M.-D. DAMACEANU, M. BRUMA
New Organic Semiconducting Materials and Field-Effect Transistors Made from Them

Abstract.
New organic materials based on oligomers containing fluorene or thiophene units have been synthesized and characterized in order to be used as active layers in field-effect transistors (OFETs). The oligomer solutions were cast onto quartz plates and the resulting thin films where then investigated from the electronic and optical properties point of views. Electrochemical characterization of these molecules as films evidenced their reversible oxidation processes at low oxidation potentials, corresponding to the formation of radical cations, and in some cases dications, a necessary condition for OFET active material. Some of them presented reversible reduction process corresponding to the for- mation of radical anions. Their electronic energy scheme is well matched to the high work-function metal electrodes (Au or Pt). The absorption maxima of the films are strongly shifted to blue region, as compared with the absorption of oligomer solutions. Molecular modeling evidenced the closely packed stacking arrangements in cast films. High mobility OFETs in top- or bottom-contact configuration were realized with the vacuum-evaporated films of the synthesized organic materials.

Keywords: thiophene oligomers, semiconducting materials, field-effect transistors, active layers.