Hyungjin Lee

Highly Conductive and Flexible Silver Nanowire-Based Microelectrodes on Biocompatible Hydrogel

We successfully fabricated silver nanowire (AgNW)-based microelectrodes on various substrates such as a glass and polydimethylsiloxane by using a photolithographic process for the first time. The AgNW-based microelectrodes exhibited excellent electrical conductivity and mechanical flexibility. We also demonstrated the direct transfer process of AgNW-based microelectrodes from a glass to a biocompatible polyacrylamide-based hydrogel. The AgNW-based microelectrodes on the biocompatible hydrogel showed excellent electrical performance. Furthermore, they showed great mechanical flexibility as well as superior stability under wet conditions. We anticipate that the AgNW-based microelectrodes on biocompatible hydrogel substrates can be a promising platform for realization of practical bioelectronics devices.

Continuous Patterning of Copper Nanowire-Based Transparent Conducting Electrodes for Use in Flexible Electronic Applications

Simple, low-cost and scalable patterning methods for Cu nanowire (NW)-based flexible transparent conducting electrodes (FTCEs) are essential for the widespread use of Cu NW FTCEs in numerous flexible optoelectronic devices, wearable devices, and electronic skins. In this paper, continuous patterning for Cu NW FTCEs via a combination of selective intense pulsed light (IPL) and roll-to-roll (R2R) wiping process was explored. The development of continuous R2R patterning could be achieved because there was significant difference in adhesion properties between NWs and substrates depending on whether Cu NW coated area was irradiated by IPL or not. Using a custom-built, R2R-based wiping apparatus, it was confirmed that nonirradiated NWs could be clearly removed out without any damage on irradiated NWs strongly adhered to the substrate, resulting in continuous production of low-cost Cu NW FTCE patterns. In addition, the variations in microscale pattern size by varying IPL process parameters/the mask aperture sizes were investigated, and possible factors affecting on developed pattern size were meticulously examined. Finally, the successful implementation of the patterned Cu NW FTCEs into a phosphorescent organic light-emitting diode (PhOLED) and a flexible transparent conductive heater (TCH) were demonstrated, verifying the applicability of the patterned FTCEs. It is believed that our study is the key step toward realizing the practical use of NW FTCEs in various flexible electronic devices.

Highly Sensitive, Transparent, and Durable Pressure Sensors Based on Sea‐Urchin Shaped Metal Nanoparticles

Highly sensitive, transparent, and durable pressure sensors are fabricated using sea-urchin-shaped metal nanoparticles and insulating polyurethane elastomer. The pressure sensors exhibit outstanding sensitivity (2.46 kPa-1 ), superior optical transmittance (84.8% at 550 nm), fast response/relaxation time (30 ms), and excellent operational durability. In addition, the pressure sensors successfully detect minute movements of human muscles.

Flexible metal nanowire-parylene C transparent electrodes for next generation optoelectronic devices

We prepared high performance metal nanowire (NW)-parylene C transparent electrodes (TEs) using pyrolytic deposition of a parylene C protection layer onto a silver nanowire (AgNW) or copper nanowire (CuNW) film at room temperature for the first time. The AgNW-parylene C TE showed superior optoelectronic properties such as high optical transmittance (94.7%) and low sheet resistance (41.6 Ω sq−1), comparable to a conventional indium tin oxide (ITO) TE. The AgNW-parylene C TE fabricated on a plastic substrate possessed outstanding flexibility. Moreover, the AgNW-parylene C and CuNW-parylene C TEs exhibited significantly improved oxidation and chemical stability due to the outstanding gas barrier properties of the parylene C protection layer. Furthermore, the potential suitability of the AgNW-parylene C TE was successfully demonstrated by fabricating flexible polymer solar cells. We expect that the flexible metal NW-parylene C TEs can be used as key elements for a variety of next generation optoelectronic devices.