Novel organic semiconductors and processing techniques for organic field-effect transistors

The performance of organic field-effect transistors (FETs) is dictated by the active material employed in such devices, The tendency of the molecules to self-assemble into highly ordered structures greatly influences charge carrier transport. Also, with the ultimate goal to realize easily produced, cheap and large area electronics, solution processing is crucial. In this aspect, we synthesized dodecyl substituted hexa-peri-hexabenzoeoronene HBC-C-12 which is a soluble disk-shaped molecule with the tendency to pack into columnar stacks. We devised a zone-casting technique that uniaxially aligned these molecules, enabling the solution processing of macroscopically ordered semiconducting layers, resulting in an improvement of the charge carrier mobility of up to two orders of magnitude compared to non-oriented films. Furthermore, a donor-acceptor copolymer was deposited from solution, giving a charge carrier mobility of mu(sat)=0.17 cm(2)/Vs even though no macroscopic order could be observed. This is surprising since any disorder acts as trapping sites and inhibits charge carrier transport. We explain this phenomenon by a close pi-stacking distance of the backbones. Finally, giant graphene molecules were successfully deposited via a novel soft-landing technique, allowing the processing of insoluble molecules into highly oriented and pure thin films. This is a promising way for achieving high performance FETs. (C) 2008 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim.