The Experts below are selected from a list of 5934 Experts worldwide ranked by ideXlab platform
Kwang-soon Ahn - One of the best experts on this subject based on the ideXlab platform.
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Enhanced Efficiency of Nanoporous-Layer-covered TiO 2 NanotubeArrays for Front Illuminated Dye-sensitized Solar Cells
Journal of Electrochemical Science and Technology, 2016Co-Authors: Soon-hyung Kang, Jae Hong Kim, Chel-jong Choi, Hyunsoo Kim, Soo-yong Lee, Kwang-soon AhnAbstract:ABSTRACT Nanoporous-Layer-covered TiO 2 nanotube arrays (Type II TNTs) were fabricated by two-step electrochemical anodization.For comparison, conventional TiO 2 nanotube arrays (Type I TNTs) were also prepared by one-step electrochemical anod-ization. Types I and II TNTs were detached by selective etching and then transferred successfully to a transparent F-dopedSnO 2 (FTO) substrate by a sol-gel process. Both FTO/Types I and II TNTs allowed front side illumination to exhibit inci-dent photon-to-current efficiencies (IPCEs) in the long wavelength region of 300 to 750 nm without the absorption of lightby the iodine-containing electrolyte. The Type II TNT exhibited longer electron lifetime and faster charge transfer than theType I TNT because of its relatively fewer defect states. These beneficial effects lead to a high overall energy conversionefficiency (5.32 %) of the resulting dye-sensitized solar cell.Keywords : dye-sensitized solar cell, nanotube array, electron lifetime, charge transfer, front side illumination
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Enhanced performance of reversely transferred, doubly open-ended TiO_2 nanotube arrays for front-illuminated dye-sensitized solar cells
Journal of the Korean Physical Society, 2016Co-Authors: Hyunsoo Kim, Jae Hong Kim, Kwang-soon Ahn, Soo-yong Lee, Soon-hyung KangAbstract:Doubly open-ended conventional TiO_2 nanotube arrays (Type I) and Nanoporous-Layer-covered nanotube arrays (Type II) were transferred to transparent fluorine-doped tin oxides (FTOs) for front-illuminated dye-sensitized solar cells (DSSCs). FTO/Type II exhibited a long electron lifetime ( τ _ e ) and rapid electron transport compared to FTO/Type I because of the reduced surface defect-state-mediated recombination rate. In particular, Type II transferred reversely to the FTO (FTO/Type II-rev) had beneficial geometric effects, leading to a decrease in pore size from the bottom to the top and a Nanoporous TiO_2 thin bottom Layer. These enabled more effective light scattering near the FTO and facilitated lateral electron movement toward the FTO, leading to a shortened electron pathway and a reduced recombination rate. The significantly enhanced electron lifetime and the shortened electron transit time of the FTO/Type II-rev improved the charge collection efficiency significantly. Furthermore, the enhanced light scattering increased the light harvesting efficiency. These beneficial geometric effects of FTO/Type II-rev contributed to the greatly enhanced overall cell efficiency (7.61%) of the DSSC compared to the DSSCs with FTO/Type I (5.27%) and FTO/Type II (6.65%).
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Enhanced efficiency of dye-sensitized solar cells through TiCl4-treated, Nanoporous-Layer-covered TiO2 nanotube arrays
Journal of Power Sources, 2011Co-Authors: Jeong-hyun Park, Jae-yup Kim, Jae Hong Kim, Chel-jong Choi, Hyunsoo Kim, Yung-eun Sung, Kwang-soon AhnAbstract:TiCl4-treated, Nanoporous-Layer-covered TiO2 (Type II) nanotube arrays are fabricated through a two-step anodization process followed by treatment with TiCl4. A dye-sensitized solar cell (DSSC) with TiCl4-treated, Nanoporous-Layer-covered Type II TiO2 nanotubes is compared with other DSSCs based on untreated Type II and both untreated and TiCl4-treated, conventional TiO2 (Type I) nanotube arrays. The TiCl4 surface treatment's effects on dye adsorption, charge transport, and electron lifetime are dependent on the morphologies of the TiO2 nanotubes. The TiCl4-treated Type I nanotubes allow higher dye adsorption, whilst the TiCl4-treated Type II nanotubes provide much faster electron transport and enhanced electron lifetime. This is because there are fewer defect traps in the nanostructure well-aligned without bundling, which contributes to the significantly improved cell performance over the DSSC with the TiCl4-treated Type I nanotubes.
