New Concepts for the Development of Active Functional Polymers for p and n-Type OFET- Applications
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0965-S06-04
New Concepts for the Development of Active Functional Polymers for p and n-Type OFET- Applications Silvia Janietz, Udom Assawapirom, and Dessislava Sainova Polymer Electronics, FhG-IAP, Geiselbergstr. 69, Potsdam, 14476, Germany
ABSTRACT 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 OFETapplication. The resultant devices demonstrate ambipolar electronic transport with charge carrier mobilities in the range of 10-5 cm2/Vs without specific optimization procedures..
INTRODUCTION The development of organic field effect transistors (OFETs) based on semiconducting polymers is an important and challenging topic of the modern microelectronics which enables devices that combine the advantages of easy processing, low weight, mechanical flexibility and ability of properties-tuning by structural modifications. Most of the reported active polymers are p-type among which regioregular poly (3-hexylthiophene) (P3HT) belongs to the particularly interesting materials. This is a result of the excellent solution processability of P3HT which is combined with self-organizing properties and formation of lamellar structures enabling efficient π-stacking of the conjugated backbones. Consequently very high field effect mobility values have been reported for P3HT ( up to 0.1 cm2/V.s) [1]. The present work reveals a synthetic route to introduce fixed acceptor molecules – in this case 1,4-Dithienyl2,3,5,6-tetrafluorobenzene – in different concentrations in the poly(3-hexylthiophene) backbone while preserving the regioregularity of the 3-hexylthiophene segments in the polymer chain. The result is an improved stability and reproducibility of the OFET-devices. Compared to the p-type semion
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