Mitsuru Imaizumi - Academia.edu (original) (raw)
Papers by Mitsuru Imaizumi
DENKI-SEIKO[ELECTRIC FURNACE STEEL], 1986
GaAs crystals were grown on Si substrates •k(100) 2•‹off•l by metalorganic chemical
Scientific reports, Jan 16, 2017
Tandem solar cells are suited for space applications due to their high performance, but also have... more Tandem solar cells are suited for space applications due to their high performance, but also have to be designed in such a way to minimize influence of degradation by the high energy particle flux in space. The analysis of the subcell performance is crucial to understand the device physics and achieve optimized designs of tandem solar cells. Here, the radiation-induced damage of inverted grown InGaP/GaAs/InGaAs triple-junction solar cells for various electron fluences are characterized using conventional current-voltage (I-V) measurements and time-resolved photoluminescence (PL). The conversion efficiencies of the entire device before and after damage are measured with I-V curves and compared with the efficiencies predicted from the time-resolved method. Using the time-resolved data the change in the carrier dynamics in the subcells can be discussed. Our optical method allows to predict the absolute electrical conversion efficiency of the device with an accuracy of better than 5%. W...
Scientific Reports, 2016
In-situ characterization is one of the most powerful techniques to improve material quality and d... more In-situ characterization is one of the most powerful techniques to improve material quality and device performance. Especially in view of highly efficient tandem solar cells this is an important issue for improving the cost-performance ratio. Optical techniques are suitable characterization methods, since they are non-destructing and contactless. In this work, we measured the power dependence of photoluminescence (PL) from the InGaP and GaAs subcells of an industry-standard triple-junction solar cell. High luminescence yields enhance the luminescence coupling, which was directly verified by time-resolved PL measurements. We present a new method to determine the internal luminescence efficiencies of InGaP and GaAs subcells with the aid of luminescence coupling. High luminescence efficiencies of 90% for GaAs and more than 20% for InGaP were found, which suggest that the material quality of the grown GaAs layer is excellent while the intrinsic luminescence limit of InGaP is still not reached even for high excitation conditions. The PL method is useful for probing the intrinsic material properties of the subcells in flat band condition, without influence of transport. Since no calibration of absolute PL is required, a fast screening of the material quality is possible, which should be extremely helpful for the solar cell industry.
2015 IEEE 42nd Photovoltaic Specialist Conference (PVSC), 2015
2006 IEEE 4th World Conference on Photovoltaic Energy Conference, 2006
A paper-thin, lightweight InGaP/GaAs solar cell with high efficiency and flexibility has been dev... more A paper-thin, lightweight InGaP/GaAs solar cell with high efficiency and flexibility has been developed. A high-efficiency thin-film cell can be obtained for cell fabrication both before and after removing the substrate. Introducing a tunnel junction as the contact layer between the cell and metal film improves cell characteristics (Fill Factor (FF) and open-circuit voltage (Voc)). A highly doped n-type layer
2015 IEEE 42nd Photovoltaic Specialist Conference (PVSC), 2015
3Rd World Conference Onphotovoltaic Energy Conversion 2003 Proceedings of, May 18, 2003
... Akihiko Oh? and Tomihiro Kamiya4 1, National Space Development Agency of JapanWASDA), 2-1-1 S... more ... Akihiko Oh? and Tomihiro Kamiya4 1, National Space Development Agency of JapanWASDA), 2-1-1 Sengen, Tsukuba, lbaraki 305-8505, Japan, 2. SHARP Corporation, 282-1 Hajikami, Shinjo, Nara 639-2198, Japan. 3. Toyota ...
Clinical Nutrition Supplements, 2003
In this study, the mechanism for the unique minority-carrier injection-enhanced annealing phenome... more In this study, the mechanism for the unique minority-carrier injection-enhanced annealing phenomena and the origin of the major radiation-induced defect in InGaP top cell materials are discussed in comparison with InP. The optimal design for the InGaP base layer thickness of the InGaP/GaAs 2-junction cells for current matching at EOL is examined. It is also found that the radiation tolerance of InGaP/middle cell/Ge 3-junction tandem solar cells can be improved by thinning the InGaP top cell layer thickness, by reducing base layer carrier concentration of the GaAs bottom cells, and by looking for radiation-resistant middle cell materials.
