
indacenodithiophene-based, solution-processed, small-molecule OFETs, and it is also one of the highest
PCE reports for the indacenodithiophene-based, solution-processed, small-molecule OSCs. This report
makes indacenodithiophene-based small molecules the third type of high-efficiency (5% PCE), solution-
processed, small-molecule OSCs donor materials, in addition to benzodithiophene (BDT) and
dithienosilole (DTS).
Received 9th April 2014
Accepted 11th July 2014
DOI: 10.1039/c4tc00721b
www.rsc.org/MaterialsC
limited to benzodithiophene14 and dithienosilole21,22 with deep
highest occupied molecular orbital (HOMO) levels, which could
1. Introduction
provide a high open circuit voltage (Voc) in solar cell devices.
New high performance donor materials for solution-processed,
small-molecule BHJ solar cells are urgently needed.
During the past two decades, polymer solar cells (PSCs) have
attracted considerable attention due to their potential applica-
tions in low-cost, exible, large-area photovoltaic devices.1–6
Through prolonged effort, single-junction PSCs have exceeded
9% PCE.7 However, polymer donor materials always suffer from
batch-to-batch variations, difficulty of purication, and broad
molecular weight distributions. In contrast, solution-processed,
small-molecule, bulk-heterojunction (BHJ) solar cells could
overcome these issues very well.8–13 Recently, dramatic progress
has been made, and PCE of 6–8% have been achieved by small-
molecule BHJ OSCs.14–20 Despite the recent appreciable
advances, the overall small-molecule device performances are
relatively low compared with their polymer counterparts. In
addition, the high PCE small-molecule donor materials were
The copolymers based on indacenodithiophene have been
employed in PSCs due to highly planar structures and high
carrier mobility.23–28 PSCs based on tetraphenyl-substituted
indacenodithiophene have exhibited PCE of more than 7%.29
The indacenodithiophene-based, small-molecule donor mate-
rials could also be promising due to the highly planar structures
and hole mobility of the indacenodithiophene segment. At the
end of 2013, Hou et al. reported the rst indacenodithiophene-
based, small-molecule donor materials, and the PCE of these
molecule-based solar cells reached around 4%.30 At the begin-
ning of 2014, Zhan et al. reported a similar small molecule,
which could be used as both donor and acceptor and exhibited
the highest PCE, around 3%.31 In addition, Cao and Su et al. also
reported indacenodithiophene-based small molecules with
tunable side chains.32 This pioneering work on indacenodi-
thiophene-based small molecules made this type of material a
promising candidate for high performance solar cell donors,
besides benzodithiophene14 and dithienosilole.21,22
aCAS Key Laboratory of Bio-based Materials, Qingdao Institute of Bioenergy and
Bioprocess Technology, Chinese Academy of Sciences, Qingdao 266101, People's
Republic of China. E-mail: yangrq@qibebt.ac.cn; Fax: +86-532-80662778; Tel: +86-
532-80662700
bInstitute of Material Science and Engineering, Ocean University of China, Qingdao
266100, People's Republic of China. E-mail: mlsun@ouc.edu.cn; Fax: +86-532-
66781927; Tel: +86-532-66781690
cCollege of Chemistry, Key Lab of Environment-Friendly Chemistry and Application of
the Ministry of Education, Xiangtan University, Xiangtan 411105, People's Republic of
China. E-mail: zhuwg18@126.com; Fax: +86-731-58292251; Tel: +86-731-58298280
dCenter of Super-Diamond and Advanced Films (COSDAF), City University of Hong
Kong, Hong Kong
Besides the aforementioned small-molecule backbone
design, which determine the main photoelectronic properties of
donor materials, side-chain engineering also plays a critical role
in improving molecular solubility and lm-forming properties,
which is a prerequisite for their applications in solution-pro-
cessed solar cells.33,34 Side-chain engineering of polymer-donor
materials can signicantly improve PSC performance when the
eShenzhen Research Institute, City University of Hong Kong, High-Tech Zone, Nanshan
District, Shenzhen 518057, China
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Scheme 1 Synthetic routes for the small molecules.
Fig. 1 Molecular structures of the small molecules.
two molecules were characterized by 1H NMR, 13C NMR and MS.
The melting points of the two molecules were measured by the
micro-melting point apparatus. BTIDT-C6 has a higher melting
point at 110.2 ꢀC, as BTIDT-OC12 has much lower melting point
at 69.4 ꢀC, which suggests BTIDT-C6 exhibits better stability
than BTIDT-OC12. The DSC analysis of BTIDT-C6 reveals that
polymer-conjugated backbone is completely same.35–38 It is also
necessary for small-molecule donor materials. Moreover, it is
easy to modulate the small-molecule crystallinity by choosing
different side chains. Crystallinity could have great inuence on
the device performances for solution-processed, small-molecule
solar cells. In particular, it will inuence the acceptor/donor
interpenetrating network, which leads to the changes of
roughness in AFM morphology and crystal-domain size.39,40
With proper side chains, the small molecule-based solar cells
will produce higher device performances with high Jsc and FF,
which originates from the good donor/acceptor interpenetra-
tion network in the active layer.
