Transistor polythiophene

Polythiophene can be synthesized by electrochemical polymerization or chemical oxidation of the monomer. A large number of substituted polythiophenes have been prepared, with the properties of the polymer depending on the nature of the substituent group. Oligomers of polythiophene such as (a-sexithienyl thiophene) can be prepared by oxidative linking of smaller thiophene units (33). These oligomers can be sublimed in vacuum to create polymer thin films for use in organic-based transistors. 

Bao, Z. Lovinger, A. 1999. Soluble regioregular polythiophene derivatives as semiconducting materials for thin film field-effect transistors. Chem. Mater. 11 2607-2612. 

Ong, B. Wu, Y. Liu, P. 2005. Design of high-performance regioregular polythiophenes for organic thin-film transistors. Proc. IEEE 93 1412-1419. 

In this article we report the synthesis and electrochemical properties of the polymer derived from oxidation of X, poly(I), and the characteristics of a microelectrochemical transistor based on the polymer. Poly(I), which is formed by electrochemical oxidation of X, Equation 1, consists of a conducting polymer backbone, polythiophene. 

Recently, several molecule-based microelectrochemical devices have been developed by the Wrighton group.(14.15.21-22) A microelectrode array coated with poly(I) results in a microelectrochemical transistor with the unique characteristic that shows "turn on" in two gate potential, Vq, regimes, one associated with the polythiophene switching from an insulator to a conductor upon oxidation and one associated with the v2+ + conventional redox centers. 

Scheme IV, A poly(I)-based microelectrochemical transistor that turns on when VG is moved from VG (ie +0.4 V vs. Ag+/Ag) where polythiophene is reduced and insulating to Vq4 (ie +0.7 V vs. Ag+/Ag) where polythiophene is oxidized and conducting. This transistor also turns on to a smaller extent at E0/ (V2+/+), Vq1 = -0.63 V vs. Ag+/Ag. At VG significantly (>0.2 V) more negative (Vq2 < -0.8 V vs. Ag+/Ag) or positive (+0.4 V > Vq > -0.4 V vs. Ag+/Ag) of E° (V2+/+) only the reduced or oxidized form of viologen redox centers is present, respectively, and this device is...

The poly(I)-based transistor is the first illustration of a microelectrochemical transistor based on a combination of a conducting and a conventional redox polymer as the active material. The transistor "turns on" at VG corresponding to oxidation of the polythiophene backbone. The resistivity of poly(I) declines by a factor of 105 upon changing VG from 0.4 V to 0.8 V vs. Ag+/Ag. When Vg is moved close to the one-electron reduction potential of V2+/+, the conventional redox conductivity gives a small degree of "turn on". A sharp Iq-Vq characteristic results, with an Ip(peak) at Vq = E° (V2+/+). Though the microelectrochemical devices based on conventional redox conduction have both slow switching speed and a... 

Polythiophenes (PTs)/CNTs composites have emerged as an intriguing system for use as photovoltaic devices and field effect transistors [57]. Swager and Bao independently reported methods for the assembling of PTs/CNTs systems and showed their great potential as transparent conductive films [58]. Another interesting application arises from the possibility to functionalize the polythiophene backbone for applications as chemical sensors [134]. 

A polyacetylene field-effect transistor has been described622 but the response time is slow, apparently because the carrier mobility is low. An FET has been made from polythiophene but source-drain currents were less than 20 nA for drain voltages up to 50 V. The hole mobility was very low, calculated to be 2 x 10 5 cm2 V-1 s 1 623). 

Several n-conjugated polymers and oligomers (polyacetylene, several polythiophenes, Ooct-OPV5 oligomers, and phthalocyanines) have been used for the active layer of the transistors. 

Wu Y, Liu P, Ong BS, Srikumar T, Zhao N, Botton G, Zhu S. (2005) Controlled orientation of liquid-crystalline polythiophene semiconductors for high-performance organic thin-film transistors. Appl Phys Lett 86 142102. 

Ong BS, Wu Y, Liu P, Gardner S. (2004) High-Performance semiconducting polythiophenes for organic thin-film transistors. / Am Chem Soc 126(11) 3378-3379. 

Mechanically durable and structurally flexible polythiophene derivatives have been prepared that are useful as semiconducters in thin film field effect transistors and are soluble in chlorobenzene. Materials prepared from these agents have a bandgap between 1.5 and 3.0 eV that enhance their function as film transistors. 

Thin film transistor devices were fabricated by spin coating using a 1% solution of the selected polythiophene dissolved in chlorobenzene and drying in vacuo at 80°C for 20 hours. No precautions were taken to exclude oxygen, moisture, or light during device fabrication. From transistors with dimensions of 5000 x 60 m, electrical properties were determined as summarized in Table 1. 

Figure 1.2 illustrates the typical design of a printed transistor the source and drain electrodes are mounted on a polyester foil, followed by the semiconducting layer of polymer (i.e. polythiophenes), the insulating layer of polymer insulators is on top and, as the final layer, the gate electrode. 

New applications of organic transistors demand increased switching speed which might be achieved mainly either by new materials or by reduced dimensions of the device. For cheap production, materials are usually limited to those processible from solution. In this section we will follow the second route of reduced dimensions and restrict the material basis to oligio- and polythiophenes, i.e. DH7T and rr-P3HT. 

A great deal of work has been done to characterize the structure of films cast from chemically prepared polythiophenes.96 Most of this work has been conducted on undoped PTh s because of their importance in electronic devices, such as thin-film transistors and photovoltaics. Depending on composition and processing conditions, the crystallinity can be as high as 30% in polythiophenes.97 A layered structure is usually formed in PTh crystals between extended chains held together by ir-slacking, with additional structural order introduced by alkyl side-chain interactions in functionalized PTh s.98 Chemically synthesized PTh powders exhibit a... 

Synthesis of ultrapure, processable, and high-mobility organic transistor semiconductors (thiophene oligomers, anthradithiophenes, benzodithiophenes, phtalocyanins, polythiophenes) 01ACR359. 

Koezuka, H., Tsumura, A., and Ando, T., Field-effect transistor with polythiophene thin-fihn, Synth. Metal, 18, 699, 1987. 

S.J., Chang, T.Y., Chang, C.W., Joo, M.K., Ryu, C.Y. and Cho, K.W., Enhancement of field-effect mobility due to surface-mediated molecular ordering in regioregular polythiophene thin film transistors, Adv. Func. Mater, 15, 77-82, 2005. 

Kline, R.J., McGehee, M.D. and Toney, M.F., Highly oriented crystals at the buried interface in polythiophene thin-film transistors, Nat Mater, 5, 222-228, 2006. 

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