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 (mu(e)) and 0.1 +/- 0.03 (mu(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.