Abstract
Owing to the mixed electron/hole and ion transport in the aqueous environment, poly(3,4-ethylenedioxythiophene):poly(styrenesulfonate)-based organic electrochemical transistor has been regarded as one of the most promising device platforms for bioelectronics. Nonetheless, there exist very few in-depth studies on how intrinsic channel material properties affect their performance and long-term stability in aqueous environments. Herein, we investigated the correlation among film microstructural crystallinity/composition, device performance, and aqueous stability in poly(3,4-ethylenedioxythiophene):poly(styrenesulfonate) films. The highly organized anisotropic ordering in crystallized conducting polymer films led to remarkable device characteristics such as large transconductance (∼20 mS), extraordinary volumetric capacitance (113 F·cm−3), and unprecedentedly high [μC*] value (∼490 F·cm−1V−1s−1). Simultaneously, minimized poly(styrenesulfonate) residues in the crystallized film substantially afforded marginal film swelling and robust operational stability even after >20-day water immersion, >2000-time repeated on-off switching, or high-temperature/pressure sterilization. We expect that the present study will contribute to the development of long-term stable implantable bioelectronics for neural recording/stimulation.
Highlights
Owing to the mixed electron/hole and ion transport in the aqueous environment, poly(3,4-ethylenedioxythiophene):poly(styrenesulfonate)-based organic electrochemical transistor has been regarded as one of the most promising device platforms for bioelectronics
Conductive films as well as complicated devices based on PEDOT:PSS can be fabricated via a series of solution-based processes using commercially available aqueous PEDOT:PSS solution, wherein hydrophobic short PEDOT chains are aggregated in the form of nanoparticles wrapped with hydrophilic long PSS chains, and a certain portion of deprotonated styrene sulfonate units are in close proximity to conjugated EDOT moieties as dopants[26]
In this research, crystallized PEDOT:PSS (Crys-P) film was prepared by solvent-assisted crystallization[38] and utilized as an organic electrochemical transistors (OECTs) channel layer after patterning (Fig. 1)
Summary
Owing to the mixed electron/hole and ion transport in the aqueous environment, poly(3,4-ethylenedioxythiophene):poly(styrenesulfonate)-based organic electrochemical transistor has been regarded as one of the most promising device platforms for bioelectronics. When an electrical bias is applied to the gate electrode, the conductivity of the organic layer is controlled by driving small cations (or anions) from the electrolyte medium to the channel layer, thereby dedoping (or doping) the constituent organic conductor, resulting in the efficient modulation of source-to-drain current[20] In this regard, OECTs employ the whole volume of organic film as an effective channel, unlike typical organic field-effect transistors (OFETs) where the interface between semiconducting and dielectric layers functions as a major channel. We can infer that stable device performance, and prolonged operational reliability of OECTs, can be substantially improved by strictly controlling the microstructural crystallinity of hydrophobic conjugated moieties (i.e., PEDOT) and the amount/allocation of hydrophilic moieties (i.e., PSS) in the channel layer, for aqueous electrolyte conditions and bioelectronic applications. Several research groups have reported on practical issues in organic bioelectronics including aqueous stability[24,34,35,36,37], but there exist few in-depth studies addressing the aqueous stability of the OECT channel material itself (without chemical crosslinking) and device performance under critical stress conditions, nor have any studies looked at correlating the observed phenomena with the microstructural crystallinity and composition of constituent organic conductors
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