Yang Doo Kim

Uniformly embedded silver nanomesh as highly bendable transparent conducting electrode

Ag-nanomesh-based highly bendable conducting electrodes are developed using a combination of metal nanotransfer printing and embossing for the 6-inch wafer scale. Two Ag nanomeshes, including pitch sizes of 7.5 and 10 μm, are used to obtain highly transparent (approximately 85% transmittance at a wavelength of 550 nm) and electrically conducting properties (below 10 Ω sq(-1)). The Ag nanomeshes are also distinguished according to the fabrication process, which is called transferred or embedded Ag nanomesh on polyethylene terephthalate (PET) substrate, in order to compare their stability against bending stress. Then the enhancement of bending stability when the Ag nanomesh is embedded in the PET substrate is confirmed.

Enhancement of light extraction efficiency of OLEDs using Si 3 N 4 -based optical scattering layer

An optical scattering layer, consisting of a Si3N4 nano-pillar array and a spin-coated hydrogen silsesquioxane (HSQ) planarization layer, was introduced to an organic light-emitting diode (OLED) substrate to increase the out-coupling efficiency. After plasma enhanced chemical vapor deposition (PECVD) of the Si3N4 layer, the nano-pillar array was created using nanoimprint lithography and reactive ion etching. As the Si3N4 pillar array has a refractive index of 2.0, photons generated in the organic layer are scattered by the Si3N4 structures and thus have a higher chance of being emitted from the device. The spin-coated HSQ planarization layer produces a flat substrate, which is essential for depositing a uniform organic material layer and assuring the electric conductivity of the transparent conducting oxide (TCO) layer. In this study, Si3N4 nano-structures with a height of 100 or 300 nm were used to enhance the out-coupling efficiency of the OLED devices. Although the electrical conductivity of the TCO layer deposited on the light scattering layer was slightly degraded, the OLED devices formed with the light scattering layer exhibited a higher luminous power at given electrical power. Consequently, the use of a planarized 300-nm-thick Si3N4 layer increased the external quantum efficiency of the OLED device by 50% at 10,000 cd/m2 compared to the reference OLED device fabricated on a flat glass substrate.

Various Metallic Nano-Sized Patterns Fabricated Using an Ag Ink Printing Technique

This paper presents a new simple metal patterning technique, which is based on soft nanoimprint lithography. By using this method with a commercial Ag nano particle ink, a nano-sized metal pattern was successfully fabricated. The problem of the residual layer of patterned Ag layer was minimized by controlling the concentration of the solution and the process conditions. By using this method, we could easily fabricate various patterns without reference to any shape. Furthermore, we fabricated an Ag mesh type pattern for the application of conducting transparent glass.

Enhanced light extraction efficiency in organic light emitting diodes using a tetragonal photonic crystal with hydrogen silsesquioxane

We report an organic light emitting diode (OLED) with a hydrogen silsesquioxane as a scattering material, for enhancing light extraction efficiency. A tetragonal photonic crystal was used as pattern type, and fabricated using a direct printing technique. Planarization was accomplished using TiO₂ solgel solution, having a refractive index identical to that of the indium zinc oxide transparent electrode. The current efficiency and power efficiency of the OLED increased by 17.3% and 43.4% at 10  mA/cm², respectively, without electric degradation.

Fabrication of oxide-based nano-patterned sapphire substrate to improve the efficiency of GaN-based of LED

In this study, an oxide-based nano-patterned sapphire substrate (ONPSS) was used as the substrate for a nitride-based light emitting diode (LED) in order to enhance the LEDs internal quantum efficiency and light extraction efficiency. The ONPSS was fabricated by a direct spin-on-glass printing technique, which is simple, easy, and relatively low-cost technique. Conventional PSSs are generally fabricated by photolithography and a sapphire etching process. However, the process reported here, it is possible to fabricate an oxide-based PSS without the sapphire etching process. After a GaN-based blue LED device was grown on the ONPSS, we measured the photoluminescence and electroluminescence intensity to confirm the light extraction efficiency and internal quantum efficiency of the LED. Compared to a GaN LED grown on an unpatterned sapphire, the ONPSS-based LED exhibited a 100% increase in light output power without electrical degradation.

