I. Introduction
The organic electrochemical transistor (OECT) [1], is a transistor with a channel allowing both ionic and electronic conduction. PEDOT:PSS is the typically used organic mixed ionic-electronic conductor. The channel is in contact with an electrolyte. The transistor current in the channel is modulated by ions injected from the electrolyte into the channel. The ions can enter and leave the transistor channel, and they can be transported inside it. OECT exhibits the typical characteristics of a depletion field effect transistor, in which the electrolyte has the role of the gate electrode [1], [2]. The length of the channel varies between few micrometers [3] to millimeters [4]. Compared with other technologies, the transconductance of OECTs can be higher than of electrolyte- and ionic liquid-gated transistors, and transistors based on silicon, oxide-gated graphene, and ZnO [3]. Although slower than its inorganic counterparts, the response time can be fast enough for amplifying neural signals [5]. This makes OECT a promising device for bioelectronic sensing applications [6], [7].