Impacts of Gate Voltage on the Stability of Crosslinked PEDOT:PSS Organic Electrochemical Transistors

<br/>Organic electrochemical transistors (OECTs) have shown great potentials for biosensing and bioelectronics because of their low working voltage and compatibility with an aqueous solution. The operation of OECTs is based on modulating the drain current by injecting/extracting ions into/from the active channel by gate voltage, which leads to doping and de-doping of it. The repetitive OECT measurements often lead a performance degradation, which is not favored for biosensing applications. In this work, we show that the magnitude of gate voltage in the off state (V_{g, off}) is crucial to the stability of the transfer curve of an OECT based on interdigitated electrodes (IDEs). A high V_{g, off} such as +0.5 V promotes a larger scale of Na⁺ ion injection, leading to a recognizable drain current decay in the transfer characteristics of the PEDOT:PSS OECTs under repeated operations. By lowering the V_{g, off} to +0.2 V, the OECTs can be stabilized at the cost of a lower on/off ratio. The crosslinking of PEDOT:PSS by GOPS can reduce the drain current decay and improve stability. For instance, crosslinked OECTs show a stable on/off ratio under a very demanding device operation voltage condition (V_g,off= +0.5 V, V_ds = -0.5 V). Control experiments exclude the possibility of PEDOT:PSS film decomposition as the reason for drain current decay. So the repetitive Na⁺ ion intercalation at high V_{g, off} is the most probable cause of the decay. The improved stability is most likely due to the suppression of the microstructural damages induced by expansion-shrinking during the switching between the “doped” and “de-doped” states.