Oligothiophene FETs

Selenophene-based FET materials had not been studied until 2003, when Kunugi et al. evaluated the semiconducting characteristics of quaterselenophene (11) [101], The hole mobility (3.6 x 10 cm s ) of 11 is comparable to that of quaterthiophene. This is in good agreement with the above description that doped oligoselenophenes have nearly the same conductivities as oligothiophenes. 

FET applications of thiophene-based materials have a two-decade history. Pioneering work was conducted by Koezuka and co-workers [33], The device utilized electrochemically synthesized polythiophene as the channel layer, its mobility being 10 cm V s . This work was followed by Garnier and co-workers [13], who used sexithiophene as the channel layer and recorded an enhanced mobility of 10 cm s . Akimichi et al. [14] made FET devices using alkyl-capped oligothiophenes and mentioned that the alkyl substitution not only improves the chemical stability of the oligothiophenes but also enhances the mobility. A similar substitution effect was also observed with other oligomers [34, 35]. 

The other aspect is related to the basic studies of the charge-transport processes and mechanisms in the molecular conductive materials. This is because fundamental transport properties such as mobility can be easily defined on these electronic devices. Optical processes can be appropriately dealt with similarly. In this section, we highlight the thin-film electronic devices of FETs and LEDs based on the oligothiophenes in relation to the devices using other organic materials. Details of the fabrication and action characteristics of the devices using those materials can be seen in recent papers and reports. 

In the FET configurations the interface of the gate insulator and organic semiconductor layer plays a cmcial role in charge transport [205,214]. Gamier et al. found that an oligothiophene (sexithiophene) showed a mobility of 0.46 ca fWs on CYEPL with a high... 

The above discussion is also true of transport results of the oligothiophenes. Note here that mobility measured for most of the organic glasses is defined as drift mobility [187]. This mobility is usually smaller than conductivity mobility [187] as defined on FET devices. 

Ohshita J, Izumi Y, Kim DH, Kunai A, Kosuge T, Kunugi Y, Naka A, Ishikawa M (2(X)7) Applications of silicon-bridged oligothiophenes to organic FET materials. Oiganometallics 26 6150-6154... 

The charge mobility in sexithiophene was originally estimated from the SCLC of a symmetric sandwich configuration (see section 5.3.1.2). However, the most widely used technique now is that of field-effect. The first FET based on an oligothiophene (sexithiophene) was reported in 1989 by Horowitz and coworkers [64], with a mobility of a few 10 cm s V . Since then, the performance of oUgothiophene FETs... 

K. Waragai, H. Akimichi, S. Hotta, H. Kano and H. Sakaki, FET characteristics of substituted oligothiophenes with a series of polymerization degrees, Synth. Metal., 1993,57,4053. 

Research on organic/polymeric FETs has not been confined to oligothiophene/ poly thiophene materials. Important advances have been made with other classes of materials such as fullerenes [12, 13], fused ring compounds such as pentacene [14, 15], and the phthalocyanines. While most of this chapter is focused on oligo-and poly-thiophene FETs, there are a few brief discussions of FETs with other organic materials to illustrate some key points. 

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