ꢀ
the melting temperature is 96.7 C. However, the DSC curve of
BTIDT-OC12 does not show any useful information. It may be
that the low melting point of BTIDT-OC12 or amorphous nature
leads to the DSC measurement difficulty.
2.2. Optical properties
In this work, we synthesized two indacenodithiophene-based
small molecules, BTIDT-C6 and BTIDT-OC12 (Fig. 1). By opti-
mizing the side chains, the hole mobility of the materials is
modulated, which has been proven by the OFET performances.
The side chains also help the small molecule donor materials to
form extremely smooth donor/acceptor bulk heterojunction
thin lms, which produce near 5% PCE solar cells. To the best
of our knowledge, this is the rst report about indacenodi-
thiophene-based, solution-processed, small-molecule OFET,
and it is also one of the highest PCE reports for indacenodi-
thiophene-based, solution-processed, small-molecule donor
materials.
The UV-vis spectra of BTIDT-C6 and BTIDT-OC12 in chloroform
solution and in thin lm are shown in Fig. 2, and the corre-
sponding absorption properties are summarized in Table 1. The
absorption spectra of BTIDT-C6 and BTIDT-OC12 are found to
be similar both in solution and lm. These two molecules show
two peaks at ꢁ400 nm and ꢁ600 nm in both solution and lm.
Compared with the absorption peak at 587 nm of BTIDT-C6 in
solution, the absorption peak of BTIDT-C6 thin lm has a red
shi of ꢁ16 nm, whereas BTIDT-OC12 does not show a clear red
shi. This indicates an effective p–p packing in the BTIDT-C6
2. Results and discussion
2.1. Synthesis and thermal properties
BTIDT-C6 and BTIDT-OC12 were synthesized by the routes
shown in Scheme 1. Sn-IDT-C6 was prepared according to the
literature.25 Sn-IDT-OC12 was synthesized by an improved
experimental procedure. The TMS groups on 1,4-bis-(5-trimethyl-
silylthiophen-2-yl)-2,5-benzene-dicarbonate were introduced to
facilitate the later intramolecular cyclization reactions. As a
result, the yields of product 2 could be increased. By the Stille
condensation of the 4-bromo-7-(5-(5-(2-ethylhexyl)-thiophen-2-
yl)-thiophen-2-yl)-2,1,3-benzothiadiazole with Sn-IDT-C6 and
Sn-IDT-OC12, respectively, the targeted molecules BTIDT-C6
Fig.
2 Normalized UV-vis absorption spectra of BTIDT-C6 and
and BTIDT-OC12 were synthesized. The chemical structures of BTIDT-OC12 in chloroform solution and in film.
7524 | J. Mater. Chem. C, 2014, 2, 7523–7530
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Table 1 Optical and electrochemical properties of BTIDT-C6 and BTIDT-OC12
lmax
lmax
Eogpt
lm per eV
Molecules
solution per nm
lm per nm
Ecgv eV
EHOMO eV
ELUMO eV
BTIDT-C6
BTIDT-OC12
587
586
603
574
1.82
1.78
1.66
1.61
ꢂ5.37
ꢂ5.34
ꢂ3.71
ꢂ3.73
Fig. 3 Cyclic voltammogram of BTIDT-C6 and BTIDT-OC12.
thin lm. The optical band gaps of BTIDT-C6 and BTIDT-OC12
are estimated to be 1.82 eV and 1.78 eV, respectively, according
to Eogpt ¼ 1240/l.
2.3. Electrochemical properties
The electrochemical properties of BTIDT-C6 and BTIDT-OC12
were investigated by cyclic voltammetry (CV) (Fig. 3). A three
electrode cell consisting of a glassy carbon working electrode, a
platinum wire counter electrode and a saturated calomel
reference electrode has been used. The potentials were inter-
nally calibrated using the Fc/Fc+ redox couple. The redox
potential of the Fc/Fc+ internal reference is found to be 0.43 V vs.
SCE. According to the empirical equation,
EHOMO ¼ ꢂ(Eox + 4.4) (eV)
ELUMO ¼ ꢂ(Ered + 4.4) (eV)
The HOMO energy levels of these molecules are highly
similar (ꢁꢂ5.35 eV). The electrochemical band gaps of BTIDT-
C6 and BTIDT-OC12 are 1.66 eV and 1.61 eV, respectively. The
low HOMO energy levels indicate that these two molecules
maintain good stability in the air and could afford a high open
circuit voltage (Voc) in solar cell devices.
