A chrysene-based liquid crystalline semiconductor for organic thin-film transistors

Article abstract of DOI:10.1039/c7tc05063a

We report the synthesis and characterization of a non-liquid crystalline material, 2-phenylchrysene (Ph-CHR), and a liquid crystalline material, 2-(4-dodecyl phenyl)chrysene (C12-Ph-CHR), and discuss their organic thin-film transistor (OTFT) device perfor

Full text of DOI:10.1039/c7tc05063a

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ISSN 2050-7526
PAPER
~
Nguyên T. K. Thanh, Xiaodi Su et al.
Fine-tuning of gold nanorod dimensions and plasmonic properties using
the Hofmeister effects
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Chrysene-based Liquid Crystalline Semiconductor for Organic
Thin-Film Transistors
Received 00th January 20xx,
Accepted 00th January 20xx
Celebrating 50 years of Professor Fred Wudl’s contributions to Organic Electronics
Yaowu He,a Wenjun Xu,a Imran Murtaza,b,c Chao Yaoa, Yanan Zhua, Aiyuan Li a, Chao He a and
Hong Menga *
DOI: 10.1039/x0xx00000x
www.rsc.org/
We report the synthesis and characterization of a non-liquid crystalline material, 2-phenylchrysene (Ph-CHR) and a liquid
crystalline material, 2-(4-dodecyl phenyl)chrysene (C12-Ph-CHR) and discuss their organic thin-film transistors (OTFTs)
device performance. The concept of designing chrysene derivatives is derived from the similar electronic structure of
chrysene and [1]benzothieno[3,2-b][1]benzothiophene (BTBT), which is a very famous core for organic semiconductors.
OTFTs, based on Ph-CHR and C12-Ph-CHR, are fabricated by vacuum-deposition on octyltrichlorosilane (OTS(8)) treated
Si/SiO2 substrates. Our experimental results show that OTFTs based on Ph-CHR possess higher mobility than that of OTFTs
based on BTBT derivative 2-phenyl[1]benzothieno[3,2-b][1]benzothiophene (Ph-BTBT). The liquid crystalline material C12-
Ph-CHR achieves the highest carrier mobility of up to 3.07 cm2V-1s-1 with on/off ratio of 3.3×106 for polycrystalline organic
thin-film transistors in ambient air. The results indicate that chrysene derivative C12-Ph-CHR is a promising candidate for
applications in electronic devices.
using Sm E precursor thin films and achieved the highest mobility
up to 13.9 cm2V-1s-1 in OTFTs. Our group has also recently reported
Introduction
Organic thin film transistors (OTFTs) which have the advantages
of low manufacturing costs and large area fabrication process are
expected to be used as the key elements for realizing the next
generation electronics, such as for flexible displays and printed
electronics.1,2 The design and synthesis of small molecule organic
materials used as semiconductors in OTFTs have increased
significantly in recent years because they can be easily synthesized
in large quantities and have reliable device performance. Numerous
efforts on synthesis have been devoted to develop superior organic
semiconductor materials with high charge carrier mobilities.
[1]Benzothieno[3,2-b][1]benzothiophene (BTBT) derivatives have
attracted scientists’ attentions due to their high carrier mobility
and stability in ambient air. Recently, the liquid-crystalline
materials based on OTFTs have attracted much interest because
liquid crystals can form well-ordered polycrystalline thin-films
depending on the deposition method and thermal annealing of the
liquid crystal phase.3-11 Lino and co-workers reported a liquid
crystalline material Ph-BTBT-10 with Sm E phase4 which was able to
form a uniform and molecularly smooth polycrystalline thin film by
a series of air-stable liquid crystalline semiconductor materials
based on [1]benzothieno[3,2-b]benzothiophene (BTBT) derivatives,
which exhibit highly ordered liquid crystal phase with high mobility
in OTFTs.12-14 However, it is still a great challenge to develop novel
organic semiconductors with high mobility as well as good air
stability and simple synthesis method for practical applications of
OTFTs.
