High-performance organic semiconductors for thin-film transistors based on 2,6-bis(2-thienylvinyl)anthracene

Article abstract of DOI:10.1039/b719738a

We have synthesized two novel organic semiconductors, which have a symmetrically substituted thienylvinylene anthracene backbone. They show good electrical performances on SiO₂/Si, with high field-effect mobilities of up to 0.4 cm² V^-1 s^-1, and can easily be synthesized in large quantities. In addition, the high mobility of such semiconductors can be achieved at low substrate deposition temperatures. The Royal Society of Chemistry.

Full text of DOI:10.1039/b719738a

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PAPER
www.rsc.org/materials | Journal of Materials Chemistry
High-performance organic semiconductors for thin-film transistors
based on 2,6-bis(2-thienylvinyl)anthracene†
Myoung-Chul Um,a Junhyuk Jang,b Jihoon Kang,a Jung-Pyo Hong,a Do Yeung Yoon,a
a
Seong Hoon Lee, Jang-Joo Kim and Jong-In Hong
b
a
*
*
Received 21st December 2007, Accepted 26th February 2008
First published as an Advance Article on the web 20th March 2008
DOI: 10.1039/b719738a
We have synthesized two novel organic semiconductors, which have a symmetrically substituted
thienylvinylene anthracene backbone. They show good electrical performances on SiO2/Si, with high
field-effect mobilities of up to 0.4 cm2 Vꢀ1 sꢀ1, and can easily be synthesized in large quantities. In
addition, the high mobility of such semiconductors can be achieved at low substrate deposition
temperatures.
Introduction
In the past few decades, acene and thiophene oligomers have
been extensively studied for use as organic semiconductors in
devices such as field-effect transistors (FETs),1–3 organic light-
emitting diodes (OLEDs),4 photovoltaic cells,5 sensors,6 and
radio frequency identification (RF-ID) tags.7 So far, pentacene
Fig. 1 Structures of (H)TVAnt (R ¼ H; TVAnt, R ¼ hexyl; HTVAnt).
has shown remarkable properties as the best thin-film material
with very high field-effect mobilities (0.3–0.7 cm2 Vꢀ1 sꢀ1 on
a Si/SiO2 substrate,8 1.5 cm2 Vꢀ1 sꢀ1 on a chemically modified
Si/SiO2 substrate,9 and 3.0 cm2 Vꢀ1 sꢀ1 on a modified alumina
substrate)10 and rubrene as the best single-crystal material
(15.4 cm2 Vꢀ1 sꢀ1).11 However, pentacene-based devices have
poor air stability and rapid device-performance degradation.12
Therefore, environmentally stable, organic semiconducting
materials with high mobilities and on : off current ratios that
can be deposited at low substrate temperatures are still needed.
Very recently, several groups have developed semiconductors
with high stability and conductivity by choosing conjugated
vinylene-based oligomers.13 In fact, the presence of a double
bond of a defined configuration (i) reduces the overall aromatic
character of the planar structures and hence increases the p-elec-
tron localization, and (ii) restricts the rotational freedom
inherent to thiophenes,14 which increases the energy-band
gap.15 The introduction of a vinylene unit into oligomeric struc-
tures is a well-known method for forming coplanar molecules
with an extended p-conjugated length, which should help to
maximize the organization of the molecules in thin films. The
devices derived from oligothiophenes end-capped with a styryl
unit not only show very high field-effect mobilities (up to
0.1 cm2 Vꢀ1 sꢀ1) and on : off ratios (up to 105) but are also found
to be exceptionally long-lived and stable in continuous operation
under atmospheric conditions.13a In this study, we report the
synthesis of 2,6-bis(2-thienylvinyl)anthracene (TVAnt) and
hexyl-substituted HTVAnt (Fig. 1),13b and their excellent
field-effect mobilities (up to 0.4 cm2 Vꢀ1 sꢀ1) and high on : off
ratio (up to 105–106) of their TFT devices. In particular, TVAnt
has 7 times higher mobility in comparison with dithiophen-20-
yl-2,6-anthracene (DTAnt) without vinyl groups under similar
conditions.16 Furthermore, TVAnt and HTVAnt exhibit high
thermal stability when compared with pentacene-based organic
semiconductors as determined by thermal gravimetric analysis
(TGA).