Fig. 4 (A) ID versus VG transfer characteristic and (B and C) output
characteristic IDS versus VDS at different VGS of the BTIDT-C6- and
BTIDT-OC12-based OFETs.
of 1.1 ꢃ 10ꢂ4 cm2 Vꢂ1 sꢂ1. BTIDT-OC12 with longer side chains
increases numbers of alkyl, which decreases the contents of
active conjugated compositions. And the amorphous nature of
BTIDT-OC12 molecule is another reason for low OFET mobility.
2.4. Field-effect transistor (FET) characteristics
Fig. 4 shows the transfer and output curves of the OFET devices The AFM height images (2 mm ꢃ 2 mm) of the BTIDT-C6 and
based on BTIDT-C6 and BTIDT-OC12. The device performances BTIDT-OC12 on SiO2/silicon substrates are shown in Fig. 5, and
of BTIDT-C6 and BTIDT-OC12 are summarized in Table 2. The the root-mean-square (RMS) are 0.310 nm and 0.278 nm for
BTIDT-C6 and BTIDT-OC12, respectively. The results show that
OFET device of BTIDT-C6 showed a higher hole mobility of 5.4
ꢃ 10ꢂ4 cm2 Vꢂ1 sꢂ1 than that of BTIDT-OC12 with hole mobility
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Table 2 OFET device performances of BTIDT-C6 and BTIDT-OC12
Table 3 Device performances of the BTIDT-C6- and BTIDT-OC12-
based solar cells
Molecules
m (cm2 Vꢂ1 sꢂ1
)
On/off ratio
VTh (V)
Jsc/mA
5.4 ꢃ 10ꢂ4
1.1 ꢃ 10ꢂ4
1 ꢃ 104
1 ꢃ 103
ꢂ2.5
ꢂ2
Molecules/acceptor
D/A ratio
Voc/V
cmꢂ2
FF
PCE/%
BTIDTC6
BTIDTOC12
BTIDTC6/PC61BM
BTIDTC6/PC61BM
BTIDTC6/PC61BM
BTIDTC6/PC71BM
BTIDTOC12/PC61BM
BTIDTOC12/PC61BM
BTIDTOC12/PC61BM
BTIDTOC12/PC71BM
1 : 2
1 : 3
1 : 4
1 : 3
1 : 2
1 : 3
1 : 4
1 : 3
0.94
0.92
0.92
0.91
0.96
0.94
0.93
0.94
7.10
7.57
7.04
11.01
5.62
6.03
46.65
49.80
51.80
48.17
38.63
43.54
43.30
43.30
3.11
3.47
3.35
4.83
2.08
2.47
2.38
4.06
5.91
10.00
curve of the OSC devices based on the blend of BTIDT-C6 or
BTIDT-OC12/PC61BM or PC71BM under the illumination of AM
1.5G, 100 mW cmꢂ2. Table 3 summarized the detailed device
performances. Finally, the best solar cell obtained from BTIDT-
C6:PC71BM (1 : 3) showed a PCE of 4.83% with an Voc of 0.91 V, a
Jsc of 11.01 mA cmꢂ2, and an FF of 48.17%, and BTIDT-OC12
showed a PCE of 4.06% with an Voc of 0.94 V, a Jsc of 10.00 mA
cmꢂ2, and an FF of 43.30% at the same conditions. We can nd
that the characteristically high Voc of the OSCs devices is
obtained by BTIDT-C6 (0.91 V) and BTIDT-OC12 (0.94 V)
because of their deep HOMO energy levels.
Fig. 5 AFM height images (2 mm ꢃ 2 mm) of (a) the BTIDT-C6 (b) the
BTIDT-OC12 on SiO2/silicon substrates.
the side chain helps the molecule form very uniform lm for
OFET devices.
