Browsing by Author "Chen, Ting-Gang"

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Antireflective scheme for InGaP/InGaAs/Ge triple junction solar cells based on TiO2 biomimetic structures
(2012)
Hung, Kuo-Hsuan
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Chen, Ting-Gang
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Yang, Tung-Ting
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Yu, Peichen
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Hong, Chung-Yu
In this work, we demonstrate the device design, characterization, fabrication and analysis of biomimetic anti reflective structures on III-V multi-junction solar cell. The cell without anti reflective structure has a severe change of refractive index between the cell and air, causing a huge reflection (about 30%) and decrease the cell efficiency significantly. We can reduce light reflection by coating a proper material on the cell, diminishing the refractive index difference between cell and air interface. The optimization of single antireflection coating and biomimetic structure will be discussed and the experimental results will also be presented.
Characteristics of large-scale nanohole arrays for thin-silicon photovoltaics
(2014-04-01)
Chen, Ting-Gang
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Yu, Peichen
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Chen, Shih-Wei
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Chang, Feng-Yu
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Huang, Bo-Yu
Nanostructured crystalline silicon is promising for thin-silicon photovoltaic devices because of reduced material usage and wafer quality constraint. This paper presents the optical and photovoltaic characteristics of silicon nanohole (SiNH) arrays fabricated using polystyrene nanosphere lithography and reactive-ion etching (RIE) techniques for large-area processes. A post-RIE damage removal etching is subsequently introduced to mitigate the surface recombination issues and also suppress the surface reflection due to modifications in the nanohole sidewall profile, resulting in a 19% increase in the power conversion efficiency. We show that the damage removal etching treatment can effectively recover the carrier lifetime and dark current-voltage characteristics of SiNH solar cells to resemble the planar counterpart without RIE damages. Furthermore, the reflectance spectra exhibit broadband and omnidirectional anti-reflective properties, where an AM1.5 G spectrum-weighted reflectance achieves 4.7% for SiNH arrays. Finally, a three-dimensional optical modeling has also been established to investigate the dimension and wafer thickness dependence of light absorption. We conclude that the SiNH arrays reveal great potential for efficient light harvesting in thin-silicon photovoltaics with a 95% material reduction compared to a typical cell thickness of 200 mu m. Copyright (c) 2012 John Wiley & Sons, Ltd.
Direct near-field mapping of photoelectric response induced by localized surface plasmon of silver nano-islands on a silicon solar cell
(2012)
Yang, Cheng-Ying
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Chen, Ting-Gang
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Chiang, Chien-Lang
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Liou, Yi-Ying
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Tsai, Wen-Che
We investigate the possibility to enhance the absorption in solar cells by employing localized plasmon polaritons excited in metallic nanostructure. one possible mechanism for increased absorption for the presence of the metallic nanostructure are the giant near-field enhancement. The localized near-field enhancement of electric field is near the surface of nanostructure within several ten nanometers. To observed the effect of localized surface Plasmon, the photoelectric conversion characteristics of a solar cell with metal nanostructure are investigated by using an illumination-collection mode scanning near-field optical microscopy and near-field optical beam induced current (NOBIC) technique.
Fabrication and Device Modeling of Micro-textured Conductive Polymer/Silicon Heterojunction Solar Cells
(2012)
Chen, Ting-Gang
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Huang, Bo-Yu
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Huang, Yang-Yue
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Chen, En-Chen
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Yu, Peichen
In this paper, hybrid heterojunction solar cells are demonstrated based on a highly conductive polymer PEDOT:PSS directly spun-cast on an n-type crystalline silicon with microscale surface textures. The fabrication conditions suggest that the organic coverage on the micro-textured surface is excellent and key to achieve high efficiency. The simple solution-based fabrication processes achieved a cell power conversion efficiency of 10.2%. Device modeling had been performed to investigate the interface defect density dependence of cell performances. A power conversion efficiency of above 20% is projected for the hybrid heterojunction cells, showing promises for low-cost photovoltaics.
