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R W Birkmire - One of the best experts on this subject based on the ideXlab platform.
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design of a vapor transport deposition process for thin Film materials
Journal of Vacuum Science and Technology, 2006Co-Authors: Gregory M Hanket, B E Mccandless, W A Buchanan, S Fields, R W BirkmireAbstract:A vapor transport process for continuous deposition of elemental and compound thin Film materials is presented. The process saturates a carrier gas with a vapor from a subliming source. The saturated mixture is directed over a substrate at lower temperature, resulting in a supersaturation condition and subsequent Film growth. The process geometry, comprising the dimensions of the saturation and deposition zones, carrier gas pressure and flow rate, and saturation zone temperature are determined by calculating worst-case characteristic times and simply insuring that the residence time of the carrier gas sufficiently exceeds these times. A model was used to design a system, which is currently being used to deposit 1–10μm thick Cdte Films on a 10×10cm2 translating substrate. The process produces Film thickness uniformity to within ±5% in the translation direction and across the deposition zone, with a material utilization of 50%. Linear translation speed of 12.5cm∕min has been demonstrated in depositing a 4.5μm Cdte Film. The vapor transport process has also been used to deposit CdxZn1−xTe alloy Films over a wide range of compositions by addition of ZnTe to the source. Photovoltaic conversion efficiencies of >13% for Cdte and >12% for CdxZn1−xTe have been achieved by devices fabricated from vapor transport deposited Films deposited on to moving CdS coated substrates. Refinements are suggested for commercial-scale deposition.A vapor transport process for continuous deposition of elemental and compound thin Film materials is presented. The process saturates a carrier gas with a vapor from a subliming source. The saturated mixture is directed over a substrate at lower temperature, resulting in a supersaturation condition and subsequent Film growth. The process geometry, comprising the dimensions of the saturation and deposition zones, carrier gas pressure and flow rate, and saturation zone temperature are determined by calculating worst-case characteristic times and simply insuring that the residence time of the carrier gas sufficiently exceeds these times. A model was used to design a system, which is currently being used to deposit 1–10μm thick Cdte Films on a 10×10cm2 translating substrate. The process produces Film thickness uniformity to within ±5% in the translation direction and across the deposition zone, with a material utilization of 50%. Linear translation speed of 12.5cm∕min has been demonstrated in depositing a 4.5...
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recrystallization and sulfur diffusion in cdcl2 treated Cdte cds thin Films
Progress in Photovoltaics, 1997Co-Authors: B E Mccandless, L V Moulton, R W BirkmireAbstract:The role of CdCl2 in prompting recrystallization, grain growth and interdiffusion between CdS and Cdte layers in physical vapor-deposited CdS/Cdte thin-Film solar cells is presented. Several Cdte/CdS thin-Film samples with different Cdte Film thicknesses were treated in air at 415°C for different times with and without a surface coating of CdCl2. The samples were characterized by scanning electron microscopy, transmission electron microscopy, energy dispersive x-ray spectroscopy, x-ray diffractometry and optical absorption. The results show that CdCl2 treatment enhances the recrystallization and diffusion processes, leading to a compositional variation within the Cdte layer due to diffusion of sulfur from the CdS. The highest sulfur concentrations observed after 30 min treatments with CdCl2 at 415°C are near the solubility limit for sulfur in Cdte. The compositional distributions indicated by x-ray diffraction measurements of samples with different Cdte thickness show that the S-rich Cdte1−xSx region lies near the Cdte/CdS interface. A multiple-step mixing process must be inferred to account for the diffraction profiles obtained. © 1997 John Wiley & Sons, Ltd.
B E Mccandless - One of the best experts on this subject based on the ideXlab platform.
