Shu-Chia Shiu

National Taiwan University, Taipei, Taipei, Taiwan

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Publications (41)49.59 Total impact

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    ABSTRACT: In the past decades, Si has been the most important material for electronics. By exploiting this mature semiconductor fabrication technique, it is also highly desired to use Si for applications in other areas. Here we report the use of Si micro-structures for optical-communications and Si nano-structures for energy applications. Sub-micron Si waveguides is fabricated on Si substrates rather than SOI (silicon on insulator) substrate using laser reformation technique. This method helps solve the incompatible problem for the integration of optics and electronics on a single Si chip. The typical thickness of the oxide layer on the CMOS transistor layer is below 100nm which, however, creates excessive optical loss due to the light coupling into Si substrate. Besides, fabricating Si photonics on Si wafer is much cheaper than that on SOI wafer. The method is using high-power pulse laser to melt high-aspect ratio Si ridges. This creates a structure with wider upper portion and narrower lower portion, which can be further oxidized and forming waveguides. For energy applications, Si nanostructures are fabricated using the metal-assisted chemical etching (MacEtch) technique. Si nanostructures could greatly reduce the surface reflection to enhance light harvest. In addition, Si nanowires are further combined with organic materials to form hetero-junction solar cells using low-cost solution process. Furthermore, the Si nanostructures and MacEtch process are refined to form completely single-crystal Si thin film. Thus the material cost of Si solar cells can be potentially reduced to only 1/10 of current ones.
    Proc SPIE 11/2012;
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    ABSTRACT: Silicon nanowire (SiNW) arrays are widespread applied on hybrid photovoltaic devices because SiNW arrays can substitute the pyramid texture and anti-reflection coating due to its strong light trapping. Also, SiNWs can be prepared through a cost-efficient process of metal-assisted chemical etching. However, though longer SiNW arrays have lower reflectance, the top of long SiNWs aggregate together to make junction synthesis difficult for SiNW/organic hybrid solar cell. To control and analyze the effect of SiNW array morphology on hybrid solar cells, here we change the metal deposition condition for metal-assisted chemical etching to obtain different SiNW array morphologies. The experiment was separated to two groups, by depositing metal, say, Ag, before etching (BE) or during etching (DE). For group BE, Ag was deposited on n-type Si (n-Si) wafers by thermal evaporation; then etched by H2O2 and HF. For group DE, n-Si was etched by Ag+ and HF directly. Ag was deposited on n-Si during etching process. Afterwards, residual Ag and SiO2 were removed by HNO3 and buffered HF, successively; then Ti and Ag were evaporated on the bottom of Si to be a cathode. Finally, SiNWs were stuck on the poly(3,4-ethylenedioxythiophene):poly(styrenesulfonate) that was spincoated on the ITO coated glass to form SiNW/organic heterojunction. The results show that group BE has reflectance lower than that in group DE in solar spectrum. However, group BE has smaller power conversion efficiency (PCE) of 8.65% and short-circuit current density (Jsc) of 24.94 mA/cm2 than group DE of PCE of 9.47% and Jsc of 26.81 mA/cm2.
    Proc SPIE 10/2012;
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    ABSTRACT: In this work, we develop a technique to form vertically aligned silicon nanowire (SiNW) arrays without aggregation at the top by cost and energy efficient metal-assisted chemical wet etching. The SiNW/PEDOT:PSS heterojunction solar cells are also fabricated with nanowire length varying from 0.758 °m to 5.27 °m. The 0.758-°m-SiNW/poly(3,4-ethylenedioxythiophene):poly(styrenesulfonate) (PEDOT:PSS) solar cell has the best power conversion efficiency of 8.65% and short circuit current density of 24.94 mA/cm2.
