Papers - Araki Kenji
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Electrical conduction of Si/ITO/Si junctions fabricated by surface activated bonding Reviewed
Liang J., Ogawa T., Araki K., Kamioka T., Shigekawa N.
Proceedings of 2017 5th International Workshop on Low Temperature Bonding for 3D Integration, LTB-3D 2017 2017.6
Language：English Publishing type：Research paper (scientific journal) Publisher：Proceedings of 2017 5th International Workshop on Low Temperature Bonding for 3D Integration, LTB-3D 2017
© 2017 JSPS 191st Committee on Innovative Interface Bonding Technology. The electrical properties of n-Si/ITO/n-Si, n-Si/ITO/p-Si, and p-Si/ITO/n-Si junctions fabricated by surface activated bonding (SAB) were investigated. The current-voltage (I-V) characteristics of n-Si/ITO/n-Si, n-Si/ITO/p-Si, and p-Si/ITO/n-Si junctions showed excellent linearity. The interface resistance of n-Si/ITO/p-Si junctions was found to be 0.0249 O·cm2, which is the smallest value observed in all the samples.
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Orlando V., Gabás M., Galiana B., Espinet-González P., Palanco S., Nuñez N., Vázquez M., Araki K., Algora C.
Progress in Photovoltaics: Research and Applications 25 ( 1 ) 97 - 112 2017.1
Language：English Publishing type：Research paper (scientific journal) Publisher：Progress in Photovoltaics: Research and Applications
Copyright © 2016 John Wiley & Sons, Ltd. Accelerated life tests are frequently used to provide reliability information in a moderate period of time (weeks or months), and after that, a failure analysis is compulsory to detect the failure origins. In this paper, a failure analysis has been carried out after a temperature accelerated life test on lattice matched GaInP/Ga(In)As/Ge triple junction commercial solar cells. Solar cells were forward biased in darkness inside three climatic chambers in order to emulate the photo-generated current under nominal working conditions (a concentration level of 820 suns). After the accelerated aging test, a characterization of the resulting cells by means of quantum efficiency, dark and illumination I–V curves, electroluminescence, scanning electron microscope, energy dispersive X-ray, scanning transmission electron microscope and X-ray photoelectron spectroscopy has been carried out. Current is identified as the cause of degradation while temperature just dominates the accelerating factor of the aging test. Current promotes the front metal damage produced by the chemical evolution of the electroplating impurities together with those of the tab soldering process. Semiconductor structure does not seem to be responsible of any failure. Therefore, this kind of lattice matched GaInP/Ga(In)As/Ge triple junction solar cells, that as of 2016, are the workhorse of CPV technology, exhibits as a very robust device if the front metal connection is properly accomplished. Copyright © 2016 John Wiley & Sons, Ltd.
DOI： 10.1002/pip.2818
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Analysis of impact to optical environment of the land by flat-plate and array of tracking PV panels Reviewed
Araki K., Nagai H., Lee K., Yamaguchi M.
Solar Energy 144 278 - 285 2017
Language：English Publishing type：Research paper (scientific journal) Publisher：Solar Energy
© 2017 Elsevier Ltd The impact to the optical environment result from shading of PV panels becomes concerned. This paper describes how to calculate illumination level on the land around tracking PV (both isolated and arrayed) panel. The land under the flat-plate PV is dark by shading, but the influence from the tracking PV is not very significant, typically half in average. This is because shadow by tracking panel moves. The shading influence is further decreased with the increase of pedestal height. With this advantage, tracking PV can be combined with agriculture as a double use of the land.
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Ikeda K., Araki K., Ota Y., Lee K., Nishioka K., Yamaguchi M.
2017 IEEE 44th Photovoltaic Specialist Conference, PVSC 2017 1 - 4 2017
Language：English Publishing type：Research paper (scientific journal) Publisher：2017 IEEE 44th Photovoltaic Specialist Conference, PVSC 2017
© 2017 IEEE. For the purpose of designing the high efficient static solar concentrator on automobile, we discuss the way to increase the aperture area. The 2-dimensional (2D) single and double refraction models based on the Snell's law are prepared under the conditions of random azimuth and large off-angle of the incident ray. We find that the center height of the lens is a key parameter to increase the aperture size. For lens array systems, the optimum center height is determined by the upper limit which is required to suppress the shadowing loss at the adjacent lenses. We demonstrate the ray tracing of the 2D lens model.