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design of a vapor transport deposition process for thin Film materials
Journal of Vacuum Science and Technology, 2006Co-Authors: Gregory M Hanket, B E Mccandless, W A Buchanan, S Fields, R W BirkmireAbstract:A vapor transport process for continuous deposition of elemental and compound thin Film materials is presented. The process saturates a carrier gas with a vapor from a subliming source. The saturated mixture is directed over a substrate at lower temperature, resulting in a supersaturation condition and subsequent Film growth. The process geometry, comprising the dimensions of the saturation and deposition zones, carrier gas pressure and flow rate, and saturation zone temperature are determined by calculating worst-case characteristic times and simply insuring that the residence time of the carrier gas sufficiently exceeds these times. A model was used to design a system, which is currently being used to deposit 1–10μm thick Cdte Films on a 10×10cm2 translating substrate. The process produces Film thickness uniformity to within ±5% in the translation direction and across the deposition zone, with a material utilization of 50%. Linear translation speed of 12.5cm∕min has been demonstrated in depositing a 4.5μm Cdte Film. The vapor transport process has also been used to deposit CdxZn1−xTe alloy Films over a wide range of compositions by addition of ZnTe to the source. Photovoltaic conversion efficiencies of >13% for Cdte and >12% for CdxZn1−xTe have been achieved by devices fabricated from vapor transport deposited Films deposited on to moving CdS coated substrates. Refinements are suggested for commercial-scale deposition.A vapor transport process for continuous deposition of elemental and compound thin Film materials is presented. The process saturates a carrier gas with a vapor from a subliming source. The saturated mixture is directed over a substrate at lower temperature, resulting in a supersaturation condition and subsequent Film growth. The process geometry, comprising the dimensions of the saturation and deposition zones, carrier gas pressure and flow rate, and saturation zone temperature are determined by calculating worst-case characteristic times and simply insuring that the residence time of the carrier gas sufficiently exceeds these times. A model was used to design a system, which is currently being used to deposit 1–10μm thick Cdte Films on a 10×10cm2 translating substrate. The process produces Film thickness uniformity to within ±5% in the translation direction and across the deposition zone, with a material utilization of 50%. Linear translation speed of 12.5cm∕min has been demonstrated in depositing a 4.5...
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recrystallization and sulfur diffusion in cdcl2 treated Cdte cds thin Films
Progress in Photovoltaics, 1997Co-Authors: B E Mccandless, L V Moulton, R W BirkmireAbstract:The role of CdCl2 in prompting recrystallization, grain growth and interdiffusion between CdS and Cdte layers in physical vapor-deposited CdS/Cdte thin-Film solar cells is presented. Several Cdte/CdS thin-Film samples with different Cdte Film thicknesses were treated in air at 415°C for different times with and without a surface coating of CdCl2. The samples were characterized by scanning electron microscopy, transmission electron microscopy, energy dispersive x-ray spectroscopy, x-ray diffractometry and optical absorption. The results show that CdCl2 treatment enhances the recrystallization and diffusion processes, leading to a compositional variation within the Cdte layer due to diffusion of sulfur from the CdS. The highest sulfur concentrations observed after 30 min treatments with CdCl2 at 415°C are near the solubility limit for sulfur in Cdte. The compositional distributions indicated by x-ray diffraction measurements of samples with different Cdte thickness show that the S-rich Cdte1−xSx region lies near the Cdte/CdS interface. A multiple-step mixing process must be inferred to account for the diffraction profiles obtained. © 1997 John Wiley & Sons, Ltd.
M M Aljassim - One of the best experts on this subject based on the ideXlab platform.
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the effect of oxygen on interface microstructure evolution in cds Cdte solar cells
Progress in Photovoltaics, 2002Co-Authors: D S Albin, Y Yan, M M AljassimAbstract:Microstructural changes at the CdS/Cdte solar cell interface where close-spaced sublimation (CSS) is used as the growth technique to deposit the p-type Cdte absorber layer are studied by systematic layer characterization at various stages during heterojunction growth. CdS layers grown by both chemical bath deposition (CBD) and CSS provide a basis for determining the effects of CdS crystallinity, grain size, and oxygen content on the subsequent Cdte layer. As-grown CBD CdS Films exhibit small grains and variations in optical properties attributed to Film impurities. In contrast, CSS yields CdSFilms with good crystallinity, larger grains, and nearly ideal optical properties. The hexagonal nature of CSS-grown CdS is seen to nucleate hexagonal Cdte during the initial stages of Cdte Film growth. Cubic CdS deposited by CBD in contrast promotes cubic Cdte nucleation. Oxygen anneals in the latter case can aid hexagonal Cdte nucleation. Auger electron spectroscopy (AES) and transmission electron microscopy (TEM) of the CdS/Cdte interface show CdS-dependent differences in interdiffusion at the interface. This interdiffusion appears to be determined by the oxygen level in the CdS. When low-oxygen-containing CSS CdS Films are used, sulfur diffusion is substantial, leading to significant consumption of the CdS layer. When these same Films are annealed in oxygen, the consumption is reduced. Te diffusion into the CdS layer is also observed to decrease with oxygen anneals. Optical modeling shows that Te alloying with the CdS layer can greatly reduce the short-circuit current of CdS/Cdte devices.
Y Yan - One of the best experts on this subject based on the ideXlab platform.
