Nara Kim

Highly Conductive PEDOT:PSS Nanofibrils Induced by Solution‐Processed Crystallization

The fabrication of electronic devices based on organic materials, known as ’printed electronics’, is an emerging technology due to its unprecedented advantages involving fl exibility, light weight, and portability, which will ultimately lead to future ubiquitous applications. [ 1 ] The solution processability of semiconducting and metallic polymers enables the cost-effective fabrication of optoelectronic devices via high-throughput printing techniques. [ 2 ] These techniques require high-performance fl exible and transparent electrodes (FTEs) fabricated on plastic substrates, but currently, they depend on indium tin oxide (ITO) coated on plastic substrates. However, its intrinsic mechanical brittleness and inferior physical properties arising from lowtemperature ( T ) processing below the melting T of the plastic substrates (i.e., typically below 150 °C) have increased the demand for alternative FTE materials. [ 3 ]

Highly Stretchable and Highly Conductive PEDOT:PSS/Ionic Liquid Composite Transparent Electrodes for Solution-Processed Stretchable Electronics

Stretchable conductive materials have received great attention owing to their potential for realizing next-generation stretchable electronics. However, the simultaneous achievement of excellent mechanical stretchability and high electrical conductivity as well as cost-effective fabrication has been a significant challenge. Here, we report a highly stretchable and highly conducting polymer that was obtained by incorporating an ionic liquid. When 1-ethyl-3-methylimidazolium tetracyanoborate (EMIM TCB) was added to an aqueous conducting polymer solution of poly(3,4-ethylenedioxythiophene):poly(styrenesulfonate) (PEDOT:PSS), it was found that EMIM TCB acts not only as a secondary dopant but also as a plasticizer for PEDOT:PSS, resulting in a high conductivity of >1000 S cm-1 with stable performance at tensile strains up to 50% and even up to 180% in combination with the prestrained substrate technique. Consequently, by exploiting the additional benefits of high transparency and solution-processability of PEDOT:PSS, we were able to fabricate a highly stretchable, semitransparent, and wholly solution-processed alternating current electroluminescent device with unimpaired performance at 50% strain by using PEDOT:PSS/EMIM TCB composite films as both bottom and top electrodes.

Controlling Molecular Ordering in Aqueous Conducting Polymers Using Ionic Liquids

The molecular ordering of aqueous conducting polymers is controlled using a rational method. By introducing various ionic liquids, which have designed electrostatic interactions to PEDOT:PSS solutions, the evolution of the molecular ordering of the PEDOT is manipulated. Consequently, highly ordered nanostructures are achieved with a reduced π-π stacking distance of ≈3.38 Å and, thus, a maximum σdc of ≈2100 S cm-1 .

Highly Deformable and See‐Through Polymer Light‐Emitting Diodes with All‐Conducting‐Polymer Electrodes

Despite the high expectation of deformable and see-through displays for future ubiquitous society, current light-emitting diodes (LEDs) fail to meet the desired mechanical and optical properties, mainly because of the fragile transparent conducting oxides and opaque metal electrodes. Here, by introducing a highly conductive nanofibrillated conducting polymer (CP) as both deformable transparent anode and cathode, ultraflexible and see-through polymer LEDs (PLEDs) are demonstrated. The CP-based PLEDs exhibit outstanding dual-side light-outcoupling performance with a high optical transmittance of 75% at a wavelength of 550 nm and with an excellent mechanical durability of 9% bending strain. Moreover, the CP-based PLEDs fabricated on 4 µm thick plastic foils with all-solution processing have extremely deformable and foldable light-emitting functionality. This approach is expected to open a new avenue for developing wearable and attachable transparent displays.

High-performance, polymer-based direct cellular interfaces for electrical stimulation and recording

Due to the trade-off between their electrical/electrochemical performance and underwater stability, realizing polymer-based, high-performance direct cellular interfaces for electrical stimulation and recording has been very challenging. Herein, we developed transparent and conductive direct cellular interfaces based on a water-stable, high-performance poly(3,4-ethylenedioxythiophene):polystyrene sulfonate (PEDOT:PSS) film via solvent-assisted crystallization. The crystallized PEDOT:PSS on a polyethylene terephthalate (PET) substrate exhibited excellent electrical/electrochemical/optical characteristics, long-term underwater stability without film dissolution/delamination, and good viability for primarily cultured cardiomyocytes and neurons over several weeks. Furthermore, the highly crystallized, nanofibrillar PEDOT:PSS networks enabled dramatically enlarged surface areas and electrochemical activities, which were successfully employed to modulate cardiomyocyte beating via direct electrical stimulation. Finally, the high-performance PEDOT:PSS layer was seamlessly incorporated into transparent microelectrode arrays for efficient, real-time recording of cardiomyocyte action potentials with a high signal fidelity. All these results demonstrate the strong potential of crystallized PEDOT:PSS as a crucial component for a variety of versatile bioelectronic interfaces.Polymer electrodes: Crystallized films are suitable for cardiac interfaceCardiomyocyte cells can be cultured and made to pulse on demand using transparent polymers with good stability. Conductive thin films formed from poly(3,4-ethylenedioxythiophene):polystyrene sulfonate (PEDOT:PSS) have low impedances, making them ideal for bioelectronic interfaces. But they suffer from severe fragility in aqueous environments. Myung-Han Yoon from Korea’s Gwangju Institute of Science and Technology and colleagues have made PEDOT:PSS films that show no degradation up to three weeks underwater. They achieved this by immersing the films in concentrated sulfuric acid to initiate solvent-assisted crystallization. The crystalline films had improved electrical/electrochemical properties and biocompatibility over approaches such as polymer cross-linking, and supported photolithographic patterning into microelectrode arrays. Using cardiac cells as a model, the researchers demonstrated the feasibility of modulating beating frequencies with direct electrical stimulation under 1V while simultaneously capturing real-time action potentials and calcium signals.The high performance polymer-based conductive cellular interface was developed by a solvent-assisted crystallization of PEDOT:PSS. The crystallized PEDOT:PSS(c-PEDOT:PSS) exhibited mechanical and electrical robustness over 21days as well as excellent electrical conductivity and electrochemical activities. Thanks to such advantageous properties for the cellular interfaces, the beating rates of cardiomyocytes cultured on c-PEDOT:PSS were successfully modulated through pulsed direct stimulation under 1 V. In addition, c-PEDOT:PSS incorporated Multielectrode arrays (MEAs) recorded real-time action potentials originated from cardiomyocytes with high signal fidelity. we expect c-PEDOT:PSS with high-performance and high-stability to be a promising candidate for long-term bioelectronic interface development.