3Rd World Conference Onphotovoltaic Energy Conversion 2003 Proceedings of, May 18, 2003
In this study, the mechanism for the unique minority-carrier injection-enhanced annealing phenome... more In this study, the mechanism for the unique minority-carrier injection-enhanced annealing phenomena and the origin of the major radiation-induced defect in InGaP top cell materials are discussed in comparison with InP. The optimal design for the InGaP base layer thickness of the InGaP/GaAs 2-junction cells for current matching at EOL is examined. It is also found that the radiation tolerance of InGaP/middle cell/Ge 3-junction tandem solar cells can be improved by thinning the InGaP top cell layer thickness, by reducing base layer carrier concentration of the GaAs bottom cells, and by looking for radiation-resistant middle cell materials.
2008 33rd IEEE Photovolatic Specialists Conference, 2008
ABSTRACT Recently, InGaP/GaAs/Ge 3-junction solar cells are widely used for space because of thei... more ABSTRACT Recently, InGaP/GaAs/Ge 3-junction solar cells are widely used for space because of their higher conversion efficiency and better radiation-resistance compared to GaAs and Si solar cells. In this study, effects of base carrier concentration in GaAs and InGaP sub-cells upon their radiation resistance are analyzed by using radiative recombination lifetime and damage constant K for minority-carrier lifetime of GaAs and InGaP. In addition, analytical results are also compared with the experimental results of InGaP solar cells irradiated with 1-MeV electrons, 30-keV and 200-keV protons. In low irradiation fluence, n-on-p structure cells are found to be more radiation resistant than p-on-n structure cells. Better radiation-resistance of sub-cells can be realized by optimal design based on fundamental approach for radiative and non-radiative recombination properties of InGaP and radiation-resistance of InGaP/GaAs/Ge 3-junction cells will also be improved by optimal design of sub cells.
27Th European Photovoltaic Solar Energy Conference and Exhibition, Oct 26, 2012
3Rd World Conference Onphotovoltaic Energy Conversion 2003 Proceedings of, May 18, 2003
Mission Demonstration-test Satellite No. 1 (MDS-1), launched in February 2002, successfully obser... more Mission Demonstration-test Satellite No. 1 (MDS-1), launched in February 2002, successfully observed the radiation tolerance of six kinds of solar cells developed for terrestrial use for a year in the very severe radiation environment of a geostationary transfer orbit. CIGS cells demonstrated super radiation tolerance, InGaP/GaAs tandem cells, sufficient tolerance, and poly-crystalline silicon cells reasonable tolerance. The flight degradation trend
3Rd World Conference Onphotovoltaic Energy Conversion 2003 Proceedings of, May 18, 2003
Thin Solid Films, 2008
In this study, optical coatings were investigated as substitutes for the coverglass on flexible t... more In this study, optical coatings were investigated as substitutes for the coverglass on flexible thin-film space solar cells. The inherent low emissivity of copper-indium-gallium-diselenide (CIGS) thin-film solar cells was increased using optical coatings for thermal balance in space. Evaporated silicon dioxide (SiO 2 ) and an additional aluminum oxide (Al 2 O 3 ) coating on the CIGS solar cell increased the emissivity from 0.18 to 0.77. Higher emissivity was realized with the Al 2 O 3 /SiO 2 double-layer coating than with the SiO 2 single-layer coating. The straightforward double-layer coating gives the CIGS solar cells appropriate radiative properties for keeping the cell within a permissible temperature range in space.
2016 IEEE 43rd Photovoltaic Specialists Conference (PVSC), 2016
Abstract Radiation resistance of six types of solar cells developed for terrestrial use has been ... more Abstract Radiation resistance of six types of solar cells developed for terrestrial use has been demonstrated in space by the MDS-1 Tsubasa satellite which flew in a geostationary transfer orbit where the radiation environment is severe. Open-circuit voltage and short-...
2010 35th IEEE Photovoltaic Specialists Conference, 2010
... Exploration Agency, 2-1-1 Sengen, Tsukuba, Ibaraki 305-8505, Japan 2: SHARP Corporation, 492 ... more ... Exploration Agency, 2-1-1 Sengen, Tsukuba, Ibaraki 305-8505, Japan 2: SHARP Corporation, 492 Minosho-cho, Yamatokoriyama, Nara 639-1186 ... from SSS-1 to SSS-2 will be cell efficiency, achieved by adopting an inverted metamorphic triple junction (IMM-3J) structure cell. ...
