Solid‐State Homojunction Electrochemical Transistors and Logic Gates on Plastic

Abstract Organic electrochemical transistors (OECTs) have attracted significant attention due to their unique ionic–electronic charge coupling, which holds promise for use in a variety of bioelectronics. However, the typical electronic components of OECTs, such as the rigid metal electrodes and aqueous electrolytes, have limited their application in solid‐state bioelectronics that requires design flexibility and a variety of form factors. Here, the fabrication of a solid‐state homojunction OECT consisting of a pristine polymer semiconductor channel, doped polymer semiconductor electrodes, and a solid electrolyte is demonstrated. This structure combines the photo‐crosslinking of all of the electronic OECT components with the selective doping of the polymer semiconductor. Three Lewis acids (gold (III) chloride (AuCl 3 ), iron (III) chloride (FeCl 3 ), and copper (II) chloride (CuCl 2 ) ) are utilized as dopants for the metallization of the polymer semiconductor. The AuCl 3 ‐doped polymer semiconductor with an electrical conductivity of ≈100 S cm −1 is successfully employed as the source, drain, and gate electrodes for the OECT, which exhibited a high carrier mobility of 3.4 cm 2 V −1 s −1 and excellent mechanical stability, with negligible degradation in device performance after 5000 cycles of folding at a radius of 0.1 mm. Homojunction OECTs are then successfully assembled to produce NOT, NAND, and NOR logic gates.