Ion effects on salt-in-water electrolyte gated polymer electrochemical transistors

Abstract

Aqueous electrolyte-gated polymer transistors attracted intensive attention in the field of implantable bionics and biochemical sensors due to their simple fabrication process, low operating voltage, and biocompatibility of salt-in-water. In these devices, under gate bias, the free cations and anions in the water solution gate will drift toward the gate electrode or electrolyte/active layer interface, respectively. Under high enough bias, some ions might insert into the active layer and dope the polymer in electrochemical transistors. Therefore, the ions play a crucial role in the salt-in-water electrolyte-gated polymer electrochemical transistors. In this work, the poly (3-hexylthiophene-2, 5-diyl) (P3HT) electrochemical transistors based on different cations and anions contained in the aqueous electrolytes were characterized. The various measurements imply that the larger perchlorate ions can penetrate the P3HT film much more heavily than the smaller chloride ions and the electrochemical bulk doping occurs in the perchlorate devices while the chloride devices involve surface doping. This is why the perchlorate ions can electrochemically dope the P3HT film more heavily than the chloride ions, leading to the larger transconductance and switching ratio. The various anions show different electrochemical doping processes, leading to various electrical hysteresis characteristics. In addition, the cations can affect the doping relaxation process for the electrochemical transistors. Both cation and anion effects on the device performance and doping/dedoping processes have been investigated in this work.