Experimental
General
1H and 13C NMR spectra were recorded using an Advance 300
1
MHz Bruker spectrometer in CDCl3. H NMR chemical shifts
in CDCl3 were referenced to CHCl3 (7.27 ppm), and 13C NMR
chemical shifts in CDCl3 were reported relative to CHCl3
(77.23 ppm).
Physical measurement
TGA analyses were performed on a TGA Q50 TA instrument at
10 C minꢀ1 under a nitrogen atmosphere. DSC analyses were
ꢁ
performed on a DSC2910 TA instrument at 10 C minꢀ1 under
ꢁ
nitrogen flow. UV–vis absorption spectra were recorded on
a Beckman Coulter DU 800 spectrophotometer using 2.5 cm
path-length quartz cells. For solid-state measurements,
oligomers were thermally evaporated in a vacuum chamber on
aDepartment of Chemistry, College of Natural Sciences, Seoul National
University, Seoul 151-747, Korea. E-mail: jihong@snu.ac.kr; Fax:
+82-2-889-1568; Tel: +82-2-880-6682
bDepartment of Materials Science and Engineering, Seoul National
University, Seoul 151-744, Korea. E-mail: jjkim@snu.ac.kr; Fax: +82-2-
885-9671; Tel: +82-2-880-7085
˚
quartz plates to form 300 A thick films at the deposition rate
of 0.5 A sꢀ1. XRD analyses were carried out at room temperature
˚
with a Mac Science (M18XHF-22) diffraction meter using CuKa
radiation as the X-ray source at 50 kV and 100 mA. Data were
† Electronic supplementary information (ESI) available: More detailed
device data, including CV, AFM and POM. See DOI: 10.1039/b719738a
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collected in the conventional q–2q configuration (2.5–30ꢁ) from
concentrated ammonium hydroxide (70 mL) was added zinc
power (6.0 g). The reaction was refluxed overnight. The insoluble
material was removed by filtration and washed with hot DMSO.
The solution was precipitated in 200 mL of 1 N HCl. The
product was collected by filtration to give 1.86 g (75%) of
2,6-bis(dihydroxymethyl)anthracene. 1H NMR (300 MHz,
DMSO): d 8.49 (s, 2 H), 8.04 (d, 2 H, J ¼ 8.7 Hz), 7.94 (s, 2 H),
7.46 (d, 2 H, J ¼ 8.7 Hz), 5.40 (t, 2 H, J ¼ 5.6 Hz), 4.69 (d, 4 H,
J ¼ 5.6 Hz). High-resolution mass spectrometry (HRMS): Calcd.
for C16H14O2 238.0994. Found: 238.1003.
thin films thermally evaporated in a vacuum chamber on SiO2/
ꢀ1
˚
˚
Si substrates at 0.5 A s for 300 A. AFM images of the same
vacuum-deposited thin films were taken using a PSIA XE-100
advanced scanning microscope. The voltammetric apparatus
used was a CH Instruments model 700C electrochemical
workstation. Cyclic voltammograms (CVs) were obtained at
room temperature in a three-electrode cell with a working
electrode (Au), a reference electrode (Ag/AgCl), and a counter
electrode (Pt) in dichlorobenzene containing tetrabutylammo-
nium hexafluorophosphate (Bu4N+PF6ꢀ, 0.1 M) as a supporting
electrolyte at a scan rate of 100 mV sꢀ1. All the potentials were
calibrated with the standard ferrocene/ferrocenium redox couple
(E ¼ +0.41 V measured).
2,6-Bis(dibromomethyl)anthracene. Phosphorus tribromide
(4.4 g, 16.30 mmol) was added dropwise to a suspension of
2,6-bis(dihydroxymethyl)anthracene (1.5 g, 6.29 mmol) in DMF
(30 mL) at 0 ꢁC. Upon formation of a yellow precipitate, the
mixture was warmed to room temperature and stirred for 4 h.
