Browsing by Author "Chen, J. -Y."

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Efficiency improvement of Si solar cells using metal-enhanced nanophosphor fluorescence
(2014-01-01)
Chen, J. -Y.
;
Huang, C. K.
;
Hung, W. B.
;
Sun, K. W.
;
Chen, T. M.
In this study, Eu2+-doped barium silicate (Ba2SiO4:Eu2+) nanophosphors dispersed in a surfactant solution were spin-coated on commercially available silicon solar cells to form colloidal crystals on the surface. The crystals then act as luminescence down-shifting centers to generate low-energy photons for incident ultraviolet light. The fluorescence from the Ba2SiO4:Eu2+ nanophosphors was further enhanced by coating a metal-enhanced layer composed of Ag nanoparticles and a SiO2 spacer. The solar cells showed an enhancement of 0.86 mA/cm(2) in short-circuit current density and approximately 0.64% increase in power conversion efficiency when coated with nanophosphors, SiO2 spacers, and Ag nanoparticles. The properties of cells integrated with the metal-enhanced layer were characterized to identify the roles of nanophosphors and Ag nanoparticles in improved light harvesting. These experiments demonstrated that the colloids of Ba2SiO4:Eu2+ acted as luminescence down-shifting centers in the ultraviolet region and the metallic nanoparticles also helped to enhance fluorescence in the visible region to increase light absorption within the measured spectral regime. (C) 2013 Elsevier B.V. All rights reserved.
Electron-Boson Coupling Constant of Oxygen-Deficient Y(0.7)Ca(0.3)Ba(2)Cu(3)O(7-delta) Measured by Ultrafast Spectroscopy
(2011-01-01)
Luo, C. W.
;
Chen, J. -Y.
;
Huang, T. C.
;
Wu, K. H.
;
Lin, J. -Y.
The ultrafast dynamics in an (001) oxygen-deficient Y(0.7)Ca(0.3)Ba(2)Cu(3)O(7-delta) thin film were measured by using the ultrafast spectroscopy. According to the model of time-dependent distributions of electrons in the case of electron-phonon relaxation, the electron-boson coupling constant lambda could be directly obtained from the relaxation time of the transient reflectivity change (Delta R/R). For the overdoped case with T (c)=61.3 K and the underdoped case with T (c)=65.5 K, the relaxation time of Delta R/R is around 4.32 ps and 3.66 ps, respectively, which correspond to lambda similar to 0.06. However, the lambda become larger (similar to 0.15) in the optimal doped region with T (c)=82.1 K while the relaxation time of Delta R/R shrinks to similar to 1.51 ps. These results indicate that the lambda is strongly hole-doping dependent, which may govern the T (c) of cuprate superconductors.
Electron-Boson Coupling Constant of Oxygen-Deficient Y0.7Ca0.3Ba2Cu3O7-delta Measured by Ultrafast Spectroscopy
(2011-01-01)
Luo, C. W.
;
Chen, J. -Y.
;
Huang, T. C.
;
Wu, K. H.
;
Lin, J. -Y.
The ultrafast dynamics in an (001) oxygen-deficient Y0.7Ca0.3Ba2Cu3O7-delta thin film were measured by using the ultrafast spectroscopy. According to the model of time-dependent distributions of electrons in the case of electron-phonon relaxation, the electron-boson coupling constant lambda could be directly obtained from the relaxation time of the transient reflectivity change (Delta R/R). For the overdoped case with T (c)=61.3 K and the underdoped case with T (c)=65.5 K, the relaxation time of Delta R/R is around 4.32 ps and 3.66 ps, respectively, which correspond to lambda similar to 0.06. However, the lambda become larger (similar to 0.15) in the optimal doped region with T (c)=82.1 K while the relaxation time of Delta R/R shrinks to similar to 1.51 ps. These results indicate that the lambda is strongly hole-doping dependent, which may govern the T (c) of cuprate superconductors.