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

Abstract

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 cm2 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 (μe) and 0.1 ± 0.03 (μh) cm2 V–1 s–1, respectively. Moreover, OTFTs based on both polymer show good air-stability with negligible changes after stored in ambient over 3 ...