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Umme Farva,박진호,Mahmood Alam Khan 한국화학공학회 2012 Korean Journal of Chemical Engineering Vol.29 No.10
CuInSe2 (CIS) nanoparticles have been prepared by the hot-injection method with sizes ~25 nm, and the thermal annealing influence on the size, morphology and optoelectronic properties of crystalline CuInSe2 nanoparticles has been elucidated. Microstructural analysis of synthesized nanoparticles was performed by various characterization methods including high-resolution transmission electron microscopy (HR-TEM), Scanning TEM (STEM), Xray diffraction, X-ray photoelectron spectroscopy (XPS) and photoluminescence (PL) spectroscopy. The fast Fourier transform (FFT) pattern of HR-TEM image of annealed CuInSe2 nanoparticles illustrates that the particles have quasisingle crystal tetragonal structure, as also confirmed by the XRD pattern. The HR-TEM image clearly shows the fringe widths are in order without any defect with 0.32 nm. Microstructural analysis results clearly indicate that the synthesized and air-annealed nanoparticles are in highly crystalline state with near stoichiometric atomic composition.
박진호,Umme Farva,정우식,Eui Jung Kim,Do Hoon Kim 한국화학공학회 2008 Korean Journal of Chemical Engineering Vol.25 No.5
This paper reports an alternative method for the growth of GaN epitaxial layer on (0001) Al2O3 substrate by hot-wall vapor phase epitaxy technique. Tris (N,N-dimethyldithiocarbamato)-gallium (III), Ga(mDTC)3 was introduced as a precursor material for the seed layer formation in the growth of GaN. Optimal growth conditions with seed layers formed by the Ga(mDTC)3 concentration of 0.047 mol/L were identified: Growth temperature was found to be 850 oC, and optimal distance between the reactant outlet and substrate was determined to be 12.5 cm. Characterization results showed that this growth method produce high-crystallinity GaN epitaxial layers at a relatively lower growth temperature compared to the existing growth techniques and simplify the growth process
Younghee Na,Umme Farva,조성민,박진호 한국화학공학회 2009 Korean Journal of Chemical Engineering Vol.26 No.6
A simplified anodized aluminum oxide (AAO) nano-template fabrication process was developed in this study, which can be suited for the large area device applications. The pores of various sizes and depths were realized from the thin (less than 1 μm) aluminum film deposited on the sapphire substrate. The optimum morphological structure was obtained by adjusting the applied voltage, types of acid solution, its concentration and temperature which has evolved after two phases of anodization followed by chemical etching. The Ar plasma pre-treatment method was developed and applied to improve the surface roughness of thin aluminum film without severely sacrificing the deposited layer thickness.
Low Temperature Nanopowder Processing for Flexible CIGS Solar Cells
박진호(Park, Chinho),박준영(Farva, Umme),Krishnan, Rangarajan,Park, Jun Young,Anderson, Timothy J. 한국신재생에너지학회 2010 한국신재생에너지학회 학술대회논문집 Vol.2010 No.06
CuIn_{1-x}-GaxSe₂ based materials with direct bandgap and high absorption coefficient are promising materials for high efficiency hetero-junction solar cells. CIGS champion cell efficiency(19.9%, AM1.5G) is very close to polycrystalline silicon(20.3%, AM1.5G). A reduction in the price of CIGS module is required for competing with well matured silicon technology. Price reduction can be achieved by decreasing the manufacturing cost and by increasing module efficiency. Manufacturing cost is mostly dominated by capital cost. Device properties of CIGS are strongly dependent on doping, defect chemistry and structure which in turn are dependent on growth conditions. The complex chemistry of CIGS is not fully understood to optimize and scale processes. Control of the absorber grain size, structural quality, texture, composition profile in the growth direction is important to achieving reliable device performance. In the present work, CIS nanoparticles were prepared by a simple wet chemical synthesis method and their structural and optical properties were investigated. XRD patterns of as-grown nanopowders indicate CIS(Cubic), CuSe₂(orthorhombic) and excess selenium. Further, as-grown and annealed nanopowders were characterized by HRTEM and ICP-OES. Grain growth of the nanopowders was followed as a function of temperature using HT-XRD with overpressure of selenium. It was found that significant grain growth occurred between 300-400?C accompanied by formation of {beta}-Cu_{2-x}Se at high temperature(500?C) consistent with Cu-Se phase diagram. The result suggests that grain growth follows VLS mechanism which would be very useful for low temperature, high quality and economic processing of CIGS based solar cells.
Nguyen Tam Nguyen Truong,박진호,Matthew Lowell Monroe,Umme Farva,Timothy James Anderson 한국화학공학회 2011 Korean Journal of Chemical Engineering Vol.28 No.7
Bulk hetero-junction solar cells with CdSe nanoparticles-P_3HT (poly 3-hexyl thiophene) composite active layer were fabricated, and the control of morphological feature of the nanoparticle-polymer composite thin films was investigated. A binary solvent composed of a primary solvent with intermediate polarity and a secondary solvent with high polarity was found to be effective in controlling the dispersion of the CdSe nanocrystals in the P_3HT matrix, and the modification of the nanocrystal surface by liquid-liquid extraction process was found to be effective in achieving the desired composite film morphology. Surface roughness of the active layer was optimized for various loadings of CdSe nanoparticles and could be reproducibly controlled to less than 10 nm.