Organic field-effect transistors (OFETs) without any encapsulation of polymer semiconductor layers that still exhibit unipolar n-type characteristics under air conditions are very rare. In this study, we use fluorinated bithiophene as a donor, and bis(2oxoindolin-3-ylidene)-benzodifuran-dione (BIBDF, P1) and azasubstituted BIBDF (P2) as acceptor units to develop air-stable and unipolar electron transport polymer semiconductors. Unencapsulated OFETs based on P1 and P2 were fabricated and directly evaluated under air conditions. The highest effective mobility (μ e,max eff ) of 0.23 cm 2 V −1 s −1 was obtained for P2-based devices with high I on /I off ratio of >10 6 and low threshold voltage of 1.1 V. Moreover, P2 had high air stability and maintained unipolar electron transport with μ e,max eff of up 0.1 cm 2 V −1 s −1 and I on /I off ratio of >10 6 during the 60 days of air storage. The work provides an effective molecular design strategy to develop air-stable and high-performance n-channel unencapsulated polymer transistors that can be directly operated under air conditions.

A green and efficient synthetic protocol suitable for the preparation of isoindigo-based polymer was developed using aldol polymerization.

Conjugated polymer-based organic thin film transistors (OTFTs) have received tremendous attention due to their potential applications. In addition to their high performances, air stability is also essential for application and another main property that OTFTs have. In this paper, three aza-heterocycle (BABDF)-based polymers were designed and synthesized using strong donor thiophene–vinylene–thiophene (TVT), weak donor thiophene–cyanovinylene–thiophene (TCNT), and weak acceptor dithiazole (TZ) as co-units. The lowest unoccupied molecular orbital (LUMO)/highest occupied molecular orbital (HOMO) energy levels were effectively lowered by introducing TCNT and TZ units, especially for PBABDF-TZ, for which the too much deep LUMO/HOMO energy levels of −4.28/–6.06 eV were obtained. These levels are low enough for air-stable electron transport and large enough for the hole injection barriers in OTFTs. Consequently, the unencapsulated bottom-gate/top-contact (BG/TC) devices exhibited unipolar electron transport under air conditions. Furthermore, these devices had high air stability and maintained unipolar electron transport with a mobility of up to 0.01 cm2 V–1 s–1 during the one-year characterization period. Very low LUMO and HOMO levels were necessary for electron transport and the hole barriers, respectively, and both were important for long-term, air-stable n-channel polymer transistors.

Two donor–acceptor (D–A) conjugated polymers were synthesized using a strongly electron-deficient unit as the acceptor, and dithiophene and (E)-2-(2-(thiophen-2-yl)vinyl)thiophene as the donor units.

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