Benzo[d][1,2,3]thiadiazole (isoBT): Synthesis, Structural Analysis, and Implementation in Semiconducting Polymers

Article abstract of DOI:10.1021/acs.chemmater.6b02813

Benzo[d][2,1,3]thiadiazole (BT) is a markedly electron-deficient heterocycle widely employed in the realization of organic semiconductors for applications spanning transistors, solar cells, photodetectors, and thermoelectrics. In this contribution, we imp

Full text of DOI:10.1021/acs.chemmater.6b02813

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Article
Benzo[d][1,2,3]thiadiazole (isoBT). Synthesis, Structural
Analysis, and Implementation in New Semiconducting Polymers
Zhihua Chen, Jennifer Brown, Martin Drees, Mark Seger, Yan Hu, Yu Xia, Damien Boudinet, Meko McCray,
Massimiliano Delferro, Tobin J. Marks, Chuang-Yi Liao, Chung-Wen Ko, Yi-Ming Chang, and Antonio Facchetti
Chem. Mater., Just Accepted Manuscript • DOI: 10.1021/acs.chemmater.6b02813 • Publication Date (Web): 12 Aug 2016
Downloaded from http://pubs.acs.org on August 14, 2016
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Chemistry of Materials
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Benzo[d][1,2,3]thiadiazole (isoBT). Synthesis, Structural Analysis,
and Implementation in New Semiconducting Polymers
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†
†
†
†
†
†
Zhihua Chen* , Jennifer Brown , Martin Drees , Mark Seger , Yan Hu , Yu Xia , Damien Bou-
†
†
§
‡
∥
dinet , Meko McCray , Massimiliano Delferro , Tobin J. Marks , Chuang-Yi Liao , Chung-Wen
Ko , Yi-Ming Chang , Antonio Facchetti
*,†,
∥
∥
∥
†
Polyera Corporation, 8045 Lamon Avenue, Skokie, Illinois 60077, USA
‡
Department of Chemistry and the Materials Research Center, Northwestern University, 2145 Sheridan Road, Ev-
anston, Illinois 60208, USA
§
Argonne National Laboratory, Cass Avenue, Darien IL
∥
Raynergy Tek Incorporation, 2F, No. 60, Park Ave. 2, Hsinchu Science Park, Hsinchu, Taiwan 30075
Supporting Information Placeholder
ABSTRACT: Benzo[d][2,1,3]thiadiazole (BT) is a markedly electron-deficient heterocycle widely employed in the
realization of organic semiconductors for applications spanning transistors, solar cells, photodetectors, and thermo-
electrics. In this contribution we implement the corresponding isomer, benzo[d][1,2,3]thiadiazole (isoBT), along
with new 6-fluoro-isoBT and 5,6-difluoro-isoBT units as synthons for constructing alternating co-polymers with
tetrathiophene (P1-P3). New isoBT-based small molecules as well as the corresponding BT-quaterthiophene based
polymers (P4-P6) are synthesized and characterized to probe architectural, electronic structural, and device per-
formance differences between the two families. The results demonstrate that isoBT complements BT in enabling
2
high-performance opto-electronic semiconductors with P3 exhibiting hole mobilities surpassing 0.7 cm /Vs in field-
effect transistors and power conversion efficiencies of 9% in bulk-heterojunction solar cells.
INTRODUCTION
π
-Conjugated molecules and polymers comprising
electron-accepting (A) and electron-donating (D)
units in the core or main chain are among the most
performing semiconductor families spanning applica-
tions from electronic circuits and sensors based on or-
1
-11
ganic thin-film transistors (OTFTs),
cells such as the bulk-heterojunction (BHJ-OSC)
photovoltaic
12-26
2
7-32
and dye-sensitized (DSSC) devices,
photodetec-
Among the electron
accepting functionalities, benzo[d][2,1,3]thiadiazole
BT) and its halogenated derivatives, have realized sev-
eral D-A polymers with remarkable performance (Fig-
Figure 1. Chemical structure of representative BT-based
small molecules and polymers used in organic electronics.
3
3-37
38-40
tors,
and thermoelectrics.
(
The commercial availability of BT, synthetic access to
the halogenated precursors, and facile bromination at
the 4,7 BT positions have greatly facilitated the
availability of this core. Furthermore, the electron-poor
41-53
ure 1). For instance, BT-based small-molecules and
polymers have shown maximum OTFT hole mobilities
2
41,51
of 0.20 and 1.92 cm /Vs, respectively, as well as BHJ-
OSC and DSSC with power conversion efficiencies as
nature
of
BT,
further
tunable
via
substitution/halogenation at the 5,6 positions, has
4
2,53
large as 11.7 and 7.1 %, respectively.
with detectivity of ~10 Jones
Photodetectors
and thermoelectric
devices with a Seebeck coefficient (Z) of 230 V/K have
been instrumental in controlling the frontier molecular
17,58-59
orbitals (FMOs) of the resulting systems. Finally,
the low steric demands at the BT 4,7 para-positions
promotes structural planarization and enhances
12
54-55
ꢀ
5
6-57
also been demonstrated.
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Page 2 of 15
intramolecular charge transfer and the extent of
π
-
Synthesis of Polymer P1
17
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6
conjugation in BT-based (macro)molecules. Recent
important studies have also addressed why BT (or
F BT, see Figure 2), and its mono- and di-fluoro (F BT
Synthesis of Compound 2:
Compound benzo[1,2,3]thiadiazole (1, 193 mg, 1.4 mmol)
was dissolved in concentrated sulfuric acid (95-98%, 20
mL) and N-bromosuccinimide (NBS) (556 mg, 3.1 mmol)
was then added in one portion. The resulting solution was
0
1
and F BT) based polymers are highly crystalline and
2
the origin of the intermolecular interactions that
2,44,60-65
promote film texturing.
4
o
heated to 50 C and maintained at this temperature over-
-
2
night. Upon cooling to rt, the reaction mixture was
poured onto ice water (about 100 mL). This mixture was
extracted with chloroform (100 mL), and the organic layer
was washed with additional water (3 x 100 mL), dried over
anhydrous magnesium sulfate, and concentrated in vacuo,
N
N
N
N
3
1
7
S
2DT
N
S
N
S
S
S
0
1
2
3
4
5
6
7
8
9
0
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0
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8
9
0
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5
6
7
8
9
0
S
4
S
S
S
5
6
(F)x
(F)x
(F)x
n
2DT
FxisoBT
FxisoBT-T2
P1 (x= 0); P2 (x=1 ); P3 (x= 2)
(
F at 6 position)
2
leading to a beige solid as the product (2, 370 mg, 89.8%).
S
N
S
S
3
N
N 1
N
N
2DT
1
N
H NMR (CDCl , 400 MHz): 7.69-7.71 (d, J = 8.0 Hz, 1H),
3
S
S
S
4
7
6
7.65-7.67 (d, J = 8.0 Hz, 1H). Elemental Analysis: (Calcd: C:
24.52, H: 0.69, N: 9.53); Found: C: 23.47, H: 0.75, N: 8.55
S
S
S
5
n
(F)x
(F)x
(F)x
2DT
FxBT
FxBT-T2
P4 (x= 0); P5 (x= 1); P6 (x= 2)
Synthesis of Compound 3:
Figure 2. Chemical structures of BT and isoBT units and
polymers investigated in this study.
Under Ar, compound 3S (1.61 g, 1.6 mmol) was mixed with
anhydrous tetrahydrofuran (THF) (70 mL), and the
resulting solution was cooled by an isopropyl alcohol
The BT isomer, benzo[1,2,3]thiadiazole (isoBT), is a
known heterocycle which finds applications in several
(
IPA)/dry ice batch. A solution of n-BuLi (2.5 M in hexane,
1
.3 mL, 3.3 mmol) was then added slowly over a course of
6
6-69
fields of chemical science.
abovementioned properties of BT combined with the
greater steric demands of vs. at the
All of the
about 5 mins. The reaction mixture was allowed to be
stirred at this temperature for 1 h, before the cooling bath
was removed and the reaction was allowed to warm to rt.