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Enhanced electron lifetime in CdS quantum dot-sensitized solar cells with Nanoporous-Layer-covered TiO2 nanotube arrays
Journal of Applied Physics, 2011Co-Authors: Sung Woo Jung, Jeong-hyun Park, Jae Hong Kim, Chel-jong Choi, Hyunsoo Kim, Wonjoo Lee, Kwang-soon AhnAbstract:CdS quantum dots (QDs) of 6.8–6.9 nm were assembled in situ on conventional TiO2 nanotube arrays (Type I) and Nanoporous-Layer-covered nanotube arrays (Type II). The QD-sensitized solar cell with the Type II nanotubes exhibited significantly enhanced overall energy conversion efficiency, despite having less assembled QDs. This was due to the Type II nanotube arrays having fewer defects and suppressed recombination rate (or back electron transport) from surface traps in the TiO2 to electron traps in the QDs, resulting in significantly improved electron lifetime.
Claude Lévy-clément - One of the best experts on this subject based on the ideXlab platform.
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Impedance of porous Si
Journal of Applied Physics, 1994Co-Authors: Wu‐mian Shen, Micha Tomkiewicz, Claude Lévy-clémentAbstract:The impedance of photoelectrochemically etched n‐Si was measured in a liquid junction made of a methanolic solution of oxidized and reduced dimethylferrocene. The results show that both the equivalent circuit and each of the individual elements are almost identical with those of the smooth Si that was used as a substrate. These results were interpreted in terms of a depletion Layer model in which the space‐charge Layer is present only at the bottom of the macropores and at the interface between the electrolyte and the smooth part of the substrate. The poles that separate the pores are completely depleted of majority carriers. The Nanoporous Layer that is deposited on top of the macropores and can be removed by KOH is completely transparent to the impedance measurements.
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Morphology of porous n-type silicon obtained by photoelectrochemical etching II: Study of the tangled Si wires in the Nanoporous Layer
Journal of Luminescence, 1993Co-Authors: Ana Albu-yaron, Stéphane Bastide, Jean-luc Maurice, Claude Lévy-clémentAbstract:Abstract Visible luminescence observed from the Nanoporous Layer of the two (100)-orinted low doped and highly doped PEC-etched n-type Si is explained as being due to the existence of single crystal silicon quantum wires within their structure. The nanometer-size tangled Si structure is contained and attached to a regular geometric Si macroarray. TEM studies also reveal subtle variations in morphology between the two Layers studied, which could explain the blueshift in the spectrum of the low-doped specimen — thinner and more rigid irregular wires — as compared to the highly doped specimen.
Hao-chih Yuan - One of the best experts on this subject based on the ideXlab platform.
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multi scale surface texture to improve blue response of Nanoporous black silicon solar cells
Applied Physics Letters, 2011Co-Authors: Fatima Toor, Howard M. Branz, Matthew Page, K M Jones, Hao-chih YuanAbstract:We characterize the optical and carrier-collection physics of multi-scale textured p-type black Si solar cells with conversion efficiency of 17.1%. The multi-scale texture is achieved by combining density-graded Nanoporous Layer made by metal-assisted etching with micron-scale pyramid texture. We found that (1) reducing the thickness of nanostructured Si Layer improves the short-wavelength spectral response and (2) multi-scale texture permits thinning of the nanostructured Layer while maintaining low surface reflection. We have reduced the nanostructured Layer thickness by 60% while retaining a solar-spectrum-averaged black Si reflectance of less than 2%. Spectral response at 450 nm has improved from 57% to 71%.
