Organic-based field-effect transistors: Critical analysis of the semiconducting characteristics of organic materials

Conjugated polymers, e.g., polyacetylene and polythiophenes, conjugated thiophene oligomers and metallophthalocyanines have been proposed in the literature as organic semiconductors for the fabrication of organic-based field-effect transistors, FET. The poor performances generally shown by these FET have been attributed to the very low carrier mobility in organic semiconductors, and the improvement of this parameter has been the objective of a large number of works. The analysis of the mode of operation of organic-based FET, which operate through the formation of an accumulation layer, shows that an ohmic contribution has to be taken into account in the total observed current output of the devices. The conductivity of the organic semiconductor plays thus a significant role in the FET characteristics, although this point has been up to now rarely considered. In this regard, most of the claims in the literature about high mobility achievements are shown to be of limited significance. Conjugated oligomers are actually the only class of organic semiconductors presenting high mobility together with low conductivity, which, furthermore, indicates that interchain transfer of charge may be a much more efficient process than generally believed.