After stirring for 1.5 h, the reaction mixture was cooled by
S
N
benzothiadiazole 1 position rise interesting questions
of whether isoBT is a suitable building block for
organic electronics, whether halogen-functionalized
derivatives can be synthesized and integrated into
semiconducting materials, the nature of the electronic
structure, molecular structure, physico-chemical
properties, and device performance differences in BT-
versus isoBT-based molecules and the corresponding
IPA/dry ice bath again. A solution of Me SnCl solution (1
3
M, 3.5 mL, 3.5 mmol) was then added in one portion. The
reaction was stirred at this temperature for additional 30
mins, before the cooling bath was removed and the
reaction was stirred at rt overnight. Most of the solvent
was removed in vacuo, and the residue was treated with
pentane (about 15 mL). This solution was filtered through
a 0.45 ꢀm PTFE syringe filter, and the filtrate was
concentrated in vacuo, dried in vacuum, leading to a
slightly orange oil, which solidified after cooling at
(
macro)molecules.
Here we report the synthesis of the new 5-fluoro-
benzo[1,2,3]thiadiazole (F isoBT) and 5,6-difluoro-
1
1
refrigerator (1.86 g, 87.3%). H NMR (CD Cl , 400 MHz):
2
2
benzo[1,2,3]thiadiazole (F isoBT) structures and their
2
7.12 (d, J = 3.6 Hz, 2H), 7.01 (d, J = 3.6 Hz, 2H), 6.99 (s, 2H),
2.74 (d, J = 7.2 Hz, 4H), 1.72 (s, br, 2H), 1.16-1.34 (m, br,
80H), 0.84-0.91 (m, br, 12H), 0.38 (s, 18H).
use, in conjunction with isoBT (or F isoBT), in
0
synthesizing the alternating quaterthiophene-based
co-polymers P1-P3 (Figure 2). Structural analysis is
carried out for isoBT molecules, rapresentative iso-BT
Synthesis of Polymer P1:
building blocks [F isoBT-T2], and polymers, as well as
x
Compounds 2 (34.3 mg, 0.12 mmol) and tin reagent 3
(155.6 mg, 0.12 mmol) were added to a Schlenk flask with
tris(dibenzylideneacetone) dipalladium(0) (Pd dba ) (2.2
the corresponding BT molecular [FxBT-T2] and
polymeric systems (P4-P6), using single crystal and
thin-film XRD techniques, respectively. Finally, all
polymers are incorporated into OTFT and BHJ-OSC
devices and the device performance compared and
contrasted.
2
3
mg, 0.0024 mmol) and tri(o-tolyl)phosphine (tol P) (5.7
3
mg, 0.018 mmol). The flask was subject to vacuum and
then backfilled with Ar, and this cycle was repeated four
times. Under Ar, anhydrous toluene (15 mL) was added,
o
and the resulting mixture was heated to 90 C and main-
EXPERIMENTAL SECTION
tained at this temperature for about 20 h. Bromobenzene
(0.5 mL) was added to the reaction mixture and it was
Synthesis
o
Materials and general characterization methods, synthesis
maintained at 90 C for an additional 4 h. Upon cooling to
of F -isoBT-T2, and synthesis of polymer P4-P6 and their
rt, the reaction mixture was precipitated in methanol
(about 200 mL), and the precipitate was collected by filtra-
tion and washed with methanol. This crude product was
x
corresponding monomers are reported in the Supporting
Information (SI).
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Chemistry of Materials
J = 6.4 Hz, 4H), 1.69 (m, br, 2H), 1.25 (m, br, 80H), 0.88 (t,
then subject to Soxhlet extraction with methanol (21 h),
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5
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9
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5
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5
5
5
5
5
5
5
6
ethyl acetate (20 h), and finally extracted with chloroform.
Upon cooling to rt, the chloroform extract was concentrat-
ed to about 5 mL, which was precipitated in methanol
J = 6.8 Hz, 12H).
Synthesis of Compound 9:
(
about 100 mL). The precipitate was collected by filtration,
Compound 8 (400 mg, 0.40 mmol) was dissolved in a mix-
ture of THF (10 mL) and acetic acid (1 mL) under nitrogen
at rt. NBS (160 mg, 0.89 mmol) was added in one portion.
The resulting mixture was stirred overnight and the prod-
uct was precipitated with methanol/water (1:1, 20 mL). The
precipitate was washed with methanol and this crude
product was recrystallized from ethyl acetate (about 5 mL)
washed with methanol, and dried in vacuum, leading to a
dark red/brown solid as the polymer product P1 (87.8 mg,
1
o
6
6.3%). H NMR (400 MHz, CDCl CDCl , 100 C): 8.13 (m,
2 2
br, 1H), 7.90-7.97 (m, br, 2H), 7.39 (s, br, 1H), 7.22-7.40 (m,
br, 4H), 2.91 (m, br, 4H), 1.91 (m, br, 2H), 1.28-1.51 (m, br,
0
1
2
3
4
5
6
7
8
9
0
1
2
3
4
5
6
7
8
9
0
1
2
3
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5
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7
8
9
0
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5
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7
8
9
0
1
2
3
4
5
6
7
8
9
0
80H), 0.93 (m, br, 12H). GPC: Mn = 14.1K, PDI = 1.9. Ele-
mental Analysis: (Calcd: C: 74.02, H: 9.41, N: 2.47); Found:
C: 74.01, H: 9.01, N: 2.51.
in the fridge, yielding a yellow solid as the product (430 mg,
1
86%). H NMR (400 MHz, CDCl ): 7.82 (1H, s), 7.63 (d, J =
3
1
2 Hz, 1H), 7.25 (d, J = 8 Hz, 1H), 2.57 (d, J = 8.8 Hz. 4H),
Synthesis of Polymer P2
1.74 (m, br, 2H), 1.24-1.40 (m, br, 80H), 0.87 (t, J = 6.8 Hz.
12H). Elemental Analysis: (Calcd: C: 64.78, H: 8.86, N:
2.44); Found: C: 64.35, H: 9.04, N: 2.48.
Synthesis of Compound 5:
To a mixture of compound 4 (875 mg, 5.98 mmol) in water
(6 mL) was added 12M HCl (1.5 mL) slowly at rt. Sodium
nitrite (620 mg, 8.98 mmol) was then added slowly at rt.
THF (3 mL) was added to aid solubility and the reaction
was stirred at rt overnight. To the above solution was add-
ed potassium carbonate aqueous solution (10%, ~7 mL)
until the pH was ~9. The material was extracted with di-
chloromethane (DCM) and washed with water. The organ-
ic layer was dried over anhydrous Na SO , filtered, and
Synthesis of Polymer P2:
Compound
9
(100.0 mg, 0.079 mmol), 5,5'-
bis(trimethylstannyl)-2,2'-bithiophene (10) (39.4 mg,
0.079 mmol), Pd dba (3.0 mg, 0.003 mmol), tol P (3.1 mg,
2
3
3
0.01 mmol) were placed in a Schlenk flask. The system was
vacuumed and backfilled with argon four times, before
anhydrous chlorobenzene (10 mL) was added via syringe.
