Chemistry Letters Vol.37, No.7 (2008)
(a)
(b)
767
Table 1. FET characteristics of 2-, 3-, and 4-based top contact
devices on ODTS-treated substratesa
0.0001
0.006
0.004
0.002
0
2.5E-005
Compound Tsub/ꢂC Mobility/cm2 Vꢁ1 sꢁ1 On/off ratio Threshold/V
VG = 50 V
1E-005
1E-006
1E-007
1E-008
1E-009
1E-010
1E-011
2E-005
1.5E-005
1E-005
5E-006
0
2
3
4
20
50
20
50
20
50
0.10
0.24
0.01
0.05
0.02
0.02
8 ꢃ 105
3 ꢃ 106
3 ꢃ 104
2 ꢃ 106
3 ꢃ 104
1 ꢃ 104
22
24
32
28
39
39
VG = 45 V
VG = 40 V
VG = 35 V
VG = 30 V
0
10
20
VG / V
30
40
50
0
10
20
VD / V
30
40
50
aSiO2: 200 nm, active layer: 30 nm, L=W ¼ 50=1000, S=D electrode: 50-nm
Au.
Figure 3. (a) Output characteristics of 2. (b) Transfer character-
istics of 2.
resulting in large barrier in the charge carrier injection from the
electrode to molecules.
ꢀ-stacking structure. The packing structure of 2 is a herringbone
type as shown in Figure 2b, which is in contrast to the ꢀ-stacking
in the corresponding thiazolothiazole derivatives.6 The herring-
bone packing is effective for increasing of dimensionality as
seen in pentacene, which leads to the highest performance in
thin-film transistors.12
The orientation of vacuum deposited thin films of 2–4 was
investigated by X-ray diffraction (XRD) analysis.10 The XRD
of the film of 2 deposited on SiO2/Si substrates at rt showed a
weak reflection peak. The d-spacing obtained from the first
In summary, we have developed novel benzo[1,2-d:4,5-d0]-
bisthiazole derivatives for n-channel OFETs. The herringbone
packing was revealed in the crystal of 2 by the X-ray analysis.
The field-effect electron mobility of the thin film of 2 was
0.24 cm2 Vꢁ1 sꢁ1, and the threshold voltage was much lower
than the corresponding thiazolothiazole derivative 1.
This work was supported by a Grant-in-Aid for Scientific
Research (No. 19350092) from the Ministry of Education,
Culture, Sports, Science and Technology, Japan, and Mizuho
Foundation for the Promotion of Sciences.
˚
reflection peak (2ꢁ ¼ 6:30) is 14.0 A. The simulation pattern
obtained from the single crystal data of 2 shows a (400) peak
at 2ꢁ ¼ 6:25 with a very small (200) peak. Since the long axis
˚
of molecule is in the direction of a axis (56.8 A) of the unit cell,
References and Notes
1
b) H. Meng, M. Bendikov, G. Mitchell, R. Helgeson, F. Wudl, Z. Bao,
molecule 2 may be perpendicular on the substrate. On the other
hand, the films of 3 and 4 showed no clear peaks, suggesting
amorphous or disordered structures on the substrate. These
results indicate poor intermolecular interactions of these com-
pounds on the substrate, which is unfavorable for the efficient
carrier transport. The thin films deposited on octadecyltrichloro-
silane (ODTS)-treated SiO2/Si substrates have the similar XRD
patterns to those on untreated substrates. Thus, the XRD of the
films of 2 deposited on the ODTS-treated substrate at rt and
´
Newman, C. D. Frisbie, D. A. da Silva Filho, J.-L. Bredas, P. C. Ewbank,
´
a) J. A. Rogers, Z. Bao, K. Baldwin, A. Dodabalapur, B. Crone, V. R.
Raju, V. Kuck, H. Katz, K. Amundson, J. Ewing, P. Drzaic, Proc.
Huang, D. J. Gundlach, T. N. Jackson, M. G. Kane, I. G. Hill, M. S.
2
ꢂ
˚
50 C showed a reflection peak at ca. 2ꢁ ¼ 6:70 (13.2 A).
The films of 3 and 4 exhibited no peaks even at higher substrate
temperatures.
3
4
a) R. A. Street, W. S. Wong, S. E. Ready, M. L. Chabinyc, A. C. Arias,
S. Limb, A. Salleo, R. Lujan, Mater. Today 2006, 9, 32. b) L. Zhou,
The FET devices were fabricated with top contact configu-
ration. Figure 3 shows the drain current (ID) versus source–drain
voltage (VD) and gate voltage (VG) at a drain voltage of 50-V
characteristics for the n-channel OFETs of 2 deposited at
Tsub ¼ 50 ꢂC on ODTS-treated substrates. The ID–VG curves
showed no hysteresis behavior. The FET characteristics of 2–4
are summarized in Table 1. The mobilities of 2- and 3-based
devices increased at higher substrate temperatures, whereas that
of 4-based device did not change. The device of 2 exhibited good
mobility of 0.24 cm2 Vꢁ1 sꢁ1, on/off ratio of 2:9 ꢃ 106 and
threshold voltage of 24 V. The mobility is a little lower than that
of the thiazolothiazole derivative 1. This is probably due to the
difference in intermolecular interactions between molecules.
On the other hand, the threshold voltage of 2-based device
is much decreased compared to that of 1 (67 V). This can be
attributed to the better contact between the semiconductor and
electrodes as well as the higher electron affinity. The devices
based on 3 and 4 exhibited poorer characteristics than that of
2, in particular as to the higher threshold voltages instead of
the lower LUMO levels of 3 and 4. This result can be attributed
to their amorphous-like morphology as shown in the XRD study,
a) R. C. G. Naber, B. de Boer, P. W. M. Blom, D. M. de Leeuw, Appl.
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C. Sommer, G. Jakopic, G. Leising, B. Stadlober, I. Graz, N. Gaar, R.
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9
10 Supporting Information is available electronically on the CSJ-Journal
11 Crystallographic data reported in this manuscript have been deposited
with Cambridge Crystallographic Data Centre as supplementary
publication no. CCDC-685937.
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