Browsing by Author "Sun, K. W."

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Biomimetic nanostructured antireflection coating and its application on crystalline silicon solar cells
(2011-07-18)
Chen, J. Y.
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Chang, W. -L.
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Huang, C. K.
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Sun, K. W.
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應用化學系
In this report, we demonstrate the implementation of biomimetic nanostructured antireflection coatings with polymethyl methacrylate (PMMA) layer on the micro-textured surface of silicon crystalline solar cells. To reduce cost, the process combines colloidal lithography, cast molding method, and reversal nanoimprint lithography. The technique is simple, low cost, and does not cause damage to the thin and brittle conventional crystalline solar cells. The antireflection properties of this biomimetic nanostructure coating are considered as effective as those of a conventional single-layer SiN(x) thin film. The resultant structures alone could reduce the average reflectance of solar cell from 13.2% to 7.8% and enhance power conversion efficiency from 12.85% to 14.2%. (C)2011 Optical Society of America
Carrier capture and relaxation in charged quantum dots triggered by vibrational relaxation
(2008-01-01)
Kechiantz, A. M.
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Sun, K. W.
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應用化學系分子科學碩博班
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Institute of Molecular science
Local polarization and the strain of the crystal lattice around the charged quantum dot in semiconductors must vibrate to relax when the mobile carrier is captured by the dot and makes it uncharged. Triggered vibrations induce the sudden perturbation of electronic states in the quantum dot. The Hamiltonian of electron interaction with a local vibrating field and carrier capture time are calculated. It is shown that the principle of uncertainty has a strong influence on this effect. The calculated values of electron capture time are on a sub-picosecond timescale at a high pumping intensity, and are strongly dependent on the scale of quantum confinement. The calculations fit well with photoluminescence rising times tau = 0.45ps [K. Gundogdu, K.C. Hall, T.F. Boggess, D.G. Deppe, O.B. Shchekin, Appl. Phys. Lett. 85 (2004) 4570.] and tau = 1.7ps [K.W. Sun, A. Kechiantz, B.C. Lee, C.P. Lee, Appl. Phys. Lett. 88 (2006) 163117.] which are observed in the experiments on p-doped InAs quantum dots. (C) 2007 Elsevier B.V. All rights reserved.
Carrier Dynamics in InAs/GaAs Quantum Rings
(2009)
Lin, C. H.
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Ling, H. S.
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Sun, K. W.
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Lee, C. P.
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Lin, S. D.
We have investigated the temperature dependence of the carrier relaxation dynamics in InAs/GaAs self-assembled quantum rings by using the time-resolved photoluminescence technique with a time resolution of similar to 250 ps. The carrier relaxation in the QRs not only shows strong dependence on the lattice temperature, it is also significant slower than the carrier relaxation in the quantum dots at temperature above 150 K.
d-d Transition and Electrical Transport in Single Co:ZnO Nanorod
(2011)
Wen, C. -S.
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Sun, K. W.
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應用化學系
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Department of Applied Chemistry
This work demonstrated techniques that were applied on the measurements of a single Co:ZnO nanorod. We have resolved photoluminescence peaks that were associated with the d-d transitions and phonon replica due to the presence of the doped cobalt ions which have replaced the Zn ion sites. We also showed temperature dependence of the resistance and the activation energy of single nanorods with different Co doping levels.
Effect of double heterojunctions on the plasmon-phonon coupling in a GaAs/Al(0.24)Ga(0.76)As quantum well
(2008-12-01)
Lee, H. C.
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Sun, K. W.
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Lee, C. P.
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應用化學系
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電子工程學系及電子研究所
Quasi-two-dimensional (Q2D) Coulomb interactions between plasmons and phonons in a GaAs quantum well are studied numerically. Based on the dielectric continuum model, the plasmon-confined phonon coupling and plasmon-symmetric (+/-) interface phonon coupling are considered. By using renormalized phonon propagators, six branches involving plasmon-like and phonon-like modes are obtained and used to study the effect on the hot-carrier average energy-loss rate (AELR). Plasmon-like modes are demonstrated to enhance the AELR around the sheet carrier density of 10(11) cm(-2) due to a significant contribution of the plasmon-symmetric (+) interface phonon coupled mode. The importance of interface phonon modes on the plasmon-phonon coupling (PPC) is also indicated. If the interface phonon is not considered, the AELR enhancement due to the PPC will not appear. In addition, the carrier temperature is found to be important for the AELR enhancement. As the carrier temperature is as low as possible, the AELR enhances more remarkably because the effect of reabsorption of plasmon-like modes for hot carriers (hot-plasmon effect) can be greatly suppressed.
