Jungho Jin

Flexible Transparent Conducting Hybrid Film Using a Surface-Embedded Copper Nanowire Network: A Highly Oxidation-Resistant Copper Nanowire Electrode for Flexible Optoelectronics

We report a flexible high-performance conducting film using an embedded copper nanowire transparent conducting electrode; this material can be used as a transparent electrode platform for typical flexible optoelectronic devices. The monolithic composite structure of our transparent conducting film enables simultaneously an outstanding oxidation stability of the copper nanowire network (14 d at 80 °C), an exceptionally smooth surface topography (R(rms) < 2 nm), and an excellent opto-electrical performances (Rsh = 25 Ω sq(-1) and T = 82%). A flexible organic light emitting diode device is fabricated on the transparent conducting film to demonstrate its potential as a flexible copper nanowire electrode platform.

A Biomimetic Composite from Solution Self-Assembly of Chitin Nanofibers in a Silk Fibroin Matrix

A chitin nanofiber-silk biomimetic nanocomposite with enhanced mechanical properties is self-assembled from solution to yield ultrafine chitin nanofibers embedded in a silk matrix.

Chitin Nanofiber Transparent Paper for Flexible Green Electronics

A transparent paper made of chitin nanofibers (ChNF) is introduced and its utilization as a substrate for flexible organic light-emitting diodes is demonstrated. Given its promising macroscopic properties, biofriendly characteristics, and availability of the raw material, the utilization of the ChNF transparent paper as a structural platform for flexible green electronics is envisaged.

Rollable transparent glass-fabric reinforced composite substrate for flexible devices.

Recently, there has been considerable interest in fl exible displays, as they facilitate the fabrication of displays that are thin, lightweight, robust, conformable, and fl exible. [ 1 ] To enable a fl exible display, a fl exible substrate must be used as the fundamental starting component in place of a conventional glass substrate. In general, metal foils, ultra-thin glasses, and plastic fi lms are considered candidates for a fl exible substrate. [ 2 ] In particular, fl exible displays using plastic substrates based on organic polymers have been a major topic not only because these show outstanding fl exibility and optical clarity at the same time, but also because they offer the possibility of a reduction in cost, coupled with a roll-to-roll process and ink-jet printing technology. [ 3 ] Common examples of commercially available polymers are polyethylene terephthalate (PET), polyether sulfone (PES), polyethylene naphthalate (PEN), polycarbonate (PC), and polyimide (PI). [ 1 , 4 ] To replace conventionally used glass substrates, a plastic substrate must be equipped with the properties of glass, such as optical transparency, thermal/chemical stability, O 2 /H 2 O permeability, low birefringence (or retardation), dimensional stability, and a low coeffi cient of thermal expansion (CTE). [ 1 ] Among these properties, the low CTE of plastic substrates coupled with dimensional stability is arguably the most important requirement, as it is directly related to compatibility with all other necessary display layers to be integrated onto them. [ 1 ] Although there have been extensive studies of fl exible devices built on polymer substrates, such as electrophoretic displays and organic thin-fi lm transistors (OTFTs), little progress have been made even with high-temperature processed devices such as active-matrix liquid crystal displays (AMLCDs). [ 5 ] Major obstacles include the high CTEs of polymers insuffi cient for the display layer integrations. Moreover, polymers usually have low glass transition temperatures ( T g s) where abrupt CTE changes are accompanied. This greatly limits their practical application in terms of the process temperature. Even polymers with a high T g , e.g., PES, are known to have a CTE of ∼ 50 ppm K − 1 , much higher than the typically required level (less than 20 ppm K − 1 ). [ 1 ] Other highT g polymers such as polytetrafl uoroethylene (PTFE) and poly(ether ether ketone) (PEEK) also have signifi cant drawbacks for implementation into large-area plastic electronics, as they are unfavorable in terms of cost. PI has a low CTE of ∼ 20 ppm K − 1 and a high

H+-type and OH−-type biological protonic semiconductors and complementary devices

Proton conduction is essential in biological systems. Oxidative phosphorylation in mitochondria, proton pumping in bacteriorhodopsin, and uncoupling membrane potentials by the antibiotic Gramicidin are examples. In these systems, H+ hop along chains of hydrogen bonds between water molecules and hydrophilic residues – proton wires. These wires also support the transport of OH− as proton holes. Discriminating between H+ and OH− transport has been elusive. Here, H+ and OH− transport is achieved in polysaccharide- based proton wires and devices. A H+- OH− junction with rectifying behaviour and H+-type and OH−-type complementary field effect transistors are demonstrated. We describe these devices with a model that relates H+ and OH− to electron and hole transport in semiconductors. In turn, the model developed for these devices may provide additional insights into proton conduction in biological systems.

