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RISS 인기검색어
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- 저자 : Venkataraj, Selvaraj (검색결과 3 건)
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CdS microspheres composed of nanocrystals and their photocatalytic activity.
Rengaraj, Selvaraj,Jee, Sun Hee,Venkataraj, Selvaraj,Kim, Younghun,Vijayalakshmi, Selvaraj,Repo, Eveliina,Koistinen, Arto,Sillanp??, Mika American Scientific Publishers 2011 Journal of nanoscience and nanotechnology Vol.11 No.3
<P>A simple and template-free solution phase synthesis method has been developed for the preparation of novel CdS hollow microspheres using cadmium nitrate and thioacetamide precursors. In this manuscript, we demonstrate that process parameters such as the reaction time, precursor ratio, and reaction temperature strongly influence the morphology of the final product. The synthesized products have been characterized by a variety of methods, including X-ray powder diffraction (XRD), Raman spectroscopy, high-resolution scanning electron microscopy (HR-SEM), high-resolution transmission electron microscopy (HRTEM), energy-dispersive X-ray diffraction (EDX) analysis, X-ray photoelectron spectroscopy (XPS), and UV-visible diffused reflectance spectroscopy (UV-DRS). XRD analysis confirmed the cubic structure of the CdS microspheres, which has also been further supported by Raman spectroscopy. The HR-SEM measurements revealed the spherical morphology of the CdS microspheres which has been evolved by the oriented aggregation of the primary CdS nanocrystals. The TEM measurements confirmed the hollow shell-like structure of the spheres; the formation of their hollow interiors can be explained by the Ostwald ripening mechanism. UV-DRS studies showed that the band gap of the CdS microspheres increased with increasing cadmium-nitrate-to-thioacetamide ratio. Furthermore, studies of photocatalytic activity revealed that the synthesized CdS hollow microspheres exhibit an excellent photocatalytic performance in rapidly degrading methyl tert-butyl ether (MTBE) in aqueous solution under visible-light illumination. These results suggest that CdS microspheres will be an interesting candidate for photocatalytic detoxification studies under visible light radiation.</P>
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Weimin Li,Xia Yan,Armin G. Aberle,Selvaraj Venkataraj 한국물리학회 2017 Current Applied Physics Vol.17 No.12
Cu(In,Ga)Se2 thin-film solar cells have attracted strong interest in the photovoltaic community due to their high efficiency and demonstrated industrial relevance. As the most commonly used back electrode for CIGS solar cells, molybdenum (Mo) is typically deposited on soda-lime glass substrates by magnetron sputtering. During the high-temperature CIGS absorber formation process step, alkali (Na) atoms diffuse from the soda-lime glass substrate into the CIGS absorber via the Mo contact, a process that is known to improve the cell efficiency. However, Na diffusion from soda-lime glass sheets is an uncontrolled process, which adds to batch-to-batch variations due to fluctuations in the glass quality and process parameters such as the CIGS formation temperature. Hence, a diffusion barrier layer between the glass substrate and the Mo back electrode is required to prevent this uncontrolled impurity diffusion. In this study, a TiN diffusion barrier layer is deposited by reactive magnetron sputtering of a metallic Ti target, using various N2 flow conditions. It is observed that the adhesion, microstructure, and morphology of the Mo films get significantly improved by the introduction of a TiN barrier layer, which in turn leads to better cell efficiencies. Hence, the TiN/Mo bilayer design developed in this work seems to be a good choice for enhancing the efficiency of CIGS solar cells.
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Xue Zheng,Weimin Li,Armin G. Aberle,Selvaraj Venkataraj 한국물리학회 2016 Current Applied Physics Vol.16 No.10
Thin-film chalcopyrite Cu(In1x,Gax)Se (CIGS) solar cells have recently achieved an efficiency of ~22% at the lab scale, making the technology more promising for commercial applications than most other thinfilm solar cells. Using numerical device simulations, this study provides approaches to enhance the efficiency of ultra-thin CIGS solar cells. Effects of various Ga grading profiles in the CIGS absorber and of surface bandgap modifications are simulated. Our simulation results reveal that, in ultra-thin CIGS solar cells, back grading is an effective and practical approach to increase the cell efficiency, while front grading is unfeasible due to unacceptable current and fill factor losses. The quality of the back surface is of particular importance in moderately graded cells, while interface and bulk defect properties dominate in extremely graded cells. By introducing an ordered vacancy compound (OVC) layer with a downwardshifted valence band at the CIGS surface, the interface recombination losses can be significantly suppressed due to the reduced hole concentration. The thickness of the OVC layer and the valence band offset (VBO) between the OVC and CIGS materials are critical parameters for the cell efficiency. The simulations reveal that an optimized CIGS cell with a 300 nm thick CIGS absorber, a back-graded absorber profile and a 70 nm thick OVC layer at the CIGS surface can reach a 1-Sun efficiency of over 12%.
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