Efficiency enhancement of silicon solar cells using a nano-scale honeycomb broadband anti-reflection structure
(2012-01-02)
Huang, C. K.
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Sun, K. W.
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Chang, W-L.
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應用化學系
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Department of Applied Chemistry
This experiment demonstrates the process for manufacturing a ZnO honeycomb sub-wavelength structure using nanosphere lithography technology exhibiting excellent anti-reflection properties from the UV to NIR wavelength regions. This honeycomb nanostructure, combined with commercially available crystalline Si solar cells, show substantially improved conversion efficiency from 15.6% to 16.6% using optimized honeycomb sizes and precursor concentrations of ZnO. The present work develops an unsophisticated and economical technique suitable for industrial applications in producing a uniform and low-reflective texture. (C)2011 Optical Society of America
Efficiency enhancement of the poly-silicon solar cell using self-assembled dielectric nanoparticles
(2011-08-01)
Huang, C. K.
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Lin, H. H.
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Chen, J. Y.
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Sun, K. W.
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Chang, W. -L.
In this study, silica nanospheres dispersed in a surfactant solution were spin-coated on commercially available silicon solar cells to form colloidal crystals on the surface. This self-assembled nanoparticle layer served as an anti-reflection (AR) layer for solar cell devices. The self-assembled layer exhibits excellent anti-reflection properties in the UV and NIR wavelength regions, and the reflectance spectra match the theoretical prediction done using the rigorous coupled-wave analysis model. We also showed that the overall conversion efficiency of polycrystalline Si solar cells coated with the silica nanospheres was increased from 11% to 12.3% when using optimized spin-coating parameters and nanoparticle concentrations. (C) 2011 Elsevier B.V. All rights reserved.
Efficiency improvement of Si solar cells using metal-enhanced nanophosphor fluorescence
(2014-01-01)
Chen, J. -Y.
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Huang, C. K.
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Hung, W. B.
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Sun, K. W.
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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.
Electrical and Optical Properties of a Single Sb(2)Se(3) Nanorod
(2009-06-01)
Ko, T. Y.
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Yang, C. H.
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Sun, K. W.
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Chang, H. W.
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Sarkar, B.
In this paper we present the methods to chemically synthesize the Sb(2)Se(3) nanorods and study the electrical and optical properties of a single Sb(2)Se(3) nanorod with an average size of 70 nm in diameter and a length of about 1 mu m to 2 mu m. The techniques we devised can immobilize and allocate a single nano-object on an electron beam (E-beam) patterned smart substrate. It can also overcome the limitation of the spatial resolution of conventional optical techniques (similar to 1 mu m) to obtain optical spectroscopy in an individual nano-object less than 100 nm in size. We also demonstrate the techniques in using E-beam defined metallic coordination markers as electrodes to measure the conductance of a single Sb(2)Se(3) nanorod.
Electrical and Optical Properties of a Single Sb2Se3 Nanorod
(2009-06-01)
Ko, T. Y.
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Yang, C. H.
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Sun, K. W.
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Chang, H. W.
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Sarkar, B.
In this paper we present the methods to chemically synthesize the Sb2Se3 nanorods and study the electrical and optical properties of a single Sb2Se3 nanorod with an average size of 70 nm in diameter and a length of about 1 mu m to 2 mu m. The techniques we devised can immobilize and allocate a single nano-object on an electron beam (E-beam) patterned smart substrate. It can also overcome the limitation of the spatial resolution of conventional optical techniques (similar to 1 mu m) to obtain optical spectroscopy in an individual nano-object less than 100 nm in size. We also demonstrate the techniques in using E-beam defined metallic coordination markers as electrodes to measure the conductance of a single Sb2Se3 nanorod.
Electrical characterization and Raman spectroscopy of individual vanadium pentoxide nanowire
(2011-10-01)
Shen, W. -J.
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Sun, K. W.
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Lee, C. S.
