Ju-Hyeon Shin

To enhance the electrochemical characteristics of Si anodes for use in secondary batteries, a Ni-based Si-pattern substrate is evaluated. This Ni-based Si pattern is fabricated by a combination of nanoimprint lithography, plasma-enhanced chemical vapor deposition, and electroforming processes; its micro-morphology is determined using scanning electron microscopy (SEM) and transmission electron microscopy (TEM). The discharge capacity of this pattern is found to be similar to 2552 mAh g(-1) after the 1st cycle at 1.0 C rate, which represents a suitably high current density. After 100 cycles, the pattern exhibits a 732 mAh g(-1) charge capacity and 47% charge capacity retention. This Ni-based-Si pattern therefore possesses an excellent rate capability, with the electrode having a discharge capacity of 412 mAh g(-1), despite a relatively rapid 10 C rate. Moreover, the anode cell maintains its high capacity, even after 100 cycles, because of the high electrical conductivity of Ni, the r...

ABSTRACT A cylindrical Si3N4 nanopattern whose heights was 200 nm was fabricated on a glass substrate, and an aluminum-doped zinc oxide (AZO) layer was grown on the nanopatterned glass substrate. The nanopattern was applied to an amorphous silicon solar cell in order to increase the light-scattering effect, thus enhancing the efficiency of the solar cell. The reflectance of the solar cell on the Si3N4 nanopattern decreased and its absorption increased. Compared to a flat substrate, the short-circuit current density (Jsc) and conversion efficiency of a solar cell on the Si3N4 nanopatterned substrate were improved by 17.9% and 24.2%, respectively, as determined from solar simulator measurements.

ABSTRACT In nature, some living things exhibit special wettability properties such as superhydrophobicity. Many scientists have tried to mimic these properties for utilizing them in various applications. Especially, surface morphology is as important as the surface energy to create the superhydrophobicity. In this study, we used a hybrid method—a combination of sol–gel-based nanoimprint lithography and hydrothermal growth—to tune the surface morphology. Ten kinds of TiO2 structures were fabricated using this method and their wetting properties for various liquids and evaporation of water were analyzed. In particular, TiO2 nano- and hierarchical structures, which possess superhydrophobicity, were compared on the basis of these measurements. From these analyses, we confirmed that TiO2 hierarchical structures formed the most stable superhydrophobic state, which have the contact angles over 160° for water and the longest time for natural evaporation of water, compared to other ten kinds of TiO2 structures.

ABSTRACT 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.

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.

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.

ABSTRACT This work reports the fabrication of superhydrophobic and oleophobic surfaces with an overhang structure by reverse nanoimprint lithography. An overhang structure is difficult to fabricate by conventional lithography; however, it was conveniently formed by reverse imprint lithography, employed in conjunction with reactive ion etching. The obtained overhang structure was coated with a fluoroalkylsilane monolayer to reduce its surface energy. Further, four different types of nanopatterns were separately embedded on the surface of the obtained overhang structure by modified reverse imprint lithography to enhance its oil-repelling properties. The embedded nanopatterns resulted in different overhang angles, thereby enhancing the oil-repelling properties. The morphology and wetting characteristics of the overhang structure were investigated by scanning electron microscopy and contact angle measurements. This study demonstrates that an overhang structure can be successfully fabricated on a substrate by reverse nanoimprint lithography; moreover, oleophobic structures can be realized using materials with contact angles <90°

ABSTRACT A moth-eye pattern made of silica (SiO2) nanoparticles mixed with MIBK (methyl isobutyl ketone) was fabricated on a glass substrate using a direct printing method. The patterned glass was annealed to improve hardness and a heptdecafluoro-1,1,2,2-tetrahydrodecyl trichloro-silane based self-assembled monolayer (HDFS-SAM) was applied to the moth-eye pattern to reduce surface energy which improves hydrophobic properties. Compared to flat glass, the moth-eye patterned glass with a HDFS-SAM coating showed reduced reflectance, strong hardness, and high efficiency. As a result, the JSC of photovoltaic module was increased up to 1.9755 mA/cm2 and efficiency was improved by 4.66% by the increased current density (JSC) of photovoltaic system, and the external quantum efficiency was enhanced over the entire visible spectrum.