The resulting mixture was warmed and stirred at 90 °C for
18 h. The reaction was cooled to rt and precipitated in
methanol (50 mL). The crude product was collected by
filtration, washed with methanol, and subject to Soxhlet
extraction under nitrogen with methanol (16 h), ethyl ace-
tate (16 h), and hexanes (16 h). The polymer product was
extracted into chlorobenzene (100 mL), and the extract
was precipitated in methanol (100 mL). The precipitate
was collected by filtration, washed with methanol, and
dried under vacuum to afford a brown solid as the final
2
4
1
concentrated to a tan powder (720 mg, 78%). H NMR,
(400 MHz, CDCl ): 7.41 (m, br, 1H), 7.78 (dd, J = 7.6 Hz, J =
3
1
9
2.4 Hz, 1H), 8.61 (dd, J = 9.2 Hz, J = 4.4 Hz, 1H). F NMR
(CDCl ): -109.2 (m, 1F).
3
Synthesis of Compound 6:
Compound 5 (600 mg, 3.9 mmol) was dissolved in oleum
(60 mL). NBS (1.5 g, 8.6 mmol) was added in one portion
o
and the reaction mixture was heated to 60 C overnight.
1
The solution was then cooled to rt and poured over 500
mL ice water. The product was extracted with DCM and
washed with H O until the H O layer was neutral. The
product P2 (75.3 mg, 82.7%). H NMR (400 MHz,
o
CDCl CDCl , 100 C): 8.12 (s, br, 1H), 7.76-7.79 (m, br, 1H),
2
2
7.52 (s, br, 1H), 7.23-7.32 (m, br, 4H), 2.92 (m, br, 4H), 1.91
(m, br, 2H), 1.28-1.52 (m, br, 80H), 0.94 (m, br, 12H). GPC:
Mn = 25.7 K, PDI = 1.4. Elemental Analysis: (Calcd: C:
73.04, H: 9.45, N: 2.37); Found: C: 72.40, H: 9.48, N: 2.43.
2
2
organic layer was dried over Na SO , filtered, and concen-
2
4
trated to yield a tan powder as the compound 3 (950 mg,
80%), which was directly used for next step without fur-
1
ther purification. H NMR, (400 MHz, CDCl ): 7.67 (d, J =
3
8Hz, 1H). Elemental Analysis: (Calcd: C: 23.10, H: 0.32, N:
8.98); Found: C: 22.79, H: 0.34, N: 8.59
Synthesis of Polymer P3
Synthesis of Compound 8:
Synthesis of Compound 12:
Compound 6 (600 mg, 1.92 mmol), 4-(2-decyltetradecyl)-
2-trimethylstannyl thiophene (7) (2.47 g, 4.23 mmol),
Pd dba (70 mg, 0.08 mmol), and tri(2-furyl)phosphine
A solution of 2,4,5-trifluoroaniline (11) (25 g, 170 mmol) in
anhydrous pyridine (14.4 mL, 178 mmol) was treated with
acetic anhydride (16.9 mL, 178 mmol) and heated to 120 °C
for 2 hours. After cooling to room temperature, the solu-
tion was poured into ice-cold water (150 mL). The result-
ing precipitate was filtered, dissolved in ethyl acetate,
dried over anhydrous Na SO , filtered, and concentrated.
The residue was dried to give 2,4,5-trifluoroacetanilide
(12) (29.63 g, 92%) as a yellow solid. H NMR (CDCl3,
400MHz): 8.35-8.26 (m, 1H), 7.24 (s, br, 1H), 7.01-6.93 (m,
1 H), 2.22 (s, 3H); F NMR (CDCl3): -133.5 (m, 1F), -139.6 –
2
3
(70 mg, 0.31 mmol) were added to an air free flask which
was then purged and backfilled 4 cycles with vacuum/Ar.
Under Ar, anhydrous THF (50 mL) was added via syringe
o
and the solution was stirred at 80 C for 16 h. Upon cooling
2
4
to rt, the reaction mixture was concentrated in vacuo. The
residue was purified by column chromatography on silica
gel (hexanes), yielding a yellow solid as compound 8 (650
1
1
19
mg, 34%). H NMR (400 MHz, C D Cl ): 7.99 (s, 1H), 7.73
2
2
4
(
d, J = 12 Hz), 7.43 (s, 1H), 7.16 (d, J = 11.6 Hz, 2H), 2.64 (d,
-139.7 (m, 1F), -140.1 – -140.3 (m, 1F).
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Page 4 of 15
1
concentrated to give the product (16) (6.59 g, 82%). H
1
2
3
4
5
6
7
8
9
1
1
1
1
1
1
1
1
1
1
2
2
2
2
2
2
2
2
2
2
3
3
3
3
3
3
3
3
3
3
4
4
4
4
4
4
4
4
4
4
5
5
5
5
5
5
5
5
5
5
6
Synthesis of Compound 13:
A dried 3-neck, 1L round-bottom flask was charged with
phosphorus pentasulfide (P S ) (34.08 g, 153 mmol) and
NMR (CDCl , 400 MHz): 8.40 (dd, J = 6.92 Hz, J = 9.12 Hz,
3
1
9
1H), 7.88 (dd, J = 7.16 Hz, J = 8.08 Hz, 1H). F NMR
(CDCl ): -129.6 – -129.7 (m, 1F), -134.1 – -134.2 (m, 1F).
2
5
3
diluted with anhydrous toluene (500 mL). Compound
,4,5-trifluoroacetanilide (12) (29 g, 153 mmol) was added
2
Synthesis of Compound 17:
in one portion and the bright yellow suspension was
heated to 90 °C for 15 hours. After cooling to room tem-
perature, the reaction was washed with aqueous NaOH
Compound 16 (550 mg, 3.2 mmol) was dissolved in oleum
(40 mL). NBS (1.2 g, 7.0 mmol) was added in one portion
o
and the reaction mixture was heated to 50 C overnight.
(
15%, 250 mL). The aqueous phase was extracted with
The solution was then cooled to rt and poured over ice
water (200 mL). Precipitation observed and suspension
was filtered. The brown precipitate was then dissolved in
DCM and flushed through a short pad of silica gel. The
solvent was evaporated and the product was dried to a
light tan powder as the product (17) (0.38 g, 36%), which
0
1
2
3
4
5
6
7
8
9
0
1
2
3
4
5
6
7
8
9
0
1
2
3
4
5
6
7
8
9
0
1
2
3
4
5
6
7
8
9
0
1
2
3
4
5
6
7
8
9
0
ethyl acetate (200 mL). The organic phases were com-
bined, dried over anhydrous Na SO , filtered, and concen-
2
4
trated. The crude product was passed through a silica gel
column prepared with chloroform and concentrated to
give 2,4,5-trifluorothioacetanilide (13) (23.23 g, 74%) as a
1
yellow solid. H NMR (CDCl3, 400 MHz): 8.69-8.62 (m,
was directly used for next step without further purifica-
1
9
19
1H), 8.47 (s, 1H), 7.08-7.01 (m, 1H), 2.76 (s, 3H). F NMR
(CDCl3): -128.5 (m, 1F), -134.3 – -134.5 (m, 1F), -139.4 – -
139.5 (m, 1F).
tions. F NMR (CDCl ): -120.7 (d, J = 17.6 Hz, 1F), -124.1 (d,
3
J = 21.5 Hz, 1F).
