Energy R and nter

Mungyeong, South Korea

Energy R and nter

Mungyeong, South Korea
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Williams B.P.,Cornell University | Pinge S.,Cornell University | Kim Y.-K.,Energy R and nter | Kim J.,Energy R and nter | Joo Y.L.,Cornell University
Langmuir | Year: 2015

The rheology of petroleum coke (petcoke) water slurries was investigated with a variety of nonionic and anionic dispersants including poly(ethylene oxide) (PEO)-b-poly(propylene oxide) (PPO)-b-PEO triblock copolymers (trade name: Pluronic, BASF), poly(vinyl alcohol) (PVA), polyvinylpyrrolidone (PVP), poly(ethylene oxide) (PEO), poly(carboxylate acid) (PCA), sodium lignosulfonate (SLS), and poly(acrylic acid) (PAA). Each effective dispersant system shared very similar rheological behavior to the others when examined at the same volume fraction from its maximum petcoke loading. Triblock copolymer, Pluronic F127 (F127), was found to be the best dispersant by comparing the maximum petcoke loading for each dispersant. The yield stress was measured as a function of petcoke loading and dispersant concentration for F127, and a minimum dispersant concentration was observed. An adsorption isotherm and atomic force microscopy (AFM) images reveal that this effective dispersion of petcoke particles by F127 is due to the formation of a uniform monolayer of brushes where hydrophobic PPO domains of F127 adhere to the petcoke surface, while hydrophilic PEO tails fill the gap between petcoke particles. F127 was then compared to other Pluronics with various PEO and PPO chain lengths, and the effects of surface and dispersant hydrophilicity were examined. Finally, xanthan gum (XG) was tested as a stabilizer in combination with F127 for potential industrial application, and F127 appears to break the XG aggregates into smaller aggregates through competitive adsorption, leading to an excellent degree of dispersion but the reduced stability of petcoke slurries. © 2015 American Chemical Society.

Myong S.Y.,Energy R and nter
Recent Patents on Nanotechnology | Year: 2012

Thermalization of photogenerated carriers in bulk materials is the main bottleneck for the conversion efficiency of conventional inorganic solar cells. Furthermore, the achieved conversion efficiency has nearly saturated during the last decade despite extensive research. Therefore, new device concepts to break through the efficiency barrier are highly requested. Nanotechnologies are the building blocks for next-generation solar cells because low-dimensional quantum structures can possibly reduce thermalization and extend the light absorption range. In addition, very thin nanostructured inorganic solar cells provide us with good opportunity to reach highly competitive mass production. Hereafter, recently invented inorganic solar cells using quantum structures will be reviewed. © 2012 Bentham Science Publishers.

Myong S.Y.,Energy R and nter
Recent Patents on Nanotechnology | Year: 2014

The recent trends of US patents on the front transparent electrode of thin-film silicon (Si) photovoltaic (PV) devices are reviewed. The various transparent conductive oxide (TCO) materials have been invented to satisfy a multifunctional prerequisite for the front electrode: high electrical conductivity, high optical transparency, effective light trapping, anti-reflection effect, and diffusion barrier. The recent surge of filed patents reflects the great importance of the front TCO technology for high efficiency thin-film Si PV devices. Among the TCO materials, properties of commercially available F-doped tin oxide (SnO2:F)-coated glass substrates are compared. SnO2:F-coated glass substrates share 20-30% of the cost for production of thin-film Si PV modules - evaluated values from mass production at KISCO. Therefore, the cost and technological innovation must be established for cost-effective mass production of large-area thin-film Si multijunction PV modules. © 2014 Bentham Science Publishers.

Myong S.Y.,Energy R and nter | Kwon S.W.,Energy R and nter
Solar Energy Materials and Solar Cells | Year: 2013

We investigate the unique structural and optical properties of an alternately H2-diluted protocrystalline silicon multilayers (pc-Si:H) compared to a hydrogenated amorphous silicon (a-Si:H) layer. Strong evidence for the isolated nano-sized silicon (nc-Si) grains embedded in the a-Si:H matrix is provided. The vertically regular distribution of the nc-Si grains is concluded as the main reason for the fast light-induced metastability with the low degradation for the fabricated pc-Si:H multilayer solar cell by localizing the photocreation of dangling bonds near the defective grain-boundary layers. © 2013 Elsevier B.V.

Yang J.-H.,Korea Advanced Institute of Science and Technology | Myong S.Y.,Energy R and nter | Lim K.S.,Korea Advanced Institute of Science and Technology
Solar Energy | Year: 2015

We have investigated the application of ultrathin lithium fluoride (LiF) interlayers for effective light harvesting in hydrogenated amorphous silicon (a-Si:H)/hydrogenated microcrystalline silicon (μc-Si:H) tandem solar cells. It is proved that the LiF interlayers are not suitable for intermediate reflectors of the tandem solar cells despite their low refractive index and low lateral conductivity. A poor vertical conductivity leads to the formation of a highly resistive tunnel junction. On the contrary, novel hydrogenated n-type silicon-oxide (n-SiO. x:H)/LiF back reflectors are successfully employed in the tandem solar cells, reducing plasmonic absorption losses in nanotextured Al back contacts and providing effective refractive index grading. It is found that the ultrathin LiF interlayer mitigates nanotextures of the Al back contact. The spectral response of μc-Si:H bottom cells is markedly elevated in a near-infrared wavelength region. As a result, a conversion efficiency is improved by 8.1% compared to the reference cell with a conventional zinc oxide (ZnO) back reflector thanks to an increase in a short-circuit current by 5.5%. Consequently, the initial efficiency of 10.4% is attained. © 2015 Elsevier Ltd.

