Perfluoroalkyl Hybrid Ethylene Glycol Side Chains: A Solution to Water Related Challenges in n-Type Organic Mixed...

The water molecule is regarded as a double-edged sword in organic mixed ionic-electronic conductors (OMIECs), particularly for n-type semiconductors. On the one hand, hydration facilitates ion transport within OMIECs; on the other hand, water acts as an electron trap, capturing electrons in n-type materials. Excessive hydration may disrupt the continuity of OMIECs crystalline domains, leading to device degradation. To address these challenges, we propose an innovative strategy by incorporating perfluoroalkyl hybridized ethylene glycol (fag) side chains into the polymer. The strong hydrophobicity of fluoroalkyl segments effectively repels water from polymer backbone, thereby reducing electron trapping. Meanwhile, the ethylene glycol components facilitate efficient ion transport. These findings are confirmed by electrochemical impedance spectroscopy (EIS) and electrochemical quartz crystal microbalance with dissipation monitoring (EQCM-D). Additionally, the electron-withdrawing nature of fluorine lowers the lowest unoccupied molecular orbital (LUMO) energy level, which in turn enhances stability in aqueous environments. We also discovered that the incorporation of fag side chains also promotes polymer self-assembly and improves crystallinity. Grazing-incidence wide-angle X-ray scattering (GIWAXS) reveals a face-on/edge-on mixed orientation in fag-based polymers, facilitating efficient ion-electron transport. Consequently, organic electrochemical transistors (OECTs) fabricated from fag-based OMIECs demonstrate state-of-the-art n-type performance, achieving a µC* figure of merit of 189.78 F cm^-1 V^-1 s^-1. Furthermore, they exhibit excellent stability, retaining 68% of their initial performance after 50 000 switching cycles in aqueous electrolyte. This study demonstrates that a rational approach to molecular design can effectively alleviate the detrimental effects of water, providing a novel strategy for the development of high-performance and stable n-type OMIECs.