Synthesis of Compound 18:
Compound 17 (370 mg, 1.12 mmol), tin reagent 7 (1.43 mg,
Synthesis of Compound 14:
A flame-dried, 1 L round-bottom flask with a condenser
was charged with sodium hydride (5.15 g, 129 mmol, 60%
by wt) and diluted with anhydrous toluene (500 mL). The
suspension was treated with 2,4,5-trifluorothioacetanilide
(13) (22 g, 107 mmol) in one portion and stirred at room
temperature for 2 hours. Dimethylformamide (100 mL)
was added and the reaction was refluxed at 110 °C for 3
hours. The solution was cooled to room temperature and
washed with brine (500 mL). The aqueous phase was ex-
tracted with ethyl acetate (300 mL). The organic phases
were combined, dried over anhydrous Na SO , filtered,
and concentrated. The crude product was passed through
a silica gel column prepared with chloroform and concen-
trated to give 5,6-difluoro-2-methylbenzothiazole (14)
(16.54 g, 83%) as a yellow solid. H NMR (400 MHz,
CDCl3): 7.73 (dd, J = 7.08 Hz, J = 10.48 Hz, 1H), 7.59 (dd, J
2.45 mmol), Pd dba3 (41 mg, 0.04 mmol), and tri(2-
2
furyl)phosphine (41 mg, 0.18 mmol) were added to an air
free flask which was then purged and backfilled with vac-
uum/Ar 4 times. Under Ar, anhydrous THF (40 mL) was
o
added via syringe and the solution was stirred at 85 C for
16 h. Upon cooling to rt, the reaction mixture was flushed
through a pad of silica gel with the aid of DCM and then
concentrated in vacuo. The concentrated solid was then
recrystallized in 10 mL heptane in the freezer, leading to a
1
yellow solid as the product (18) (407.6 mg, 36%). H NMR
(CD Cl , 400 MHz): 8.15 (s, 1H), 7.48 (d, J = 6 Hz, 1H), 7.28
2
4
2
2
(s, 1H), 7.20 (s, 1H), 2.67 (dd, J = 10.4 Hz, J = 6.8 Hz, 2H),
1.71 (m, br, 2H), 1.32 (m, br, 2H), 1.26 (m, br, 80H), 0.87 (t,
1
9
J = 6.0 Hz, 12H). F NMR (CD Cl ): -131.9 (d, J = 17.3 Hz,
2
2
1
1F), -134.3 (d, J = 17.3 Hz, 1F).
1
9
= 7.52 Hz, J = 8.96 Hz, 1H), 2.83 (s, 3H). F NMR (CDCl3):
-138.4 – -138.5 (m, 1F), -139.4 – -139.5 (m, 1F).
Synthesis of Compound 19:
Compound 18 (400 mg, 0.40 mmol) was dissolved in a
mixture of THF (10 mL) and acetic acid (1 mL) at rt. NBS
(155 mg, 0.87 mmol) was added in one portion. The re-
sulting mixture was stirred overnight and the product was
extracted with DCM and washed with water. The organic
layer was dried over anhydrous Na SO , filtered and con-
Synthesis of Compound 16:
A solution of 5, 6-difluoro-2-methylbenzothiazole (14) (10
g, 54 mmol) and hydrazine monohydrate (40 mL, 820
mmol) was stirred for 2 days at 115 °C. The reaction was
cooled to room temperature, neutralized to pH = ~7 with
concentrated HCl solution, and extracted with dichloro-
methane (4 x 250 mL). The organic phases were com-
bined, dried over anhydrous Na SO , and concentrated.
The yellow oil crystallized overnight to give 4,5-difluoro-
2-aminothiophenol (15) (7.52 g), which was mixed with
water (100 mL). A solution of 12M HCl (26 mL) was added
slowly at room temperature, followed by addition of sodi-
um nitrite (4.82 g, 70 mmol). THF (50 mL) was added to
facilitate the dissolution of solids and the reaction was
stirred at room temperature overnight. The reaction mix-
2
4
centrated. The residue was then subjected to a short silica
gel column with hexane as eluent to yield a yellow solid as
1
the product (19) (0.32 g, 70%). H NMR (CD Cl , 400
2
2
MHz): 8.03 (s, 1H,). 7.33 (s, 1H), 2.62 (dd, J = 8.8 Hz, J = 7.2
2
4
1
9
F
Hz, 4H), 1.26 (m, br, 82H), 0.87 (t, J = 6.0 Hz, 12H).
NMR (CD Cl ): -131.4 (d, J = 16.9 Hz, 1F), -133.9 (d, J = 9.4
2
2
Hz, 1F). Elemental Analysis: (Calcd: C: 63.79, H: 8.63, N:
2.40); Found: C: 63.74, H: 8.64, N: 2.40.
Synthesis of Polymer P3:
Compound 19 (150 mg, 0.13 mmol), compound 10 (63.2
mg, 0.13 mmol), Pd dba (4.6 mg, 0.005 mmol), tol P (6.2
ture was neutralized with saturated aqueous K CO (200
mL) and extracted with DCM (2 x 300 mL). The organic
phases were combined, dried over anhydrous Na SO , and
2
3
2
3
3
mg, 0.02 mmol) were placed in a Schlenk flask. The sys-
2
4
4
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Chemistry of Materials
poration) was spin-coated and photopatterned to define
tem was vacuumed and backfilled with argon four times,
1
2
3
4
5
6
7
8
9
1
1
1
1
1
1
1
1
1
1
2
2
2
2
2
2
2
2
2
2
3
3
3
3
3
3
3
3
3
3
4
4
4
4
4
4
4
4
4
4
5
5
5
5
5
5
5
5
5
5
6
before anhydrous chlorobenzene (12 mL) was added via
syringe. The resulting mixture was warmed and stirred at
the patterned semiconductor island between source and
drain followed by a second D2200 layer. The resulting gate
dielectric capacitance was 3.5-4.2 nF/cm . Finally, the de-
vice was completed by sputtering/photolithography of a
500 Å Ag gate electrode. All TFTs were tested in the dark
in a probe station (Signatone) in ambient environment
using Keithley 4200 two source electrometer.
2
90 °C for 18 h. The reaction was cooled to rt and precipi-
tated in methanol (100 mL). The crude product was col-
lected by filtration, washed with methanol, and subject to
Soxhlet extraction under nitrogen with methanol (10 h),
ethyl acetate (13 h), and hexanes (9 h). Finally, the poly-
mer product was extracted into chloroform (120 mL), and
the extract was precipitated in methanol (200 mL). The
precipitate was collected by filtration, washed with meth-
anol, and dried under vacuum to afford a dark-blue solid
Gravure Printed Top-gate Bottom Contact TFTs: For gra-
vure printing, the P3 formulation (10 mg/mL in a mixture
of 1,2,3,4-tetrahydronaphthalene-based solution) was
printed on PEN substrates with Ag source-drain electrodes
(W/L = 1000/60 um) using a Norbert Schlafli Labratester
gravure printer, at the speed of around 5 m/min and the
impact factor of 5. After printing, the substrate was trans-
0
1
2
3
4
5
6
7
8
9
0
1
2
3
4
5
6
7
8
9
0
1
2
3
4
5
6
7
8
9
0
1
2
3
4
5
6
7
8
9
0
1
2
3
4
5
6
7
8
9
0
1
as the final product P3 (135 mg, 88.5%). H NMR (400
o
MHz, CDCl CDCl , 100 C): 8.26 (s, br, 1H), 7.56 (s, br, 1H),
2
2
7.23-7.34 (m, br, 4H), 2.93 (m, br, 4H), 1.90 (m, br, 2H),
1.28-1.51 (m, br, 80H), 0.93 (m, br, 12H). GPC: Mn = 23.6
K, PDI: 1.5. Elemental Analysis: (Calcd: C: 71.95, H: 9.22,
N: 2.33); Found: C: 71.87, H: 9.34, N: 2.40.
o
ferred to a hotplate to bake at 110 C for 5 mins in ambient
to form the semiconductor films approximately 50-100 nm
in thickness. The TFTs were completed by spin-coat a 500-
700 nm thick CYTOP (809M, AGC) layer as the gate die-
OTFT Device Fabrication
2
Top-gate Bottom Contact TFTs with Unpatterend Semicon-
ductor/Gate Layers: Top-gate bottom contact TFTs were
fabricated using P1-P6 as the semiconductor layer. Eagle
100 glasses (Corning Inc.) were used as device substrates.
