A New Composite Structure of PEDOT/PSS: Macro-Separated Layers by a Polyelectrolyte Brush

Synthesis of PEDOT:PSS Brushes Grafted from Gold Using ATRP for Increased Electrochemical and Mechanical Stability

We report PEDOT:PSS brushes grafted from gold using surface-initiated atom-transfer radical polymerization (SI-ATRP) which demonstrate significantly enhanced mechanical stability against sonication and electrochemical cycling compared to spin-coated analogues as well as lower impedances than bare gold at frequencies from 0.1 to 105 Hz. These results suggest SI-ATRP PEDOT:PSS to be a promising candidate for use in microelectrodes for neural activity recording. Spin-coated, electrodeposited, and drop-cast PEDOT:PSS have already been shown to reduce impedance and improve biocompatibility of microelectrodes, but the lack of strong chemical bonds of the physisorbed polymer film to the metal leads to disintegration under required operational stresses including cyclic mechanical loads, abrasion, and electrochemical cycling. Rather than modifying the metal electrode or introducing cross-linkers or other additives to improve the stability of the polymer film, this work chemically tethers the polymer to the surface, offering a simple, scalable solution for functional bioelectronic interfaces.

Metal-Free Transparent Three-Dimensional Flexible Electronics by Selective Molecular Bridges

Flexible and transparent electronics is a new generation of device enabling modern interactive designs, which facilitates the recent development of low-cost, lightweight, and flexible materials. Although conventional indium tin oxide material still dominates the major market, its brittleness and steadily increasing price drive scientists to search for other alternatives. To meet the high demand, numerous metallic or organic conductive materials have been developed, but their poor adhesion toward supporting substrates and the subsequent circuit patterning approach remains problematic. In this study, a robust metal-free flexible conductive film fabrication strategy is introduced. The flexible polyethylene terephthalate (PET) film is utilized as the base, where a poly(3,4-ethylenedioxythiophene)-poly(styrenesulfonate) (PEDOT:PSS) conductive layer is tightly linked onto this supporting substrate. An interface activation process, i.e., oxygen plasma treatment, generates PET surface active spots to react with the subsequently introduced poly(vinyl alcohol) (PVA) molecule functional groups. This spatially selective PVA molecular bridge therefore acts as a dual-function intermediate layer through covalent bonding toward PET and hydrogen bonding toward PEDOT:PSS to conjugate two distinct materials. This PEDOT:PSS/PVA/PET film delivers superior physical properties, such as a high conductivity of 38.2 Ω/sq and great optical transmittance of 84.1%, which are well tunable under conductive polymer thickness controls. The film is also durable and can maintain original electrical properties even under serious bending for hundreds of cycles. Relying on these outstanding performances, arbitrary conductive circuits are built on this flexible substrate and can function as normal electronics when integrated with multiple electronic parts, e.g., light-emitting diodes (LEDs). Superior electrical signal outputs are achieved when complicated stereo structures including folding, splicing, interlacing, and braiding are incorporated, enabling the use of these films for flexible three-dimensional electronics assembling. Space identifying smart key and lock pair, origami rabbit-carrot touch response, pressure-stimulated jumping frog, and moving dinosaur recognition designs realize these PEDOT:PSS/PVA/PET film-based human-machine interactive devices. This flexible, transparent, and conductive film generation approach by molecular bridge creation should facilitate future development of flexible or foldable devices with complex circuits.

Poly(3,4-ethylenedioxythiophene) Electrosynthesis in the Presence of Mixtures of Flexible-Chain and Rigid-Chain Polyelectrolytes

The electrochemical synthesis of poly(3,4-ethylenedioxythiophene) (PEDOT) was first carried out in the presence of mixtures of flexible-chain and rigid-chain polyacids and their Na-salts. Earlier on with the example of polyaniline, we have shown the non-additive effect of the rigid-chain component of polyacid mixtures on the electrodeposition of polyaniline films, their morphology and spectroelectrochemical properties. In this study, we confirmed the non-additive effect and showed that such mixed PEDOT-polyelectrolyte films possess unique morphology, spectroelectrochemical and ammonia sensing properties. The electrosynthesis was carried out in potential cycling, galvanostatic and potentiostatic regimes and monitored by in situ UV-Vis spectroscopy. UV-Vis spectroelectrochemistry of the obtained PEDOT-polyelectrolyte films revealed the dominating influence of the rigid-chain polyacid on the electronic structure of the mixed complexes. The mixed PEDOT-polyacid films demonstrated the best ammonia sensing performance (in the range of 5 to 25 ppm) as compared to the films of individual PEDOT-polyelectrolyte films.

First-Principle Study on p-n Control of PEDOT-Based Thermoelectric Materials by PTSA Doping

PEDOT

Tos, a PSS-free PEDOT-based material, is a promising possible organic thermoelectric material for a practical conversion module because the material reportedly has a large power factor. However, since PEDOT:Tos is mainly reported to be a p-type thermoelectric material, the development of PSS-free PEDOT with n-type thermoelectric properties is desirable. Thus, in order to search for PSS-free PEDOT with n-type thermoelectric properties, we investigated the doping concentration of PTSA dependence of the thermoelectric property using the first-principle calculation. The band structure and the density of state indicated that the n-type thermal electromotive force was attributed to the electrons' large effective mass. Such electrons were produced thanks to the binding of the dopant PTSA to the benzene ring. The contribution of the electron to the Seebeck coefficient increased with increasing PTSA doping concentrations.