Naphthalenediimide-Benzothiadiazole Copolymer Semiconductors: Rational Molecular Design for Air-Stable Ambipolar Charge Transport

Rational design of air-stable ambipolar polymeric semiconductors was achieved by covalently connecting naphthalenediimide (NDI) units with benzothiadiazole (BZ) through thiophene (T) linkers, namely, PNDI- mT (BZ) mT ( m = 1, 2), in which well-coplanar mT (BZ) mT moieties as a whole act as donors rather than acceptors reported in previous studies. Decreasing the number of thiophene linkers from m = 2 to 1 lowers both LUMO and HOMO energy levels. As a result, the carriers in organic thin film transistors (OTFTs) could be switched from unipolar p -channel only to ambipolar transport. In ambient conditions, PNDI- 2T (BZ) 2T presents an average hole mobility of 0.07 ± 0.02 cm 2 V –1 s –1, while PNDI- T (BZ) T exhibits balanced ambipolar charge transport in a bottom-gate/top-contact device architecture, the average electron and hole mobilities was 0.05 ± 0.02 ( μ e ) and 0.1 ± 0.03 ( μ h ) cm 2 V –1 s –1, respectively. Moreover, OTFTs based on both polymer show good air-stability with negligible changes after stored in ambient over 3 months.