• Current Photovoltaic Research
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• v.5 no.1
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• pp.25-27
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• 2017

Nanoscale textured black silicon has attracted intensive attention due to its great potential as applications in multicrystalline silicon-based solar cells. It absorbs sunlight over a broad range of wavelengths but introduces large recombination centers, non-uniform doping into cell. In this study, we present a metal-assisted chemical etching technique plus alkaline etching process to fabricate nanoscale pyramid structures with optimized condition. To make the structures, silver nanoparticles-loaded mc-Si wafer was submerged into $H_2O_2/HF$ solution first for nanohole texturing the wafer and textured wafer etched again with KOH solution for making nanoscale pyramid structures. The average reflectivity (350-1050 nm) is about 8.42% with anti-reflection coating.

• Advances in nano research
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• v.5 no.3
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• pp.231-244
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• 2017

Graphene oxide (GO) was prepared by modified Hummer's method to produce reduced graphene oxide (RGO) following standard thermal and chemical reduction processes. Prepared RGO colloids were utilized to fabricate RGO films over glass and FTO coated glass substrates through drop-coating. A systematic study was performed to evaluate the effect of reduction degree on the optical and electrical properties of the RGO film. We demonstrate that both the reduction process (thermal and chemical) produce RGO films of similar optical and electrical behaviors. However, the RGO films fabricated using chemically reduced GO colloid render better performance in dye sensitized solar cells (DSSCs), when they are used as counter electrodes (CEs). It has been demonstrated that RGO films of optimum thicknesses fabricated using RGO colloids prepared using lower concentration of hydrazine reducer have better catalytic performance in DSSCs due to a better catalytic interaction with redox couple. The better catalytic performance of the RGO films fabricated at optimal hydrazine concentration is associated to their higher available surface area and lower grain boundaries.

• Korean Journal of Materials Research
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• v.29 no.12
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• pp.757-763
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• 2019

A stacked high-voltage (900 V) Al electrolytic capacitor made with ZrO₂ coated anode foils, which has not been studied so far, is realized and the effects of Zr-Al-O composite layer on the electric properties are discussed. Etched Al foils coated with ZrO₂ sol are anodized in 2-methyl-1,3-propanediol (MPD)-boric acid electrolyte. The anodized Al foils are assembled with stacked structure to prepare the capacitor. The capacitance and dissipation factor of the capacitor with ZrO₂ coated anode foils increase by 41 % and decrease by 50 %, respectively, in comparison with those of Al anode foils. Zr-Al-O composite dielectric layer is formed between separate crystalline ZrO₂ with high dielectric constant and amorphous Al₂O₃ with high ionic resistivity. This work suggests that the formation of a composite layer by coating valve metal oxide on etched Al foil surface and anodizing it in MPD-boric acid electrolyte is a promising approach for high voltage and volume efficiency of capacitors.

• Advances in nano research
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• v.2 no.1
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• pp.23-56
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• 2014

The significant growth of the Si photovoltaic industry has been so far limited due to the high cost of the Si photovoltaic system. In this regard, the most expensive factors are the intrinsic cost of silicon material and the Si solar cell fabrication processes. Conventional Si solar cells have p-n junctions inside for an efficient extraction of light-generated charge carriers. However, the p-n junction is normally formed through very expensive processes requiring very high temperature (${\sim}1000^{\circ}C$). Therefore, several systems are currently under study to form heterojunctions at low temperatures. Among them, carbon nanotube (CNT)/Si hybrid solar cells are very promising, with power conversion efficiency up to 15%. In these cells, the p-type Si layer is replaced by a semitransparent CNT film deposited at room temperature on the n-doped Si wafer, thus giving rise to an overall reduction of the total Si thickness and to the fabrication of a device with cheaper methods at low temperatures. In particular, the CNT film coating the Si wafer acts as a conductive electrode for charge carrier collection and establishes a built-in voltage for separating photocarriers. Moreover, due to the CNT film optical semitransparency, most of the incoming light is absorbed in Si; thus the efficiency of the CNT/Si device is in principle comparable to that of a conventional Si one. In this paper an overview of several factors at the basis of this device operation and of the suggested improvements to its architecture is given. In addition, still open physical/technological issues are also addressed.

• Journal of the Korean Ceramic Society
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• v.47 no.2
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• pp.113-116
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• 2010

The silica coated $Fe_3O_4$ nanoparticles have been synthesized using a micro-emulsion method. The $Fe_3O_4$ nanoparticles with the sizes 6 nm in diameter were synthesized by thermal decomposition method. Hydrophobic $Fe_3O_4$ nanoparticles were coated silica using surfactant and tetraethyl orthosilicated (TEOS) as a $SiO_2$ precursor. Shell thickness of silica coated $Fe_3O_4$ can be controlled (11~20 nm) through our synthetic conditions. The $Fe_3O_4$ and silica coated $Fe_3O_4$ nano powders were characterized by transmission electron microscopy (TEM), x-ray diffraction (XRD) and vortex magnetic separation (VMS).

