Hyun-Chul Ki

The study of light waveguide effects on ZnO nanorod arrays

Two different types of ZnO nanorods (hexagonal pyramid-shaped nanorod and hexagonal prism-shaped nanorod) were integrated on light emitting diodes (LEDs) for the investigation of light waveguide effects, which were evaluated using electroluminescence (EL) and current-voltage (I–V) characteristics. EL intensity in LEDs with hexagonal prism-shaped ZnO nanorod arrays were improved by 18% while EL intensity in LEDs with hexagonal pyramid-shaped ZnO nanorods were reduced by 25% compared to bare LEDs. 3D-finite dimension time domain (3D-FDTD) programs were used to simulate the light waveguide effect on the two different shapes of ZnO nanorods. In addition, photonic crystals (PCs) effects in ZnO nanorod arrays were simulated to verify the light waveguide effect. It was found that light in a hexagonal prism-shaped ZnO nanorod propagated from the bottom to the top end. However, the light in a hexagonal pyramid-shaped ZnO nanorod was dissipated on the lateral face. The light extraction efficiency in ZnO nanorod arrays was dominated by the top end shape and planar density of ZnO nanorods.

Design and Properties Related to Anti-reflection of 1.3μm Distributed Feedback Laser Diode

We have investigated the effect of the quality of 1.3 um distributed feed back laser diode (DFB-LD) on the design of anti-reflection (AR) coatings. Optimal condition of AR coating to prevent internal feedback from both facets and reduce the reflection-induced intensity noise of laser diode was simulated with Macleod Simulator. Coating materials used in this work were and , of which design thickness were 105 nm and 165 nm, respectively. AR coating films were deposited by Ion-Assisted Deposition system. The electrical and optical properties of 1.3 um laser diode were characterized by Bar tester and Chip tester. Threshold current and slop-efficiency of DFB-LD were 27.56 mA 0.302 W/A. Far field pattern and wavelength of DFB-LD were (Vertical), 1313.8 nm, respectively.

Anti-Reflection Thin Film For Photoelectric Conversion Efficiency Enhanced of Dye-Sensitized Solar Cells

DSSCs (dye-sensitized solar cells) based on TiO2/SiO2 multi layer AR (anti-reflection) coating on the outer glass FTO (fluorine-doped tin oxide) substrate are investigated. We have coated an AR layer on the surface of a DSSCs device by using an IAD (ion beam-assisted deposition) system and investigated the effects of the AR layer by measuring photovoltaic performance. Compared to the pure FTO substrate, the multi layer AR coating increased the total transmittance from 67.4 to 72.9% at 530 nm of wavelength. The main enhancement of solar conversion efficiency is attributed to the reduction of light reflection at the FTO substrate surface. This leads to the increase of Jsc and the efficiency improvement of DSSCs.

Enhanced Electrochemical Properties of Dye-sensitized Solar Cells Using Flexible Stainless Steel Mesh Electrodes with Ti Protective Layer

Stainless steel (SS) mesh was used to fabricate photoelectrode for flexible dye-seisitzed solar cells (DSSCs) in order to evaluate them as replacements for more expensive transparent conductive oxide(TCO). We fabricated the DSSCs with new type of photoelectrode, which consisted of flexible SS mesh coated with 100 nm thickness titanium (Ti) protective layer deposited using electron-beam deposition system. SS mesh DSSCs with protective layer showed higher efficiency than those without a protective layer. The best cell property in the present study showed the open circuit voltage (Voc) of 0.608 V, short-circuit current density (Jsc) of 5.73 mA cm, fill factor (FF) of 65.13%, and efficiency (η) of 2.44%. Compared with SS mesh based on DSSCs (1.66%), solar conversion of SS mesh based on DSSCs with protective layer improved about 47%.

A Formation of Hole Pattern on Ti Electrode by Lift-off and Its Application to TCO-less Dye-sensitized Solar Cells

In this study, we propose Ti hole pattern structure on the transparent conductive oxide (TCO) less dye-sensitized solar cells (DSSCs) using the lift-off process to improve the low light transmittance and low efficiency caused by opaque Ti electrode. The formation of Ti hole patterns make it possible to move the dye adsorption and electrolyte. The DSSCs with Ti hole patterns showed a higher photoelectric conversion efficiency (PCE) than those with general structure by 11.1%. As a result, The Ti hole pattern structure can be improved to increase the light absorption of the dyes and PCE of the TCO-less DSSCs is also increased.

