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Oxygen-Controlled Seed Layer in DC Sputter-Deposited ZnO:Al Substrate for Si Thin-Film Solar Cells
Seung-Yoon Lee,Taehyun Hwang,Woojin Lee,Sangheon Lee,Hongsik Choi,Seh-Won Ahn,Heon-Min Lee,Byungwoo Park IEEE 2015 IEEE journal of photovoltaics Vol.5 No.2
<P>Oxygen-controlled seed layer in Al-doped ZnO (ZnO:Al) thin films deposited by the industrially compatible dynamic dc magnetron sputter results in both enhanced electron mobilities and appropriate etched morphologies for the Si thin-film solar cells. At the relatively low deposition temperature of 300 °C, optimized ZnO:Al film grown on the seed layer has the carrier mobility of 45 cm<SUP>2</SUP>/V·s and proper postetching morphology with around 1-2-μm crater size. Reduced angular distribution of the (002) grains analyzed by the diffraction rocking curve is shown as the key structural feature for the improved carrier mobility. Finally, the performance of the microcrystalline Si solar cell on the developed ZnO:Al substrate shows high-efficiency potential of the tandem solar cell adapting this transparent conductive oxide substrate.</P>
Effect of the Extract of Herbal Drugs Mixture on Brain Function in Rats
Yoon Jo Oh,Ah-ram Lee,Jin-Joo Hue,Yea Eun Lee,Lan Li,Jung-Su Lee,Min-hang Cho,Sang Yoon Nam,Young Won Yun,Byungwoo Ahn,Jae-Hwang Jeong,Sang-Hwa Lee,Beom Jun Lee 한국실험동물학회 2006 Laboratory Animal Research Vol.22 No.4
Green tea, Crataegus oxycantha fruit, gingko leaves and tangleweed were known to increase blood circulation and improve brain function. The mixture containing green tea (50 g), Crataegus oxycantha fruit (50 g), gingko leaves (20 g), and tangleweed (20 g) was water-extracted and freeze-dried to powder. The pharmacological effect of the extract of herbal drugs on acetylcholinesterase (AChE) in an in vitro enzyme system and in rats was investigated. The extract of herbal drugs at the doses of 10, 25, 50 and 100 ㎍/㎖ decreased activity of AChE by 8.8, 22.1, 43.1 and 63.0%, respectively. The treatment of the extract of herbal drugs at the dose of 0.1 g/㎏ b.w. to rats for 5 and 10 consecutive days reduced AChE activity in the brain by 12.8 and 26.9 %, respectively, corresponding to increases by 26.4 and 59.7% in the concentration of acetylcholine (ACh) in the brain of rats, compared with the control rats. The levels of ATP in the brain also increased in treatment group in a time-dependent manner. The liver toxicity was not shown as determined by serum biochemistry. These results suggest that a composition of these herbal drugs may improve brain function by increasing the levels of acetylcholine and ATP.
Optical Properties of Long Wave Infrared Spoof Plasmon using Hexagonal Periodic Silver Hole Arrays
Byungwoo Lee,Hoe Min Kwak,Ha Sul Kim 한국진공학회(ASCT) 2016 Applied Science and Convergence Technology Vol.25 No.2
A two-dimensional metal hole array (2DMHA) structure is fabricated by conventional photo-lithography and electron beam evaporation. The transmittance of the 2DMHA is measured at long wave infrared (LWIR) wavelengths (λ~10 to 24 μm). The 2DMHA sample shows transmittance of 70 and 67% at 15.4 μm due to plasmonic resonance with perforated silver and gold thin films, respectively, under surface normal illumination at LWIR wavelengths. The measured infrared spectrum is separated into two peaks when the size of the hole becomes larger than a half-pitch of the hole array. Six degenerated plasmon modes (1,0) at the metal/Si surface split to three modes at an incident beam angle of 45° with respect to the surface normal direction, and wavelength shifts of the transmitted spectrum are observed in a red shift and blue shift at the same time.
