Browsing by Author "Hsu, C. Y."

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Effect of Selenization Processes on CIGS Solar Cell Performance
(2018-07-01)
Wu, C. H.
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Wu, P. W.
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Chen, J. H.
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Kao, J. Y.
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Hsu, C. Y.
Cu(In, Ga)Se-2 (CIGS) films were fabricated by a two-step process method using sputtering from Cu0.7Ga0.3 and In targets. The metallic precursor structures of In/CuGa/In were prepared, and CuGa film was adjusted to the thicknesses of 150, 200, 250 and 300 nm, in order to optimize the CIGS film. After selenization, three independent CIGS (112), CIGS (220/204) and CIGS (312/116) began to crystallize at similar to 280 degrees C and phase peaks continued growing until 560 degrees C. Experimental results showed that with a single stage selenization method, the excessive stoichiometry of the CIGS films was obtained. Using three sequential stages for the selenization process, with a annealing time of 20 min, the stoichiometry of the CIGS absorbers with the Cu/(In + Ga) and Ga/(In + Ga) showed atomic ratios of 0.94 and 0.34, respectively. The intensity of the (112) XRD diffraction peak became stronger, indicating an improvement in the crystallinity. Raman spectra of CIGS absorbers showed a main peak (174 cm(-1)) and two weak signals (212 and 231 cm(-1)). TEM image for electron diffraction pattern showed that the grains were randomly oriented. CIGS solar cell device prepared with a proper selenization, a maximum efficiency of 12.45% was obtained.
Effects of sputtering pressure and Al buffer layer thickness on properties of AZO films grown by rf magnetron sputtering
(2010-08-20)
Tseng, C. H.
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Wang, W. H.
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Chang, H. C.
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Chou, C. P.
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Hsu, C. Y.
Transparent and conductive Al-doped (2 wt.%) zinc oxide (AZO) films were deposited on inexpensive soda-lime glass substrates by using rf magnetron sputtering at room temperature. This study analyzed the effects of argon sputtering pressure, which varied in the range from 0.46 to 2.0 Pa, on the morphological, electrical and optical properties of AZO films. The only (0 0 2) diffraction peak of the film were observed at 20 similar to 34.45 degrees, exhibiting that the AZO films had hexagonal ZnO wurtzite structure, and a preferred orientation with the c-axis perpendicular to the substrate. By applying a very thin aluminum buffer layer with the thickness of 2 nm, findings show that the electrical resistivity was 9.46 x 10(-4) Omega-cm, and the average optical transmittance in the visible part of the spectra was approximately 81%. Furthermore, as for 10 nm thick buffer layer, the electrical resistivity was lower, but the transmittance was decreased. (C) 2010 Elsevier Ltd. All rights reserved.
Evaluation of the characteristics of the microelectrical discharge machining process using response surface methodology based on the central composite design
(2012-10-01)
Lin, Y. C.
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Tsao, C. C.
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Hsu, C. Y.
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Hung, S. K.
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Wen, D. C.
Evaluation of the characteristics of a microelectrical discharge machining (Micro-EDM) process is challenging, because it involves complex, interrelated relationships so a proper modeling approach is necessary to clearly identify the crucial machining variables and their interrelationships in order to initiate more effective strategies to improve Micro-EDM qualities (electrode wear (EW), material removal rate (MRR) and overcut). This paper uses a response surface method (RSM) based on the central composite design (CCD) for Micro-EDM problems with four EDM variables (peak current, pulse on-time, pulse off-time and electrode rotation speed). Experimental results indicate that peak current is the EDM variable that most affects the Micro-EDM qualities for SK3 carbon tool steel while pulse off-time had a significant interaction with that. The results show that RSM based on the CCD could efficiently be applied for the modeling of Micro-EDM qualities (EW, MRR, and overcut), and it is an economical way to obtain the performance characteristics of Micro-EDM process parameters with the fewest experimental data.
GROWTH OF AZO FILMS ON BUFFER LAYERS BY RF MAGNETRON SPUTTERING
(2010-12-20)
Chen, C. W.
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Tseng, C. H.
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Hsu, C. Y.
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Chou, C. P.
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Hou, K. H.