The solids were collected by filtration and were washed with water
and hexane to give rise to a yellow solid (2.2 g, 98%) of 2,6-bis
(dibromomethyl)anthracene. The product was further purified
Fabrication of TFT devices
The field-effect measurements were carried out using top-contact
FETs. TFT devices with a channel length (L) of 50 mm and
a channel width (W) of 500 mm were fabricated on thermally
oxidized, highly n-doped silicon substrates. The SiO2 gate dielec-
1
by recrystallization from DMF. H NMR (400 MHz, DMSO):
d 8.56 (s, 2 H), 8.15 (s, 2 H), 8.12 (d, 2 H, J ¼ 11.5 Hz), 7.56
(d, 2H, J ¼ 8.7 Hz), 4.93 (s, 4 H). High-resolution mass spectro-
metry (HRMS): calcd for C16H12Br2361.9306. Found: 361.9277.
˚
tric was 300 nm thick. The organic semiconductor (300 A) was
ꢀ1
evaporated (0.1 A s at 1 ꢂ 10ꢀ6 torr) onto a non-pretreated
or OTS-pretreated oxide surface. Gold source and drain elec-
trodes were evaporated on top of the films through a shadow
mask. All measurements were performed at room temperature
using a 4155C Agilent semiconductor parameter analyzer, and
mobilities (m) were calculated in the saturation regime by using
the relationship: msat ¼ (2IDSL)/(WC(Vg ꢀ Vth)2), where IDS is
the source–drain saturation current; C (1.18 ꢂ 10ꢀ8 F) the oxide
capacitance, Vg the gate voltage, and Vth the threshold voltage.
˚
2,6-Bis(diethylphosphorylmethyl)anthracene. 2,6-Bis(dibromo-
methyl)anthracene (2.2 g, 6.04 mmol) was added to triethylphos-
phite (50 mL), and the resulting solution was refluxed for 12 h.
The solvent was removed in vacuo, and the residue was purified
by column chromatography on silica gel using ethyl acetate–
1
dichloromethane (2 : 1) as the eluent. Yield (90%). H NMR
(300 MHz, CDCl3): d 8.35 (s, 2H), 7.97 (d, 2H, J ¼ 8.7 Hz),
7.90 (s, 2H), 7.46 (d, 2H, J ¼ 8.7 Hz), 4.03 (m, 8H), 3.39
(d, 4H, J ¼ 21.8 Hz), 1.26 (t, 12H, J ¼ 7.0 Hz). 13C NMR
(300 MHz, CDCl3): 131.54, 130.83, 128.75, 128. 61, 128.39,
127. 84, 125. 67, (62.26, 62.16), (35.10, 33.27), (16.44, 16.30).
MS (EI) m/z: (M+) calcd for C24H32O6P2 478.16; found 478.
Synthesis
2,6-Bis(chloromethyl)anthraquinone. A mixture of 2.6-dime-
thylanthraquinone (3.8 g, 16.09 mmol), SO2Cl2 (50 mL), and
2,20-azobis(2-methylpropionitrile) (0.16 g, 0.96 mmol) was
refluxed for 24 h. Excess SO2Cl2 was removed by distillation in
vacuo. The solid residue was collected by filtration, washed
several times with petroleum ether, dried, and recrystallized
from DMF to yield 3.8 g (78%) of 2,6-bis(chloromethyl)anthra-
2,6-Bis(2-thienylvinyl)anthracene. LDA (1.5 M in cyclohexane,
2.9 mL, 5.22 mmol) was added dropwise to a stirred solution of
2,6-bis(diethylphosphorylmethyl)anthracene (1.0 g, 2.09 mmol)
in anhydrous THF (50 mL) at ꢀ78 ꢁC under nitrogen. The
mixture was stirred for 1 h and then thiophene-2-carbaldehyde
(0.58 g, 5.22 mmol) in THF (10 mL) was added dropwise over
a period of 10 min. After the mixture was stirred for 2 h at
1
quinone. H NMR (300 MHz, CDCl3): d 8.41 (m, 4 H), 7.98
(s, 2 H), 5.00 (s, 4 H). High-resolution mass spectrometry
(HRMS): calcd for C16H10Cl2O2 304.0057. Found: 304.0034.