Lee, Jeong-Sik,Jang, Deok-Jin,Lee, Nuribalhae,Ko, Hyoung-Gon,Kim, Hyoung,Kim, Yong-Seok,Kim, Byungwoo,Son, Junehee,Kim, Sung Hyun,Chung, Heekyoung,Lee, Mun-Yong,Kim, Woon Ryoung,Sun, Woong,Zhuo, Min,A The Society 2009 The Journal of neuroscience Vol.29 No.26
<P>The cAMP cascade and vascular endothelial growth factor (VEGF) are critical modulators of depression. Here we have tested whether the antidepressive effect of the cAMP cascade is mediated by VEGF in the adult hippocampus. We used a conditional genetic system in which the Aplysia octopamine receptor (Ap oa(1)), a G(s)-coupled receptor, is transgenically expressed in the forebrain neurons of mice. Chronic activation of the heterologous Ap oa(1) by its natural ligand evoked antidepressant-like behaviors, accompanied by enhanced phosphorylation of cAMP response element-binding protein and transcription of VEGF in hippocampal dentate gyrus (DG) neurons. Selective knockdown of VEGF in these cells during the period of cAMP elevation inhibited the antidepressant-like behaviors. These findings reveal a molecular interaction between the cAMP cascade and VEGF expression, and the pronounced behavioral consequences of this interaction shed light on the mechanism underlying neuronal VEGF functions in antidepression.</P>
Lee, Sangheon,Flanagan, Joseph C.,Kim, Jaewook,Yun, Alan Jiwan,Lee, Byungho,Shim, Moonsub,Park, Byungwoo American Chemical Society 2019 ACS APPLIED MATERIALS & INTERFACES Vol.11 No.21
<P>Here, we report the successful application of core/patchy-shell CdSe/CdSe<SUB><I>x</I></SUB>Te<SUB>1-<I>x</I></SUB> type-II heterojunction nanorods (HNRs) to realize efficient sensitized solar cells. The core/patchy-shell structure designed to have a large type-II heterointerface without completely shielding the CdSe core significantly improves photovoltaic performance compared to other HNRs with minimal or full-coverage shells. In addition, cosensitization with CdS grown by successive ionic layer adsorption and reaction further improves the power conversion efficiency. One-diode model analysis reveals that the HNRs having exposed CdSe cores and suitably grown CdS result in significant reduction of series resistance. Investigation of the intercorrelation between diode quality parameters, diode saturation current density (<I>J</I><SUB>0</SUB>) and recombination order (β = (ideality factor)<SUP>−1</SUP>) reveals that HNRs with open CdSe cores exhibit reduced recombination. These results confirm that the superior performance of core/patchy-shell HNRs results from their fine-tuned structure: photocurrent is increased by the large type-II heterointerface and recombination is effectively suppressed due to the open CdSe core enabling facile electron extraction. An optimized power conversion efficiency of 5.47% (5.89% with modified electrode configuration) is reported, which is unmatched among photovoltaics utilizing anisotropic colloidal heterostructures as light-harvesting materials.</P> [FIG OMISSION]</BR>
Lee, Sangheon,Flanagan, Joseph C.,Lee, Byungho,Hwang, Taehyun,Kim, Jaewook,Gil, Bumjin,Shim, Moonsub,Park, Byungwoo American Chemical Society 2017 ACS APPLIED MATERIALS & INTERFACES Vol.9 No.37
<P>One-dimensionally elongated nanoparticles with type-II staggered band offset are of potential use as light-harvesting materials for photovoltaics, but only a limited attention has been given to elucidate the factors governing the cell performance obtainable from such materials. Herein, we describe a combined strategy to enhance charge collection from CdSe/CdSexTe1-x type-II heterojunction nanorods (HNRs) utilized as light harvesters for sensitized solar cells. By integrating morphology- and composition-tuned type-II HNRs into solar cells, factors that yield interfaces favorable both for the electron injection into TiO2 and hole transfer to electrolyte are examined. Furthermore, it is shown that a more efficient photovoltaic system results from cosensitization with CdS quantum dots (QDs) predeposited on a TiO2 scaffold, which improves charge collection from HNRs. Electrochemical impedance spectroscopy (EIS) analysis suggests that such a synergistically enhanced system benefits from the decreased recombination within HNRs and facilitated charge transport through the cosensitized TiO2 electrode, even with the activation of a recombination path presumably related to the photogenerated holes in CdS QDs.</P>
Lee, Byungho,Lee, Sangheon,Cho, Duckhyung,Kim, Jinhyun,Hwang, Taehyun,Kim, Kyung Hwan,Hong, Seunghun,Moon, Taeho,Park, Byungwoo American Chemical Society 2016 ACS APPLIED MATERIALS & INTERFACES Vol.8 No.45
<P>Organic-inorganic hybrid perovskite solar cells have emerged as promising candidates for next-generation solar cells. To attain high photovoltaic efficiency, reducing the defects in perovskites is crucial along with a uniform coating of the films. Also, evaluating the quality of synthesized perovskites via facile and adequate methods is important as well. Herein, CH3NH3PbI3 perovskites were synthesized by applying second solvent dripping to nonstoichiometric precursors containing excess CH3NH3I. The resulting perovskite films exhibited a larger average grain size with a better crystallinity compared to that from stoichiometric precursors. As a result, the performance of planar perovskite solar cells was significantly improved, achieving an efficiency of 14.3%. Furthermore, perovskite films were effectively analyzed using a conductive AFM and noise spectroscopy, which have been uncommon in the field of perovskite solar cells. Comparing the topography and photocurrent maps, the variation of photocurrents in nanoscale was systematically investigated, and a linear relationship between the grain size and photocurrent was revealed. Also, noise analyses with a conductive probe enabled examination of the defect density of perovskites at specific grain interiors by excluding the grain-boundary effect, and reduced defects were clearly observed for the perovskites using CH3NH3I-rich precursors.</P>
Optical Properties of Long Wave Infrared Spoof Plasmon using Hexagonal Periodic Silver Hole Arrays
Lee, Byungwoo,Kwak, Hoe Min,Kim, Ha Sul The Korean Vacuum Society 2016 Applied Science and Convergence Technology Vol.25 No.2
A two-dimensional metal hole array (2DMHA) structure is fabricated by conventional photo-lithography and electron beam evaporation. The transmittance of the 2DMHA is measured at long wave infrared (LWIR) wavelengths (${\lambda}{\sim}10$ to $24{\mu}m$). The 2DMHA sample shows transmittance of 70 and 67% at $15.4{\mu}m$ due to plasmonic resonance with perforated silver and gold thin films, respectively, under surface normal illumination at LWIR wavelengths. The measured infrared spectrum is separated into two peaks when the size of the hole becomes larger than a half-pitch of the hole array. Six degenerated plasmon modes (1,0) at the metal/Si surface split to three modes at an incident beam angle of $45^{\circ}$ with respect to the surface normal direction, and wavelength shifts of the transmitted spectrum are observed in a red shift and blue shift at the same time.