Development of Active Functional Polymers for p- and n-type OFET- Applications

Here we present a concept to improve the field effect transistor performance of P3HT in terms of threshold voltage stability as well as the stability in ambient atmosphere by introducing a strong acceptor dopant in the main polymer chain. In our concept the direct introduction of the acceptor dopant in the polymer main chain ensures the strucural stability against diffusion processes. P3HTs with different contents of acceptor molecules which are fixed linked in the main chain of the polymer, have been synthesized using the McCullough Grignard metathesis method. As acceptor unit has been integrated tetrafluorbenzene (TFB). The introduced dopant amount has been varied in order to obtain an optimum between the processability of the polymers and the resultant transistor performance. Compared to the p-type semionducting polymers the n-type organic materials are markedly less developed. Recently an interesting solution to this task has been proposed in the form of a conjugated ladder-type poly(benzo-bisimidazobenzo-phenanthroline) (BBL) showing either ambipolar or n-type field effect properties dependent upon the sample preparation and processing. However this rigid-chain ladder polymer is not soluble in the common organic solvents resulting in a rather complicated technological transfer. We report the significant improvement of the BBL-processing utilizing aqueous colloidal dispersions and their OFET-application. The resultant devices demonstrate ambipolar electronic transport with charge carrier mobilities in the range of 10^-5cm²/Vs without specific optimization procedures.