ꢁ
ꢀ78 C and for 12 h at room temperature, 5 mL of water was
2,6-Bis(hydroxymethyl)anthraquinone. A suspension of 2,6-
bis(chloromethyl)anthraquinone (3.5 g, 11.47 mmol) in 300 mL
of water and 400 mL of DMSO was refluxed with vigorous
stirring. Upon heating for 4 h, a clear solution was obtained.
The reaction mixture was refluxed for 38 h and then cooled to
room temperature. The crystalline product was collected by
filtration and recrystallized from DMF to give 3.0 g (98%) of
2,6-bis(hydroxymethyl)anthraquinone. 1H NMR (300 MHz,
DMSO): d 8.17 (m, 4 H), 7.85 (d, 2 H, J ¼ 10.7 Hz), 5.57 (s, 2 H),
4.70 (s, 4 H). High-resolution mass spectrometry (HRMS): calcd
for C16H12O4 268.0735. Found: 268.0749.
added and the solvent was evaporated. The residue was washed
with water and MeOH. The desired product was separated by
sublimation. High-resolution mass spectrometry (HRMS): calcd
for C26H18S2 394.0850. Found: 394.0852. Anal. calcd: C, 79.15;
H, 4.60; S, 16.25; found: C, 79.24; H, 4.56; S, 16.21%.
2,6-Bis[2-(5-hexylthienyl)vinyl]anthracene. LDA (1.5 M in
cyclohexane, 3.2 mL, 5.75 mmol) was added dropwise to a stirred
solution of 2,6-bis(diethylphosphorylmethyl)anthracene (1.2 g,
2.50 mmol) in anhydrous THF (50 mL) at ꢀ78 ꢁC under
nitrogen. The mixture was stirred for 1 h and then 5-hexylthio-
phene-2-carbaldehyde (1.47 g, 7.50 mmol) in THF (20 mL)
was added dropwise over a period of 10 min. After the mixture
was stirred for 2 h at ꢀ78 ꢁC and for 12 h at room temperature,
2,6-Bis(dihydroxymethyl)anthracene. To
a
solution of
2,6-bis(hydroxymethyl)anthraquinone (2.8 g 10.43 mmol) in
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5 mL of water was added and the solvent was evaporated. The
residue was washed with water and MeOH. The desired product
was separated by sublimation. High-resolution mass spectro-
metry (HRMS): calcd for C38H42S2 562.2728. Found:
562.2728. Anal. calcd: C, 81.09; H, 7.52; S, 11.39; found: C,
80.99; H, 7.03; S, 11.63%.
Results and discussion
The synthesis of (H)TVAnt starts with the preparation of 2,6-
dimethylanthraquinone from the Diels–Alder reaction of isoprene
and p-benzoquinone.17 Treatment of 2,6-dimethylanthraquinone
with an excess of sulfuryl chloride in the presence of a catalytic
amount of 2,20-azobis(2-methylpropionitrile) (AIBN) at reflux-
ing temperature afforded 2,6-bis(chloromethyl)anthraquinone,
which is the key intermediate for the preparation of anthracene
derivatives. Refluxing 2,6-bis(chloromethyl)anthraquinone in
a mixture of water and Me2SO gave the alcohol derivative, which
was then reduced with Zn and NH4OH to give 2,6-bis(hydroxy-
methyl)anthracene in good yield. Treatment of the resulting diol
with phosphorus tribromide in DMF at room temperature
gave 2,6-bis(bromomethyl)anthracene. One of the precursors
of the Horner–Emmons olefination, 2,6-bis(diethylphosphoryl-
methyl)anthracene, was prepared by reaction of the dibromide
with triethylphosphite. The organization of oligomers in thin
films can be maximized by the introduction of vinylene units.
