Tuning the Air Stability of N-Type Semiconductors via Poly(2-vinylpyridine): The Importance of Humidity and Molecular Weight.

The environmental instability of n-type semiconducting polymers remains a limitation for organic thin-film transistors (OTFTs), as oxygen diffusion and oxidation reduces device performance. Herein, a simple stabilization strategy using poly(2-vinylpyridine) (P2VP), a synthetically accessible, hygroscopic, insulating polymer, is shown. Building on earlier work showing short-term stabilization with this insulating additive, the molecular weight of P2VP is systematically varied and it is demonstrated that higher molecular weight chains form larger domains that reduce oxygen access to the crystalline regions of the benchmark n-type polymer P(NDI2OD-T2). Structural characterization reveals that P2VP domains absorb atmospheric moisture, which both decreases the free volume available for oxygen penetration and partitions oxygen away from semiconductor crystallites. As such, devices containing P2VP exhibit enhanced stability over seven days and can be regenerated by mild heating, whereas neat P(NDI2OD-T2) devices remain degraded. These findings provide mechanistic insight into how insulating polymer blends mediate oxygen-water interactions and highlight polymer blending as a scalable strategy for improving the operational stability of n-type OTFTs.