Regioregular Polythiophene FETs

Regioregular poly(3-alkylthiophene)s have been shown to have very different properties from their corresponding regiorandom polymers, such as smaller bandgaps, better ordering and crystallinity in their solid states, and substantially improved electroconductivities [88]. The transistor properties of poly(3-alkylthiophene)s have been studied by Bao et al. and field-effect mobility as high as 0.05cm V s and on/off ratios close to 10 have been reported [84]. 

Devices have been prepared by both casting and spin-coating and the off-currents of cast devices usually tend to be higher than those made from spin-coating, probably due to the higher thickness of the former [84]. However, the mobilities obtained 

9 Oligo- and Poly thiophene Field Effect Transistors Oligo- and poly thiophene field effect 

Two methods have been shown useful in lowering the off-current while keeping the field-effect mobility almost unchanged [84]. In the first method, the films were treated with ammonia by bubbling N2 through ammonium hydroxide aqueous solution (see Table 2 entries 7 and 14). It was also found that thermal treatments such as heating the samples under N2 at 100°C for 5 min can lower off-currents (see Table 2 entry 11). However, heating to 150 C lowers the mobility dramatically. 

Transistors made from regioregular poly(3-alkylthiophene)s with octyl (POT) and dodecyl (PDT) substituents have also been fabricated and their electrical characteristics have been studied [89], POT has a similar field-effect mobility as PHT, while PDT has a much lower mobility of the order of 10 cm V s . Both PHT and PDT have very strong, sharp diffraction peaks at 5.4° 16 (16.36 A) and 

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