The semiconducting materials were synthesized by the Horner–
Emmons coupling reactions between the phosphonate and alde-
hyde derivatives, as shown in Scheme 1. The Horner–Emmons
coupling reaction is well known for forming all-trans
configurations.18 TVAnt and HTVAnt, purified by sublimation,
were identified by high-resolution mass spectrometry and
elemental analyses, while their thermal stability was investigated
using thermal gravimetric analysis (TGA). Thermal decomposi-
tion temperatures were 336 ꢁC for TVAnt and 376 ꢁC for
HTVAnt, while, by contrast, pentacene began to decompose at
260 ꢁC (due to sublimation), confirming the high thermal
stability of (H)TVAnt compounds (Fig. 2).
Fig. 2 Thermal gravimetric analysis (TGA) of TVAnt and HTVAnt.
after 295 ꢁC (Fig. 3a). A typical focal conic texture and a fan
shaped texture were observed at 265 ꢁC, indicating that HTVAnt
exhibits a highly ordered, liquid crystalline structure such as
a smectic phase. The solid–solid phase transitions below
ꢁ
255 C have not been identified yet.
The UV–vis spectrum of a dilute solution of TVAnt in toluene
showed absorption peaks at 426, 400, 345 and 328 nm, which
were similar to the spectra of HTVAnt (Fig. 4). The long-wave-
length absorptions in the films of the two compounds showed
slight red-shifts compared to those in solutions. Interestingly,
in the PL spectra, the differences in emission maxima between
the solution and film states of TVAnt and HTVAnt were 100
and 70 nm, respectively, indicating the presence of extremely
strong intermolecular interactions in the film states.19
The UV–vis spectra of TVAnt and HTVAnt, as deposited thin
films, showed long-wavelength absorption edges at 486 and 477
nm, respectively, which corresponded to HOMO–LUMO energy
gaps of 2.55 and 2.59 eV, and which were significantly higher
than that of pentacene (2.2 eV).20 Further insight into the
electronic properties of these compounds was provided by cyclic
voltammetry (CV). CV measurements of TVAnt and HTVAnt in
0.1 M Bu4N+PF6ꢀ–dichlorobenzene solution showed an irrever-
sible oxidation peak. The onset potentials of oxidation were
located at 0.62 eV and 0.4 eV vs. ferrocene (FOC). Regarding
the energy level of the FOC/ferrocenium reference (ꢀ4.8 eV),
Differential scanning calorimetry (DSC) measurements for
HTVAnt showed phase transitions at 19 ꢁC (10.1 kJ molꢁꢀ1),
100 C (4.5 kJ molꢀ1), 255 C (30.5 kJ molꢀ1, melting), 289 C,
and 295 ꢁC, while an isotropic phase transition was observed
ꢁ
ꢁ
Scheme 1 Synthesis of 2,6-bis[2-(5-hexylthienyl)vinyl]anthracene.
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Fig. 3 (a) Differential scanning calorimetry of HTVAnt at a scanning
rate of 10 ꢁC minꢀ1 for heating and cooling cycles. (b) Polarized optical
micrograph of the HTVAnt phase at 266 ꢁC.
Fig. 5 XRD patterns of (a) TVAnt and (b) HTVAnt thin films vacuum-
deposited on OTS-treated SiO2/Si at Tsub ¼ 75 ꢁC.
Fig. 4 UV–vis absorption spectra of TVAnt and HTVAnt.
the HOMO energy levels of TVAnt and HTVAnt were ꢀ5.42
and ꢀ5.20 eV, respectively, which were lower than that of penta-
cene, thus indicating their high oxidative stability (Fig. S7†).21
The morphological characteristics were investigated by X-ray
diffraction (XRD) (Fig. 5a and b). The thin-film XRD pattern of
TVAnt displayed a primary diffraction peak at 2q ¼ 4.34ꢁ
Fig. 6 Noncontact mode AFM (topogaphy and amplitude) image (2 ꢂ
2 mm area) of TVAnt and HTVAnt at 75 ꢁC: (a) TVAnt, (b) HTVAnt.