FABRICATION AND MODELING OF LARGE-SCALE SILICON NANOWIRE SOLAR CELLS FOR THIN-FILM PHOTOVOLTAICS
(2012)
Cheng, Yu-Chih
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Chen, Ting-Gang
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Chang, Feng-Yu
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Huang, Bo-Yu
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Pan, Huai-Te
Nanostructured crystalline silicon is promising for thin photovoltaic devices due to reduced material usage and wafer quality constraint. In this study, a simple and cost-effective method is presented for producing large-area silicon nanowire (SiNW) arrays with various lengths by employing the polystyrene nanosphere lithography and the metal-assisted chemical etching (MACE). The nanowire structure exhibits broadband and omnidirectional antireflection properties, where the lowest AM1.5G-spectrum-weighted reflectance of SiNW arrays is 4.38%, compared to 8.84% of the conventional single layer antireflection coating (SLARC). Next, we made SiNW array structures into solar cells and its power efficiency achieved 10.8%. Afterward, the SiNW array solar cells were analyzed by external and internal quantum efficiency measurement which shows the device performance primarily limited by direct and indirect interfacial recombination of charge carriers. We further develop a modeling technique based on three-dimensional (3) optical and two-dimensional (20) electrical simulations which are tailored for the nanostructured silicon photovoltaic devices. The optical simulation employs a rigorous couple wave analysis (RCWA) technique to calculate the distribution of electromagnetic field in order to obtain the generation rate within the nanostructure. Next, an electrical calculation is based on a 20 self-consistent drift-diffusion and Poisson solver using a finite element method (FEM). We investigate the influence to the device performance of carrier diffusion length with three different structures. The simulation results show that a short diffusion length does not seriously deteriorate the short-circuit current density and power conversion efficiency of a core-shell PN junction solar cell compared to the conventional planar structure. Our work suggests that SiNW solar cells can achieve efficient light harvesting and photoelectric conversion with less and lower-grade materials than the conventional technology, which is promising for thin silicon photovoltaics.
Flexible Silver Nanowire Meshes for High-Efficiency Microtextured Organic-Silicon Hybrid Photovoltaics
(2012-12-01)
Chen, Ting-Gang
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Huang, Bo-Yu
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Liu, Hsiao-Wei
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Huang, Yang-Yue
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Pan, Huai-Te
Hybrid organic-silicon heterojunction solar cells promise a significant reduction on fabrication costs by avoiding energy-intensive processes. However, their scalability remains challenging without a low-cost transparent electrode. In this work, we present solution-processed silver-nanowire meshes that uniformly cover the microtextured surface of hybrid heterojunction solar cells to enable efficient carrier collection for large device area. We systematically compare the characteristics and device performance with long and short nanowires with an average length/diameter of 30 mu m/115 nm and 15 mu m/45 nm, respectively, to those with silver metal grids. A remarkable power conversion efficiency of 10.1% is achieved with a device area of 1 x 1 cm(2) under 100 mW/cm(2) of AM1.5G illumination for the hybrid solar cells employing long wires, which represents an enhancement factor of up to 36.5% compared to the metal grid counterpart. The high-quality nanowire network displays an excellent spatial uniformity of photocurrent generation via distributed nanowire meshes and low dependence on efficient charge transport under a high light-injection condition with increased device area. The capability of silver nanowires as flexible transparent electrodes presents a great opportunity to accelerate the mass deployment of high-efficiency hybrid silicon photovoltaics via simple and rapid soluble processes.