2.5. Photovoltaic properties
The external quantum efficiency (EQE) curves of the devices
based on BTIDT-C6/PC61BM or PC71BM and BTIDT-OC12/
PC61BM or PC71BM (1 : 3) are shown in Fig. 7. Both the devices
exhibited a photoresponse range from 300 to 800 nm, with a
maximum EQE of 67.9% for BTIDT-C6/PC71BM and 60.0% for
BTIDT-C12/PC71BM. To conrm the accuracy of the photovol-
taic measurements, the Jsc (10.89 mA cmꢂ2 for BTIDT-C6/
PC71BM and 9.95 mA cmꢂ2 for BTIDT-C12/PC71BM) were
calculated from the integration of the EQE curves, which agree
well with the Jsc (11.01 mA cmꢂ2 for BTIDT-C6 and 10.00 mA
cmꢂ2 for BTIDT-C12) obtained from the J–V measurements. In
addition, the EQE curves of the PC71BM-based devices show
higher EQE response in the region (500–700 nm), which
contribute to the higher Jsc of the PC71BM-based devices.44
Mobility measurements via the space charge limited current
We fabricated the OSC devices with the structure of ITO/
PEDOT:PSS/small molecule:PC61BM/Ca/Al using the method of
solution processing as in our previous studies.41–43 The blends of
small molecules and PC61BM at various weight ratios of 1 : 2,
1 : 3 and 1 : 4 have been used to optimize their device perfor-
mances. We found BTIDT-C6- or BTIDT-OC12-based device
performances do not signicantly change with varying the DA
ratio within the range of 1 : 2 to 1 : 4, which will be benecial to
future industrial manufacture. We further optimized the device
performances using a PC71BM acceptor with device congura-
tion ITO/PEDOT:PSS/small molecule:PC71BM (1 : 3)/Ca/Al. The
thicknesses of BTIDT-C6/PC61BM, BTIDT-C6/PC71BM, BTIDT-
OC12/PC61BM and BTIDT-OC12/PC71BM lms were 100 nm,
103 nm, 96 nm and 98 nm, respectively. Fig. 6 shows the J–V
Fig. 6 J–V curves of the OSC devices based on the blend of BTIDT-
C6 or BTIDT-OC12/PC61BM or PC71BM under the illumination of AM Fig. 7 EQE curves of the OSC devices based on the blend of BTIDT-
1.5G, 100 mW cmꢂ2
C6 or BTIDT-OC12/PC61BM or PC71BM.
.
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(SCLC) method disclose the hole mobility of 8.5 ꢃ 10ꢂ6 cm2 Vꢂ1
Atomic force microscopy (AFM) was used to investigate the
sꢂ1 for the BTIDT-C6:PC61BM device, 2.8 ꢃ 10ꢂ5 cm2 Vꢂ1 sꢂ1 for morphologies of the two organic molecules: the PC71BM blend
the BTIDT-C6:PC71BM device, 5.4 ꢃ 10ꢂ6 cm2 Vꢂ1 sꢂ1 for the lms. As shown in Fig. 9, the roughness of the blend lms is
BTIDT-OC12:PC61BM device and 1.6 ꢃ 10ꢂ5 cm2 Vꢂ1 sꢂ1 for the 0.378 nm and 0.377 nm for the BTIDT-C6/PC71BM and BTIDT-
BTIDT-OC12:PC71BM device (Fig. 8). The PC71BM-based device OC12/PC71BM lms, respectively. The surfaces of the molecule/
shows higher hole mobility than that of the PC61BM device. This PC71BM blend lms are both smooth and uniform.
could be another potential reason that the PC71BM device
exhibits larger Jsc than the PC61BM device. The SCLC results
show that the hole mobility of BTIDT-C6 is higher than that of
3. Conclusions
BTIDT-OC12, which agree well with that of the OFET measure-
ments. As a result, the high hole mobility could improve the Jsc
and FF in OSC devices, which make hole transport easier in the
OSCs active layer.45,46
Two indacenodithiophene-based A–D–A-type small molecules,
BTIDT-C6 and BTIDT-OC12, have been designed and synthe-
sized. The side chains do not show obvious inuence on the
optical and electrochemical properties of these two molecules.
However, the photovoltaic performance and OFET properties
show a close relationship with different side chains. BTIDT-C6
with shorter side chains improves the hole mobility up to ve
times more than BTIDT-OC12 and has a higher PCE of 4.83%,
which makes indacenodithiophene-based small molecules the
third type of high-efficiency (5% PCE), solution-processed, OSC
small-molecule donor materials, besides benzodithiophene
(BDT) and dithienosilole (DTS).
4. Experimental
4.1. Materials
All starting reagents were commercially obtained as analytical
reagents and directly used without any purication. Toluene and
THF were puried by vacuum distillation under nitrogen prior to
use. 5-(Tri-n-butylstannyl)-50-(2-ethylhexyl)-2,20-bithiophene, 5-tri-
methylsilyl-2-(tri-n-butylstannyl)-thiophene, 4-dodeoxy-1-bromobe-
nene and (4,4,9,9-tetrakis(4-hexylphenyl)-4,9-dihydro-s-indaceno-
[1,2-b:5,6-b0]dithiophene-2,7-diyl)-bis(trimethylstannane) (Sn-IDT-
C6) were synthesized as reported in the literature.25,47–49
Fig. 8 Current density (J)–voltage (V) curves for BTIDT-C6/PC61BM or
PC71BM blend films and BTIDT-OC12/PC61BM or PC71BM blend films
(the symbols are experimental data for transport of hole and the red
lines are fitted according to the space-charge-limited-current model).
4.2. Instruments and measurements
Nuclear magnetic resonance (NMR) spectra were taken on a
Bruker AVANCE-III 600 Spectrometer. High resolution mass
spectra (MS) were recorded under APCI mode on a Bruker Maxis
UHR-TOF spectrometer. Melting points were measured with a
SGWX-4A micro melting point apparatus. UV-Vis absorption
spectrum was measured with a Hitachi U-4100 pectrophotometer.
