High-mobility organic thin-film transistors based on α,α^′-didecyloligothiophenes

We have fabricated organic thin-film transistors and integrated circuits based on the small-molecule organic semiconductors α,α^′-didecylquaterthiophene, α,α^′-didecylquinquethiophene, and α,α^′-didecylsexithiophene. The organic semiconductors were deposited by thermal evaporation, with solution-processed and cross linked poly-4-vinylphenol serving as the gate dielectric layer. We have found that bottom-contact devices based on these materials have better electrical performance than top-contact devices, presumably due to more efficient carrier injection from bottom contacts due to the presence of the relatively long alkyl chains substituted at the α- and ω-positions of the oligothiophene molecules. Bottom-contact transistors have carrier mobility as large as 0.5 cm²/V s and on/off current ratio as large as $105,$ and ring oscillators fabricated using bottom-contact transistors and α,α^′-didecylsexithiophene as the organic active layer have signal propagation delay as low as 30 μs per stage.