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Araki K., Nagai H., Herrero R., Antón I., Sala G., Lee K., Yamaguchi M.
Solar Energy 147 448 - 454 2017
Language：English Publishing type：Research paper (scientific journal) Publisher：Solar Energy
© 2017 Elsevier Ltd CPV (Concentrator photovoltaic) requires accuracy in optical alignment. Optical misalignment in the module was measured and analyzed. Such information was useful to identify assembly problems and improved module performance. 1-D and 2-D Monte Carlo simulations were developed to analyze the impact of alignment errors by assembly errors. The 1-D simulation was useful to anticipate the power output of the module, whereas 2-D was for acceptance angle. The 2-D model showed that the gap from Pmp-based acceptance angle (Pmp: Power at the maximum power point) from that of Isc-based (Isc: Short-circuit current) was a function of deviation of assembles misalignment in the module. The rough rule for the acceptable assembles misalignment is that the standard deviation of the assemble misalignment will be less than 10% of acceptance angle of the optics, whereas that of power output of the single module is 20%. This fact implies that the inspection of the acceptance angle is highly recommended in the CPV module production.
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Araki K., Herrero R., Anton I., Sala G., Nagai H., Lee K., Yamaguchi M.
2017 IEEE 44th Photovoltaic Specialist Conference, PVSC 2017 1 - 5 2017
Language：English Publishing type：Research paper (scientific journal) Publisher：2017 IEEE 44th Photovoltaic Specialist Conference, PVSC 2017
© 2017 IEEE. The acceptance angle of concentrator modules measured by short circuit current I sc is always larger than that by maximum power Pm even by use of advanced concentrator optics that keep uniform illumination onto the concentrator cells. The purpose of this study is to investigate the cause of that myth. An expanded Monte Carlo method that calculates acceptance angle of CPV modules was developed with considering 2-dimensional misalignment error vector. It was shown that the gap from Pm-based acceptance angle from that of I sc -based was a function of deviation of assembles misalignment in the module. The rough rule for acceptable assembles misalignment is that the standard deviation of assemble misalignment level will be less than 10 % of acceptance angle of the optics.
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Ahmad N., Ota Y., Araki K., Lee K., Yamaguchi M., Nishioka K.
Japanese Journal of Applied Physics 56 ( 9 ) 2017
Language：Japanese Publishing type：Research paper (scientific journal) Publisher：Japanese Journal of Applied Physics
© 2017 The Japan Society of Applied Physics. In this study, we propose a new concentrator photovoltaic (CPV) system design with a large-acceptance-angle lens, which tracks the sun on the basis of a new 30-min intermittent tracking method that does not require a special high-precision CPV tracking system. This will reduce costs, because a large percentage of the cost of a typical CPV system comes from the expensive accurate tracking system. The present system had a concentration ratio of 111 and an acceptance angle of 4.5°. We conducted an experiment to evaluate the thermal and electrical performances of the system in an outdoor test site in Miyazaki Japan. The experimental results were compared with optical thermal and electrical simulation results. The simulated results showed good agreement with the experimental ones.
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Araki K., Lee K., Yamaguchi M.
Solar Energy 153 445 - 453 2017
Language：English Publishing type：Research paper (scientific journal) Publisher：Solar Energy
© 2017 Elsevier Ltd Bandgap optimization of the tandem cells has been calculated by many scientists under the standard air-mass 1.5 spectrum or the site-specific conditions using statistics of meteorological observations and spectrum data. Calculation of the optimized bandgap combination at the specific site required many annually-observed atmospheric parameters. It is not realistic, because most of the installation site does not have detailed annual spectrum information. This paper has two purposes. One is to quantitatively understand the impact of the variance of the atmospheric conditions to the bandgap optimization design. Another is to propose the practical method to take the spectrum information of the specific site by even in a single day's measurement. For evaluating the impact of the atmospheric conditions, both the best and the worst distributions were taken from the measurement data. With including other meteorological and geographical data variance, the dataset of the annual spectrum with different sun-height was generated and distribution of the calculated optimized bandgap combination was examined. The optimum bandgaps varied by aerosol depth, water precipitation, latitude, and seasonal sunshine duration change as it was expected. It was also found that the optimization of the bandgaps combination at the specific site, considering ever-changing spectrum, may be determined by the matching condition to the sun height at the culmination on the winter solstice, because the distributions of optimum bandgap combinations were much closed to those of annual integration, in spite of the fact that they were calculated by a single time (single date) of the measurement. Different from AM1.5 the sun height can be taken two times a day throughout a year.