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應用化學系
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Department of Applied Chemistry
We measured I-V characteristics, electrical resistance, and Raman spectra in the temperature range from room temperature to above 600 K to obtain nanodevices. Measurements were taken on a single V(2)O(5) nanowire deposited on a Si template, where two- and four-point metallic contacts were previously made using e-beam lithography. In both two- and four-point probe measurements, the I-V curves were clearly linear and symmetrical with respect to both axes. Drastic reduction in electrical resistance and deviation from single valued activation energy with increasing temperature indicated phase transitions taking place in the nanowire. From temperature-dependent HR-Micro Raman measurements, reductions from V(2)O(5) to VO(2)/V(2)O(3) phases took place at a temperature as low as 500 K, when electrons were injected to the nanowire through electrical contacts.
Electron transport mechanisms in individual cobalt-doped ZnO nanorods
(2012-11-01)
Ko, T. Y.
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Tsai, M. -H.
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Lee, C. -S.
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Sun, K. W.
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應用化學系
This study examined carrier transport in single cobalt-doped zinc oxide (Co:ZnO) nanorods in temperatures ranging from 80 to 405 K. Measurements were taken on single nanorods deposited on a Si template, where two- and four-point metallic contacts were previously made using e-beam lithography, dielectrophoresis, and focused ion beam. In both two-and four-point probe measurements, the current-voltage curves were clearly linear and symmetrical with respect to both axes. The electrical measurements were carried out according to three different measuring methods to accurately determine the resistivity of the single Co:ZnO nanorods. The Co-doped nanorods exhibited ferromagnetic behavior at room temperature. The remanence permanent magnet of the nanorods increased with increasing Co concentration, however, this was accompanied by the decrease in electrical resistivity. The transport properties were dominated by the thermal activation of electrons from the Fermi level to the conduction band for a temperature above 140-160 K, and to the impurity band at a lower temperature. The electronic transport of the nanorods was influenced by the surface states when exposed in the air.
Enhanced light harvesting of Si solar cells via luminescent down-shifting using YVO4:Bi3+, Eu3+ nanophosphors
(2013-11-01)
Huang, C. K.
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Chen, Y. C.
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Hung, W. B.
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Chen, T. M.
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Sun, K. W.
The colloids of YVO4 nanoparticles on microtextured Si surface are demonstrated to have promising potential for efficient solar spectrum utilization in crystalline Si solar cells. The solar cells showed an enhancement of 4% in short-circuit current density and approximately 0.7% in power conversion efficiency when coated with YVO4 nanoparticles. The properties of cells integrated with YVO4 nanoparticles were characterized to identify the role of YVO4 in improved light harvesting. The current experiments conclude that the colloids of YVO4 nanoparticles not only act as luminescent down-shifting centers in the ultraviolet region but also serve as an antireflection coating for enhancing the light absorption in the measured spectral regime. Copyright (c) 2012 John Wiley & Sons, Ltd.
Enhancement of the light conversion efficiency of silicon solar cells by using nanoimprint anti-reflection layer
(2010-03-01)
Chen, J. Y.
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Sun, K. W.
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應用化學系
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Department of Applied Chemistry
In this report, the results of the fabrication of nanostructured Si molds by e-beam lithography and chemical wet etching are presented. A home-made pneumatic nanoimprint system was used to transfer the mold patterns to a PMMA layer on a Si template using the spin-coating replication/hot-embossing techniques. The patterned PMMA layer was peeled off from the Si template and directly transferred onto the surface of a poly-Si P-N junction solar cell device to serve as the anti-reflection (AR) layer. It provides a simple and low-cost means for large-scale Use in the production of AR layers for improving solar cell performance. A drastic reduction in reflectivity of the AR layer over a broad spectral range was demonstrated. In addition, the great improvement on the light harvest efficiency of the solar cells from 10.4% to 13.5% using the nanostructured PMMA layer as the AR layer was validated. (C) 2009 Elsevier B.V. All rights reserved.
Growth of Vertically Aligned ZnO Nanorod Arrays as Anti-reflection Layer in Silicon Solar Cell
(2010)
Chen, J. Y.
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Sun, K. W.
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應用化學系
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Department of Applied Chemistry
We have investigated solution-grown ZnO nanorod arrays as the anti-reflection(AR) layer for Si solar cells. The nanorod morphology, controlled through synthetic chemistry, has a great effect on the AR layer performance. We demonstrate that the light harvest efficiency of the solar cells can be greatly improved from 10.4% to 12.8% by using the vertical aligned ZnO nanorod arrays as the AR layer on poly-Si solar cells.
Growth of vertically aligned ZnO nanorod arrays as antireflection layer on silicon solar cells
(2010-05-01)
Chen, J. Y.