The structure of chrysene is composed of four aromatic rings
fused in a linear manner and is similar to that of BTBT. Whereas, the
synthesis method of chrysene derivatives is simpler as compared to
that of the BTBT derivatives. The energy levels of BTBT, and
chrysene core were modelled by B3LYP-G∗. The chemical structures,
lowest unoccupied molecular orbital (LUMO) and highest occupied
molecular orbital (HOMO) levels of these two compounds are
shown in Figure 1 and the LUMO, HOMO energy levels and HOMO-
LUMO gaps are summarized in Table S1. It can be seen that the
Figure 1. The calculated frontier orbital (HOMO and LUMO)
distribution of BTBT and chrysene
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Scheme 1 Synthetic approach for Ph-CHR and C12-Ph-CHR
derivative, Ph-BTBT.14 OTFTs based on C12-Ph-CHR demonstrated
high carrier mobility of up to 3.07 cm2V-1s-1 with on/off ratio of
3.3×106, which is among the highest mobilities shown by
polycrystalline thin films of chrysene derivatives. 19, 20
Results and discussion
Synthetic procedures
Synthetic route of chrysene derivatives Ph-CHR and C12-Ph-CHR are
shown in Scheme 1. The target organic semiconductor materials
can be easily prepared through four simple procedures. First, the
compound (E/Z)-1-[2-(3-bromophenyl)ethenyl]naphthalene (3) was
Figure 2 Hole transfer integrals for the molecular pairs taken
from single crystals of BTBT and Chrysene.
band gaps and the HOMO energy levels of BTBT and chrysene easily synthesized in large scale from commercially available
are strikingly similar. The calculated results indicate that chrysene reagents by Wittig reaction. In particular, the key intermediate
and BTBT core possess similar electronic structure.
compound 2-bromochrysene (4) was synthesized by
a
photochemical reaction using cis/trans isomer mixture 1-[2-(3-
bromophenyl)ethenyl]naphthalene as precursor with 92% yield. Ph-
CHR and C12-Ph-CHR were synthesized by Suzuki coupling reaction
between 5a or 5b and 2-bromochrysene with high yield and pure
compounds were obtained by sublimation. The chemical structures
were characterized by HRMS and NMR.
The charge transfer integrals were calculated from the single
crystals of BTBT and chrysene by the modeling software.15-17 As
shown in Figure 2 and Table S2, chrysene exhibits strong transfer
integrals of 51.52, 40.08 and 40.08 meV for all the three pairs while
for BTBT, strong electronic coupling is found only in one pair each.
The calculation results indicate that chrysene is expected to have
higher mobility than BTBT, owing to the stronger electronic
couplings.
Photochemical and Thermal Properties
In order to obtain the HOMO and LUMO energy levels and study
the air stability of the materials, Ph-CHR and C12-Ph-CHR, UV-vis
spectra and cyclic voltammogram (CV) of their dichloromethane
solutions were tested in nitrogen. Figure 3a shows the UV-vis
spectra of the materials Ph-CHR and C12-Ph-CHR. Our experimental
results reveal that those two materials display similar absorption
characteristics. The maximum absorption edges of Ph-CHR and C12-
Ph-CHR are 380 and 379 nm, indicating that their energy gaps are
3.26 and 3.27 eV, respectively. All peaks of their fluorescence
spectra range from ∼350 nm to ∼450 nm, showing blue emission
With these results and expectations in mind, we focused our
attention on chrysene derivatives and successfully designed and
synthesized a non-liquid crystalline material of 2-phenyl chrysene
(Ph-CHR) and a liquid crystalline material of 2-(4-dodecyl phenyl)
chrysene (C12-Ph-CHR). The alkyl chain can improve the carrier
mobility of the materials, while the phenyl group can enhance the
thermal stability and molecular density.18 We present here an
efficient synthetic method of chrysene derivatives Ph-CHR and C12-
Ph-CHR, their electrochemical and optical properties, thin film
morphology and OTFT performance. The Ph-CHR-based OTFTs show
better charge transport properties than those based on BTBT
(Figure 3c). The fluorescence quantum yield (Φ) of the materials Ph-
CHR and C12-Ph-CHR were measured using 2-amino pyridine as a
2 | J. Name., 2012, 00, 1-3
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Figure 4 DSC of Ph-CHR (a) and C12-Ph-CHR (b).
