Ultra‐Stable Organic Electrochemical Transistors With Suppressed Swelling via Molecular Weight Modulation

ABSTRACT Organic electrochemical transistors (OECTs) are promising for next‐generation bioelectronics due to their high performance and biocompatibility. Nevertheless, they still face tremendous operational stability challenges due to the limited robustness of the organic mixed ionic–electronic conductor (OMIEC) channel. Here, by modulating the molecular weight (MW) of OMIEC, enhanced OECT and relevant circuit operation stabilities are demonstrated, showing more than 3,000,000 full cycles (∼42 h) with less than 15% current variation in an OECT, and 150,000 cycles (∼4 h) with less than 5% voltage variation in an OECT‐based inverter, which are among the highest of reported OECT‐based electronics. Specifically, p(g2T‐T), a typical p‐type OMIEC, with varying MW (7–43 kDa), is synthesized, where lower‐MW p(g2T‐T) (∼9 kDa) exhibits superior device performance and cycling stability in OECTs, outperforming those in high‐MW counterparts (>30 kDa). It is indicated that low‐MW p(g2T‐T) maintains higher volumetric capacitance, ordered orientation, and reduced swelling. Therefore, irreversible microstructural degradation is effectively avoided, along with better performance yield. Furthermore, MW regulation enables physiological signal sensing with high tolerance to body fluid environments for 7 days. These findings highlight MW modulation as a versatile approach to suppress excessive swelling, advancing the design of durable OECT‐based electronics.