Synthesis and characterization of organic semiconducting polymers for organic thin-film transistors

Abstract

Organic thin-film transistors (OTFTs) based on semiconducting materials have been the focus of much research activity as a promising alternative to conventional amorphous silicon thin-film transistors (TFTs) for low-cost electronic applications such as memory devices, smart cards, and driving circuits of large-area display devices. Among semiconducting materials, polymer semiconductors have been the subject of particular attention because of their superior mechanical stability and processability. Furthermore, recent improvements in the charge carrier mobilities and stabilities of devices fabricated with semiconducting polymers have resulted in TFT characteristics as good as those of vacuum-deposited oligomers. We report here the synthesis and TFT properties of various solution processable semiconducting polymers. Firstly, new selenophene-based semiconducting copolymers for high performance OTFTs are reported. A series of new selenophene-based organic semiconducting copolymers, $poly(5,5\prime-bis(3-dodecylthiophen-2-yl)-2,2\prime-biselenophene)$ (PDT2Se2) and $poly(5,5\prime-bis(4,4\prime-didodecyl-2,2\prime-bithiophen-5-yl)-2,2\prime-biselenophene)$ (PDT4Se2), were synthesized by Stille and oxidative reactions. X-ray-diffraction (XRD) and theoretical calculations were used to show that PDT2Se2 films have well organized interlayer packing and $\pi-\pi$ stacking, whereas the films of PDT4Se2 have a long-range amorphous structure. The TFT characteristics of these polymers are strongly dependent on the intermolecular ordering of the polymer chains. PDT2Se2 exhibited a high hole transporting mobility of $0.02cm^2 V^{-1}s^{-1}$ due to its excellent intermolecular ordering, whereas PDT4Se2 exhibited a very poor mobility of $1.4\times10^{-5}cm^2 V^{-1}s^{-1}$. Secondly, new semiconducting polymers containing 3,6-dimethyl(thieno[3,2-b]thiophene or selenopheno[3,2-b]selenophene) for OTFTs are reported. A series of new organic semiconducting polymers containing the f...