eV), which hinders the charge injection from organic
semiconductors to Au electrodes in OTFTs. The LUMO levels of Ph-
CHR and C12-Ph-CHR of -2.53 and -2.51 eV, respectively, can be
calculated according to the optical band gaps. These values are
significantly lower than those of Cn-Ph-BTBT (n = 0, 6 and 12).12,14
Figure 3 (a)
As shown in Figure S1, the materials Ph-CHR and C12-Ph-CHR
display good thermal stability with decomposition temperatures of
320 and 340°C, respectively, as measured by thermogravimetric
analysis (TGA). No phase transition is found for Ph-CHR in
differential scanning calorimetry (DSC) scans before it began to
decompose. In cooling process, DSC curve of C12-Ph-CHR shows
three phase transitions: an isotropic-liquid crystal (LC1) transition at
302.0°C, a LC1 – LC2 transition at 291.5°C and a LC2 – crystal
transition at 71.7°C (Figure 4).
UV-vis
spectra (a), cyclic voltammogram (b), fluorescence spectra (c) and
quantum yield (d) of compounds Ph-CHR and C12-Ph-CHR in
dichlormethane.
reference (Fig. 3d).19 For the estimation of
Φ, 0.1 M H2SO4 solution
of 2-amino pyridine and dichloromethane was used to prepare
solutions of Ph-CHR and C12-Ph-CHR with an optical density of less
than 1. From these solutions fluorescence spectra were taken and
by integration, the fluorescence quantum yields of 15% and 20%
were estimated for Ph-CHR and C12-Ph-CHR, respectively.
OTFT Devices with Vapor-Deposited Thin Film
In order to investigate the semiconductor performance of the
non-liquid crystalline material Ph-CHR and the liquid crystalline
material C12-Ph-CHR, OTFT devices with a bottom-gate/top-contact
structure were fabricated by vacuum deposition on OTS(8)-treated
Si/SiO2 substrates and were characterized under ambient conditions.
The thickness of the organic semiconductor thin films was about 50
nm. For both Ph-CHR and C12-Ph-CHR, various substrate
temperatures (Tsub) were selected in order to obtain the best device
CV tests were carried out to measure the HOMO energy levels of
the materials Ph-CHR and C12-Ph-CHR under a standard three
electrode cell electrochemical workstation (Figure 3b). The energy
levels were estimated using -4.8 eV as the HOMO level for the
standard ferrocene/ferrocenium (Fc/Fc+) redox system with
a
dichloromethane solution containing 0.1 M TBAPF6.20,21 Both Ph-
CHR and C12-Ph-CHR exhibit low-lying HOMO levels, estimated to
be -5.79 and -5.78 eV, respectively, which are lower than that of
BTBT derivatives Cn-Ph-BTBT (n= 0, 6 and 12).12,14 It indicates that
Ph-CHR and C12-Ph-CHR are relatively air stable organic
semiconductor materials.22-24 However, the HOMO levels of those
two materials do not match well with the work function of Au (5.1
performance. Table
1 summarizes the OTFTs performance
containing the carrier mobility, on/off current ratio (Ion/Ioff),
threshold voltage (Vth) and subthreshold swing (S) for each device.