High-performance hybrid plastic films: a robust electrode platform for thin-film optoelectronics

We report a novel flexible hybrid plastic film that can be used as a robust electrode platform for typical thin-film optoelectronic devices. Silver nanowires (AgNWs) were embedded on the surface of a glass-fabric reinforced transparent composite (GFRHybrimer) film to form a flexible transparent conducting substrate with excellent opto-electrical properties, superior thermal stability, and impressive mechanical flexibility. A highly efficient and flexible inverted organic solar cell with a power conversion efficiency (PCE) of 5.9% under 100 mW cm−2 AM 1.5G illumination was fabricated on the AgNW–GFRHybrimer film. The AgNW–GFRHybrimer film exhibits potential as an excellent transparent electrode for low cost flexible optoelectronic devices.

Thermally resistant UV-curable epoxy–siloxane hybrid materials for light emitting diode (LED) encapsulation

A UV-curable epoxy–siloxane hybrid material (epoxy hybrimer) was fabricated by photo-cationic polymerization of a sol–gel derived cyclo-aliphatic epoxy oligosiloxane (CAEO) blended with oxetane cross-linker in the presence of an onium salt. Antioxidants for fabrication of the UV-curable epoxy hybrimer with high thermal resistance against yellowing were incorporated in the UV-curable epoxy hybrimer. The UV-curable epoxy hybrimer with the antioxidants showed high thermal resistance without yellowing during 120 °C thermal aging. High thermal resistance of the UV-curable epoxy hybrimer was similar and higher compared to those of commercial thermally curable silicone and UV-curable epoxy LED encapsulants, respectively. The thermally resistant UV-curable epoxy hybrimer was successfully encapsulated on a LED without any cracking or delamination, and maintained a flat surface on the LED without distortion of the designed flat shape. Before/after thermal and blue light aging, the performance of the LED encapsulated by the UV-curable epoxy hybrimer was not changed. On the basis of its excellent properties as a LED encapsulant, the UV-curable epoxy hybrimer can be utilized as a UV-curable LED encapsulant for white LEDs.

Chitin microneedles for an easy-to-use tuberculosis skin test.

An easy-to-use tuberculosis skin test is developed with chitin microneedles that deliver purified protein derivative at the correct skin depth and result in a positive test in BCG-immunized guinea pigs.

Chitin nanofiber micropatterned flexible substrates for tissue engineering

Engineered tissues require enhanced organization of cells and extracellular matrix (ECM) for proper function. To promote cell organization, substrates with controlled micro- and nanopatterns have been developed as supports for cell growth, and to induce cellular elongation and orientation via contact guidance. Micropatterned ultra-thin biodegradable substrates are desirable for implantation in the host tissue. These substrates, however, need to be mechanically robust to provide substantial support for the generation of new tissues, to be easily retrievable, and to maintain proper handling characteristics. Here, we introduce ultra-thin (<10 μm), self-assembled chitin nanofiber substrates micropatterned with replica molding for engineering cell sheets. These substrates are biodegradable, mechanically strong, yet flexible, and easily manipulated into the desired shape. As a proof-of-concept, fibroblast cell proliferation, elongation, and alignment were studied on the developed substrates with different pattern dimensions. On the optimized substrates, the majority of the cells aligned (<10°) along the major axis of micropatterned features. With the ease of fabrication and mechanical robustness, the substrates presented herein can be utilized as versatile system for the engineering and delivery of ordered tissue in applications such as myocardial repair.

Sol-gel derived transparent zirconium-phenyl siloxane hybrid for robust high refractive index LED encapsulant.

We report a zirconium-phenyl siloxane hybrid material (ZPH) that can be used as a robust LED encapsulant. The ZPH encapsulant was fabricated via hydrosilylation-curing of sol-gel derived multifunctional (vinyl- and hydride-functions) siloxane resins containing phenyl-groups and Zr-O-Si heterometallic phase for achieving a high refractive index (n ≈ 1.58). In thermal aging, the ZPH LED encapsulant exhibited superior performances with a high optical transparency (∼88% at 450 nm) and exhibited high thermal stability (no yellowing at 180 °C for 1008 h), compared to a commercial LED encapsulant (OE-6630, Dow Corning Corporation). This suggests potential for ZPH to be a robust LED encapsulant.