Al(2)O(3)-doped zinc oxide (in AZO, the Al(2)O(3) contents are approximately 2 wt.%) films have been grown by radio frequency (RF) magnetron sputtering at room temperature under varied sputtering pressures ranging from 3.5-15 mTorr. The electrical resistivity of AZO films is about 2.22 x 10(-3) Omega cm (sheet resistance similar to 89 Omega/square for a thickness similar to 250 nm), and the visible range transmittance is a bout 80% at the argon sputtering pressure of 15 mTorr and a RF power of 100 W. This study analyzes the structural, morphological, electrical and optical properties of AZO thin films grown on soda-lime glass substrate with 2, 5, and 10 nm thick Al buffer layers (and SiO(2) buffer). For the films deposited on the 2 nm thick Al buffer layer, we obtained ac-axis-oriented AZO/Al thin film on glass with the XRD full-width at half maximum (FWHM) of 0.31 and root mean square (RMS) surface roughness of about 3.22 nm. The lowest resistivity of 9.46 x 10(-4) Omega cm (sheet resistance similar to 37.87 Omega/square for a thickness similar to 250 nm) and a high transmittance (80%) were obtained by applying a 2 nm thick Al buffer layer. In contrast, the resistivity was slightly increased by applying the SiO(2) buffer layer.
Influence of oxygen flow rate on photocatalytic TiO2 films deposited by rf magnetron sputtering
(2012-02-01)
Chiou, A. H.
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Kuo, C. G.
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Huang, C. H.
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Wu, W. F.
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Chou, C. P.
Titanium dioxide (TiO2) thin films having anatase (1 0 1) crystal structure were prepared on non-alkali glass substrates by rf (13.56 MHz) magnetron sputtering using a TiO2 ceramic target under various oxygen partial pressures. At a fixed substrate temperature of 400 A degrees C and total gas pressure of 1 Pa after 3 h deposition. Effects of oxygen partial pressure on the structural, surface morphology, and photocatalytic activities of the TiO2 thin films were investigated. We performed both photoinduced decomposition of methylene blue (MB) and photoinduced hydrophilicity under UV light illumination. The XRD patterns exhibited a broad-hump shape indicating the amorphous structure of TiO2 thin films. The results showed that when the [O-2/(Ar + O-2)] flow rate increased to 50%, the photoinduced decomposition of MB and photoinduced hydrophilicity were enhanced. The water contact angle after 9 min UV illumination was approximately 4.5A degrees, and the methylene blue (MB) solution decomposition from 12 down to 3.34 mu mol/L for 240 min UV irradiation.
Influence of TiO2 buffer layer and post-annealing on the quality of Ti-doped ZnO thin films
(2013-07-01)
Lin, Y. C.
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Hsu, C. Y.
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Hung, S. K.
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Wen, D. C.
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機械工程學系
Ti-doped ZnO (TZO) thin films were grown on soda lime glass (SLG) substrate without and with a TiO2 buffer layer by radio frequency magnetron sputtering and then annealed under vacuum at 450 and 500 degrees C for 20 min. The structural, electrical, and optical properties of TZO films were investigated. XRD analysis shows that all TZO films are highly textured along the c-axis and perpendicular to the substrate. The structural properties of TZO films are improved by controlling the annealing temperature and inserting a TiO2 buffer layer. When the films were annealed at 450 degrees C, the crystallinity increased, but it then decreased slightly with increase in annealing temperature from 450 to 500 degrees C. Due to superior crystallinity, TZO films annealed at 450 degrees C exhibited lower resistivity and higher average transmittances in the visible region. The improvements in crystallinity, resistivity and transmittance are more obvious when a TiO2 buffer layer was inserted. The decrease in resistivity is mainly attributed to an increase in Hall mobility rather than carrier concentration. When the TZO films deposited on bare SLG substrate, the energy band gaps was decreased after annealing at 450 and 500 degrees C due to the decrease in carrier concentration. However, the absorption edge of TZO films deposited on TiO2-buffered substrate was blue shifted, and the energy band gap was increased due to the increase of carrier concentration. In this study, the TZO film with optimal properties was grown on the TiO2-buffered substrate and post annealed at 450 degrees C, achieving a resistivity of 3.76 x 10(-3) Omega-cm and an average transmittance above 85%. Therefore, it can be concluded that inserting a buffer layer at an early stage of film deposition to improve crystallinity can help achieve low resistivity, high transmittance, and high energy band gap in transparent conducting TZO thin films. (C) 2013 Elsevier Ltd and Techna Group S.r.l. All rights reserved.