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Static concentrator photovoltaics for automotive applications Reviewed
Masuda T., Araki K., Okumura K., Urabe S., Kudo Y., Kimura K., Nakado T., Sato A., Yamaguchi M.
Solar Energy 146 523 - 531 2017
Language：English Publishing type：Research paper (scientific journal) Publisher：Solar Energy
© 2017 Elsevier Ltd This research investigated the benefits of utilizing solar power as an energy source for future passenger vehicles and an innovative static concentrator photovoltaic module for practical automotive applications. Due to strict emissions standards, alternative energy sources must be found for vehicles in the future. It was estimated that replacing all passenger vehicles with hybrid vehicles (HVs) equipped with an 800 W rated-power solar module that generates an average output of 1.8 kW h/day would reduce CO2 emissions by 63% in Japan. To confirm the validity of this estimation, a test vehicle was created by installing a 6.8 m2 solar module onto a commercially available plug-in HV. An average power generation of 2.1 kW h/day was obtained by this solar module over 100 days under real-world conditions, which was larger than the power required to achieve the estimated CO2 emissions reduction. In addition, an innovative static low-concentrator with III–V cells was studied to help reduce the installation area of the solar module on the vehicles, which is essential for practical passenger vehicles. A new concentrator design method was proposed that can be easily integrated into a standard vehicle design procedure by utilizing numerical optimization in a CAD-friendly environment. Both design equations and a design example are discussed in this paper. The proposed lens design (asymmetric-aspheric type) can expand the acceptance incident angle of solar light and increase the annual energy yield of a solar panel, while maintaining the essential thin structure for automotive applications. In spite of the wide range of sun positions, this asymmetric-aspherical lens can maintaining stable illumination on the cell while suppressing the maximum spot intensity to 20×.
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Optimization of static concentrator photovoltaics with aspherical lens for automobile Reviewed
Ota Y., Nishioka K., Araki K., Ikeda K., Lee K., Yamaguchi M.
2017 IEEE 44th Photovoltaic Specialist Conference, PVSC 2017 1 - 4 2017
Language：English Publishing type：Research paper (scientific journal) Publisher：2017 IEEE 44th Photovoltaic Specialist Conference, PVSC 2017
© 2017 IEEE. In this paper, we optimized the basic aspherical lens for automobile using optical method. Since the panel is installed in horizontal, the distribution of incident angle that is important to concentrator optics design needs to be newly defined. By optimization of lens structure, the optical efficiency increased to 46.7%.
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Next environment-friendly cars: Application of solar power as automobile energy source Reviewed
Masuda T., Araki K., Okumura K., Urabe S., Kudo Y., Kimura K., Nakado T., Sato A., Yamaguchi M.
2017 IEEE 44th Photovoltaic Specialist Conference, PVSC 2017 1 - 5 2017
Language：English Publishing type：Research paper (scientific journal) Publisher：2017 IEEE 44th Photovoltaic Specialist Conference, PVSC 2017
© 2017 IEEE. We investigate the benefits of utilizing solar power as an energy source for future automobiles. Since there are strict emission standards developed by governments, we must find an alternative energy source for the future automobiles. We show that replacing all passenger cars with hybrid vehicles equipped with a 800 W rated-power solar module would reduce greenhouse gas (GHG) emission by 63% in Japan. We obtained an average power generation of 2.1 kWh/day over 100 days by solar modules installed on a Prius under the real environment, which was larger than the required power to achieve the GHG emission reduction. We also investigate an innovative statistic low-concentrator with III-V cells in order to reduce installation area for the automobiles. We show that our proposed design (asymmetric-aspheric design) can expand the acceptance incident angle and increase the annual energy yield, while keeping thin structure, which is essential to automobile application.
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Fabrication and performance analysis of a mechanical stack InGaP/GaAs//Si solar cell Reviewed
Lee K., Nakamura K., Kamioka T., Kojima N., Lee H., Wang L., Araki K., Ohshita Y., Ogura A., Yamaguchi M.