The organic molecule lms on quartz used for absorption spec-
tral measurement were prepared by spin-coating their chloroform
solutions. Cyclic voltammetry (CV) was performed using a
CHI660D electrochemical workstation with a glassy carbon
working electrode, a saturated calomel reference electrode (SCE)
and a platinum wire counter electrode at a scan rate of 100 mV
sꢂ1. Tetrabutylammonium phosphorus hexauoride (Bu4NPF6,
0.1 M) in acetonitrile was used as the supporting electrolyte.
Surface roughness and morphologies of thin lms were charac-
terized by atomic force microscopy (AFM) on an Agilent 5400 or
VEECO Multimode V working at the tapping mode.
4.3. Fabrication of eld-effect transistor (FET) devices
Fig. 9 (a) AFM height and (b) phase images of the BTIDT-C6:PC71BM
(1 : 3) blend films; (c) AFM height and (d) phase images of the BTIDT-
OC12:PC71BM (1 : 3) blend films. All the images are 5 mm ꢃ 5 mm.
Bottom-gate/bottom-contact transistors were fabricated on Au-
patterned SiO2/Si substrate (W/L ¼ 3173 : 10). The thickness of
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SiO2 is 100 nm, and the high doped silicon was used as the mL) was then added slowly. The mixture was stirred at room
bottom-gate electrode. Aer standard cleaning (15 min ultra- temperature overnight and then poured into water and extracted
sonic process in acetone, isopropanol and DI-water, sequen- with chloroform. The combined organic extracts were dried over
tially), 5 mg mLꢂ1 small molecules dissolved in chlorobenzene Na2SO4 and ltered, and the solvent was removed under reduced
were spin-coated on the substrates at a speed of 1000 RPM for 1 pressure. The resulting solid was washed with hexanes to give (2)
min and the active layer around 20 nm was formed on the as a white, solid crude product. The white product was then
substrate aer coating. The substrates were then annealed on a directly dissolved in acetic acid (25 mL) and 1 mL of concentrated
hot plate at 50 ꢀC (BTIDT-C12 sample) or 100 ꢀC (BTIDT-C6 hydrochloric acid was added to the solution. The mixture was
sample) for 30 min before the device test. I–V curves were stirred at 80 ꢀC for 2 h. Aer pouring into water, the mixture was
measured by a Keithley 6212 source meter, an Agilent 4155C extracted with chloroform. The combined organic extracts were
semiconductor parameter analyzer and an HP 4284A LCR meter dried over Na2SO4 and ltered, and the solvent was removed
in the MBRAUN nitrogen glove box under darkness.
under reduced pressure. The resulting solid was washed with
water, an aqueous sodium carbonate solution and methanol to
give (3) as a yellow solid (1.28 g, 51%). 1H NMR (600 MHz, CDCl3):
d (ppm) 7.38 (s, 2H), 7.23 (d, J ¼ 4.9 Hz, 2H), 7.14 (dd, J ¼ 6.9 Hz,
8H), 6.96 (d, J ¼ 4.9 Hz, 2H), 6.76 (d, J ¼ 8.4 Hz, 8H), 3.89 (t, J ¼ 6.5
Hz, 8H), 1.73 (m, 8H), 1.41(m, 8H), 1.35–1.20 (m, 64H), 0.87 (t, J ¼
7.0 Hz, 12H).
4.4. Fabrication and characterization of organic solar cells
Photovoltaic devices were fabricated on pre-patterned indium
tin oxide (ITO)-coated glass substrates with a layered structure
of ITO/PEDOT:PSS/donor:acceptor/Ca(10 nm)/Al(100 nm). The
ITO-coated glass substrates were cleaned in ultrasonic baths of
acetone, toluene, methanol and isopropyl alcohol sequentially.
An oxygen plasma treatment was then made for 20 min, spin-
coated with PEDOT:PSS at 5000 rpm and dried under argon for
20 min at 120 ꢀC. Subsequently, the active layer was spin-coated
from different blend weight ratios of donor (15 mg mLꢂ1) and
PCBM in deoxygenated anhydrous chloroform solution on the
ITO/PEDOT:PSS substrate. The active layer thickness was
measured by a Dektak 150 prolometer and was ꢁ100 nm.
Finally, Ca (10 nm) and aluminum (100 nm) were thermally
evaporated under a vacuum of ꢁ2 ꢃ 10ꢂ4 Pa on top of the active
layer. The photovoltaic performance was measured under illu-
mination at 100 mW cmꢂ2 AM 1.5G irradiation using a Xe arc
lamp in an argon atmosphere (<0.1 ppm H2O and O2), and the
current density–voltage (J–V) curves were obtained using
Keithley 2400. The external quantum efficiency (EQE) was
obtained by a source meter, silicon photodiode and a computer-
controlled light source-monochromator-lock-in system.