Influence of ZnO buffer layer deposition parameters on the structure and properties of Ga-doped ZnO thin films
(2011-04-01)
Chu, C. Y.
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Hsu, C. Y.
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Hong, J. H.
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Chou, C. P.
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Chen, C. W.
A series of transparent conductive films of gallium-doped zinc oxide (GZO) were deposited on glass substrates with various zinc oxide (ZnO) buffer layers by radio frequency (rf) magnetron sputtering. To investigate the influence of the ZnO buffer layer deposition parameters on the structure and properties of GZO films, the various ZnO buffer layers were prepared with varying annealing temperatures, sputtering pressures, thicknesses, and different if powers. The crystallinity and grain sizes of the GZO films were investigated by the x-ray diffraction (XRD). Only the (002) diffraction peak located at 2 theta similar to 34.2 degrees appears in XRD spectrums indicating a hexagonal wurtzite structure with its strongly preferred orientation along the c-axis. It was found that the GZO film quality (low resistivity and high transmittance) could be improved by varying the ZnO buffer layer deposition parameters. The resistivity of the GZO films decreases from 5.01x10(-3) to 9.45x10(-4) Omega cm and the visible range transmittance increases from 81.12 to 84.42%, when the GZO films were deposited on a 50 nm ZnO buffer layer annealed at 400 degrees C.
Structural and optoelectronic properties of Al-doped zinc oxide films deposited on flexible substrates by radio frequency magnetron sputtering
(2011-09-01)
Tseng, C. H.
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Huang, C. H.
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Chang, H. C.
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Chen, D. Y.
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Chou, C. P.
Al-doped zinc oxide (AZO) thin films were deposited onto flexible polyethylene terephthalate substrates, using the radio frequency (RF) magnetron sputtering process, with an AZO ceramic target (The Al(2)O(3) content was about 2 wt.%). The effects of the argon sputtering pressure (in the range from 0.66 to 2.0 Pa), thickness of the Al buffer layer (thickness of 2, 5, and 10 nm) and annealing in a vacuum (6.6 x 10(-4) Pa), for 30 min at 120 degrees C, on the morphology and optoelectronic performances of AZO films were investigated. The resistivity was 9.22 x 10(-3) Omega cm, carrier concentration was 4.64 x 10(21) cm(-3), Hall mobility was 2.68 cm(2)/V s and visible range transmittance was about 80%, at an argon sputtering pressure of 2.0 Pa and an RF power of 100 W. Using an Al buffer decreases the resistivity and optical transmittance of the AZO films. The crystalline and microstructure characteristics of the AZO films are improved by annealing. (C) 2011 Elsevier BM. All rights reserved.
Structure and properties of GZO thin films grown on ZnO buffer layers
(2011-02-01)
Chu, C. Y.
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Huang, C. H.
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Kao, L. M.
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Chou, C. P.
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Hsu, C. Y.
Thin gallium-doped zinc oxide (in GZO the Ga(2)O(3) contents are approximately 3 wt%) films having different ZnO buffer layers were deposited using radio frequency (rf) magnetron sputtering. The use of a grey-based Taguchi method to determine the processing parameters of ZnO buffer layer deposition has been studied by considering multiple performance characteristics. A Taguchi method with an L(9) orthogonal array, signal-to-noise (S/N) ratio, and analysis of variance (ANOVA) is employed to investigate the performance characteristics in the deposition operations. The effect and optimization of ZnO buffer deposition parameters (rf power, sputtering pressure, thickness, and annealing) on the structure, morphology, electrical resistivity, and optical transmittance of the GZO films are studied. Annealing treatment and reduction in thickness resulted in a decrease in root-mean-square (RMS) surface roughness of the ZnO buffer layer. Using the optimal ZnO buffer layer obtained by the application of the grey-based Taguchi method, the electrical resistivity of GZO films was decreased from 2.94 x 10(-3) to 9.44 x 10(-4) Omega cm and the optical transmittance in the visible region was slightly increased from 84.81% to 85.82%. (C) 2010 Elsevier Ltd. All rights reserved.
The Photocatalytic Activity and Compact Layer Characteristics of TiO2 Films Prepared Using Radio Frequency Magnetron Sputtering
(2014)
Chang, H. C.
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Huang, H. H.
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Wu, C. Y.
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Hsu, R. Q.
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Hsu, C. Y.