Prior to the semiconductor deposition, 500 Å gold source
and drain electrode were thermally evaporated through a
stencil mask to define the transistor channel (W/L =
1000/60 ꢀm), followed by a 3,4-difluorothiophenol (Sig-
ma-Aldrich) contact treatment (spin dray of a 5 % solution
in anisole). Polymers P1-P6 were dissolved in 1,2-
dichlorobenzene at a concentration of ~6 mg/ml. The
formulations were spin coated on to the substrates at 1000
lectric (Ci = 3.0 nF/cm ), followed with thermal evapora-
tion of a 500 Å thick Ag gate electrode. All TFTs were test-
ed under dark in a probe station (Signatone) in ambient
environment using a Keithley 4200 two source electrome-
ter.
BHJ-OSC Device Fabrication and test procedure
Conventional OSC devices: These devices were fabricated
by first spin casting a thin layer of PEDOT (about 35 nm,
Clevios PVP AI 4083) onto precleaned ITO substrates. Pol-
ymers P1-P6 (6-8 mg/mL) and PC70BM (1:1.5 weight ratio)
were dissolved in chlorobenzene. 1-2% (by volume) diio-
dooctane were added to the solution before spin casting
the active layers (film thickness ~ 100-270 nm). Finally, 0.6
nm of LiF and 100 nm of Al were evaporated as the top
electrode. Device were encapsulated using a blanket of
EPOTEK OG116-31 UV-curable epoxy (Epoxy Technologies)
and a cover slip. The active area of the device defined by
o
rpm for 60 sec, and baked at 100 C on a hotplate for 5
mins in ambient to form the semiconductor films approx-
imately 30-100 nm in thickness. The TFTs were completed
by spin-coat a 500-700nm thick CYTOP (809M, AGC) lay-
2
er as the gate dielectric (Ci = 3.0 nF/cm ), followed with
thermal evaporation of a 500 Å thick gold gate electrode.
All TFTs were tested under dark in a probe station (Signa-
tone) in ambient environment using a Keithley 4200 two
source electrometer.
2
the mask aperture was 0.096 mm . The photovoltaic char-
acteristics of devices were tested in air. The current-
voltage (I-V) curves were obtained by a Keithley 2400
source-measure unit. The photocurrent was measured
−
2
Top-gate Bottom Contact TFTs with Patterned Semiconduc-
tor/Gate Layers: Top-gate bottom contact TFTs were fabri-
cated using P3 or P6 as the semiconductor layer. PET sub-
strates coated with a thin layer of a photocurable polymer
(Polyera B3000) were used as device substrates. Prior to
the semiconductor deposition, a 500 Å silver film was
sputtered and the source/drain electrodes were defined
with standard photolithography (W/L = 100/13 ꢀm), fol-
lowed by a 3,4-difluorothiophenol (Sigma-Aldrich) con-
tact treatment (spin dray of a 5 % solution in anisole). Pol-
ymers P1 and P6 were dissolved in 1,2,3,4-
tetrahydronaphthalene at a concentration of ~3 mg/ml.
The formulations were spin coated on to the substrates at
under simulated AM1.5G irradiation (100 mW cm ) using
a xenon-lamp-based solar simulator (Newport 91160A
300W Class-A Solar Simulator, 2 inch by 2 inch uniform
beam). The light intensity was set using a NREL calibrated
silicon photodiode with a color filter. External quantum
efficiency was measured using Newport’s QE setup. Inci-
dent light from a xenon lamp (300 W) passing through a
monochromator (Newport, Cornerstone 260) was focused
on the active area of the cell. The output current was
measured using
a current pre-amplifier (Newport,
70710QE) and a lock-in amplifier (Newport, 70105 Dual
channel Merlin). A calibrated silicon diode (Newport
70356) was used as a reference.
o
1000 rpm for 60 sec, and baked at 100 C on a hotplate for 5
mins in ambient to form semiconductor films approxi-
mately 30-50 nm in thickness. Next, D2200 (Polyera Cor-
Blade-coated conventional OSC devices: These devices were
fabricated by spin-coating a layer of PEDOT:PSS (about 40
5
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Chemistry of Materials
nm, Clevios AI 4083) on a pre-cleaned ITO glass which
Page 6 of 15
-
1
2
3
4
5
6
7
8
9
1
1
1
1
1
1
1
1
1
1
2
2
2
2
2
2
2
2
2
2
3
3
3
3
3
3
3
3
3
3
4
4
4
4
4
4
4
4
4
4
5
5
5
5
5
5
5
5
5
5
6
was dried at 120 °C for 10 min in air. Polymer P3 (14 mg mL
1
-1
)
and [70]PCBM (21 mg mL ) were dissolved in 1 mL of
chlorobenzene with 2% 1-chloronaphthalene. Then the
active ink was blade-coated on top of the PEDOT:PSS layer
o
at 70 C in ambient under an relative humidity of 50%
o
(
both ink and substrate were heated at 70 C in air), to
form a ~265 nm-thick film. Subsequently, a 0.6 nm-thick
LiF and a 100-nm-thick Al electrode were deposited by
-
6
thermal evaporation at a pressure of approximately 10
0
1
2
3
4
5
6
7
8
9
0
1
2
3
4
5
6
7
8
9
0
1
2
3
4
5
6
7
8
9
0
1
2
3
4
5
6
7
8
9
0
1
2
3
4
5
6
7
8
9
0
Torr. The active area of the device defined by the mask
2
aperture was 4 mm . The photovoltaic characteristics of
devices were tested in air, after the devices were encapsu-
lated in nitrogen-filled glove box by lamination with a
glass slide using a UV-curable epoxy glue before measure-
ment. J–V characteristics of photovoltaic devices were
taken using a Keithley 2400 source measurement unit un-
der a simulated AM1.5G spectrum with a solar simulator
2
(SAN–EI XES–40S2-CE), and the 100 mW/cm light inten-
sity was calibrated using a Si–based reference cell with a
KG5 color filter (PV Measurements, Inc.).
RESULTS AND DISCUSSION
Molecular Design and Synthetic Strategies
Before synthetic efforts, molecular orbital computa-
tions were carried out to compare the structural and
electronic properties of the isomeric BTs (F isoBT; x =
x
0
those of the known BT units F BT and F BT-T2. Details
-2) and of the 4,6-dithienyl derivatives (F isoBT-T2) to
Scheme 1. Synthesis of isoBT building blocks and poly-
mers P1-P3.
x
x
x
are reported in the Supplementary Information (Table
S1). From these computations three important conclu-
sions can be drawn: 1. The FMO energies indicate that
the isomeric BT unit is also a strong electron-accepting
functionality. 2. All isoBT-based systems have lower
HOMO energies by ~ 0.1-0.4 eV, which should enhance
(
86%) to
stannyl)dithiophene (10) to produce polymer P2 in
3% yield. Finally, attempts to synthesize 5,6- difluoro-
benzo[d][1,2,3]-thiadiazole (16) by isolating 2-amino-
,5-difluorothiophenole (see SI) failed. Thus, the most
efficient route begins by acylating 2,4,5-trifluoroaniline
11) with Ac O in pyridine to afford 12, which was then
9 and then reacted with bis(trimethyl-
8
4
BHJ-OSC V ’s. 3. The greater steric demands of S vs. N
oc
in the 1 position of the thiadiazole ring result in a far
larger equilibrium torsional angle in F isoBT-T2 (~ 30°)
(
2
x
reacted with P S to yield thioacetanilide 13 in 74%
2 5
vs. F BT-T2 (~ 1-2
°
). Note that these torsional results
are independent on the number of fluorine atoms.
x
yields. This compound affords 5,6-difluoro-2-
methylbenzothiazole (14) in 83% yields by subsequent
deprotonation with NaH followed by intra-molecular
71
The synthesis of benzo[d][1,2,3]thiadiazole building
blocks and of the corresponding polymers is shown in
Scheme 1 and some details are collected in the SI. isoBT
nuclephilic substitution. Next, the thiazole moiety of
was ring-opened by hydrolysis with hydrazine-
hydrate to afford 15, which was directly reacted with
1
4
7
2
(
NBS in fuming H SO affords 4,7-dibromo-isoBT (
1
) is commercially available and bromination with
2
NaNO under acidic conditions to provide 16 (82%).