Micro-textured conductive polymer/silicon heterojunction photovoltaic devices with high efficiency
(1970-01-01)
Chen, Ting-Gang
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Huang, Bo-Yu
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Chen, En-Chen
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Yu, Peichen
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Meng, Hsin-Fei
"In this work, hybrid heterojunction solar cells are demonstrated based on a conjugate polymer poly(3,4-ethylenedioxy-thiophene):poly(styrenesulfonate) (PEDOT:PSS) directly spun-cast on micro-textured n-type crystalline silicon wafers. The fabrication conditions suggest that the organic coverage on the micro-textured surface is excellent and key to achieve high efficiency, leading to an average power conversion efficiency of 9.84%. A one-dimensional drift-diffusion model is then developed based on fitting the device characteristics with experimentally determined PEDOT: PSS parameters and projects an ultimate efficiency above 20% for organic/inorganic hybrid photovoltaics. The simulation results reveal the impacts of defect densities, back surface recombination, doping concentration, and band alignment. (C) 2012 American Institute of Physics. [http://dx.doi.org/10.1063/1.4734240]"
Nano-patterned glass superstrates with different aspect ratios for enhanced light harvesting in a-Si:H thin film solar cells
(2012-05-07)
Chen, Ting-Gang
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Yu, Peichen
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Tsai, Yu-Lin
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Shen, Chang-Hong
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Shieh, Jia-Min
Nano-patterned glass superstrates obtained via a large-area production approach are desirable for antireflection and light trapping in thin-film solar cells. The tapered nanostructures allow a graded refractive index profile between the glass and material interfaces, leading to suppressed surface reflection and increased forward diffraction of light. In this work, we investigate nanostructured glass patterns with different aspect ratios using scalable nanosphere lithography for hydrogenated amorphous silicon (a-Si:H) thin film solar cells. Compared to flat glass cell and Asahi U-type glass cell, enhancements in short-circuit current density (J(sc)) of 51.6% and 8%, respectively, were achieved for a moderate aspect ratio of 0.16. The measured external quantum efficiencies (EQE) spectra confirmed a broadband enhancement due to antireflection and light trapping properties. (C) 2012 Optical Society of America
Phonon thermal conductivity suppression of bulk silicon nanowire composites for efficient thermoelectric conversion
(2010-09-13)
Chen, Ting-Gang
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Yu, Peichen
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Chou, Rone-Hwa
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Pan, Ci-Ling
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光電工程學系
Vertically-aligned silicon nanowires (SiNWs) that demonstrate reductions of phonon thermal conductivities are ideal components for thermoelectric devices. In this paper, we present large-area silicon nanowire arrays in various lengths using a silver-induced, electroless-etching method that is applicable to both n- and p-type substrates. The measured thermal conductivities of nanowire composites are significantly reduced by up to 43%, compared to that of bulk silicon. Detailed calculations based on the series thermal resistance and phonon radiative transfer models confirm the reduction of thermal conductivity not only due to the increased air fraction, but also the nanowire size effect, suggesting the soundness of employing bulk silicon nanowire composites as efficient thermoelectric materials. (C) 2010 Optical Society of America
Solution-processed Silicon Hybrid Heterojunction Photovoltaics with Silver Nanowires
(2012-01-01)
Huang, Bo-Yu
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Liu, Hsiao-Wei
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Chen, Ting-Gang
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Chen, En-Chen
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Chen, Bo-han
An Organic/inorganic hybrid solar cells are cheap alternatives to conventional silicon-based solar cells. The devices take the advantages of high optical absorption and carrier mobility of inorganic semiconductors, while maintaining the easy processing attributes of polymers or other soft materials. However, the conduction of holes has been a major technical barrier for the advance of such novel devices. In this study, we propose the use of silver nanowires (AgNWs) to improve the series resistance of the hybrid solar cells and further to realize solution-processed silicon-based photovoltaics. The hybrid silicon heterojunction solar cells are demonstrated based on the composite of conductive polymer PEDOT:PSS directly spun-cast on a micro-textured n-type crystalline silicon wafer, followed by the Meyer rod coating of AgNWs as the frontal metal contacts. The cross linked AgNWs offer high transparency and low sheet resistance, which can be easily fabricated using low-cost and non-toxic materials. Moreover, the industrial-standard microscale surface textures improve the antireflection and carrier collection without increasing much surface recombination. As a result, the device current density-voltage characteristics reveals a high power conversion efficiency of 6.8% under a calibrated illumination intensity of 1000 W/m(2) of the AM1.5G solar spectrum, shedding light into the attainment of rapid solution processed silicon hybrid heterojunction solar cells.