Application of Nanoscale Surface Engineering for Solid Oxide Fuel Cells and Anti-reflection Property

Abstract

Since the processing for integrated circuits (ICs) manufacturing started about half century ago, many lithography techniques have appeared to fabricate micro/nano devices. Among those techniques, nano-sphere lithography (NSL) is considered one of the economical technique to create pattern close packed with nanoscale features. In NSL, silica nano-sphere (SNS) as a lithographic mask is deposited onto a substrate surface. This method has significantly influenced on the scientific field such as solar cells, electronics and so on. In this study, we successfully applied NSL to two applications including solid oxide fuel cells (SOFCs) and anti-reflective property investigation.

There have been many researches to produce renewable energy due to the limited amount of existing fuels on earth and harmful products as a result of combustion. Among those renewable energy conversion systems, SOFCs have been attracted one of the future renewable energy because of their high fuel conversion efficiency and environmental friendly emissions. However, due to the high operating temperature (800-1000 ℃), many problems occur including thermal issues and commercialization. For these reasons, many researchers have studied LT-SOFCs (Low Temperature SOFCs) because of their advantages for low operating temperature. However, the obstacles from increased losses originated from lowering the temperature influenced the degradation of cell performance. Therefore, surface engineering investigation was conducted to reduce ohmic and activation losses by applying nanoscale deposition technique and lithography process. Because ohmic loss can be decreased by minimizing the electrolyte thickness, nanoscale surface engineering to minimize electrolyte thickness has been conducted. First, we investigated the fabrication of conventional electrolyte thin films with restrain, ed columnar grains on a nanoporous substrate to avoid unfavorable micro/nano structural defects originated from the substrate. Also, to reduce activation loss, we enhanced surface area of SOFCs by applying NSL because reaction sites can increase in proportional to increase the surface area at the interface between electrode and electrolyte. As a result, electrochemical impedance spectroscopy (EIS) shows significant decrease in electrode interfacial resistance.

Optical antireflective properties have been widely investigated for silicon based devices. Si has been attracted as a promising material because of the enhancement of photo-conversion efficiency and abundance of raw materials. However, light scattering occurs at the interface between air and Si due to the high refractive index of planar Si. This is because the discontinuity of the refractive indexes at the interface is the main reason for the scattering from the planar Si. Thus, researches to decrease reflectance from Si have been studied. Our group fabricated nanostructure arrays to decrease broadband optical antireflective property on silicon substrates using NSL technique. The morphology of the nanostructures was precisely controlled by modifying the conventional process of NSL technique. We investigated their effects on the optical characteristics based on experimentally measured reflectance results. The Si nanostructure arrays demonstrated optical antireflection performance with an average reflectance of about 1% across the spectral range from 300 to 800 nm, i.e. near-ultraviolet (NUV) to visible wavelengths. This fabrication method can be used to create a large surface area and offers a promising approach for antireflective applications.