    Photovoltaic Specialists Conference (PVSC), 2012 38th IEEE; 01/2012
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    ABSTRACT: Thin-film crystalline photovoltaic (PV) cell is a trend for future PV with its potential to achieve low cost and high efficiency. Concerning material utilization efficiency, we propose a method with a fast manufacturing method of thin crystalline Si by chemical solution. To obtain the highest efficiency of material utilization, experiments with different H2O2/HF ratio are conducted, where related mechanisms are discussed. Moreover, large-area (87.7 mm2) thin film transferred to glass is demonstrated, and with embedded nanohole structure, lowest optical reflectance of 0.26% is measured. These characteristics show that the fabricated thin film has potential for large-area crystalline thin film PV.
    Photovoltaic Specialists Conference (PVSC), 2012 38th IEEE; 01/2012
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    ABSTRACT: We report the performance enhancement of GaAs-based triple-junction solar cells using novel indium nanoparticles upon the cell front-surface to achieve the top cell current matching. The external quantum efficiency (EQE) enhancements of >; 5% in top cell at wavelengths from 350 nm to 450 nm are achieved as the cell with indium nanoparticles plasmonic structure. Besides increasing in short circuit current (ISC) of 11.20% (from 2.95 mA to 3.28 mA) and in conversion efficiency (η) of 13.5%(from 20.8% to 23.6%) are also obtained under one sun AM1.5G illumination.
    Photovoltaic Specialists Conference (PVSC), 2012 38th IEEE; 01/2012
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    ABSTRACT: We report the increasing in average external quantum-efficiency (EQE) of 11% on the top-cell of GaAs-based triple-junction solar-cell due to current matching using a graded-index SiO2-nano-pillars sub-wavelength/SiO2/TiO2 AR-coating by CF4-RIE etching with Ag-nanoparticles mask.
    Lasers and Electro-Optics (CLEO), 2012 Conference on; 01/2012
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    ABSTRACT: Crystalline Si photovoltaic modules still have high production cost due to significant consumption of the Si wafer. Reducing the large amount of Si material consumption is thus a critical issue. Here we develop a two-step metal-assisted etching technique for forming vertically-aligned Si nanohole thin films from bulk Si wafers. The formation of Si nanohole thin films includes a series of solution processes: deposition of Ag nanoparticles in an AgNO3/ HF aqueous solution, formation of Si nanohole arrays at the first-step metal-assisted etching, and side etching of the roots of the nanohole structure at the second-step metal-assisted etching. All the processes can proceed at around room temperature. A Si nanohole thin film with an average hole-size of 100 nm and a thickness of 5ìm-20ìm was hence formed at the top of the wafer. Afterwards, the Si nanohole thin film was transferred onto alien substrates. The Si nanohole thin film has the crystal quality similar to the bulk Si wafer. The above bulk Si substrate can be reused. With similar processes, other Si nanohole thin films can be formed from the above recycled Si wafer. The hole size and thickness are similar. The Si wafers recycled will significantly reduce the material consumption of Si. Thus, such technique is promising for lowering the cost of Si solar cells.m.
    Proc SPIE 09/2011;
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    ABSTRACT: We have demonstrated a new type of hybrid solar cell based on a heterojunction between poly(3,4- ethylenedioxythiophene): poly(styrenesulfonate) (PEDOT:PSS) and vertically aligned n-type GaAs nanowire (NW) arrays. The GaAs NW arrays are directly fabricated by the nano-etching of GaAs wafer with spun-on SiO2 nanospheres as the etching mask through inductively coupled plasma reactive ion etching (ICP-RIE) system. Then we attach GaAs NW arrays onto PEDOT:PSS conductive polymer to form a p-n junction. According to our research, the morphology of GaAs NW arrays strongly influences the characteristics of the GaAs NW/PEDOT:PSS hybrid solar cells. The improved interpenetrating heterojunction interface and the suppressed reflectance of GaAs NW arrays will offer great improvements in efficiency relative to a conventional planar cell. The power conversion efficiency of 5.8 % of GaAs NW/PEDOT:PSS cells under AM 1.5 global one sun illumination can be achieved.
    Proc SPIE 09/2011;
  • Hong-Jhang Syu, Shu-Chia Shiu, Chih-Fu Lin
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    ABSTRACT: Silicon nanowire/Poly(3,4-ethylenedioxythiophene):poly(styrenesulfonate) solar cells were fabricated. The nanowires of 370 nm were coated with PEDOT:PSS. The short circuit current density and power conversion efficiency are 27.46 mA/cm2 and 8.05%.