Representative output characteristics (Id-Vd) and transfer
Table 1 The OTFT performances of Ph-CHR and C12-Ph-CHR
μ
[cm2V-1s-1]b
I / I
on off
Tsub ( C)a
Compound
Ph-CHR
Vth (V)
S
°
sat
25
60
0.084 0.042 (0.15)
(7.7 ±4.4) 103
-82.7±0.2
-84.3±0.2
-47.6±1.0
-39.9±1.0
6.9±0.5
5.7±0.1
8.1±0.4
6.9±0.5
±
×
(8.4 ±5.1) 102
0.014±0.008 (0.020)
0.56±0.17 (0.86)
0.57±0.06 (0.65)
×
25
(3.0 ±1.5) 105
×
25(Doping)c
(2.4±0.1) 105
×
(4.0 ±2.3) 105
60
90
2.03±0.51 (2.71)
2.30±0.35 (3.07)
1.01±0.32 (1.44)
-48.9±0.4
-46.5±0.4
-51.5±0.5
7.0±0.3
10.1±0.3
6.6±0.6
×
C12-Ph-CHR
(2.5 ±0.6) 105
×
120
(2.2 ±0.9) 105
×
a)
b)
Note: Substrate temperature. All the data were reported in average value from more than 5 devices. The values in parenthesis
represent the maximum mobility. c) The OTFT devices were doped with F4-TCNQ.
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Figure 5 Transfer and output curves of OTFTs of C12-Ph-CHR films grown on the OTS-treated substrates at Tsub = 25°C (a, e), 60°C (b, f),
90°C (c, g), and 120°C (d, h). a), b), c) and d): Id–Vg characteristics Curves; e), f), g) and h), Id-Vd characteristics curves
characteristics (Id-Vg) of the OTFTs at various conditions are shown to obtain higher mobility in the devices fabricated at the higher
in Figure 5.
substrate temperatures. The OTFTs fabricated at Tsub = 60°C show a
higher on-current and a higher mobility of 2.03±0.51 cm2V-1s-1. This
value is four times higher than the former. As shown in Figure 5c,
the devices fabricated at Tsub = 90°C show relatively higher carrier
mobility. OTFTs based on C12-Ph-CHR exhibit an average mobility of
2.30±0.35 cm2V-1s-1 and on/off current ratio over 105 as measured
for five devices. In particular, the highest mobility of up to 3.07
cm2V-1s-1 was achieved for the C12-Ph-CHR-based OTFTs in the
saturation regime, which is higher than that of the mobility of the
parent chrysene-based devices and comparable with the highest
mobility so far reported for OTFTs based on polycrystalline thin
films of chrysene derivatives as the active hole transporting layers.
This result indicates that the polycrystalline films of C12-Ph-CHR
fabricated at Tsub = 90°C are less defective. However, the OTFTs
performance decreases with the further increase in substrate
temperature. We attribute low mobility to the discontinuity of the
film caused by cracks produced at high substrate temperature. (See
the following discussion on the film morphology). Unfortunately, all
the devices show high threshold voltages. This may be due to the
mismatch of HOMO levels of Ph-CHR and C12-Ph-CHR (∼ -5.78 eV)
with the work function of gold (5.1 eV), and hampered charge
injection caused by the charge trap states. Doping of the
semiconductor materials with an additional electron acceptor, such
as molybdenum oxide (MoOx) and 2,3,5,6-tetrafluoro-7,7,8,8-
tetracyanoquinodimethane (F4-TCNQ), could decrease the Vth of
OTFT devices.25-29 In the present study, the OTFTs based on C12-Ph-
CHR as-deposited were doped with F4-TCNQ.28 The experimental
results indicate that F4-TCNQ treatment can decrease the threshold
voltages and contact resistance without reducing the charge
mobility of the OTFTs based on C12-Ph-CHR as-deposited. (Table 1
and Figure 6).
