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Park K.M.,Korea Atomic Energy Research Institute | Lee M.B.,Daegu Technopark Nano Convergence Practical Application Center | Choi S.Y.,Kyungpook National University
Solar Energy Materials and Solar Cells | Year: 2015

Maskless reactive ion etching (RIE) texturing using a gas mixture of sulfur hexafluoride-oxygen (SF6/O2) and sulfur hexafluoride-oxygen-chlorine (SF6/O2/Cl2) was investigated to reveal the proper shape in surface features for higher efficiency multi-crystalline silicon (mc-Si) solar cells; hence, needle-like and round-top cone (RT cone) shapes were formed by RIE texturing with SF6/O2 gas, and pyramid and inverted pyramid shapes by RIE texturing with SF6/O2/Cl2 gas. RIE-textured mc-Si solar cells were fabricated on these surface features except for an inverted pyramid structure in the industrial production line. Performances of cells with RT cone and pyramid shapes were enhanced, whereas those with a needle-like cone were degraded, compared to the reference cells. Among these cells, those with RT cones represented the highest efficiency at 17.22%. By considering diode characteristics and electroluminescence images of fabricated solar cells, the proper shape for surface features was intimately related to control of the formation of a stable emitter layer as well as the reduction of surface reflectance. © 2014 Elsevier B.V. All rights reserved. Source

Park K.M.,Kyungpook National University | Lee M.B.,Daegu Technopark Nano Convergence Practical Application Center | Shin J.W.,Korea University | Choi S.Y.,Kyungpook National University
Solar Energy | Year: 2013

Maskless, random RIE texturing with a gas mixture of SF6/O2 (SO) and SF6/O2/Cl2 (SOC) was investigated to achieve higher efficiency for mc-Si solar cells. Cone structure with aspect ratio of 3.7 was highly effective for reducing surface reflectance particularly for wavelength from 310 to 700nm and triangular pyramid structure with aspect ratio of 2 revealed rather uniform reduction of reflectance with respect to the optimized wet texturing for whole wavelength range of 310-1100nm. On the contrary to results of reflectance, performances of fabricated cell were much better for triangular pyramid structure than cone structure. The degradation of cell performances for the cone structure was assigned both to the poor e-h pair generation efficiency relevant to the formation of highly defective surface layer with high density recombination centers, and ohmic shunt. The efficiency enhancement by 0.6% in mc-Si solar cells with triangular pyramid structures was assigned also to the slightly enhanced e-h pair generation efficiency with respect to the reference cell. © 2013 Elsevier Ltd. Source

Kim Y.-J.,Catholic University of Daegu | Ahn C.H.,Daegu Technopark Nano Convergence Practical Application Center | Choi M.O.,Catholic University of Daegu
European Polymer Journal | Year: 2010

Composite nanofibrous membranes were prepared by the electrospinning and the thermal treatment from poly(vinylidene fluoride) (PVDF)-tetramethyl orthosilicate (TMOS) blend solutions. The average diameter of nanofibers was reduced with increasing the concentration of TMOS in the solution due to the decrease of the solution viscosity. The EDX spectra confirmed the presence of TMOS on the external surface of the composite nanofibrous membrane. The porosity of membranes was effectively enhanced by the introduction of electrospinning technique. However, the mechanical properties, thermal stability and hydrophobicity were not markedly amplified. Thus the thermal treatment of the composite membranes was carried out, leading to the enormous enhancement of the mechanical properties and hydrophobicity. In addition, XRD results revealed that the crystal structure of PVDF in the composite membranes transformed from α-phase to β-phase due to the formation of silica particles by the thermal treatment. © 2010 Elsevier Ltd. All rights reserved. Source

Yun J.,Korea Institute of Materials Science | Lee S.,Korea Institute of Materials Science | Bae T.-S.,Korea Basic Science Institute | Yun Y.,Daegu Technopark Nano Convergence Practical Application Center | And 2 more authors.
Plasma Processes and Polymers | Year: 2011

This study discloses (i) the chemical and morphological modifications in acrylate hard-coat and bare polyethylene terephthalate polymers occurring in the course of Ar plasma treatments and (ii) the effects of these modifications on the adhesion, barrier performance, and cohesion of silicon oxide coatings deposited on the polymers. It is concluded that the deterioration in these coating properties is dominated by the formation of nanoscopic globular polymer protrusions on the polymer surface as a result of plasma treatment. The protrusions evolve even under very mild plasma conditions in which an ion fluence of less than 1 × 10 16 ions · cm -2 is applied with low-energy ion irradiation of 6 eV. The polymer protrusions dictate the nucleation and subsequent growth of a coating by promoting the development of a three-dimensional granular morphology in the coating. At the initial oxide nucleation stage, the wetting behavior of silicon oxide on the polymer surface in the presence of nanoscopic protrusions is directly limited by the area number density and size of the protrusions. Incomplete wetting of the protrusions with a silicon oxide coating hinders adhesion between the oxide and the polymer surface. The reduction in the contact area between the oxide and the protrusions is identified as the reason that a weak boundary layer forms at the oxide-polymer interface. Furthermore, the formation of nanoscopic defects, predominantly pinholes, is inevitable in the granular coating morphology on the polymer protrusions and weakens the oxide coating's barrier performance and cohesion strength. Variations in the polar surface free energy and chemical composition of the plasma-treated polymer surface are irrelevant to the wetting dynamics whenever the protrusions develop on the polymer surface. The effects of the polar surface free energy and chemical composition are valid only to the extent that the plasma treatment improves the wettability of a polymer surface without protrusion formation. © 2011 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim. Source

Jang W.G.,Keimyung University | Jeon K.S.,Daegu Technopark Nano Convergence Practical Application Center | Byun H.S.,Keimyung University
Desalination and Water Treatment | Year: 2013

A membrane material based on polyamide-imide (PAI) has received a great attention lately due to its thermal resistance, outstanding mechanical property, and low thermal expansion coefficient. In this study, we have focused on the preparation of porous PAI nanofiber membranes (PNMs) for water treatments. The preparation of PNMs was completed via the electrospinning method using PAI in a mixed solvent of dimethylacetamide and tetrahydrofuran. The resulting PNMs were then thermally treated to improve mechanical properties. These PAI-based membranes were characterized by scanning electron microscope, tensometer (tensile strength and elongation), pore characteristic, contact angle analyzer (contact angle), and dead-end cell device (water flux). We noticed that the pore diameter (1.0-0.3 μm) of PNMs was systematically controlled by simply increasing the number of PNMs layers. As these nanofiber membranes were found to be highly hydrophobic, we also attempted to prepare hydrophilic PNMs with a PAI solution containing 2-4 wt.% of diethylene glycol prior to the electrospinng. Based on contact angle tests, these modified PNMs exhibited very hydrophilic characteristics that could be utilized in water-filtration systems. © 2013 Copyright Balaban Desalination Publications. Source

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