Fabrication of a transparent conducting Ni-nanomesh-embedded film using template-assisted Ni electrodeposition and hot transfer process

In the present work, we developed a new method for fabricating Ni nanomeshes for transparent conducting electrodes using template-assisted Ni electrodeposition and a hot transfer process. By employing the direct printing of hydrogen silsesquioxane (HSQ), the microscale HSQ template was successfully transferred onto a stainless steel substrate. The Ni nanomesh was fabricated using selective Ni electrodeposition and a hot transfer process on a polycarbonate (PC) film. The Ni-nanomesh-embedded PC film exhibited approximately 77% of the transmittance of the PC film and a sheet resistance of 2–10 Ω sq−1. In addition, the transmittance and sheet resistance of the Ni-nanomesh-embedded PC film were not significantly degraded after 20000 cycles of bending tests.

Enhanced light extraction efficiency in organic light-emitting diode with randomly dispersed nanopattern.

An optical scattering layer composed of randomly dispersed nanopatterns (RDNPs) was introduced in an organic light-emitting diode (OLED) to increase the out-coupling efficiency. An RDNP was fabricated by direct printing on a glass substrate. Owing to its low haze and high transmittance, the RDNP acted as a light extraction layer in the OLED. The RDNP OLEDs showed higher current density and luminance than the reference devices at the same voltage. The current and power efficiencies of the RDNP OLED increased by 25% and 34%, respectively, without electrical degradation. Furthermore, the RDNP devices achieved an external quantum efficiency of 27.5% at 1 mA/cm².

Functional patterns for thin-film-type amorphous silicon solar cells

Three types of patterns acting as light-scattering centers were constructed on bulk glass surfaces and applied to solar cell fabrication. In order to fabricate a scattering center in the transparent conducted oxide (TCO) layer, the SiO2-based solution hydrogen silsesquioxane (HSQ; Dow Corning FOx-16) was used for direct nano-patterning. Direct nano-patterning is a simple and fast process that exploits the solvent permeability of poly(dimethylsiloxane) (PDMS). The nano- and micro-structured SiO2 layer fabricated directs diffused light into the active layer of the solar cell, enabling effective use of this layer. This increases the external quantum efficiency and conversion efficiency of the cell. Additionally, a thinner Si junction was fabricated to ensure the effect of each pattern.

A transparent embedded Cu/Au-nanomesh electrode on flexible polymer film substrates

Transparent embedded copper/gold (Cu/Au)-nanomesh electrodes are promising candidates to replace indium tin oxide (ITO). They are fabricated on a polyethylene terephthalate (PET) flexible polymer film using a transfer process on the scale of 11 mm × 11 mm. Because of the oxidation of copper, Cu-nanomesh electrodes have very low electrical conductivity. In order to solve this problem, we fabricated an electrode using a Cu/Au-bilayer. With the bilayer, we obtained a high transmittance and electric properties at wavelengths of 400–800 nm. Moreover, by controlling the pressure process, we obtained the transferred and embedded metal electrodes. We found that both the optical transmittance and the electrical conductivity of the embedded metal electrode were preserved after 50000 bending cycles. Consequently, embedded Cu/Au-nanomesh electrodes have good mechanical strength and electrical properties appropriate for flexible transparent electrodes.

Improved conversion efficiency of amorphous Si solar cells using a mesoporous ZnO pattern

To provide a front transparent electrode for use in highly efficient hydrogenated amorphous silicon (a-Si:H) thin-film solar cells, porous flat layer and micro-patterns of zinc oxide (ZnO) nanoparticle (NP) layers were prepared through ultraviolet nanoimprint lithography (UV-NIL) and deposited on Al-doped ZnO (AZO) layers. Through this, it was found that a porous micro-pattern of ZnO NPs dispersed in resin can optimize the light-trapping pattern, with the efficiency of solar cells based on patterned or flat mesoporous ZnO layers increased by 27% and 12%, respectively.