All of the devices exhibit typical p-channel field-effect
characteristics under ambient conditions. The average carrier
mobility based on eight devices for Ph-CHR is 0.084 cm2V-1s-1, which
is higher than Ph-BTBT-based OTFTs and substrate temperature has
no obvious effect on the OTFTs device performance. The C12-Ph-
CHR-based OTFTs shows better device performance than that of Ph-
CHR-based OTFTs under the same conditions. The OTFTs based on
C12-Ph-CHR and fabricated at Tsub = 25°C display the mobility as
high as 0.86 cm2V-1s-1 and an average mobility of 0.56±0.17 cm2V-1s-
1. It is worth noting that the mobility of OTFTs fabricated in this
condition varied in a relatively broader range, which indicates that
the thin films are not very uniform. It is interesting to note that the
liquid crystal material C12-Ph-CHR tends
Figure 6 C12-Ph-CHR-based OTFT characteristics: a) transfer curve
(Id–Vg characteristics) and b) output curve (Id–Vd characteristics) of
as-deposited (without doping) and the devices doped with F4-TCNQ
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Figure 8 Thin-film XRD pattern of Ph-CHR (a) and C12-Ph-CHR (b) as
deposited at various substrate temperatures
Figure 7 AFM height images of thin-films, the Ph-CHR as-deposited
(a), fabricated at Tsub = 60°C (b), and the films of C12-Ph-CHR
deposited at different substrate temperature: (c) as-deposited, (d)
60 °C, (e) 90 °C, and (f) 120°C, respectively.
reflection in the thin-films deposited at Tsub = 90 °C. When Tsub
increased to 120°C, the intensity of the peaks weakens because of
cracks in the thin film. All the results of thin films morphology agree
with OTFTs device performance.
Morphology of Vapor Deposited Thin Films
Experimental
To study the relationship between thin film morphology and
OTFTs device performance, we further study the polycrystalline thin
films based on Ph-CHR and C12-Ph-CHR fabricated at various
substrate temperatures by atomic force microscopy (AFM) and thin
film X-ray diffraction (XRD). Figure 7 shows the AFM images of the
thin-films of Ph-CHR and C12-Ph-CHR on the OTS(8)-treated Si/SiO2
substrates deposited at various substrate temperatures. The
substrate temperature significantly influences the crystalline
domain sizes of thin-films based on Ph-CHR, as shown in Figure 7a
and 7b. The surface of the films develop larger domains with the
increase in substrate temperature. According to the literature, the
larger domain size contributes to the improvement in carrier
General
All chemicals and solvents used were analytical reagents. The
synthetic route of chrysene derivatives Ph-CHR and C12-Ph-CHR
is
bromophenyl)ethenyl]naphthalene (
4,4,5,5-tetramethyl-1,3,2-dioxaborolane
presented
in
Scheme
) and 2-(4-dodecylphenyl)-
5b was prepared
1
.
(E/Z)-1-[2-(3-
3
(
)
according to the reported methods.12,31 The chemical structures
were confirmed by 1H NMR and H RMS. Thermo-gravimetric
analysis (TGA) was measured on a TA Instruments TA2950 TGA
system at a heating rate of 15 °C/min and a nitrogen flow rate of
60 cm3/min. Differential scanning calorimetry (DSC) was carried
out on a TA Instruments DSC Q1000 at a heating or cooling rate
mobility.30 However, in the thin-films of Ph-CHR deposited at Tsub
60°C, non-continuous crystallites are observed, which cause weaker
OTFTs device performance than that of OTFTs deposited at Tsub
=
of 10 °C/min under a nitrogen flow. Thin-film morphology was
=
studied in atomic force microscopy (AFM) on a SPA400HV
instrument with a SPI 3800 controller (Seiko Instruments). XRD
patterns were recorded using a Bruker D8 advance X-ray
25°C. For C12-Ph-CHR, the uniformity of the thin-films on the
substrate is also tremendously influenced by the substrate
temperature; the thin films morphology transforms from
a
diffractometer with
a Cu Kα source (λ= 1.541 Å). The
relatively rough surface at room temperature (Figure 7c) to
progressively more uniform with increase in the substrate
temperature (Figure 7d and 7e). This result of thin-film morphology
is consistent with OTFTs device performance. The thin-films have
smoother surface, and the OTFTs exhibit higher mobility. The films
based on C12-Ph-CHR as deposited at Tsub = 90 °C have the lowest
RMS roughness with a corresponding highest mobility of 3.07 cm2V-
1s-1. At the higher substrate temperature (Tsub = 120°C), a large
number of cracks are observed in the films owing to the strong
crystallization of the C12-Ph-CHR. The mobility of OTFTs fabricated
at Tsub = 120°C decreases to 1.01±0.32 cm2V-1s-1 (Figure 7f).