(4,4,9,9-Tetrakis(4-dodeoxyphenyl)-4,9-dihydro-s-indaceno-
[1,2-b:5,6-b0]dithiophene-2,7-diyl)-bis(trimethylstannane) (Sn-
IDT-OC12). To a solution of (3) (1.27 g, 1 mmol) in THF (25 mL)
at ꢂ78 ꢀC was added n-BuLi (1.56 mL, 2.5 mmol, 1.6 M in
hexane). The mixture was stirred at ꢂ78 ꢀC for 30 min and then
warmed to room temperature for 1 h. Aer cooling back to ꢂ78
ꢀC again, trimethyltin chloride (2.5 mL, 1 M in hexane) was
added dropwise. The mixture was stirred overnight at room
temperature. It was then poured into water and extracted with
hexane. The combined organic extracts were dried over Na2SO4,
and the solvent was removed under reduced pressure. The
residue was collected to give Sn-IDT-OC12 as a sticky yellow
solid (1.31 g, 80%). 1H NMR (600 MHz, CDCl3): d (ppm) 7.34 (s,
2H), 7.15 (d, J ¼ 8.7 Hz, 8H), 6.98 (s, 2H), 6.77 (d, J ¼ 8.9 Hz, 8H),
3.89 (t, J ¼ 6.5 Hz, 8H), 1.73 (m, 8H), 1.41 (m, 8H), 1.35–1.20 (m,
64H), 0.87 (t, J ¼ 7.0 Hz, 12H), 0.33 (s, 18H).
4-Bromo-7-(5-(5-(2-ethylhexyl)thiophen-2-yl)thiophen-2-yl)-
2,1,3-benzothiadiazole (4). 4,7-Dibromo-2,1,3-benzothiadiazole
(2.06 g, 7 mmol), 5-(tri-n-butylstannyl)-50-(2-ethylhexyl) ꢂ2,20-
bithiophene (3.97 g, 7 mmol) and Pd(PPh3)4 (405 mg, 0.35
4.5. Synthesis
Diethyl-1,4-bis(5-trimethylsilylthiophen-2-yl)-2,5-benzene- mmol) were mixed in toluene (40 mL) under nitrogen atmo-
dicarbonate (1). Diethyl-2,5-dibromoterephthalate (3.04 g, 8 sphere. The mixture was heated to 110 ꢀC for 24 h. Aer cooling
mmol), 5-(trimethylsilyl)-2-(tri-n-butylstannyl)-thiophene (8.91 to room temperature, it was poured into water and extracted
g, 20 mmol) and Pd(PPh3)4 (462 mg, 0.4 mmol) were mixed in with dichloromethane. The combined extracts were dried over
toluene (60 mL) under nitrogen atmosphere. The mixture was Na2SO4, and the solvent was removed under reduced pressure.
heated to reux for 48 h. Aer cooling to room temperature, it The residue was puried by column chromatography over silica
was poured into water and extracted with ethyl acetate. The gel, eluting with petroleum ether and dichloromethane (v/v, 1/1)
1
combined extracts were dried over Na2SO4 and ltered, and the to give (4) as an orange-red solid (1.20 g, 35%). H NMR (600
solvent was removed under reduced pressure. The residue was MHz, CDCl3): d (ppm) 8.02 (d, J ¼ 3.9 Hz, 1H), 7.85 (d, J ¼ 7.7 Hz,
puried by column chromatography over silica gel, eluting with 1H), 7.69 (d, J ¼ 7.7 Hz, 1H), 7.19 (d, J ¼ 3.9 Hz, 1H), 7.12 (d, J ¼
petroleum ether and ethyl acetate (v/v, 10/1) to give (1) as a white 3.5 Hz, 1H), 6.72 (d, J ¼ 3.5 Hz, 1H), 2.77 (d, J ¼ 6.8 Hz, 2H), 1.62
solid (1.29 g, 31%). 1H NMR (600 MHz, CDCl3): d (ppm) 7.81 (s, (m, 1H), 1.44–1.18 (m, 10H), 0.95–0.90 (m, 6H).
