The Polymer Society of Korea

Abstract

Organic electrochemical transistors (OECTs) have made strong interest in bioelectronics because of their distinctive capability to couple ionic and electronic transport. This feature makes them highly attractive for neuromorphic computing, biosensing, and wearable interfaces. Nevertheless, conventional OECTs rely on rigid metallic electrodes and liquid electrolytes, which restrict their integration into flexible, solid-state devices. To address this limitation, we demonstrate a solid-state homojunction OECT comprising a pristine polymer semiconductor channel, doped polymer semiconductor electrodes, and a solid electrolyte. The entire device stack is fabricated using photo-crosslinking, and the electrodes are formed by selective doping of the same polymer semiconductor. Three Lewis acids—gold(III) chloride (AuCl₃), iron(III) chloride (FeCl₃), and copper(II) chloride (CuCl₂)—are employed as molecular dopants, with AuCl₃-doped polymers showing metallic conductivity (~100 S cm⁻¹). Using these materials, we obtain source, drain, and gate electrodes that enable a device mobility of 3.4 cm² V⁻¹ s⁻¹ and excellent flexibility, with negligible degradation even after 5000 folding cycles at a bending radius of 0.1 mm. Furthermore, by integrating these homojunction OECTs, we successfully implement logic functions including NOT, NAND, and NOR gates.