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Pohang, South Korea

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. Source

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. Source

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. Source

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. Source

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. Source

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