2H), 7.18 (d, J ¼ 3.4 Hz, 2H), 7.14 (d, J ¼ 3.4 Hz, 2H), 4,21 (q, J ¼
BTIDT-C6. 4-Bromo-7-(5-(5-(2-ethylhexyl)thiophen-2-yl)-thio-
phen-2-yl)-2,1,3-benzothiadiazole (4) (283 mg, 0.58 mmol), Sn-
7.1 Hz, 4H) 1.13 (t, J ¼ 7.1 Hz, 6H), 0.34 (s, 18H).
4,9-Dihydro-4,4,9,9-(p-dodeoxyphenyl)-s-indaceno[1,2-b:5,6-b]- IDT-C6 (308 mg, 0.25 mmol) and Pd(PPh3)4 (13 mg, 0.011 mmol)
dithiophene (3). To a solution of 4-dodeoxy-1-bromobenene (6.14 were mixed in toluene (15 mꢀL) under nitrogen atmosphere. The
ꢀ
g, 18 mmol) in THF (10 mL) at ꢂ78 C was added n-BuLi (11.25 mixture was heated to 110 C for 48 h. Aer cooling to room
mL, 18 mmol, 1.6 M in hexane), the mixture was kept at ꢂ78 ꢀC temperature, it was poured into water and extracted with
for 1 h, and a solution of compound (1) (1.06 g, 2 mmol) in THF (5 dichloromethane. The combined extracts were dried over
7528 | J. Mater. Chem. C, 2014, 2, 7523–7530
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Journal of Materials Chemistry C
Na2SO4, and the solvent was removed under reduced pressure.
The residue was puried by column chromatography on silica,
eluting with petroleum ether and dichloromethane (v/v, 3/1) to
give BTIDT-C6 as a purple powder (226 mg, 52%). 1H NMR (600
MHz, CDCl3): d (ppm) 8.04 (s, 2H), 8.01 (d, J ¼ 3.8 Hz, 2H), 7.81
(m, 4H), 7.54 (s, 2H), 7.27 (d, J ¼ 8.3 Hz, 8H), 7.18 (d, J ¼ 3.8 Hz,
2H), 7.12–7.09 (m, 10H), 6.70 (d, J ¼ 3.5 Hz, 2H), 2.75 (d, J ¼ 6.7
Hz, 4H), 2.57 (t, 8H), 1.62–1.56 (m, 10H), 1.35–1.27 (m, 42H),
0.94–0.84 (m, 24H). 13C NMR (151 MHz, CDCl3): d (ppm) 156.78,
153.77, 152.49, 152.36, 144.65, 143.33, 142.12, 141.81, 141.58,
5 A. Arias, J. MacKenzie, I. McCulloch, J. Rivany and A. Salleo,
Chem. Rev., 2010, 110, 3–24.
6 R. Po, M. Maggini and N. Camaioni, J. Phys. Chem. C, 2010,
114, 695–706.
7 Z. He, C. Zhong, S. Su, M. Xu, H. Wu and Y. Cao, Nat.
Photonics, 2012, 6, 591–595.
8 Y. Chen, Y. Yan, Z. Du, X. Bao, Q. Liu, V. Roy, M. Sun, R. Yang
and C. Lee, J. Mater. Chem. C., 2014, 2, 3921–3927.
9 Y. Chen, Y. Yan, Z. Du, W. Chen, S. Wen, L. Sun, Q. Liu,
M. Sun and R. Yang, New J. Chem., 2014, 38, 1559–1564.
139.36, 137.46, 135.53, 134.87, 128.43, 128.19, 127.98, 126.28, 10 Y. Chen, Y. Yan, Z. Du, W. Chen, Q. Liu, L. Sun, M. Sun and
126.06, 125.28, 125.08, 124.71, 123.80, 123.69, 123.16, 63.15, R. Yang, Org. Electron., 2014, 15, 405–413.
41.45, 35.61, 34.21, 32.39, 31.73, 31.36, 29.17, 28.90, 25.54, 11 Y. Chen, Y. Yan, Z. Du, W. Chen, L. Han, Q. Liu, M. Sun and
23.01, 22.60, 14.15, 14.10, 10.86. MS (MALDI-TOF): calcd for
C
R. Yang, Synth. Met., 2014, 187, 24–29.
12 Q. Liu, Z. Du, W. Chen, L. Sun, Y. Chen, M. Sun and R. Yang,
Synth. Met., 2013, 178, 38–43.
108H118N4S8 [M]+, 1728.7226; found: 1728.7135.
BTIDT-OC12. 4-Bromo-7-(5-(5-(2-ethylhexyl)-thiophen-2-yl)-
thiophen-2-yl)-2,1,3-benzothiadiazole (4) (185 mg, 0.38 mmol), 13 T. Wang, Y. Chen, X. Bao, Z. Du, Y. Yang, N. Wang, M. Sun
Sn-IDT-C12 (294 mg, 0.16 mmol) and Pd(PPh3)4 (9 mg, 0.008 and R. Yang, Dyes Pigm., 2013, 98, 11–16.
mmol) were mixed in toluene (15 mL) under nitrogen atmo- 14 G. He, Z. Li, X. Wan, Y. Liu, J. Zhou, G. Long, M. Zhang and
sphere. The other procedures are just as BTIDT-OC6 molecule Y. Chen, J. Mater. Chem., 2012, 22, 9173–9180.
to give BTIDT-OC12 as a purple block solid (208 mg, 61%). H 15 J. Zhou, Y. Zuo, X. Wan, G. Long, Q. Zhang, W. Ni, Y. Liu,
1
NMR (600 MHz, CDCl3): d (ppm) 8.04 (s, 2H), 8.02 (d, J ¼ 3.8 Hz,
Z. Li, G. He, C. Li, B. Kan, M. Li and Y. Chen, J. Am. Chem.
Soc., 2013, 135, 8484–8487.