ABSTRACT As a result of the rising concerns surrounding environmental pollution, green energy technologies are beginning to replace conventional power generation technology based on fossil fuels. In particular, photovoltaic systems which convert solar energy into electricity without generating carbon dioxide have been widely used around the world as a result of their conversion energy being exceptionally high. In this investigation, we fabricated anti-reflection and light-scattering patterns on the protective glass of solar cell modules. The path length and quantity of incident light reaching the solar cell module could be increased by incorporating anti-reflection and light-scattering patterns. These patterns were fabricated on the surface of the protective glass using nanoimprint lithography (NIL) and inductively coupled plasma (ICP) processes. The amount of light reflected off the patterned protective glass decreased by up to 4% when the fabricated anti-reflection patterns were implemented. Additionally, the surface of the patterned glass was superhydrophobic as a result of the self-assembled monolayer (SAM) coating employed in this study. The lithium ion battery comprised of the solar module using patterned glass as a protective layer could be charged approximately 14% higher than the lithium ion battery comprised of the solar module using conventional textured glass as a protective layer.

ABSTRACT The substrate of an a-Si:H solar cell with microscale surface roughness generally shows high diffuse transmittance; however, it also has detrimental effects, including low open-circuit voltage and fill factor (FF). We applied planarization to the rough surface using spin-coating of ZnO nanoparticles dispersed in an ethanol-based solution. The resulting conversion efficiency of the solar cell increased by ∼18% owing to the higher open-circuit voltage and FF, with a small decrease in the diffused transmittance.

ABSTRACT In order to improve the conversion efficiency of organic photovoltaic (OPV) cells, nano-patterned poly (3,4-ethylenedioxythiophene) poly (styrenesulfonate) (PEDOT:PSS) was used as a hole transfer layer (HTL). Using nanoimprint lithography, a process that is easily applied to large-area substrates, a spherical array of PEDOT:PSS droplets was formed. The effect of the PEDOT:PSS nanostructure was characterized by optical and electrical measurements. Because the hemispherical array of PEDOT:PSS scatters light efficiently, absorption of the incident light increases when the nanostructured layer is employed. The conversion efficiency of the nano-patterned OPV cells is 25% larger than that of non-patterned OPV cells, due to the increase in short-circuit current (Jsc).

Silica nanostructures were fabricated on glass substrate using a microwave assisted direct patterning (MADP) process, which is a variety of soft lithography. During the MADP process using polydimethylsiloxane (PDMS), mold and microwave heating are performed simultaneously. Blanket thin film and micro- to nano-sized structures, including moth-eye patterns of SiO2, which consisted of coalesced silica nanoparticles, were formed on glass substrates from SiO2 nano-particle dispersed solutions with varied microwave heating time. Optical properties and surface morphologies of micro-sized hemisphere, nano-sized pillar, moth-eye and 50 nm sized line/space silica patterns were measured using UV-vis and a scanning electron microscope. X-ray diffraction analysis of SiO2 thin films with and without microwave heating was also carried out.

Carbon based spin-on organic hardmask (C-SOH) was used as an imprint resin to fabricate sub 50 nm sized patterns. Imprinting of C-SOH was done with a polyurethaneacrylate (PUA) stamp. Patternability and etch resistance of the C-SOH resin was compared to poly(methyl methacrylate) (PMMA). C-SOH can be patterned at the nanosize using imprint lithography and exhibits superior etch resistance, especially for F-based plasmas. Due to the poor etch resistance of imprint resin such as PMMA, it is seldom used as an etch mask to form nano-structures by etching the Si3N4 layer. However, such a nano-structure was able to be formed by etching the Si3N4 layer using C-SOH as an etch mask.

ABSTRACT In order to increase the conversion efficiency of organic photovoltaics (OPV), diverse-scale patterns were formed on a glass substrate using the direct printing technique. The optical properties of the patterns depended on the size, shape, height, and pitch of the patterns. Randomly distributed nano-and micro-patterns caused light scattering, which increased the diffusion transmittance. The other pattern, which was a nanosized anti-reflective pattern comprising a 300nm sized hexagonal array, decreased the reflectance of light on the surface. The optical properties of these patterns, can be used to improve solar cell efficiency by increasing the light allowed onto the light-absorbing layer. We used a direct printing method with a poly(dimethylsiloxane) (PDMS) mold to fabricate these patterns on glass substrates. These patterns were transferred from PDMS to the surface of a glass substrate. Hydrogen silsesquioxane (HSQ) was used as a resin since its properties include volatility and allow for spin-coating; it also has a reflective index similar to that of glass. This method has low cost and a simple process compared to optic-based lithography. After these patterns were formed outside the glass substrate, a conductive polymer layer and the active layer were formed by spin-coating, and the cathode was deposited by a thermal evaporator. The electrical properties of solar cells fabricated with these patterns on their surfaces were measured with a solar simulator. The conversion efficiency of the solar cells with these surface patterns showed an increase of up to 6.8% in comparison with conventional cells. (C) 2013 The Japan Society of Applied Physics