    Proc SPIE 04/2011;
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    ABSTRACT: Various Si nanostructures can be fabricated using a metal-assisted etching technique, which must be applied on bulk Si wafers, limiting its applications and wasting a significant amount of material. Here, we report a technique to form a Si nanostructured thin film created by metal-assisted chemical etching from bulk Si wafers and to transfer it onto alien substrates. To detach the Si nanostructured thin films completely from bulk Si wafers, a second-step metal-assisted chemical etching made the root of the Si nanostructures become fragile. The transferred Si nanostructures are well-aligned along the normal direction of the receiver substrate. The X-ray diffraction spectrum reveals that the transferred Si nanostructured thin films exhibit good crystal orientation and morphology. A strong light trapping effect between the nanostructures causes such films of thickness to exhibit nearly 99% absorption from . This exceeds the theoretically calculated limits of planar Si.
    Journal of The Electrochemical Society. 01/2011; 158(2):D95-D98.
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    ABSTRACT: We report the influence of controlled lengths and densities of GaN rod arrays on the output power of GaN light-emitting diodes (LEDs). The morphology-controlled GaN rod arrays are fabricated via using ZnO rod arrays as a dry etching mask. Our investigation indicates that the output power of GaN LEDs has a strong dependence on the lengths and densities of GaN rod arrays. The variation of output power of GaN LEDs with GaN rod arrays is caused by the Fabry-Pérot resonance of the film composed by GaN rod arrays. The theoretical analysis also shows a good agreement with the measurement results.
    IEEE Photonics Technology Letters 01/2011; · 2.04 Impact Factor
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    ABSTRACT: In this research, we compare hydrothermally synthesized TiO2 nanorods in an unsealed and a sealed system, respectively. Due to the variation of hydrothermal concentration, the morphology is very different. Then we further pre-fabricate a TiO2 seed layer by the sol-gel method and then hydrothermally synthesize TiO2 nanorods. The TiO2 nanorods can also be grown on the TiO2 seed layer successfully. This result exhibits the promising potential for the growth of TiO2 nanorods on versatile substrates.
    01/2011;
  • Hong-Jhang Syu, Shu-Chia Shiu, Ching-Fuh Lin
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    ABSTRACT: Silicon nanowire (SiNW)/Poly(3,4-ethylenedioxythiophene):poly(styrenesulfonate) (PEDOT:PSS) solar cells were fabricated by solution process. The effect of nanowire length to cell performance was investigated for the nanowire length varying from 0.73 μm to 5.59 μm. The nanowire length was found to have negative effect on the power conversion efficiency (PCE), in the condition of the fixed thickness of PEDOTPSS. The highest PCE of 7.02% was obtained for the wire length of 0.73 μm.
    Conference Record of the IEEE Photovoltaic Specialists Conference 01/2011;
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    ABSTRACT: A technique applying the homogenized KrF excimer laser reformation to fabricate Si cylindrical profile is presented. High-power excimer laser was used to illuminate high-aspect-ratio Si ridges which were fabricated using typical lithography and etching process. The Si ridges were then melted and reshaped to cylinders due to surface tension. The structure can be further preceded by thermal oxidation to produce wave guiding photonics. It is capable of fabricating sub-micrometer Si waveguides with extremely smooth surface.
    Nanotechnology (IEEE-NANO), 2011 11th IEEE Conference on; 01/2011
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    ABSTRACT: Herein we demonstrate an improved metal-assisted etching method to achieve highly dense and uniform silicon nanowire arrays. A pre-surface treatment was applied on a silicon wafer before the process of metal-assisted etching in silver nitrate and hydrogen fluoride solution. The treatment made silver ion continuously reduce on silver nuclei adherence on the silicon surface, leading to formation of dense silver nanoparticles. Silver nanoparticles acting as local redox centers cause the formation of dense silicon nanowire arrays. In contrast, an H-terminated silicon surface made silver ion reduce uniformly on the silicon surface to form silver flakes. The silicon nanowires fabricated with a pre-surface treatment reveals higher density than those fabricated without a pre-surface treatment. The volume fraction improves from 18 to 38%. This improvement reduces the solar-weighted reflectance to as low as 3.3% for silicon nanowires with a length of only 0.87 μm. In comparison, the silicon nanowires fabricated without a pre-surface treatment have to be as long as 1.812 μm to achieve the same reflectance.