TiO2 compact layers are used in dye-sensitized solar cells (DSSCs) to prevent charge recombination between the electrolyte and the transparent conductive substrate (indium tin oxide, ITO; fluorine-doped tin oxide, FTO). Thin TiO2 compact layers are deposited onto ITO/glass by means of radio frequency (rf) magnetron sputtering, using deposition parameters that ensure greater photocatalytic activity and increased DSSC conversion efficiency. The photoinduced decomposition of methylene blue (MB) and the photoinduced hydrophilicity of the TiO2 thin films are also investigated. The photocatalytic performance characteristics for the deposition of TiO2 films are improved by using the Grey-Taguchi method. The average transmittance in the visible region exceeds 85% for all samples. The XRD patterns of the TiO2 films, for sol-gel with spin coating of porous TiO2 /TiO2 compact/ITO/glass, show a good crystalline structure. In contrast, without the TiO2 compact layer (only porous TiO2), the peak intensity of the anatase (101) plane in the XRD patterns for the TiO2 film has a lower value, which demonstrates inferior crystalline quality. With a TiO2 compact layer to prevent charge recombination, a higher short-circuit current density is obtained. The DSSC with the FTO/glass and Pt counter electrode demonstrates the energy conversion efficiency increased.
The structural and optoelectronic properties of Ti-doped ZnO thin films prepared by introducing a Cr buffer layer and post-annealing
(2012-10-01)
Lina, Y. C.
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Hsu, C. Y.
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Hung, S. K.
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Chang, C. H.
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Wen, D. C.
This work investigates the effects of Cr buffer layers and post- annealing on the properties of titaniumdoped zinc oxide (TZO) thin films prepared by radio frequency magnetron sputter. All films had a (0 0 2) preferential orientation along the c-axis at 2 theta similar to 34 degrees. The crystallinity, grain size, Hall mobility and carrier concentration of TZO films were enhanced by introducing a Cr buffer layer and post-annealing. The decrease in resistivity was mainly attributed to the increase in Hall mobility rather than carrier concentration. As a Cr buffer layer was inserted, the film resistivity decreased by 32% to 5.41 x 10(-3) Omega cm while the energy band gap increased from 3.252 to 3.291 eV in comparison with that of the film deposited without the buffer layer. When the Cr-buffered films were annealed in a vacuum, the structural, electrical, and optical properties were improved with increasing annealing temperature. At an annealing temperature of 500 degrees C, the grain size, resistivity, and energy band gap attained the optimal values of 28.12 nm, 3.37 x 10(-3) Omega cm and 3.357 eV, respectively. The average transmittance of TZO films in the visible region was between 75% and 84%, and it decreased with increase in the grain size. The decrease in transmittance is attributed to an increase in surface roughness due to the three-dimensional island grain growth during thermal annealing. (c) 2012 Elsevier B.V. All rights reserved.
The structure and photocatalytic activity of TiO2 thin films deposited by dc magnetron sputtering
(2012-12-01)
Yang, W. J.
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Hsu, C. Y.
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Liu, Y. W.
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Hsu, R. Q.
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Lu, T. W.
This paper seeks to determine the optimal settings for the deposition parameters, for TiO2 thin film, prepared on non-alkali glass substrates, by direct current (dc) sputtering, using a ceramic TiO2 target in an argon gas environment. An orthogonal array, the signal-to-noise ratio and analysis of variance are used to analyze the effect of the deposition parameters. Using the Taguchi method for design of a robust experiment, the interactions between factors are also investigated. The main deposition parameters, such as dc power (W), sputtering pressure (Pa), substrate temperature (degrees C) and deposition time (min), were optimized, with reference to the structure and photocatalytic characteristics of TiO2. The results of this study show that substrate temperature and deposition time have the most significant effect on photocatalytic performance. For the optimal combination of deposition parameters, the (110) and (200) peaks of the rutile structure and the (200) peak of the anatase structure were observed, at 2 theta similar to 27.4 degrees, 39.2 degrees and 48 degrees, respectively. The experimental results illustrate that the Taguchi method allowed a suitable solution to the problem, with the minimum number of trials, compared to a full factorial design. The adhesion of the coatings was also measured and evaluated, via a scratch test. Superior wear behavior was observed, for the TiO2 film, because of the increased strength of the interface of micro-blasted tools. (C) 2012 Elsevier Ltd. All rights reserved.