PEDOT:PSS Morphostructure and Ion-To-Electron Transduction and Amplification Mechanisms in Organic Electrochemical Transistors.

Pasquale D’Angelo,Salvatore Iannotta,Alessio Verna,Matteo Cocuzza,Carlotta Peruzzi,Davide Vurro,Agostino Romeo,Giuseppe Tarabella,Simone Marasso

doi:10.3390/ma12010009

Abstract

Organic electrochemical transistors (OECTs) represent a powerful and versatile type of organic-based device, widely used in biosensing and bioelectronics due to potential advantages in terms of cost, sensitivity, and system integration. The benchmark organic semiconductor they are based on is poly(3,4-ethylenedioxythiophene):polystyrene sulfonate (PEDOT:PSS), the electrical properties of which are reported to be strongly dependent on film morphology and structure. In particular, the literature demonstrates that film processing induces morphostructural changes in terms of conformational rearrangements in the PEDOT:PSS in-plane phase segregation and out-of-plane vertical separation between adjacent PEDOT-rich domains. Here, taking into account these indications, we show the thickness-dependent operation of OECTs, contextualizing it in terms of the role played by PEDOT:PSS film thickness in promoting film microstructure tuning upon controlled-atmosphere long-lasting thermal annealing (LTA). To do this, we compared the LTA-OECT response to that of OECTs with comparable channel thicknesses that were exposed to a rapid thermal annealing (RTA). We show that the LTA process on thicker films provided OECTs with an enhanced amplification capability. Conversely, on lower thicknesses, the LTA process induced a higher charge carrier modulation when the device was operated in sensing mode. The provided experimental characterization also shows how to optimize the OECT response by combining the control of the microstructure via solution processing and the effect of postdeposition processing.

Highlights

Based on their proven biocompatibility and their ideal amplifying interface between ionic and electronic signals, organic electrochemical transistors (OECTs) have shown a marked suitability for studying phenomena depending on fluxes of specific ions
OECT operation relies on an efficient reduction of the oxidized p-type doped Poly(3,4ethylenedioxythiophene):polystyrene sulfonate (PEDOT:PSS) film, acting as the device channel, and is promoted by charged species of different nature and size [16,17] that are forced from an electrolytic reservoir toward the channel by an electric field applied between the gate electrode and the device channel
We studied in detail the important role played by PEDOT:PSS thickness, a key parameter for the optimization of OECT operation

Summary

Introduction

Based on their proven biocompatibility and their ideal amplifying interface between ionic and electronic signals, organic electrochemical transistors (OECTs) have shown a marked suitability for studying phenomena depending on fluxes of specific ions. OECTs have been successfully employed for studying the function of cell membranes [1] and biosystems in general [2,3,4], and for studying molecular interactions (e.g., molecular recognition [5] or enzyme-catalyzed chemical reactions [6]). The interaction between the charged species and the film bulk leads to the modulation of the current flowing through the device channel This process is favored by the negligible barrier effect for charged species crossing the electrolyte–OC interface, as reported by Rivnay et al [9]. It has been demonstrated that for OECTs the transconductance (gm ) is higher than for most solid-state devices [18], showing a correct operation even at zero gate bias [19]

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