2017 IEEE 44th Photovoltaic Specialist Conference, PVSC 2017 1 - 3 2017
Language：English Publishing type：Research paper (scientific journal) Publisher：2017 IEEE 44th Photovoltaic Specialist Conference, PVSC 2017
© 2017 IEEE. We present the measurement results and analyses of a InGaP/GaAs//Si mechanical stack four-terminal solar cell. From these results, we performed detailed discussions of the loss mechanisms and efficiency limits of InGaP/GaAs//Si mechanical stack solar cells.
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Ikeda K., Araki K., Ota Y., Lee K., Nishioka K., Yamaguchi M.
Conference Record of the IEEE Photovoltaic Specialists Conference 2016-November 566 - 569 2016.11
Language：English Publishing type：Research paper (scientific journal) Publisher：Conference Record of the IEEE Photovoltaic Specialists Conference
© 2016 IEEE. For the purpose of designing the high efficient static solar concentrator on automobile, we discuss the way to increase the aperture area. The 2-dimensional (2D) single and double refraction models based on the Snell's law are prepared under the conditions of random azimuth and large off-angle of the incident ray. We find that the center height of the lens is a key parameter to increase the aperture size. For lens array systems, the optimum center height is determined by the upper limit which is required to suppress the shadowing loss at the adjacent lenses. We demonstrate the ray tracing of the 2D lens model.
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Lee K., Araki K., Wang L., Kojima N., Ohshita Y., Yamaguchi M.
Conference Record of the IEEE Photovoltaic Specialists Conference 2016-November 1906 - 1908 2016.11
Language：English Publishing type：Research paper (scientific journal) Publisher：Conference Record of the IEEE Photovoltaic Specialists Conference
© 2016 IEEE. We present a quantitative approach to investigate and compare the material qualities of III-V on silicon (III-V/Si) solar cells by using external radiative efficiencies. We use this analysis to predict the limiting efficiencies and evaluate the criteria of material quality for achieving high efficiency III-V/Si solar cells. This result yields several implications of designing high efficiency III-V/Si solar cells.
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Fabrication and performance analysis of a mechanical stack InGaP/GaAs//Si solar cell Reviewed
Lee K., Nakamura K., Kamioka T., Kojima N., Lee H., Wang L., Araki K., Ohshita Y., Ogura A., Yamaguchi M.
Conference Record of the IEEE Photovoltaic Specialists Conference 2016-November 1957 - 1959 2016.11
Language：English Publishing type：Research paper (scientific journal) Publisher：Conference Record of the IEEE Photovoltaic Specialists Conference
© 2016 IEEE. We present the measurement results and analyses of a InGaP/GaAs//Si mechanical stack four-terminal solar cell. From these results, we performed detailed discussions of the loss mechanisms and efficiency limits of InGaP/GaAs//Si mechanical stack solar cells.
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Optimization of static concentrator photovoltaics with aspherical lens for automobile Reviewed
Ota Y., Nishioka K., Araki K., Ikeda K., Lee K., Yamaguchi M.
Conference Record of the IEEE Photovoltaic Specialists Conference 2016-November 570 - 573 2016.11
Language：English Publishing type：Research paper (scientific journal) Publisher：Conference Record of the IEEE Photovoltaic Specialists Conference
© 2016 IEEE. In this paper, we optimized the basic aspherical lens for automobile using optical method. Since the panel is installed in horizontal, the distribution of incident angle that is important to concentrator optics design needs to be newly defined. By optimization of lens structure, the optical efficiency increased to 46.7%.
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Next environment-friendly cars: Application of solar power as automobile energy source Reviewed
Masuda T., Araki K., Okumura K., Urabe S., Kudo Y., Kimura K., Nakado T., Sato A., Yamaguchi M.
Conference Record of the IEEE Photovoltaic Specialists Conference 2016-November 580 - 584 2016.11
Language：English Publishing type：Research paper (scientific journal) Publisher：Conference Record of the IEEE Photovoltaic Specialists Conference
© 2016 IEEE. We investigate the benefits of utilizing solar power as an energy source for future automobiles. Since there are strict emission standards developed by governments, we must find an alternative energy source for the future automobiles. We show that replacing all passenger cars with hybrid vehicles equipped with a 800 W rated-power solar module would reduce greenhouse gas (GHG) emission by 63% in Japan. We obtained an average power generation of 2.1 kWh/day over 100 days by solar modules installed on a Prius under the real environment, which was larger than the required power to achieve the GHG emission reduction. We also investigate an innovative statistic low-concentrator with III-V cells in order to reduce installation area for the automobiles. We show that our proposed design (asymmetric-aspheric design) can expand the acceptance incident angle and increase the annual energy yield, while keeping thin structure, which is essential to automobile application.