Optical Characteristics of Plasmonic Nano-structure Using Polystyrene Nano-beads

Abstract: We proposed and demonstrated the double layered metallic nano-hole structure using polystyrene beads process to enhance the sensitivity of surface plasmon resonance (SPR). The double layered SPR structures are calculated using the finite-difference time-domain (FDTD) method for the width, thickness, and period of the metallic nano-hole structures. The thickness of the metal film and the metallic nano-hole is 30 and 20 nm in the 214 nm wide nano-hole size, respectively. The double layered SPR structures are fabricated with monolayer polystyrene beads of 420 nm wide. The sensitivities of the conventional SPR sensor and the double layered SPR sensor are obtained to 42.2 and 52.1 degree/RIU, respectively. Keywords: Surface plasmon resonance, Metallic nano-hole, Sensor, Polystyrene, FDTD 1. 서 론 1) 최근 바이오 물질의 비표지 검출 방법으로 굴절률의 변화를 측정하여 생체 물질의 상호작용을 인지할 수 있는 표면 플라즈몬 공명(surface plasmon resonance, SPR) 센서에 관한 연구가 활발히 이루어

Optical Characteristics of Plamonic Waveguide Using Tapered Structure

Laboratory for Electromagnetic Field and Microwave Electronics, ETH Zurich, Zurich 8092, Switzerland(Received January 23, 2014; Revised February 3, 2014; Accepted February 19, 2014)Abstract: We have investigated the optical properties of plamonic waveguide with tapered structure based on InP material for photonic integrated circuit(PIC). The proposed plasmonic waveguide is covered with the Ag thin film to generate the plasmonic wave on metallic interface. The optical characteristics of plasmonic waveguide were calculated using the three-dimensional finite-difference time-domain method. The plasmonic waveguide was fabricated with the lengths of 2 to 10 μm and the widths of 400 to 700 nm, respectively. The plasmonic mode and optical loss were measured. The optimum plasmonic length is 10 μm and widths are 600 and 700 nm in the fabricated waveguide. This plasmonic waveguide can be directly integrated with other conventional optical devices and can be essential building blocks of PIC. Keywords: FDTDSurface plasmon resonance, Plamonic waveguide, Tapered structure, PIC,

Fabrication of TCO-less Dye-sensitized Solar Cells by Using Low Cost Ti Layer Deposited Glass Substrate

In this study, a transparent conductive oxide (TCO)-less dye-sensitized solar cells (DSSCs) was fabricated by using titanium (Ti) electrode to replace the Fluorine-doped tin oxide (FTO) for the reduction of manufacturing cost. Ti film was formed by electron beam evaporation method and the results showed the sheet resistance of Ti electrodes with a thikness of 500 nm similar to FTO. In case of power conversion efficiency (PCE), a DSSC with Ti electrodes showed a lower value than that with FTO by 0.38%. For the investigation of the difference, the DSSCs were measured and analyzed by using electrochemical impedance analyzer (EIS).

The surface plasmon resonance sensor with the metallic nanostructure for biosensing

In this paper, we have demonstrated a metallic nano-structured SPR sensor for an improvement of biosensing sensitivity using a metallic nano-structure. Permittivity of metal is calculated with Drude model for analysis. The sensitivity of SPR sensor with metallic nano-structure is 65 degree/RIU, and that of conventional SPR configuration is 54.8 degree/RIU. We have fabricated the random metallic nano-structures on the metallic thin film using the RIE etching process. Moreover, we have analyzed the structure using the finite-difference time-domain method for the exact characteristic.

Photoelectric Conversion Efficiency of DSSC According to Plasma Surface Treatment of Conductive Substrate

This study is explore the photoelectric conversion change of dye-sensitized solar cells with surface treatment of the conductive substrate. gases of FTO surface treatment were N2, and O2. Treatment conditions of surface were gas flux from 25 sccm to 50 sccm and RF power were from 25 W to 50 W. Treatment time and pressure were fixed 5 min and 100 mtoor. The best sheet resistance and surface roughness were obtained by O2 50 sccm and 50 W and that result were 7.643 Ω/㎠ and 17.113 nm, respectively. The best efficiency result was obtained by O2 50 sccm and 50 W and that result of Voc, Jsc, FF and efficiency were 7.03 V, 14.88 mA/㎠, 63.75% and 6.67%, respectively.