• Proceedings of the Korean Institute of Electrical and Electronic Material Engineers Conference
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• 2008.11a
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• pp.444-444
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• 2008

For the polymer tandem cell, simple and advantaged solution-based method to electron transport intermediate layer is presented which are composed $TiO_2$ nanoparticles. Device were based on a regioregular Poly(3-hexylthiophene)(P3HT) and [6,6]-phenyl $C_{61}$ butyric acid methyl ester($PC_{60}BM$) blend as a donor and acceptor bulk-heterojunction. For the middle electrode interlayer, the $TiO_2$ nanoparticles were well dispersed in ethanol solution and formed thin layer on the P3HT:PCBM charge separation layer by spin coating. The layer serves as the electron transport layer and divides the polymer tandem solar cell. The open-circuit voltage (Voc) for the polymer tandem solar cells was closed to the sum of those of individual cells.

• Journal of the Korean Institute of Electrical and Electronic Material Engineers
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• v.29 no.4
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• pp.247-249
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• 2016

In this study, we investigated the color change of the normal light gray granite as the high value color granite. By coating the metal catalyst liquid on the surface of granite stone, the metal particles were penetrated into the granite and the color of granite was changed permanently through the annealing treatment. To increase penetration depth into the granite, we used DC (direct current) bias. Two kinds of bias were used such as DC bias and pulse DC bias. And the penetration time was changed as 30 and 60 min. In all cases, the color granite were successfully obtained. Regardless of the catalyst reaction time, the penetration depth was increased by using the bias treatment. We obtained a penetration depth of 21 mm with the DC pulse bias during 60 min.

• Proceedings of the Materials Research Society of Korea Conference
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• 2010.05a
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• pp.30.1-30.1
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• 2010

Hydrogen silsesquioxane (HSQ)는 spin-on glass (SOG)의 일종으로 spin-coating이 가능하며 $400^{\circ}C$ 이상의 고온에서의 어닐링을 통해 silica로 변환되는 물질이다. 이 물질은 가시광선 영역에서 95% 이상의 높은 투과도를 나타내며 산화물로의 변환 공정이 간단하며 표면 개질이 용이하기 때문에 나노 바이오, 반도체, 광전자 소자 등의 다양한 분야로의 적용이 기대되는 물질이다. 최근 나노 기술의 발전에 따라 다양한 나노 구조물을 이용하여 소자들의 효율을 향상시키는 연구가 활발하게 진행되고 있다. 따라서 HSQ를 이용하는 소자의 효율을 높이기 위해서는 쉽고 간단하면서 생산성이 높은 HSQ 나노 구조물 제작 기술에 대한 연구가 필요하다. 현재 개발된 대면적 HSQ 나노 구조물 제작 기술로는 e-beam lithography, x-ray lithography, room temperature nanoimprint lithography 등이 있다. 하지만 이와 같은 나노 패터닝 기술들은 생산성이 낮거나 공정이 복잡한 단점이 있다. 본 연구에서는 poly(dimethylsiloxane) (PDMS) mold를 이용한 직접 printing 기술을 통해 HSQ 나노 구조물을 제작하는 기술을 개발하였다. 이 기술은 대면적에 간단한 기술로 HSQ 나노 패턴을 제작할 수 있으며 master mold의 패턴이 그대로 HSQ layer로 전사되기 때문에 제작이 까다로운 아날로그 패턴도 손쉽게 제작할 수 있는 장점을 가지고 있다. 따라서 이와 같은 HSQ 직접 printing 기술을 이용하여 HSQ 아날로그 나노 패턴을 제작하고 이의 응용기술에 대한 연구를 진행하였다.

• Korean Journal of Materials Research
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• v.17 no.3
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• pp.125-131
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• 2007

[ $TiO_{2}-solution$ ] was aaded in $SiO_{2}-solution$ by various composition. $SiO_{2}-TiO_{2}$ thin films were obtained by the dip-coating method on the $SiO_{2}$ glass substrates, and then heat-treated at various temperature. Nano-size $TiO_{2}$ particles dispersed $SiO_{2}-TiO_{2}$ films showed absorption peak by quantum size effect at short wavelength region $350{\sim}400nm$, which made them good candidates for non-linear optical materials and photo-catalytic materials. The thickness of $SiO_{2}-TiO_{2}$ films were $300{\sim}430nm$. The contact angle of $SiO_{2}-TiO_{2}$ films for water was $5.3{\sim}47.9^{\circ}$, and therefore it is clear that $SiO_{2}-TiO_{2}$ films have super hydrophilic properties and the self-cleaning effects.

• Journal of the Korean Institute of Electrical and Electronic Material Engineers
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• v.17 no.9
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• pp.1001-1005
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• 2004

Rye-sensitized solar cell (DSSC) is a new class of solar cell, which consists of nanoporous TiO$_2$ electrode, dye-sensitizer, electrolyte, and counter electrode. Such cell is operated in sunlight via the principle of photosynthetic electrochemistry. In order to obtain the good dispersion of nano size TiO$_2$ particles In slurry, the pH of solvent, the sort and quantify of solvent additive and the quantity of surfactant were adjusted. As results, the lower the pH of solvent was the lower the viscosity of the slurry became. The addition of ethylene glycol and propylene glycol to dilute HNO$_3$ brought about the lowering of viscosity and the enhancement of stability in slurry. The addition of surfactant lowered the viscosity of slurry. It was possible to obtain the homogeneous and uniformly dispersed mesoporous TiO$_2$ film using the dilute HNO$_3$ solvent of pH 2 with the addition of ethylene glycol and neutral surfactant. DSSC was assembled with TiO$_2$ electrode and Pt electrode, and its photoelectric property was measured using the monochromatic wavelength in the rangee of 350∼700 nm.