DENKI-SEIKO[ELECTRIC FURNACE STEEL], 1986
GaAs crystals were grown on Si substrates •k(100) 2•‹off•l by metalorganic chemical
Scientific reports, Jan 16, 2017
Tandem solar cells are suited for space applications due to their high performance, but also have... more Tandem solar cells are suited for space applications due to their high performance, but also have to be designed in such a way to minimize influence of degradation by the high energy particle flux in space. The analysis of the subcell performance is crucial to understand the device physics and achieve optimized designs of tandem solar cells. Here, the radiation-induced damage of inverted grown InGaP/GaAs/InGaAs triple-junction solar cells for various electron fluences are characterized using conventional current-voltage (I-V) measurements and time-resolved photoluminescence (PL). The conversion efficiencies of the entire device before and after damage are measured with I-V curves and compared with the efficiencies predicted from the time-resolved method. Using the time-resolved data the change in the carrier dynamics in the subcells can be discussed. Our optical method allows to predict the absolute electrical conversion efficiency of the device with an accuracy of better than 5%. W...
Scientific Reports, 2016
In-situ characterization is one of the most powerful techniques to improve material quality and d... more In-situ characterization is one of the most powerful techniques to improve material quality and device performance. Especially in view of highly efficient tandem solar cells this is an important issue for improving the cost-performance ratio. Optical techniques are suitable characterization methods, since they are non-destructing and contactless. In this work, we measured the power dependence of photoluminescence (PL) from the InGaP and GaAs subcells of an industry-standard triple-junction solar cell. High luminescence yields enhance the luminescence coupling, which was directly verified by time-resolved PL measurements. We present a new method to determine the internal luminescence efficiencies of InGaP and GaAs subcells with the aid of luminescence coupling. High luminescence efficiencies of 90% for GaAs and more than 20% for InGaP were found, which suggest that the material quality of the grown GaAs layer is excellent while the intrinsic luminescence limit of InGaP is still not reached even for high excitation conditions. The PL method is useful for probing the intrinsic material properties of the subcells in flat band condition, without influence of transport. Since no calibration of absolute PL is required, a fast screening of the material quality is possible, which should be extremely helpful for the solar cell industry.
2015 IEEE 42nd Photovoltaic Specialist Conference (PVSC), 2015
2006 IEEE 4th World Conference on Photovoltaic Energy Conference, 2006
A paper-thin, lightweight InGaP/GaAs solar cell with high efficiency and flexibility has been dev... more A paper-thin, lightweight InGaP/GaAs solar cell with high efficiency and flexibility has been developed. A high-efficiency thin-film cell can be obtained for cell fabrication both before and after removing the substrate. Introducing a tunnel junction as the contact layer between the cell and metal film improves cell characteristics (Fill Factor (FF) and open-circuit voltage (Voc)). A highly doped n-type layer
2015 IEEE 42nd Photovoltaic Specialist Conference (PVSC), 2015
3Rd World Conference Onphotovoltaic Energy Conversion 2003 Proceedings of, May 18, 2003
... Akihiko Oh? and Tomihiro Kamiya4 1, National Space Development Agency of JapanWASDA), 2-1-1 S... more ... Akihiko Oh? and Tomihiro Kamiya4 1, National Space Development Agency of JapanWASDA), 2-1-1 Sengen, Tsukuba, lbaraki 305-8505, Japan, 2. SHARP Corporation, 282-1 Hajikami, Shinjo, Nara 639-2198, Japan. 3. Toyota ...
Clinical Nutrition Supplements, 2003
In this study, the mechanism for the unique minority-carrier injection-enhanced annealing phenome... more In this study, the mechanism for the unique minority-carrier injection-enhanced annealing phenomena and the origin of the major radiation-induced defect in InGaP top cell materials are discussed in comparison with InP. The optimal design for the InGaP base layer thickness of the InGaP/GaAs 2-junction cells for current matching at EOL is examined. It is also found that the radiation tolerance of InGaP/middle cell/Ge 3-junction tandem solar cells can be improved by thinning the InGaP top cell layer thickness, by reducing base layer carrier concentration of the GaAs bottom cells, and by looking for radiation-resistant middle cell materials.