˚
(d-spacing 20.34 A), with second-, third- and fourth-order
diffraction peaks at 2q ¼ 8.56ꢁ, 12.70ꢁ and 16.88ꢁ, respectively.
The strong intensity of the X-ray diffraction peaks indicated
the formation of lamellar ordering and crystallinity on the
substrate. The d-spacing of TVAnt obtained from the first reflec-
˚
tion peak was 20.34 A, comparable to the molecular length
˚
obtained from the MM2 calculation (21.28 A). These spacings
Fig. 6 and Fig. S6,† which indicated near-perpendicular align-
ment of the molecules with respect to the substrate surface. On
the other hand, the XRD results of HTVAnt films exhibited
weaker reflection peaks than TVAnt with the second-order
diffraction peak at 5.55ꢁ. The film had a rather strong first-order
diffraction peak below 3ꢁ, which was hard to resolve because the
incident X-ray was overlapped with the diffracted beam. The
d-spacing of HTVAnt obtained from the (200) plane was
were consistent with the monomolecular layer thickness
obtained by atomic force microscopy (AFM), as shown in
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ꢁ
˚
31.8 xA, corresponding to the first-order diffraction of 2.78 . The
Table 1 Field-effect mobility (mTFT), on : off current ratio (Ion : Ioff) and
threshold voltage (Vth) of TVAnt and HTVAnt vacuum-deposited on
differently treated SiO2 surfaces and at different substrate temperatures
d-spacing was a little smaller than the molecular length obtained
˚
from the MM2 calculation (36.38 A), which indicated that the
(Tsub
)
molecules were inclined about 30ꢁ from the normal to the layer.
The weak intensity, especially in the higher-order peaks,
indicated that the long range order of HTVAnt was not as
good as that of TVAnt, suggesting a lower mobility for HTVAnt
compared to that of TVAnt. This is also in agreement with the
performance of the devices. When used as a channel semicon-
ductor in organic thin-film transistors (OTFTs), HTVAnt
displayed low FET mobility compared to TVAnt.
mTFT/cm2
Tsub
Vꢀ1 sꢀ1
Ion : Ioff
Vth/V
TVAnt
Bare
OTS
Bare
OTS
30
50
75
30
50
75
30
50
75
30
50
75
0.10
0.14
0.27
0.18
0.27
0.44
0.02
0.03
0.07
0.05
0.09
0.15
1.1 ꢂ 107
3.2 ꢂ 106
1.0 ꢂ 107
4.6 ꢂ 106
8.1 ꢂ 106
4.8 ꢂ 105
1.3 ꢂ 105
5.2 ꢂ 105
4.4 ꢂ 107
1.2 ꢂ 107
1.4 ꢂ 107
2.0 ꢂ 107
ꢀ34
ꢀ41
ꢀ37
ꢀ31
ꢀ36
ꢀ39
ꢀ31
ꢀ29
ꢀ28
ꢀ29
ꢀ30
ꢀ30
The OTFTs of TVAnt and HTVAnt were fabricated using top
contact geometry with Au electrodes. Gold source and drain
contacts (50 nm) were deposited onto the organic layer through
a shadow mask. The channel length (L) and width (W) were
50 and 500 mm, respectively. Thin films of the two conjugated
oligomers were formed by vacuum evaporation onto either
untreated or octadecyltrichlorosilane (OTS)-coated Si/SiO2
substrates at various temperatures (Tsub ¼ 25 ꢁC, 50 ꢁC and
75 ꢁC). All the OTFTs showed typical p-channel TFT
characteristics.
HTVAnt
conditions showed mFET over 0.1 cm2 Vꢀ1 sꢀ1 and an on : off
ratio > 105ꢀ107 under ambient conditions (Table 1). In
particular, excellent FET characteristics, including mFET higher
than 0.44 cm2 Vꢀ1 sꢀ1 (measured in the saturation regime), and
an on : off ratio > 105, were observed in TVAnt devices
fabricated on the OTS-treated substrate at Tsub ¼ 75 ꢁC (Fig. 7).