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Durability of polymeric encapsulation materials in a PMMA/glass concentrator photovoltaic system Reviewed
Miller D.C., Kempe M.D., Muller M.T., Gray M.H., Araki K., Kurtz S.R.
Progress in Photovoltaics: Research and Applications 24 ( 11 ) 1385 - 1409 2016.11
Language：English Publishing type：Research paper (scientific journal) Publisher：Progress in Photovoltaics: Research and Applications
Copyright © 2016 John Wiley & Sons, Ltd. The durability of polymeric encapsulation materials was examined using outdoor exposure at the nominal geometric concentration of 500 suns. The results for 36-month cumulative field deployment are presented for materials including: poly(ethylene-co-vinyl acetate), (EVA); polyvinyl butyral (PVB); ionomer; polyethylene/polyoctene copolymer (PO); thermoplastic polyurethane (TPU); poly(dimethylsiloxane) (PDMS); poly(diphenyl dimethyl siloxane) (PDPDMS); and poly(phenyl-methyl siloxane) (PPMS). Measurements of the field conditions including ambient temperature and ultraviolet (UV) dose were recorded at the test site during the experiment. Measurements for the experiment included optical transmittance (with subsequent analysis of solar-weighted transmittance, UV cut-off wavelength, and yellowness index), mass, visual photography, photoelastic imaging, and fluorescence spectroscopy. While the results to date for EVA are presented and discussed, examination here focuses more on the siloxane materials. A specimen recently observed to fail by thermal decomposition is discussed in terms of the implementation of the experiment as well as its fluorescence signature, which was observed to become more pronounced with age. Modulated thermogravimetry (allowing determination of the activation energy of thermal decomposition) was performed on a subset of the siloxanes to quantify the propensity for decomposition at elevated temperatures. Supplemental, Pt-catalyst- and primer-solutions as well as peroxide-cured PDMS specimens were examined to assess the source of the luminescence. The results of the study including the change in optical transmittance, observed failure modes, and subsequent analyses of the failure modes are described in the conclusions. Copyright © 2016 John Wiley & Sons, Ltd.
DOI： 10.1002/pip.2796
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Lee K., Araki K., Wang L., Kojima N., Ohshita Y., Yamaguchi M.
Progress in Photovoltaics: Research and Applications 24 ( 10 ) 1310 - 1318 2016.10
Language：English Publishing type：Research paper (scientific journal) Publisher：Progress in Photovoltaics: Research and Applications
Copyright © 2016 John Wiley & Sons, Ltd. The paper presents a quantitative approach to the investigation and comparison of the material qualities of III–V on silicon (III–V/Si) solar cells by using external radiative efficiencies. We use this analysis to predict the limiting efficiencies and evaluate the criteria of material quality in order to achieve high-efficiency III–V/Si solar cells. This result yields several implications for the design of high-efficiency III–V/Si solar cells. Copyright © 2016 John Wiley & Sons, Ltd.
DOI： 10.1002/pip.2787
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Which is optimum tracker allocation, checkerboard or rectangular grid? Reviewed
Araki K., Lee K., Yamaguchi M.
AIP Conference Proceedings 1766 2016.9
Language：English Publishing type：Research paper (scientific journal) Publisher：AIP Conference Proceedings
© 2016, American Institute of Physics Inc. All rights reserved. The optimum allocations of multiple trackers for an infinite land will be either rectangular allocation parallel to N-S and E-W axis, or checkerboard allocation. We solved an optimization problem. Type of the optimum allocation pattern and its aspect ratio depend on latitude, climate pattern, aspect ratio of panels and space factor. Roughly speaking, the checkerboard allocation will be desired to higher latitude, sunshine in summer, higher space factor, and highly landscaped rectangular solar panels. A decision flow chart was proposed by the calculation result.
DOI： 10.1063/1.4962097