Inhibition of ion diffusion in coplanar ion gel-gated organic thin-film transistors using...

The operational stability of electrolyte-gated organic field-effect transistors (EGOFETs) is often compromised by unwanted ion diffusion from the gate dielectric into the semiconducting layer, leading to charge carrier scattering, threshold voltage drift, and device degradation. Here, we demonstrate a polymer blend strategy to mitigate this issue by incorporating polystyrene (PS) into poly(3-hexylthiophene) (P₃HT) semiconducting films. By systematically varying the molecular weight of PS, we reveal that high-molecular-weight PS (M_W = 123,000, PS_123K) significantly enhances the ionic barrier properties of the blend, yielding more stable device performance under both ionic liquids and ion gels gating conditions. Electrical characterizations show that EGOFETs based on P₃HT/PS_123K retain over 70 % of their initial mobility after 10 h of continuous operation, whereas devices without PS exhibit severe performance degradation. Kelvin probe force microscopy (KPFM) imaging confirms that PS_123K suppresses ionic adsorption and potential fluctuation at the film surface. Furthermore, energy barrier simulations indicate that PS_123K/P₃HT blends dramatically increase the activation energy required for both cationic and anionic diffusions, compared to pristine P₃HT. These findings highlight the crucial role of polymer chain architecture in regulating interfacial ion transport and provide a versatile approach for improving the reliability of EGOFETs devices in ionic environments.