We found that the TFT performance depends critically on the
side chain lengths of the active materials. Typically, the addition
of an alkyl chain (hexyl) is expected to increase the structural
order of the film and thus enhance the charge transport.16a,22 In
our cases, however, the mobility of TVAnt was 3 times higher
than that of HTVAnt. HTVAnt exhibited low FET mobility
compared to TVAnt when used as a channel semiconductor in
OTFTs. This is not surprising since charge transport in organic
semiconductors is dominated by the crystal structure, and the
less-ordered HTVAnt would not be expected to give high
mobility.23
Fig. 7 shows the drain current (IDS) versus source–drain (VDS),
and transfer characteristics of TVAnt and HTVAnt TFTs grown
ꢁ
at a substrate temperature (Tsub) of 75 C. From the electrical
transfer characteristics, we extracted the following parameters
for each device and summarized them in Table 1: the carrier
mobility, on
: off current ratio, threshold voltage, and
subthreshold swing. The TVAnt devices fabricated under various
Fig. 6 shows AFM images of 30 nm-thick films of the
oligomers deposited on OTS-treated SiO2/Si at 75 ꢁC. At this
temperature, the molecules became more ordered, and a network
of interconnected grains was observed for the TVAnt sample.
The AFM step heights for the lamellar structure of TVAnt grains
(as obtained from the films deposited at 75 ꢁC) corresponded
well to the d-spacing obtained from the XRD results and the
calculated molecular length.
Conclusions
We have synthesized two novel organic semiconductors, which
have a symmetrically substituted thienylvinylene anthracene
backbone. They show good electrical performances on SiO2/Si,
with high field-effect mobilities of up to 0.4 cm2 Vꢀ1 sꢀ1, and
can easily be synthesized in large quantities. In addition, the
high mobility of such semiconductors can be achieved at low
substrate deposition temperatures. TVAnt and HTVAnt show
promising properties for applications in organic flexible
electronics. We are currently investigating OTFT devices
featuring TVAnt and HTVAnt to improve their performance,
and the introduction of other alkyl chains to TVAnt for the
synthesis of new soluble oligomers.
Fig. 7 Source–drain current (IDS) versus source–drain voltage (VDS) at
various gate voltages (VG) for a top-contact field-effect transistor using
TVAnt deposited at Tsub ¼ 75 ꢁC on OTS-treated SiO2. The transfer
characteristics in the saturation regime at a constant source–drain
voltage (VDS ¼ ꢀ100 V) are also shown.
2238 | J. Mater. Chem., 2008, 18, 2234–2239
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1644; (b) V. Podzorov, S. E. Sysoev, E. Loginova, V. M. Pudalov
and M. E. Gershenson, Appl. Phys. Lett., 2003, 83, 3504.
12 M. Yamada, I. Ikemoto and H. Kuroda, Bull. Chem. Soc. Jpn., 1988,
61, 1057.
Acknowledgements
This work was supported by grants (F0004030-2007-23,
F0004071-2007-23) from the Information Display R&D Center,
one of the 21st Century Frontier R&D Programs funded by the
Ministry of Commerce, Industry, and Energy of the Korean
Government, and Seoul R&BD.
13 (a) C. Videlot-Ackermann, J. Ackermann, H. Brisset, K. Kawamura,
N. Yoshimoto, P. Raynal, A. EI Dassmi and F. Fages, J. Am. Chem.
Soc., 2005, 127, 16346; (b) N. Drolet, J. F. Morin, N. Leclerc,
S. Wakim, Y. Tao and M. Leclerc, Adv. Funct. Mater., 2005, 15,
1671; (c) T. C. Gorjanc, I. Levesque and M. D’lori, Appl. Phys.
Lett., 2004, 84, 930; (d) H. Meng, F. Sun, M. B. Goldfinger,
F. Gao, D. J. Londono, W. J. Marshal, G. S. Blackman,
K. D. Dobbs and D. E. Keys, J. Am. Chem. Soc., 2006, 128, 9304;
(e) H. Klauk, U. Zschieschang, R. T. Weitz, H. Mong, F. Sun,
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