Air-Stable and High-Performance Unipolar n-Type Conjugated Semiconducting Polymers Prepared by a Strong Acceptor-Weak Donor Strategy

Unipolar n-type conjugated polymer materials with long-term stable electron transport upon direct exposure to the air atmosphere are very challenging to prepare. In this study, three unipolar n-type donor-acceptor (D-A) conjugated polymer semiconductors (abbreviated as PNVB, PBABDFV, and PBAIDV) were successfully developed through a strong acceptor-weak donor strategy. The weak electron donation of the donor units in all three polymers successfully lowered the molecular energy levels by the acceptor units that strongly attracted electrons. Cyclic voltammetry demonstrated that all three polymers had low highest occupied molecular orbital and lowest unoccupied molecular orbital energy levels near -6.0 and -4.0 eV, respectively. These results were consistent with the density functional theory calculations. The as-prepared polymers were then used to manufacture organic field-effect transistor (OFET) devices in bottom-gate/top-contact (BG/TC) configuration without any packaging protection. As expected, all devices exhibited unipolar electron transport properties. PBABDFV-based devices showed excellent field-effect performance and air stability, beneficial for straight-line molecular chain and closest pi-pi stacking distance to prevent water vapor and oxygen from diffusion into the active layer. This led to a maximum electron mobility (mu(e,max)) of 0.79 cm(2) V-1 s(-1) under air conditions. In addition, 0.50 cm(2) V-1 s(-1) was still maintained after 27 days of storage in ambient environment. The near-ideal transfer curve of the PBABDFV-based OFET device in BG/TC configuration under vacuum was obtained with average mobility reliability factor (r(ave)) reaching 88%.