Vertically Phase-Separated PEDOT:PSS Film via Solid–Liquid Interface Doping for Flexible Organic Electrochemical Transistors

Organic electrochemical transistors (OECTs) are seen as some of the most promising devices in organic bioelectronics. Recent interest in OECTs is sparked by the high performance of an organic semiconductor channel material, i.e., poly(3,4-ethylenedioxythiophene):poly(styrenesulfonate) (PEDOT:PSS). The capability of ion penetration and charge transport of the channel determines the performance of the OECTs. However, the uniform structure of the PEDOT:PSS channel always makes it difficult to achieve a well-balanced between the two functions. Here, we report a novel PEDOT:PSS film with a vertical phase separation structure (VPSS-P), where PSS accumulates at the surface, and PEDOT enriches at the bottom of the film. Such a unique structure improves the electrochemical stability and reduces the contact resistance, significantly enhancing OECT performance with high transconductance (70.5 mS), product of mobility (μ) and volumetric capacitance (C*) (μC* ∼ 479 F cm^–1 V^–1 s^–1), and ultralow contact resistance (∼0.79 Ω cm). Flexible OECT devices with VPSS-P show robust performance against deformation. Our findings highlight a new class of high-performance transistors and provide guidelines for designing state-of-the-art channel materials.