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13 9 efficient Cdte polycrystalline thin Film solar cells with an infrared transmission of 50
Progress in Photovoltaics, 2006Co-Authors: J Zhou, Y Yan, A Duda, J Keane, T A Gessert, R NoufiAbstract:To fabricate a high-efficiency polycrystalline thin-Film tandem cell, the most critical work is to make a high-efficiency top cell ( > 15%) with high bandgap (Eg = 1·5–1·8 eV) and high transmission (T > 70%) in the near-infrared (NIR) wavelength region. The Cdte cell is one of the candidates for the top cell, because Cdte state-of-the-art single-junction devices with efficiencies of more than 16% are available, although its bandgap (1·48 eV) is slightly lower for a top cell in a current-matched dual-junction device. In this paper, we focus on the development of a: (1) thin, low-bandgap CuxTe transparent back-contact; and (2) modified Cdte device structure, including three novel materials: cadmium stannate transparent conducting oxide (TCO), ZnSnOx buffer layer, and nanocrystalline CdS:O window layer developed at NREL, as well as the high-quality Cdte Film, to improve transmission in the NIR region while maintaining high device efficiency. We have achieved an NREL-confirmed 13·9%-efficient Cdte transparent solar cell with an infrared transmission of ∼50% and a Cdte/CIS polycrystalline mechanically stacked thin-Film tandem cell with an NREL-confirmed efficiency of 15·3%. Copyright © 2005 John Wiley & Sons, Ltd.
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the effect of oxygen on interface microstructure evolution in cds Cdte solar cells
Progress in Photovoltaics, 2002Co-Authors: D S Albin, Y Yan, M M AljassimAbstract:Microstructural changes at the CdS/Cdte solar cell interface where close-spaced sublimation (CSS) is used as the growth technique to deposit the p-type Cdte absorber layer are studied by systematic layer characterization at various stages during heterojunction growth. CdS layers grown by both chemical bath deposition (CBD) and CSS provide a basis for determining the effects of CdS crystallinity, grain size, and oxygen content on the subsequent Cdte layer. As-grown CBD CdS Films exhibit small grains and variations in optical properties attributed to Film impurities. In contrast, CSS yields CdSFilms with good crystallinity, larger grains, and nearly ideal optical properties. The hexagonal nature of CSS-grown CdS is seen to nucleate hexagonal Cdte during the initial stages of Cdte Film growth. Cubic CdS deposited by CBD in contrast promotes cubic Cdte nucleation. Oxygen anneals in the latter case can aid hexagonal Cdte nucleation. Auger electron spectroscopy (AES) and transmission electron microscopy (TEM) of the CdS/Cdte interface show CdS-dependent differences in interdiffusion at the interface. This interdiffusion appears to be determined by the oxygen level in the CdS. When low-oxygen-containing CSS CdS Films are used, sulfur diffusion is substantial, leading to significant consumption of the CdS layer. When these same Films are annealed in oxygen, the consumption is reduced. Te diffusion into the CdS layer is also observed to decrease with oxygen anneals. Optical modeling shows that Te alloying with the CdS layer can greatly reduce the short-circuit current of CdS/Cdte devices.
T D Dzhafarov - One of the best experts on this subject based on the ideXlab platform.
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diffusion and influence of cu on properties of Cdte thin Films and Cdte cds cells
Solar Energy Materials and Solar Cells, 2005Co-Authors: T D Dzhafarov, Serco Serkis Yesilkaya, Yilmaz N Canli, Murat CaliskanAbstract:Abstract The effective diffusion coefficients of Cu for thermal and photodiffusion in the Cdte Films have been estimated from resistivity versus duration of thermal or photoannealing curves. In the temperature range 60–200°C the effective coefficient of thermal diffusion ( D t ) and photodiffusion ( D ph ) are described as D t =7.3×10 −7 exp(−0.33/ kT ) and D ph =4.7×10 −8 exp(−0.20/ kT ). It is found that the diffusion doping of Cdte thin Films by Cu at 400°C results in a sharp decrease of resistivity up to 7 orders of magnitude of p-type material, depending on thickness of Cu Film. The comparative study of performance of Cdte(Cu)/CdS and Cdte/CdS cells has been studied. It is shown that the diffusion doping of Cdte Film by Cu increases efficiency of Cdte(Cu)/CdS cells from 0.9% to 6.8%. The degradation of photovoltaic parameters of Cdte(Cu)/CdS cell, during testing under forward and reverse bias at room temperature, proceeds at a larger rate than those of Cdte/CdS cell without Cu. The degradation of performance of Cdte(Cu)/CdS cells is tentatively assigned to electrodiffusion of Cu in Cdte, resulting in redistribution of concentration of Cu-related centers in Cdte Film and heterojunction region.