characteristics of the OTFT devices were measured at room
temperature in dark ambient conditions using a Keithly 4200
semiconductor parameter analyzer.
Synthesis
2-bromochrysene
(4)
:
(E/Z)-1-[2-(3-bromophenyl)ethenyl]
naphthalene (3, 6.18 g, 20 mmol) and iodine (6.1 g, 24 mmol)
were dissolved in toluene (1 L) and placed in a photochemical
vessel. The mixture solution was degassed by purging with
nitrogen for 30 min. Then 2-ethyloxirane (14.4 g, 0.2 mol) was
added and the resultant solution was irradiated with halogen
lamp (600 W, ∼450 nm). After the reaction was completed, the
Figure 8 shows the thin-film XRD patterns of Ph-CHR and C12-Ph-
CHR fabricated at various conditions. The thin-film XRD patterns of
both Ph-CHR and C12-Ph-CHR displays higher order reflections with
the increase of substrate temperature, indicating a higher order in
thin films deposited at higher substrate temperatures. The thin-
film XRD patterns of C12-Ph-CHR present the highest order
mixture was concentrated. The pure product was obtained by
recrystallization from petroleum ether. 1H NMR (300 MHz, CDCl3)
δ 8.82 – 8.70 (m, 2H), 8.64 (dd, J = 9.0, 3.3 Hz, 2H), 8.14 (d, J =
2.1 Hz, 1H), 8.07 – 7.97 (m, 2H), 7.91 (d, J = 9.1 Hz, 1H), 7.77 (dt,
J = 5.3, 2.7 Hz, 1H), 7.74 – 7.61 (m, 2H); 13C NMR (75 MHz, CDCl3)
δ 133.43, 132.39, 132.15, 131.67, 130.53, 129.74, 129.09, 128.57,
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128.20, 127.81, 126.88, 126.59, 126.13, 124.97, 123.06, 122.43, durability.
Being
isoelectronic,
[1]benzothieno[3,2-
120.80, 120.37.32
b]benzothiophene and chrysene possess similar energy levels.
The synthesis of chrysene derivatives is very simple, by
introducing a photochemical reaction, compared with that of
2-phenyl chrysene (Ph-CHR) and 2-(4-dodecylphenyl) chrysene
(C12-Ph-CHR): 2-bromochrysene
4 (10 mmol), 5a or 5b (15
the [1]benzothieno[3,2-b]benzothiophene derivatives.
The
mmol), 15 mmol (2 mol/L) K2CO3 and methyl trioctyl ammonium
chloride (15 mmol) were added to a Schleck flask. The mixture
solution was degassed by purging with N2 for 20 min. Then
Pd(PPh3)4 was added and the reaction mixture was stirred for
average carrier mobility of the OTFTs based on Ph-CHR is 0.084
cm2V-1s-1, which is higher than that of OTFTs based on BTBT
derivative Ph-BTBT. It is intriguing that the performance of the
OTFTs based on C12-Ph-CHR is dramatically improved with the
increase in substrate temperatures. The OTFTs based on C12-Ph-
two days at 110 °C. Then the reaction mixture was poured into
methanol after cooling down to room temperature. The
precipitate was filtered off, washed with water and methanol.
