Unprecedented quinoid-donor-acceptor strategy to boost carrier mobilities of semiconducting polymers for organic field-effect transistors

Quinoidal-aromatic conjugated polymers hold great application potential in organic field-effect transistors (OFETs). However, the development of high mobility quinoidal-aromatic conjugated polymers still lags behind the more popular donor-acceptor (D-A) conjugated polymers, mainly owing to the lack of rational design strategy and efficient building block. Herein, a novel quinoid-donor-acceptor (Q-D-A) strategy is demonstrated to modulate the energy-level and boost the charge carrier transport mobility of conjugated polymers as opposed to the D-A system. On the basis of this strategy, a quinoidal-aromatic conjugated polymer, namely PAQM-BT, is designed and synthesized. With the combined use of quinoid, donor and acceptor units in the backbone, the resulting Q-D-A polymer PAQM-BT displays the narrowest bandgap with the deepest-lying lowest unoccupied molecular orbital (LUMO) energy level, highest backbone coplanarity, enhanced thin-film crystallinity and smallest effective hole mass (mh*) in comparison with the corresponding D-A polymer PT3B1 and quinoid-donor (Q-D) polymer PAQM-3T. Benefitting from the more effective intra- and inter-chain charge transport, as corroborated by experiment and theoretical calculations, OFET devices based on PAQM-BT exhibit a highly boosted hole mobility of up to 5.10 cm2 V–1 s–1, which is one and four orders of magnitude higher than that of PAQM-3T and PT3B1, respectively, and is among the highest for quinoidal-aromatic conjugated polymers. The potent Q-D-A strategy not only allows energy-level to be modulated but also leads to effective charge carrier transport, opening up possibilities to the development of high mobility quinoidal-aromatic conjugated polymers based on a variety of quinoids, donors, and acceptors.