Impact of Chemical Design on the Molecular Orientation of Conjugated Donor–Acceptor Polymers for Field-Effect Transistors

Conjugated donor–acceptor polymers are a large category of cutting edge semiconductor materials with obvious advantages such as easy processing, light weight, and mechanical flexibility. By rational design of electron-withdrawing and electron-donating moieties, the intermolecular interactions between conjugated polymers can be precisely tuned, realizing the efficient control of polymer aggregation in solution and subsequent polymer packing orientation in solid states. In this Review article, the recent advances on the effect of molecular design on the polymer packing orientation are summarized. The behavior and possible mechanism of molecular orientation are first introduced. Then, the key structural factor, side chains, is systematically discussed with the main focuses on their shape (linear or branched), length, density, position, and symmetry, all of which critically affect the polymer packing. Furthermore, the appropriate substitution of conjugated segments in polymer backbone allows the modulation of the π–π interaction and conjugation length, contributing to the transition between edge-on and face-on arrangements in solid states. Such transition can also be achieved by other influencing factors such as molecular weight, additive, post-treatment, and solvent. In addition, the impact of polymer packing on charge transport in field-effect transistors is reviewed, providing further understanding of structure–property relations for high-performance organic electronic devices.