The crude products were further purified by sublimation to
obtain white powder Ph-CHR and C12-Ph-CHR. Ph-CHR: 1H NMR
(300 MHz, CDCl3) δ 8.98 – 8.67 (m, 4H), 8.22 (d, J = 1.8 Hz, 1H),
8.12 – 7.93 (m, 4H), 7.90 – 7.78 (m, 2H), 7.77 – 7.57 (m, 2H), 7.54
(t, J = 7.5 Hz, 2H), 7.42 (t, J = 7.4 Hz, 1H). HRMS (+ESI) m/z calcd.
for C24H17 (M+H)+ 305.1330, found 305.1319; C12-Ph-CHR:1H
NMR (400 MHz, CDCl3) δ 8.91 – 8.73 (m, 5H), 8.22 (d, J = 1.7 Hz,
1H), 8.12 – 7.96 (m, 5H), 7.74 (dd, J = 7.4, 4.0 Hz, 3H), 7.67 (t, J =
7.4 Hz, 1H), 7.36 (d, J = 8.0 Hz, 2H), 2.76 – 2.62 (m, 2H), 1.77 –
1.62 (m, 3H), 1.34 (d, J = 35.9 Hz, 24H), 0.91 (t, J = 6.8 Hz,
4H).HRMS (+ESI) m/z calcd. for C36H41 (M+H)+ 473.3208, found
473.3195.
CHR fabricated at Tsub
= 90°C achieved the maximum mobility of
3.07 cm2V-1s-1, which is, to the best of our knowledge, one of the
highest values for thin film transistors based on chrysene
derivatives. Based on these results, we conclude that chrysene
derivative C12-Ph-CHR can be a potential candidate for practical
application in future organic electronics.
Acknowledgements
This work was financially supported by National Natural Science
Foundation of China (Grant No.51603003), Shenzhen Science
and Technology Research Grant (JCYJ20170412151139619,
JCYJ20160331095335232,
JCYJ20160331095335232),
the
Fabrication and characterization of OTFT Devices
Shenzhen Peacock Program
(KQTD2014062714543296),
Guangdong Key Research Project (Nos. 2014B090914003,
2015B090914002), National Basic Research Program of China
(973 Program, No. 2015CB856500), China Postdoctoral Science
Foundation (2015M570892), Natural Science Foundation of
Guangdong Province (2014A030313800).
OTFTs were fabricated in
a
top-contact, bottom-gate
configuration on Si/SiO2 substrates at various substrate
temperatures. The substrates were cleaned with deionized
water, acetone and isopropanol, and dried with nitrogen before
irradiating them with UV for 10 min. Then the substrates were
treated with OTS (8) according to the reported procedure.12 The
thin-film (∼50 nm thick) of Ph-CHR or C12-Ph-CHR as the active
Notes and references
layer was vacuum-deposited on the Si/SiO2 substrates kept at
various temperatures at a rate of 1.0 – 2.0 Å·s-1 under high
vacuum (~2.0 ×10–4 Pa) condition. The gold films (
∼50 nm) as
drain and source electrodes were deposited using a shadow
mask. For the fabrication of doped devices, the as-deposited
films were dipped in 5 mmol/L solution of F4-TCNQ in CH3CN
and dried with nitrogen, before the deposition of the electrodes.
For a typical device, the drain-source channel width (W) / length
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(L) are 380
ꢀ
m / 38
ꢀm, 580 ꢀm / 58 ꢀm, 780 ꢀm / 78 ꢀm, and
980 ꢀm / 98
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2
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Id = (
W
/ 2L
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(Vg
−
Vth
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current Id at Vg = -60 V and Vg = 0 V.
Conclusions
In the present work, we designed and efficiently synthesized a
non-liquid crystalline material of Ph-CHR and a novel liquid
crystalline material of C12-Ph-CHR with thermal stability and
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Table of contents:
Chrysene and [1]benzothieno[3,2-
b
][1]benzothiophene possess similar electronic structure,
and chrysene is expected to have better semiconductor device performance than BTBT,
owing to the stronger electronic couplings.