    Applied Surface Science 01/2011; 257(6):1829-1834. · 2.54 Impact Factor
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    ABSTRACT: We demonstrated the localized surface plasmons of indium nanoparticles for enhancing the performances of silicon solar cells. At AM1.5G, the increasing in conversion efficiency of 31.17%, from 12.03% to 15.78%, was obtained.
    01/2011;
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    ABSTRACT: Si nanostructures are promising materials for future photovoltaic applications. To date the Si nanostructures are mainly formed on particular substrates or at high temperatures, greatly limiting their application flexibility. Here we report a two-step metal-assisted etching technique for forming vertically aligned Si nanohole thin films on bulk Si wafers at room temperature. The Si nanohole thin films with a thickness of 5µm can be easily transferred to alien substrates. Because of the low temperature transfer process, it enables a large variety of alien substrates such as glass and plastics to be used. In addition, we demonstrate that the bulk Si substrate can be reused to fabricate Si nanohole thin films. The consumption of bulk Si materials is significantly reduced.
    01/2011;
  • Hong-Jhang Syu, Shu-Chia Shiu, Ching-Fuh Lin
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    ABSTRACT: Ultra short silicon nanowires (SiNWs) were applied on Si/Poly(3,4-ethylenedioxy-thiophene): poly(styrenesulfonate) (PEDOT:PSS) solar cells by solution process. The short circuit current density (Jsc) is 23.72 mA/cm2, and power conversion efficiency (PCE) is 7.38%.
    Nanotechnology (IEEE-NANO), 2011 11th IEEE Conference on; 01/2011
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    ABSTRACT: The effect of mild oxygen plasma etching on poly(3-hexylthiophene) (P3HT): [6,6]-phenyl C61 butyric acid methyl ester (PCBM) blend film was investigated to improve the efficiency of inverted polymer solar cells. Our study shows that the polymer surface adjacent to the anode was modified into a more hydrophobic P3HT-rich surface, which leads to better interface contact, fine electrode selectivity, and lower series resistance in the device. Although PCBM still aggregates on the top surface, it can be removed with mild oxygen plasma etching. As a result, the power conversion efficiency increased significantly from 3.4% to 4.3% with an enhanced fill factor of 64%.
    Solar Energy Materials and Solar Cells 10/2010; 94(10):1681–1685. · 5.03 Impact Factor
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    ABSTRACT: Short period plasma exposure on poly(3-hexylthiophene):[6,6]-phenyl C<sub>61</sub> butyric acid methyl ester (P3HT:PCBM) blend film in the inverted bulk-herterojunction (BHJ) solar cells with highly transparent sol-gel derived ZnO film as electron selective layer is studied as a way to improve device performance. This study focuses on the vertical segregation of the two components in polymer thin film during the slow-drying treatment on ZnO substrates and further discovers some drawbacks on the polymer film surface that is unfavorable for carrier transport. With the use of mild plasma exposure, the surface can be modified and forms better penetrating pathways for carriers. The polymer surface adjacent to metal electrode turns into a more hydrophobic P3HT-rich surface which forms better contact, fine electrode selectivity, and lower series resistance in the device. The hole transport in P3HT interpenetrating network avoids recombination at the Ag electrode by the removal of PCBM protrusions. As a result, the current density is improved to 11.75 mA/cm<sup>2</sup> and the efficiency is increased to 3.97% with an enhanced fill factor of 62.6%. Our finding provides an efficient method for interface engineering in organic optoelectronic devices and paves a way for high power conversion efficiency for similar structures.
    Photovoltaic Specialists Conference (PVSC), 2010 35th IEEE; 07/2010