High‐Transconductance Organic Electrochemical Transistor Fabricated on Ultrathin Films Using Spray Coating

Organic electrochemical transistors (OECTs) are widely used for monitoring electrophysiological activities by exploiting advantages, such as flexibility, biocompatibility, low‐voltage operation, and high transconductance. Transconductance is a major factor that determines the sensitivity of OECT‐based sensors. In comparison with other field‐effect transistors, the transconductance of OECTs having the poly(3,4‐ethylenedioxythiophene) polystyrene sulfonate (PEDOT:PSS) channel layer is proportional to the channel thickness because the entire film acts as a channel. Therefore, the formation of a thick channel layer is essential for OECTs. However, it is difficult to form a thick film by spin coating. Herein, spray coating is introduced, and a thick and uniform PEDOT:PSS layer (1.05 μm) is successfully formed by controlling the compressed air pressure and number of coating cycles. Moreover, a high‐transconductance (7.5 mS) ultraflexible OECT with a sufficiently rapid response is fabricated (2.3 kHz).