2
, 90% Bromination of highly electron-deficient F isoBT to
2
4
2
yield),
bis(trimethystannyl)tetrathiophene
ditions to afford polymer P1 in 66% yield. 6-Fluoro-
isoBT ( ) was synthesized in 78% yields by diazo-
tation/annelation of 2-amino-5-fluorothiophenole (
which
is
reacted
with
under Stille con-
the
compound 17 was accomplished with NBS/oleum at 50
°C, and 17 was then converted to the dithienyl deriva-
tive 18, the latter brominated to 19, and 19 reacted with
10 to produce polymer P3 in excellent yield (89%). The
success of this polymerization reaction was verified by
the synthesis of three polymer P3 batches with compa-
73
3
5
4
)
7
0
with NaNO /HCl. Bromination of
5
with NBS in ole-
) in 80% yields. Alt-
6 could be used to synthesize P2 following the
2
um affords 4,7-dibromo-F isoBT (
6
rable M and PDI values (see details in the SI). Note
n
1
that polymers P1-P3 are regioirregular due to the
symmetry breaking of the isoBT building blocks. To
compare the properties of the new isoBT polymers P1-
P3 vis-à-vis the BT analogues, the new BT-based poly-
mers P4 and P5 as well as the known polymer P6 were
hough
same procedure as for P1, the reaction was not optimal
(yield<40%, low M ), thus the most efficient route in-
w
volves first the synthesis of bisthienyl derivative
(F BT-T2), which was brominated in excellent yields
8
1
6
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Page 7 of 15
Chemistry of Materials
served in F isoBT-T2 (12-17
also synthesized (see SI). All intermediates, key build-
°
, Figure 2d) is not the result
1
1
2
3
4
5
6
7
8
9
1
1
1
1
1
1
1
1
1
1
2
2
2
2
2
2
2
2
2
2
3
3
3
3
3
3
3
3
3
3
4
4
4
4
4
4
4
4
4
4
5
5
5
5
5
5
5
5
5
5
6
ing blocks, and polymers were characterized by con-
ventional chemical/physical methods.
of larger steric requirements of the isoBT ring and/or
the presence of the F atom, but likely due to structural
relaxation minimizing packing energy. Furthermore,
the exocyclic C-C distances within the isoBT series
(
ones (1.42-1.47 Å), suggesting comparable
1.45-1.47 Å) are similar to those measured for the BT
-
π
conjugation. Finally, all units pack in columnar struc-
tures where, within each column, the molecules are
arranged into a slipped co-facial fashion with an inter-
planar distance of 3.4-3.6 Å. From this structural analy-
sis it is clear that isoBT can produce planar, highly-
conjugated units capable of strong intermolecular in-
teractions.
0
1
2
3
4
5
6
7
8
9
0
1
2
3
4
5
6
7
8
9
0
1
2
3
4
5
6
7
8
9
0
1
2
3
4
5
6
7
8
9
0
1
2
3
4
5
6
7
8
9
0
Polymer Characterization
Before electrical measurements, the isoBT (P1-P3) and
BT (P4-P6) based polymers were characterized and
relevant data are collected in Table 1. Molecular masses
of the polymers were obtained by GPC at 150 °C with 1,2,4-
trichlorobenzene as eluent. The M s of P2, P3, and P5 are
n
similar (24-26 KDa; PDI 1.4-1.8) whereas those of P1 and
P4/P6 are slightly lower (14 KDa) and larger (29/31 KDa),
respectively. Optical absorption and cyclic voltammetry
(
CV) measurements were carried out on thin films de-
posited on glass, with the latter using a Pt disk working
electrode (see SI). The UV-Vis spectra of Figure 4a in-
dicate that the absorption profiles of the non-
fluorinated polymers of both polymer families (P1 and
P4) are considerably broader and blue-shifted versus
the corresponding mono- (P2 and P5) and difluorinat-
ed (P3 and P6) systems, clearly suggesting that fluorine
Figure 3. Crystal structure and packing diagram of isoBT
(
a), BT (b), several 4,7-dithyenyl isoBTs (c-f) and -BT (g-
h) derivatives. For unit cell, a axis (red), b axis (green), c
axis (blue).
Table 1. Physical properties of the indicated polymers.
[
a]
[b]
ox
[c]
Mn
KDa)
λ
max
E
g
E
E
HOMO/ELUMO
T
m
o
Crystal Structure Determination
Poly.
PDI
(
(nm) (eV)
(V)
1.18
1.16
1.30
1.12
(eV)
( C)
183
219
255
170
215
Figure 3 shows the crystal structures of the isoBT/BT
cores and of several thienyl-substituted derivatives,
along with relevant intra/intermolecular distances
P1
P2
P3
P4
P5
P6
14.1
1.9
1.4
1.5
2.9
1.8
1.7
562
624
637
656
707
700
1.87
1.75
1.80
1.68
1.61
-5.6/-3.7
-5.6/-3.7
-5.7/-3.8
-5.6/-3.9
-5.5/-3.9
-5.5/-3.9
25.7
23.6
29.4
24.6
31.2
(
black and red), angles (blue), and torsions (green).
From Figures 3a/b the greater skeletal asymmetry of
isoBT vs. BT arises from the different atomic connec-
tivity. Benzofusion at the thiophene-b-bond in isoBT
vs. the thiophene- -bond in BT results in a larger dis-
c
1.04
1.09
tortion of the pentatomic ring (larger variations in an-
gles and distances) whereas, in contrast, the benzene
fragment exhibits a reduced bond length alternation
signature of an enhanced aromatic character. When
comparing the crystal structures of the new thienyl-
substituted isoBT derivatives (Figure 3c-f) to the
known BT-based ones (Figure 3g-h), similarities and
1.66
252
[
a] Calculated from the absorption onset. [b] From the onset of first
oxidation peak. [c] From the equation EHOMO = -4.44–EOx and ELUMO
+EHOMO, respectively.
=
E
g
functionalization of isoBT/BT enhances intermolecular
interactions. The optical data also demonstrate that
the λmax of the iso-BT polymers [562 nm (P1); 624 nm
P2); 637 (P3)] are blue shifted by ~70-90 nm versus
the corresponding BT ones [656 nm (P4); 707 nm (P5);
700 (P6)]. Thus, the optical gaps of P1 P3 (1.75-1.87 eV)
differences appear. Thus, by analyzing F isoBT-T2
0
(
Figure 3c) and F isoBT-T2 (Figure 3e), both units are
2
essentially planar featuring maximum torsions of 5.2
and 3.8 , respectively, which are even smaller than the
maximum torsional values observed in the correspond-
ing F BT-T2 (4.3 , Figure 3g) and F BT-T2 (11.3 , Figure
h). Therefore, the more severely twisted core ob-
(
°
-
°
°
are larger than those of P4
-
P6 (1.61-1.68 eV), in agree-
0
4
2
7
3
7
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Chemistry of Materials
Page 8 of 15
ment with the MO computations on small molecules
Table S2, SI).
1
2
3
4
5
6
7
8
9
1
1
1
1
1
1
1
1
1
1
2
2
2
2
2
2
2
2
2
2
3
3
3
3
3
3
3
3
3
3
4
4
4
4
4
4
4
4
4
4
5
5
5
5
5
5
5
5
5
5
6
a.
(
1
0
0
0
0
.0
P1
P2
P3
P4
P5
P6
CV scans only reveal irreversible oxidations with onsets
at 1.2-1.3 V (P1-P3) and 1.0-1.1 V (P4-P6) (Figure 4b).