Myong S.Y.,Energy R and nter | Park Y.-C.,Energy R and nter | Jeon S.W.,Energy R and nter
Renewable Energy | Year: 2015

We have investigated the electrical energy yield of hydrogenated amorphous silicon (a-Si:H) single-junction and crystalline (c-Si) photovoltaic (PV) rooftop systems operated under distinct four seasons. The impact of the module type and installed tilt angle on the annual electrical energy yield has been monitored and then compared with the data predicted by the computer simulation. Despite a good temperature coefficient and less shading effect of a-Si:H single-junction modules, the energy output gain of the a-Si:H single-junction PV generator is only 2.7% compared to the c-Si PV generator installed using c-Si PV modules. It is inferred that a nominal rated power of the a-Si:H single-junction modules determined by an indoor light soaking test is not suitable for the design of PV systems operated under distinct four seasons. Thus, the nominal rated power of the a-Si:H single-junction PV modules should be determined through a proper outdoor exposure test considering thermal annealing and light soaking effects under various seasonal weather conditions. In addition, it is found that the performance of the Si-based PV rooftop systems operated under distinct four seasons could be improved by simply toggling the tilt angle considering the plane-of-array irradiance and snowfall effect. © 2015 Elsevier Ltd.

Myong S.Y.,Energy R and nter | Jeon S.W.,Energy R and nter
Applied Energy | Year: 2016

We developed bifacial transparent back contact (TBC) hydrogenated amorphous silicon (a-Si:H) semi-transparent glass-to-glass photovoltaic (PV) modules with emotionally inoffensive and esthetically pleasing colors have been developed by combining the transparent back contact and color of the back glass. Due to the high series resistance of the transparent back contact, the bifacial TBC a-Si:H semi-transparent PV modules had a lower rated power after light soaking than the monofacial opaque (metal) back contact (OBC) a-Si:H semi-transparent PV modules fabricated using the additional laser scribing patterns. However, the TBC a-Si:H semi-transparent PV module produced a higher annual electrical energy output than the OBC a-Si:H semi-transparent PV module thanks to bifacial power generation during the outdoor field test. In particular, the performance ratio of the TBC a-Si:H semi-transparent PV module measured at the optimal tilt angle of 30° surpassed its simulated prediction by a drastically high value of 124.5%. At a higher tilt angle of 85°, bifacial power generation produced a higher deviation between the measured and simulated annual performance of the TBC a-Si:H semi-transparent PV module. Since the reflected albedo has a tendency to increase toward higher tilt angles, bifacial power generation can compensate for the loss of lower direct plane-of-array irradiation at a higher tilt angle. Therefore, the TBC a-Si:H semi-transparent PV module is suitable for the vertically mounted building integrated photovoltaic modules for use in curtain walls, façades, roofs and traffic noise barriers by harvesting reflected and illuminated light. © 2015 Elsevier Ltd.

We have investigated the optimization of the sputtered metal back contact coupled with the B-doped zinc oxide (ZnO:B) back reflector for 1.43m2 p-i-n type hydrogenated amorphous silicon (a-Si:H) single-junction photovoltaic modules. The module with the Al back contact leads to the high stabilized aperture-area efficiency (ηAPER) of 7.3% with the low light-induced degradation ratio of 12.6% despite low initial ηAPER of 8.3%. However, the insertion of Ag causes a severe light-induced degradation. Through the further optimization, the stabilized maximum power of 100.2W is achieved. This is corresponding to stabilized ηAPER of 7.4%, which is the highest value for the certified industrial products of 1.43m2 a-Si:H single-junction photovoltaic modules. © 2014 Elsevier Ltd.

Light soaking and thermal annealing behaviors of an alternately hydrogen-diluted hydrogenated protocrystalline silicon (pc-Si:H) multilayer are investigated using a constant photocurrent measurement. The pc-Si:H multilayer includes isolated nano-sized silicon (nc-Si) grains embedded in a hydrogenated amorphous silicon (a-Si:H) matrix with a vertically regular distribution. A wide optical bandgap of the pc-Si:H multilayer is inspected mainly due to an non-uniform hydrogen distribution and quantum size effect. Compared to a conventional a-Si:H film, the pc-Si:H multilayer exhibits a superior light-induced metastability with a fast stabilization and low degradation. In addition, the pc-Si:H multilayer shows a reversible thermal recovery in a short annealing time. © 2013 Elsevier Ltd.

Yang J.-H.,Korea Advanced Institute of Science and Technology | Myong S.Y.,Energy R and nter | Lim K.S.,Korea Advanced Institute of Science and Technology
Solar Energy Materials and Solar Cells | Year: 2014

We have developed a hydrogenated n-type silicon oxide (n-SiOx:H)/lithium fluoride (LiF) interlayer for effective light trapping in pin-type hydrogenated amorphous silicon (a-Si:H)-based solar cells with a 200-nm thick intrinsic a-Si:H absorber. The spectral response of the fabricated solar cell is clearly enhanced in the wide wavelength range of 500-750 nm because of the reduced plasmonic absorption in the nanotextured metal back contact and effective refractive index grading. The surface morphology of the back contact is effectively smoothened by the insertion of the ultrathin (2.1 nm) LiF interlayer. As a result, the short-circuit current is improved by 10.7% from 13.1 to 14.5 mA/cm2. Consequently, we have achieved a conversion efficiency of 9.0%. © 2014 Elsevier B.V. All rights reserved.

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