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Efficient black silicon solar cell with a density-graded Nanoporous surface: Optical properties, performance limitations, and design rules
Applied Physics Letters, 2009Co-Authors: Hao-chih Yuan, Vernon E. Yost, Matthew R. Page, Paul Stradins, Daniel L. Meier, Howard M. BranzAbstract:We study optical effects and factors limiting performance of our confirmed\n16.8% efficiency �black silicon� solar cells. The cells incorporate\ndensity-graded Nanoporous surface Layers made by a one-step nanoparticle-catalyzed\netch and reflect less than 3% of the solar spectrum, with no conventional\nantireflection coating. The cells are limited by recombination in\nthe Nanoporous Layer which decreases short-wavelength spectral response.\nThe optimum density-graded Layer depth is then a compromise between\nreflectance reduction and recombination loss. Finally, we propose\nuniversal design rules for high-efficiency solar cells based on density-graded\nsurfaces.
Van P. Carey - One of the best experts on this subject based on the ideXlab platform.
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Water Wicking and Droplet Spreading on Randomly Structured Thin Nanoporous Layers
Langmuir, 2017Co-Authors: Claire K. Wemp, Van P. CareyAbstract:Growing thin, nanostructured Layers on metallic surfaces is an attractive, new approach to create superhydrophilic coatings on heat exchangers that enhance spray cooling heat transfer. This paper presents results of an experimental study of enhanced droplet spreading on zinc oxide, nanostructured surfaces of this type that were thermally grown on copper substrates. The spreading rate data obtained from experimental high speed videos was used to develop a model specifically for this type of ultrathin, Nanoporous Layer. This investigation differs from previous related studies of droplet spreading on porous surfaces, which have generally considered either ordered, thin, moderately permeable Layers, or thicker, microporous Layers. Our Layers are both very thin and have nanoscale porosity, making them low-permeability Layers that exhibit strong wicking. An added benefit is that the thermally grown, stochastic nature of our surfaces make manufacturing easily scalable and particularly attractive for spray-cooled...
Howard M. Branz - One of the best experts on this subject based on the ideXlab platform.
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multi scale surface texture to improve blue response of Nanoporous black silicon solar cells
Applied Physics Letters, 2011Co-Authors: Fatima Toor, Howard M. Branz, Matthew Page, K M Jones, Hao-chih YuanAbstract:We characterize the optical and carrier-collection physics of multi-scale textured p-type black Si solar cells with conversion efficiency of 17.1%. The multi-scale texture is achieved by combining density-graded Nanoporous Layer made by metal-assisted etching with micron-scale pyramid texture. We found that (1) reducing the thickness of nanostructured Si Layer improves the short-wavelength spectral response and (2) multi-scale texture permits thinning of the nanostructured Layer while maintaining low surface reflection. We have reduced the nanostructured Layer thickness by 60% while retaining a solar-spectrum-averaged black Si reflectance of less than 2%. Spectral response at 450 nm has improved from 57% to 71%.
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Efficient black silicon solar cell with a density-graded Nanoporous surface: Optical properties, performance limitations, and design rules
Applied Physics Letters, 2009Co-Authors: Hao-chih Yuan, Vernon E. Yost, Matthew R. Page, Paul Stradins, Daniel L. Meier, Howard M. BranzAbstract:We study optical effects and factors limiting performance of our confirmed\n16.8% efficiency �black silicon� solar cells. The cells incorporate\ndensity-graded Nanoporous surface Layers made by a one-step nanoparticle-catalyzed\netch and reflect less than 3% of the solar spectrum, with no conventional\nantireflection coating. The cells are limited by recombination in\nthe Nanoporous Layer which decreases short-wavelength spectral response.\nThe optimum density-graded Layer depth is then a compromise between\nreflectance reduction and recombination loss. Finally, we propose\nuniversal design rules for high-efficiency solar cells based on density-graded\nsurfaces.
