Semiconducting Polythiophenes for Field-Effect Transistor Devices in Flexible Electronics: Synthesis and Structure Property Relationships

Abstract

Interest in the field of organic electronics has burgeoned over the last 10 years, as the continuing improvement in performance has transitioned the technology from an academic curiosity to the focus of intense industrial and academic research. Much of this interest is driven by the belief that organic materials will be readily amenable to low-cost, large-area deposition techniques, enabling both significant cost savings and the ability to pattern flexible substrates with active electronics. Potential applications include thin-film transistor (TFT) backplanes for a variety of display modes including active matrix liquid crystal displays (AMLCDs), flexible displays such as e-paper, disposable item level radio frequency identity (RFID) tags, flexible solar cells, and cheap and disposable sensors. The primary figure of merit for charge transport in organic semiconducting materials is the charge carrier mobility. A current target for an organic TFT is to achieve a mobility of around 1 cm2/Vs, which would equal the approximate performance of the amorphous silicon currently used as semiconductor in AMLCD TFT backplanes. The opportunity to replace amorphous silicon with a printable organic semiconductor of similar electrical performance in an additive process on flexible substrates is a potentially attractive cost proposition to device manufacturers. In principle each of the components of the organic field-effect transistor (OFET) can be an organic material and several fully organic device examples have been reported [1–4]. In practice, however, one or more of the components is usually nonorganic. For the purpose of comparative evaluation of materials, a particularly common device set-up comprises of n-doped silicon as the gate electrode, with a layer of thermally grown silicon dioxide on top as the dielectric layer, and patterned source and drain electrodes. The dielectric provides a very smooth and homogeneous surface onto which to deposit the organic semiconductor, and this device