The HOMO and LUMO energies can be next estimated
by combining the CV/optical data, (Table 1). Despite
the approximate nature of CV-derived orbital energet-
ics, the experimental results are in accord with the DFT
computations, with the HOMO/LUMO energies of the
isoBT polymers lower/higher by ~0.1-0.2 eV than those
of the BT polymers. Interestingly, in sharp contrast to
other polymer families, it appears that arene fluorina-
tion has negligible influence on the positioning of the
CV/optical-derived FMOs. Finally, differential scanning
.8
.6
.4
.2
0
1
2
3
4
5
6
7
8
9
0
1
2
3
4
5
6
7
8
9
0
1
2
3
4
5
6
7
8
9
0
1
2
3
4
5
6
7
8
9
0
1
2
3
4
5
6
7
8
9
0
0.0
3
00
400
500
600
700
800
900 1000
Wavelength (nm)
b.
4.0x10
-
5
calorimetry (DSC)-derived melting temperatures (T s)
m
indicate that the T s for the isoBT polymers are greater
m
o
by 3-10 C than those of the corresponding BT poly-
-5
2.0x10
mers (Figure S1). Note, the reversibility of the DSC
scans indicates that all polymers are thermally stable
up their melting temperature, thus the presence of an
azo (–N=N-) bond does not compromise iso-BT struc-
0.0
-
5
P1
-2.0x10
-4.0x10
-6.0x10
P2
P3
P4
P5
P6
75
tural robustness. Furthermore, fluorine introduction
o
enhances Tm by 72 and 82 C on going from fluorine-
-5
free to the difluorinated polymers within the isoBT (P1
-
-
P3) and BT (P4 P6) series, respectively. Overall, the
-
5
solid-state characterization data indicate that benzo-
thiadiazole regiochemistry in polymers should affect
charge transport by deepening the HOMO energies,
influence photovoltaic response by reducing absorp-
0.0
0.5
1.0
1.5
2.0
Potential (V)
Figure 4. UV-Vis spectra of cast film of P1-P6 (a) and CV
plots of cast polymer P1-P6 films measured in anhydrous
acetonitrile containing 0.1 M Bu N PF as an electrolyte
tion and enhancing V , and minimally affect film mi-
oc
crostructure. In contrast, while fluorination has little
impact on MO energetics, it strongly affects macro-
molecule aggregation and intermolecular interactions.
Finally, since the mono-fluoro substituted BT polymer
+
-
4
6
at a scan rate of 50 mV/s (b).
or D2200(dielectric)/Au or Ag(gate). Note, the maxi-
mum processing/annealing temperature of P1-P6 films
is 100 C for 5 min in air. Measurements were carried
P5 is regioirregular as the corresponding iso-BT P2
,
and considering that within their respective families
(all regioirregular for iso-BT and mixed for BT) ther-
mal/optical/electronic trends holds, to a first approxi-
mation polymer regioregularity has small influence on
the electronic structure and solid state characteristics.
However, it is a further development of this study in-
vestigate and address the effect of iso-BT polymer
backbone regioregularity considering that it usually
°
out in ambient and Figures 5a,b show representative
transfer and output plots. From the TFT measurements
note that all polymers are p-channel semiconductors
with the hole mobility (µ ) increasing as the number of
h
fluorine substituents is increased (P1→P3, P4→P6).
When comparing the two polymer families, the isoBT
unit is as effective as BT in promoting hole transport.
Thus, µ s of the nonfluorinated polymers (P1
5
2
improves opto-electronic device performance.
↔P4)
with CYTOP as gate dielectric are low and statistically
h
2
identical (0.03-0.05 cm /Vs) despite the M of P1 (~14
n
Electronic Device Fabrication and Characterization
OTFT and BHJ-OSC devices were fabricated (see insets
of Figure 5 and SI) with all polymers/polymer blends
processed under identical conditions to provide a di-
rect performance comparison (Table 2). Thus, exten-
sive device optimization has not been carried out at
this point. The OTFT structure used is glass or
PET(substrate)/Au or Ag(source-drain)/P1-P6/CYTOP
kDa) being substantially lower than that of P4 (~29
kDa). For the monofluorinated polymers, which have
identical M values (~ 25 kDa), µ of the isoBT polymer
P2 (0.20-0.24 cm /Vs) is larger than that of the BT pol-
2
ymer P5 (0.06-0.08 cm /Vs). Finally, the difluorinated
n
h
2
polymers outperform the others, with µ of isoBT P3
h
2
0.36-0.51 cm /Vs, M ~ 23 kDa) lower than that of the
(
corresponding high-Mn P6 (0.65-0.79 cm /Vs, M ~ 31
n
2
n
8
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Chemistry of Materials
ed. The OSC performances (Figures 5c-d, S3, S4) track
those of the FET mobility, with the PCE values steadily
1
2
3
4
5
6
7
8
9
[a]
[b]
Table 2. Transistor and photovoltaic performance of
polymers P1-P6.
µ
PCE
(%)
V
(V)
oc
J
sc
FF
(%)
Pol.
2
Ion/Ioff
2
(
cm /Vs)
(mA/cm )
3
P1
0.03-0.05
0.20-0.24
~10
2.8-2.9
7.1-7.2
0.89-0,90
5.0-5.1
63-64
70-71
10
11
12
13
14
15
16
17
18
19
20
21
22
23
24
25
26
27
28
29
30
31
32
33
34
35
36
37
38
39
40
41
42
43
44
45
46
47
48
49
50
51
52
53
54
55
56
57
58
59
60
4
P2
~10
0.91-0.92 10.4-10.5
0.92-0.93 12.7-13.1
5
0
.36-0.51
~10
P3
7
8.7-9.0
73-74
[
0.65-0.72] [6-8x10 ]
4
P4
P5
0.03-0.05
~10
~10
~10
1.6-1.7
0.78-0.79
3.4-3.6
62-63
70-71
3
5
0.06-0.08
0.65-0.79
6.2-6.4
0.72-0.73 12.4-12.6
0.75-0.76 16.2-16.5
0.75-0.76 14.1-14.3
[
c]
P6
7
8.5-8.8
7.1-7.3
70-71
H
L
[0.74-0.76] [8-9x10 ]
3
0.49-0.56
~10
68-69
[
a] Values are for TFTs with CYTOP and Au contacts with unpatterned
semiconductor/gate layers. Thus, Ion/Ioff are underestimated. Values in
brackets refer to TFTs with photocrosslinkable ActivInk D2200 as gate
dielectric and Ag contacts with photolithographically patterned semi-
conductor/gate layers. Ion/Ioff are accurate. At least 10 TFTs were tested.
All TFT measurements are carried out in ambient. [b] At least 5 BHJ-
OPV devices were tested. [c] H corresponds to the P6 batch of Table 1
Figure 5. Representative transfer (a) and output (b) plots
for TFTs with structure Glass/Au/P1-P6/CYTOP/Au and
BHJ-OSC J-V (c) and EQE-λ (d) plots for the indicated
polymers and polymer blended with PC BM. Insets indi-
cate schematics of OTFT (a) and OSC (c) architectures
and materials.
(M
n n
~ 31 kDa) whereas L corresponds to a P6 batch with a lower M =
18.3 kDa and PDI = 2.0.
71
increasing upon heterocycle fluorination. Furthermore,
the maximum PCEs of the isoBT family [P1 (2.9 %), P2
(7.2 %), P3 (9.0 %)] are slightly larger than those of the
corresponding BT polymers [P4 (~ 1.7 %), P5 (6.4%),
P6 (P6-H, 8.8%)], despite the blue-shifted absorption
kDa) but comparable to that of the lower-Mn P6 batch
(
2
0.49-0.56, cm /Vs, M ~ 18 kDa). For all CYTOP-based
and, except when comparing P2↔P5, the substantially
n
3
5
lower M . Note, as for TFTs, polymer P6 with a lower
M (P6-L) affords a substantially lower PCE of 7.3%.
n
devices the Ion:Ioff ratios are ~ 10 -10 , however, these are
underestimated values considering that the semicon-
ductor/gate layers are unpatterned. Indeed rigorous
patterning via photolithography by using the dielectric
n
This result agrees with the literature PCE for P6
(7.6%).