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Sun, K. W.
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應用化學系
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Department of Applied Chemistry
In this work we investigated the effects of growth time, spin-coating rates, and solution concentration on the reflection properties of the solution-grown ZnO nanorod arrays. The vertically aligned nanorod arrays were deposited on the surface of the Si solar cells as the antireflection (AR) layer. We found that the nanorod morphology, controlled through synthetic chemistry, has a great effect on the AR layer performance. We also demonstrated that the light harvest efficiency of the solar cells was greatly improved from 10.4% to 12.8% by using the vertically aligned ZnO nanorod arrays as the AR layer on poly-Si solar cells. (C) 2010 Elsevier B.V. All rights reserved.
Improvement in the light conversion efficiency of silicon solar cells by pure hydrogen annealing
(2015-11-01)
Xie, M. H.
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Chen, J. Y.
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Sun, K. W.
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應用化學系
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電子工程學系及電子研究所
In this report, the effects of pure hydrogen gas annealing on series resistance (R-s), shunt resistance (R-sh), open circuit voltage (V-oc), short circuit current I-sc, fill factor, and efficiency were investigated systematically using standard, commercially available polysilicon solar cells. Improvements on the electrical characteristics, fill factors, and efficiency of the solar cells were observed after annealing by pure hydrogen gas at 350 degrees C for 15 min. In the best case, the conversion efficiency was raised by nearly 1% point. Judging from our experimental evidences, the improvement on cell performance could be mostly attributed to the reduction of R-s and improvement in Ag grid/emitter contact resistance in the cells during the annealing process. (C) 2015 Elsevier Ltd. All rights reserved.
Magnetophotoluminescence properties of Co-doped ZnO nanorods
(2009-04-13)
Lin, C. Y.
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Wang, W. H.
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Lee, C. -S.
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Sun, K. W.
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Suen, Y. W.
We present the detailed experimental results of the magnetic and optical properties of cobalt doped ZnO nanorods, especially the temperature and magnetic field dependence of photoluminescence up to 14 T. The Raman measurements indicate that our Co-doped ZnO nanorods have the same lattice constant as crystalline bulk ZnO. Sharp luminescence peaks centered at around 670 nm were observed at low temperature and their intensity decreased with increasing magnetic field. The luminescence peaks were attributed to d-d transitions in the Ligand field from the doped Co ions. We also observed a diamagnetic shift at a temperature of 1.5 K when the magnetic field was scanned from 0 to 14 T. The exciton radius of the Co-doped ZnO nanorods was deduced from the magnetophotoluminescence results.
Nanostructured thin films for anti-reflection applications
(2011-05-31)
Chen, J. Y.
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Sun, K. W.
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應用化學系
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Department of Applied Chemistry
Anti-reflection (AR) thin films composed of ordered arrays of tapered nanostructures on the surface of PMMA and silicon, through the hot-embossing nanoimprint of polymer using molds prepared from e-beam lithography and hydrothermally grown ZnO nanorod arrays. The use of PMMA and ZnO nanorod thin films allows the formation of anti-reflection structures on a curved or flat surface to effectively suppress the reflectance of the incident light. It provides a simple and low-cost means for large-scale use in the production of AR layers for improving optical and optoelectronic device performance, such as solar cells and photodetectors. A drastic reduction in the reflectivity of the AR layer over a broad spectral range was demonstrated. In addition, the great improvement on the light harvest efficiency of the solar cells by over 30% using the nanostructured AR layer was validated. (C) 2011 Elsevier B.V. All rights reserved.
Optical and electrical properties of single Sb(2)Se(3) nanorod
(2009-12-01)
Ko, T. Y.
;
Sun, K. W.
;
應用化學系
;
應用化學系分子科學碩博班
;
Department of Applied Chemistry
In this report. methods of solvothermal synthesis of Sb(2)Se(3) nanorods from a single-source precursor Sb[Se(2)P(O (1)Pr)(2)](3) were demonstrated The synthesized Sb(2)Se(3) nanorods were expected to have new optical and electrical properties. With the electron beam (E-beam) lithography and focus ion beam (FIB) techniques, we achieved immobilization and positioning of a single Sb(2)Se(3) nanorod on a patterned template. By using the confocal Raman microscope and two-point.-contact electrical measurement methods, we obtained optical and electrical characteristics from a single Sb(2)Se(3) nanorod (C) 2009 Elsevier B.V. All rights reserved.