Design and Synthesis of Novel Conjugated Polymers for Applications in Organic Field-effect Transistors

In recent years, much attention has been paid to organic field-effect transistors (OFETs) due to their potential applications in flexible and wearable electronic devices. Especially for OFETs based on donor-acceptor (D-A) conjugated polymers, significant progress has been made. It is crucial to design and synthesize novel high-mobility polymers, the key components of OFETs. In this review, the recent progress of these novel polymeric materials is summarized to show the systematic effect of molecular structure on the mobility. The development, design and corresponding OFET performance are systematically summarized according to the different types of the polymers. These polymers are introduced based on the types of conventional acceptors, which include diketopyrrolopyrrole (DPP), isoindigo (IID), benzodifurandione-based oligo (p-phenylene vinylene) (BDOPV), naphthalenediimide (NDI) and other novel moieties. These acceptors have been proven to be promising building blocks for high-mobility polymers due to their planar backbones, electron-deficient property, and facile chemical modifications. Based on these acceptors, p-type, ambipolar or n-type polymers can be achieved by using different donors or by introducing electron withdrawing groups onto the acceptor unit. Generally, DPP and IID based polymers are p-type or ambipolar materials. In contrast, n-type transport characteristics are observed in most of the polymers based on BDOPV and NDI. To date, a high hole mobility of up to 17.8 cm(2) V-1 s(-1) has been achieved by a DPP-based polymer, while the reported highest electron mobility is of 8.5 cm(2) V-1 s(-1) in a NDI-based polymer. Here, we have summarized some key points for high-performance polymers by investigating the relationship among molecular structure, aggregation type and device performance. In detail, high-mobility polymers generally show some features including fine-tuned highest occupied molecular orbital (HOMO) and lowest unoccupied molecular orbital (LUMO) energy levels, good main-chain p-conjugation, planar backbone, high crystallinity etc. It is really crucial to develop novel building blocks to accelerate the development of this field. This review may give a helpful guide to the design and the synthesis of other novel high-mobility polymers in the future.