3Rd World Conference Onphotovoltaic Energy Conversion 2003 Proceedings of, May 18, 2003
In this study, the mechanism for the unique minority-carrier injection-enhanced annealing phenome... more In this study, the mechanism for the unique minority-carrier injection-enhanced annealing phenomena and the origin of the major radiation-induced defect in InGaP top cell materials are discussed in comparison with InP. The optimal design for the InGaP base layer thickness of the InGaP/GaAs 2-junction cells for current matching at EOL is examined. It is also found that the radiation tolerance of InGaP/middle cell/Ge 3-junction tandem solar cells can be improved by thinning the InGaP top cell layer thickness, by reducing base layer carrier concentration of the GaAs bottom cells, and by looking for radiation-resistant middle cell materials.
2008 33rd IEEE Photovolatic Specialists Conference, 2008
ABSTRACT Recently, InGaP/GaAs/Ge 3-junction solar cells are widely used for space because of thei... more ABSTRACT Recently, InGaP/GaAs/Ge 3-junction solar cells are widely used for space because of their higher conversion efficiency and better radiation-resistance compared to GaAs and Si solar cells. In this study, effects of base carrier concentration in GaAs and InGaP sub-cells upon their radiation resistance are analyzed by using radiative recombination lifetime and damage constant K for minority-carrier lifetime of GaAs and InGaP. In addition, analytical results are also compared with the experimental results of InGaP solar cells irradiated with 1-MeV electrons, 30-keV and 200-keV protons. In low irradiation fluence, n-on-p structure cells are found to be more radiation resistant than p-on-n structure cells. Better radiation-resistance of sub-cells can be realized by optimal design based on fundamental approach for radiative and non-radiative recombination properties of InGaP and radiation-resistance of InGaP/GaAs/Ge 3-junction cells will also be improved by optimal design of sub cells.
27Th European Photovoltaic Solar Energy Conference and Exhibition, Oct 26, 2012
3Rd World Conference Onphotovoltaic Energy Conversion 2003 Proceedings of, May 18, 2003
Mission Demonstration-test Satellite No. 1 (MDS-1), launched in February 2002, successfully obser... more Mission Demonstration-test Satellite No. 1 (MDS-1), launched in February 2002, successfully observed the radiation tolerance of six kinds of solar cells developed for terrestrial use for a year in the very severe radiation environment of a geostationary transfer orbit. CIGS cells demonstrated super radiation tolerance, InGaP/GaAs tandem cells, sufficient tolerance, and poly-crystalline silicon cells reasonable tolerance. The flight degradation trend
3Rd World Conference Onphotovoltaic Energy Conversion 2003 Proceedings of, May 18, 2003
Thin Solid Films, 2008
In this study, optical coatings were investigated as substitutes for the coverglass on flexible t... more In this study, optical coatings were investigated as substitutes for the coverglass on flexible thin-film space solar cells. The inherent low emissivity of copper-indium-gallium-diselenide (CIGS) thin-film solar cells was increased using optical coatings for thermal balance in space. Evaporated silicon dioxide (SiO 2 ) and an additional aluminum oxide (Al 2 O 3 ) coating on the CIGS solar cell increased the emissivity from 0.18 to 0.77. Higher emissivity was realized with the Al 2 O 3 /SiO 2 double-layer coating than with the SiO 2 single-layer coating. The straightforward double-layer coating gives the CIGS solar cells appropriate radiative properties for keeping the cell within a permissible temperature range in space.
2016 IEEE 43rd Photovoltaic Specialists Conference (PVSC), 2016
Abstract Radiation resistance of six types of solar cells developed for terrestrial use has been ... more Abstract Radiation resistance of six types of solar cells developed for terrestrial use has been demonstrated in space by the MDS-1 Tsubasa satellite which flew in a geostationary transfer orbit where the radiation environment is severe. Open-circuit voltage and short-...
2010 35th IEEE Photovoltaic Specialists Conference, 2010
... Exploration Agency, 2-1-1 Sengen, Tsukuba, Ibaraki 305-8505, Japan 2: SHARP Corporation, 492 ... more ... Exploration Agency, 2-1-1 Sengen, Tsukuba, Ibaraki 305-8505, Japan 2: SHARP Corporation, 492 Minosho-cho, Yamatokoriyama, Nara 639-1186 ... from SSS-1 to SSS-2 will be cell efficiency, achieved by adopting an inverted metamorphic triple junction (IMM-3J) structure cell. ...