41
D2200, as exemplified for P3 and P6 (Figure S2 and
2
Table 2), produces similar µ for P6 (0.74-0.76 cm /Vs)
Finally, to further demonstrate the potential of the new
isoBT family, P3 was employed to fabricate in ambient
the first gravure-printed TFT and blade-coated BHJ-
OSC devices (see SI, Figures S6 and S7). The TFTs
exhibit excellent performance with near-zero turn-on
h
and slightly larger performance for P3 (0.65-0.72
cm /Vs, probably because of the low trapping charac-
2
8
teristics of D2200) and outstanding Ion:Ioff of ~10 . Note
that BT-quaterthiophene polymer P6 is the only
known polymer of this series and was reported with a
2
7
voltage, µ = 0.20-0.35 cm /Vs, I /I > 10 and negligible
h
on off
hysteresis, while the OPV cell achieve a respectable PCE
of 4.1-4.2%. These results are possible because of the good
processability and performance of low molecular weights
polymer P3 vs. the corresponding BT-based P6 polymer.
M ~ 46 kDa having an average mobility in bottom-
n
2
gate top-contact TFTs of 1.03 cm /Vs for films annealed
in ambient. Considering the difference in TFT architec-
ture, processing parameters, and M values, P6 results
are in line with previous studies.
n
1,76-78
4
Conventional
ITO/PEDOT/P1
photovoltaic
cells
of
structure
-P6~PC BM/LiF-Al were also fabricat-
71
9
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Page 10 of 15
(
100)
large OSC efficiencies and FFs for the new isoBT P2/P3
and BT P6 versus those of the other polymers.
1
2
3
4
5
6
7
8
9
1
1
1
1
1
1
1
1
1
1
2
2
2
2
2
2
2
2
2
2
3
3
3
3
3
3
3
3
3
3
4
4
4
4
4
4
4
4
4
4
5
5
5
5
5
5
5
5
5
5
6
a)
4
d
lam
3
3
3
3
x10
Conclusions
(
200)
In conclusion, a new polymer semiconductor family
comprising isomeric benzothiadiazole building blocks
is synthesized and characterized. To gain further in-
sights, polymers based on the well-investigated BT
units were also synthesized and analyzed. Single crystal
analysis suggests that the new iso-BT units can enable
a planar polymer backbone whereas thin-film XRD
demonstrate considerable texturing of the polymer
films. Overall, our data suggest interesting similarities
and differences between the two families, highlighting
the potential of the isoBT unit and isoBT-based poly-
mers for organic opto-electronic devices.
3
x10
(300)
P6
P5
2x10
P4
P3
1
x10
P2
0
1
2
3
4
5
6
7
8
9
0
1
2
3
4
5
6
7
8
9
0
1
2
3
4
5
6
7
8
9
0
1
2
3
4
5
6
7
8
9
0
1
2
3
4
5
6
7
8
9
0
P1
0
0
5
10 15 20 25 30 35 40
o
b)
θ - 2θ ( )
3
3x10
(
010)
dπ
P6-PC BM
1
7
3
3
The wider bandgap and considerable efficiencies of the
isoBT polymers, and particularly P3 vs. P6, may be
more suitable for tandem cells and combination with
molecular/polymer acceptors. The greater transistor
performance at lower molecular weights for the isoBT
polymers may be important for enabling more stable
rheology of formulations. We believe that this work
will promote the use of isoBT for different opto-
electronic applications to complement the current
generation high-performance BT-based semiconduc-
tors. Further investigations and optimization of the
2
1
x10
x10
P5-PC BM
7
1
P4-PC BM
71
P3-PC BM
71
P2-PC BM
71
P1-PC BM
7
1
0
0
5
10 15 20 25 30 35 40
o
θ - 2θ (
)
Figure 6. WAXRD for the indicated polymers and poly-
mer blends.
isoBT family performance will include synthesis of mo-
lecular systems,
32,48-53,81-88
the effect of the isoBT regio-
and polymer side-chain engineer-
as widely demonstrated for (hetero)BT-based
5
2,89-92
Polymer and Polymer Blend Morphology
Wide-angle x-ray diffraction (WAXRD) of the pristine
polymers and the corresponding polymer:PC BM
blends was carried out to better understand device per-
formance. As shown in Figure 6a, distinct (h00) specular
reflections indicate that all polymers are polycrystalline,
with the intensity increasing upon increasing isoBT/BT
chemistry,
5
6,93-97
ing,
semiconductors.
71
ASSOCIATED CONTENT
SUPPORTING INFORMATION
fluorination level. The first reflection located at 2
θ
= 3.97-
*S Supporting Information
The Supporting Information is available free of charge on the
ACS Publications website at DOI:
4.00° indicates that all polymers adopt a bulk edge-on
growth orientation characterized by a d-spacing (dlam) of
22.25-22.09 Å. These results further demonstrate that
fluorination promotes better organization of the polymer
long-range-ordered lamellar structures, in agreement
with the optical data, and corroborating the in-plane
charge transport measurements. Interestingly, when
going from the pristine polymers to the corresponding
OSC blends, the XRD spectra evolve differently for the
different polymers (Figure 6b). Thus, all blends exhibit
the (h00) reflection(s) at 3.95-4.09° (dlam = 22.37-21.60 Å),
however those based on P1/P2 and P4/P5 exhibit compa-
rable intensity whereas those based on P3 and P6 are sub-
stantially decreased. Furthermore, the P3 and P6 polymer
blend spectra, as well as to a lesser degree blends based
on P2, exhibit a (010) reflection at 25.10, 24.91, and 24.97°,
signatures of π-face-on oriented polymer domains having
Synthetic procedures and characterization data of the mon-
omers and polymers; DSC plots; AFM images; DFT computa-
tion Data; Single Crystal X-ray diffraction data; Selected
NMR spectra; and details for all device characterizations.
79
AUTHOR INFORMATION
Corresponding Author
*zchen@polyera.com
*
afacchetti@polyera.com
Notes
The authors declare no competing financial interest.
stacking at a distance, d , of ~ 3.5 Å. These characteristics,
in combination with the favorable fibrillary film mor-
phology established by AFM (Figure S5), enable the
π
ACKNOWLEDGMENT
8
0
10
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Chemistry of Materials
We thank AFOSR (grant FA9550-15-1-0044) for support of
(16) Mu, C.; Liu, P.; Ma, W.; Jiang, K.; Zhao, J.; Zhang, K.; Chen,
1
2
3
4
5
6
7
8
9
1
1
1
1
1
1
1
1
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2
2
2
2
2
2
2
2
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3
3
3
3
3
3
4
4
4
4
4
4
4
4
4
4
5
5
5
5
5
5
5
5
5
5
6
the research at Northwestern and the Northwestern MRSEC
for access to characterization equipment (NSF grant DMR-
1121262).
Z.; Wei, Z.; Yi, Y.; Wang, J.; Yang, S.; Huang, F.; Facchetti, A.;
Ade, H.; Yan, H. High-Efficiency All-Polymer Solar Cells Based
on a Pair of Crystalline Low-Bandgap Polymers. Adv. Mater. 2014,
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(17) Gao, C.; Wang, L.; Li, X.; Wang, H. Rational Design on D–A
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(35) Kim, L. K.; Li, X.; Ullah, M.; Shaw, P. E.; Wawrzinek, R.;
on Benzothiadiazole-Sandwiched Dihexylquaterthiophenes.
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