2H), 7.81 (m, 4H), 7.50 (s, 2H), 7.28 (d, J ¼ 8.9 Hz, 8H), 7.18 (d, J
¼ 3.8 Hz, 2H), 7.10 (d, J ¼ 3.4 Hz, 2H), 6.82 (d, J ¼ 8.9 Hz, 8H), 16 Z. Li, G. He, X. Wan, Y. Liu, J. Zhou, G. Long, Y. Zuo,
6.70 (d, J ¼ 3.4 Hz, 2H), 3.91 (t, 8H), 2.75 (d, J ¼ 6.7 Hz, 4H),
1.77–1.71 (m, 10H), 1.35–1.20 (m, 90H), 0.94–0.84 (m, 24H). 13
NMR (151 MHz, CDCl3): d (ppm) 158.13, 157.18, 154.12, 152.51,
M. Zhang and Y. Chen, Adv. Energy Mater., 2012, 2, 74–77.
17 Y. Liu, X. Wan, J. Zhou, G. Long, J. Tian and Y. Chen, Adv.
Mater., 2011, 23, 5387–5391.
C
¨
152.36, 144.65, 143.00, 142.27, 139.38, 137.47, 136.44, 134.87, 18 A. Mishra and P. Bauerle, Angew. Chem., Int. Ed., 2012, 51,
129.12, 128.21, 126.26, 126.06, 125.32, 125.08, 124.72, 123.80, 2020–2067.
123.70, 123.05, 117.53, 114.32, 67.96, 62.40, 50.91, 41.45, 34.21, 19 J. Zhou, X. Wan, Y. Liu, Y. Zuo, Z. Li, G. He, G. Long, W. Ni,
32.40, 31.91, 29.65, 29.62, 29.60, 29.58, 29.41, 29.34, 28.90,
26.09, 25.54, 23.01, 22.68, 14.15, 14.12, 10.86. MS (MALDI-TOF):
calcd for C108H118N4S8 [M]+, 2129.0779; found: 2129.0717.
C. Li, X. Su and Y. Chen, J. Am. Chem. Soc., 2012, 134, 16345–
16351.
20 T. van der Poll, J. Love, N. Thuc-Quyen and G. C. Bazan, Adv.
Mater., 2012, 24, 3646–3649.
21 Y. Sun, G. Welch, W. Leong, C. Takacs, G. C. Bazan and
A. J. Heeger, Nat. Mater., 2011, 11, 44–48.
Acknowledgements
22 A. Kyaw, D. Wang, V. Gupta, J. Zhang, S. Chand, G. C. Bazan
and A. J. Heeger, Adv. Mater., 2013, 25, 2397–2402.
23 M. Zhang, X. Guo, X. Wang, H. Wang and Y. Li, Chem. Mater.,
2011, 23, 4264–4270.
24 Y. Chen, C. Yu, Y. Fan, L. Hung, C. Chen and C. Ting, Chem.
Commun., 2010, 46, 6503–6505.
25 Y. Zhang, J. Zou, H. Yip, K. Chen, D. Zeigler, Y. Sun and
A. Jen, Chem. Mater., 2011, 23, 2289–2291.
26 C. Chen, Y. Chen and C. Yu, Polym. Chem., 2013, 4, 1161–
1166.
27 R. Ashraf, B. Schroeder, H. Bronstein, Z. Huang, S. Thomas,
R. Kline, C. Brabec, P. Rannou, T. Anthopoulos, J. Durrant
and I. McCulloch, Adv. Mater., 2013, 25, 2029–2034.
28 W. Zhang, J. Smith, S. Watkins, R. Gysel, M. McGehee,
A. Salleo, J. Kirkpatrick, S. Ashraf, T. Anthopoulos,
M. Heeney and I. McCulloch, J. Am. Chem. Soc., 2010, 132,
11437–11439.
The authors are deeply grateful to the National Natural
Science Foundation of China (Project no. 21274134,
51173199, 21172187, 51211140346), the New Century Excel-
lent Talents in University (NCET-11-0473), the Shandong
Provincial Natural Science Foundation (ZR2011BZ007), the
Hong Kong Scholar Program and Postdoctoral Science
Foundation
of
China
(XJ2012042,
2012T50630,
2013M530329), the Shenzhen Municipal Science and Tech-
nology Program (JCYJ20130401145617279) and the Qingdao
Municipal Science and Technology Program (13-1-4-200-jch,
11-2-4-22-hz) for nancial support.
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