Impact of Charge Carrier Injection/Extraction Performances in Low‐Dimension PEDOT:PSS Organic Electrochemical Transistors

Abstract Organic electrochemical transistors (OECT) are gaining momentum in future applications of biosensors and bioelectronics. Nonetheless, contact (or series) resistances (RS/D) remain underexplored, even though physical processes between the source/drain electrodes and organic mixed ionic‐electron conductors (OMIECs) drive a substantial part of their performances. To address this shortcoming, in this study, low‐dimension OECTs featuring 2 µm‐long poly(3,4‐ethylenedioxythiophene) and polystyrene sulfonate acid (PEDOT:PSS) channel are explored. Normalized contact resistances (RS/D⋅W) values as low as 1.4 W cm are obtained. It is observed that channel PEDOT:PSS thickness is not detrimental to RS/D but is impacting the cut‐off frequency. A figure‐of‐merit (h) expressing the charge‐carrier injection (or extraction, respectively) efficiency shows that planar depletion‐mode OECTs are not contact‐limited up to L = 30 µm channel length. Finally, an unprecedented approach that highlight the importance of optimizing the micro‐fabrication technologies is shown, by decreasing the contact overlap length, according to OMIECs physicochemical contact properties. Indeed, a transfer‐length method coupled to a current‐crowding model allow to fully understand the behavior of low‐dimension PEDOT:PSS OECTs and next, to optimize its circuits design. This is paving the way toward the development of OECTs‐based integrated circuits with faster switching speed, broadening further their scopes and future use as advanced bioelectronics platforms.