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Morioka, Chiharu*; Shimazaki, Kazunori*; Kawakita, Shiro*; Imaizumi, Mitsuru*; Yamaguchi, Hiroshi*; Takamoto, Tatsuya*; Sato, Shinichiro; Oshima, Takeshi; Nakamura, Yosuke*; Hirako, Keiichi*; et al.
Progress in Photovoltaics; Research and Applications, 19(7), p.825 - 833, 2011/11
Times Cited Count：24 Percentile：68.38(Energy & Fuels)Imaizumi, Mitsuru*; Morioka, Chiharu*; Sumita, Taishi*; Oshima, Takeshi; Okuda, Shuichi*
Proceedings of 37th IEEE Photovoltaic Specialists Conference (PVSC-37) (CD-ROM), p.1579 - 1582, 2011/06
InGaP single-junction and InGaP/GaAs/Ge triple-junction (3J) solar cells were irradiated with low energy electrons. The energy of electrons were selected around the threshold energy of Gallium and Indium recoiling in the InGaP system (300 keV). Simultaneous electron irradiation and current-voltage characteristics measurement of the cells revealed the fact that the short-circuit current (Isc) of InGaP cells and consequently the 3J cells does not degrade when the cells are irradiated with electrons with energies of less than 300 keV, while the open-circuit voltage (Voc) considerably degrades for both types of the cell, regardless of the electron energies. This result suggests that the effects of defects generated by the recoil of phosphorus are insufficient to decrease the minority-carrier lifetime in InGaP. In addition, the degradation of the Voc suggests an increase in surface recombination.
Elfiky, D.*; Yamaguchi, Masafumi*; Sasaki, Takuo*; Takamoto, Tatsuya*; Morioka, Chiharu*; Imaizumi, Mitsuru*; Oshima, Takeshi; Sato, Shinichiro; Elnawawy, M.*; Eldesoky, T.*; et al.
Japanese Journal of Applied Physics, 49(12), p.121201_1 - 121201_7, 2010/12
Times Cited Count：12 Percentile：45.82(Physics, Applied)One of the fundamental objectives for research and development of space solar cells is to improve their radiation resistance. InGaP solar cells with low base carrier concentrations under low-energy proton irradiations have shown high radiation resistances. In this study, an analytical model for low-energy proton radiation damage to InGaP subcells based on a fundamental approach for radiative and nonradiative recombinations has been proposed. The radiation resistance of InGaP subcells as a function of base carrier concentration has been analyzed by using the radiative recombination lifetime and damage coefficient K for the minority-carrier lifetime of InGaP. Numerical analysis shows that an InGaP solar cell with a lower base carrier concentration is more radiation-resistant. Satisfactory agreements between analytical and experimental results have been obtained, and these results show the validity of the analytical procedure. The damage coefficients for minority-carrier diffusion length and carrier removal rate with low-energy proton irradiations have been observed to be dependent on carrier concentration through this study. As physical mechanisms behind the difference observed between the radiation-resistant properties of various base doping concentrations, two mechanisms, namely, the effect of a depletion layer as a carrier collection layer and generation of the impurity-related complex defects due to low-energy protons stopping within the active region, have been proposed.
Elfiky, D.*; Yamaguchi, Masafumi*; Sasaki, Takuo*; Takamoto, Tatsuya*; Morioka, Chiharu*; Imaizumi, Mitsuru*; Oshima, Takeshi; Sato, Shinichiro; Elnawawy, M.*; Eldesoky, T.*; et al.
Japanese Journal of Applied Physics, 49(12), p.121202_1 - 121202_5, 2010/12
Times Cited Count：7 Percentile：31.03(Physics, Applied)GaAs solar cells with the lower base carrier concentration under low energy proton irradiations had shown experimentally the better radiation-resistance. Analytical model based on fundamental approach for radiative and non-radiative recombination has been proposed for radiation damage in GaAs sub-cells. The radiation resistance of GaAs sub-cells as a function of base carrier concentration has been analyzed by using radiative recombination lifetime and damage coefficient for minority carrier lifetime. Numerical analysis shows good agreement with experimental results. The effect of carrier concentration upon the change of damage constant and carrier removal rate have been studied.
Oshima, Takeshi; Sato, Shinichiro; Morioka, Chiharu*; Imaizumi, Mitsuru*; Sugaya, Takeyoshi*; Niki, Shigeru*
Proceedings of 35th IEEE Photovoltaic Specialists Conference (PVSC-35) (CD-ROM), p.002594 - 002598, 2010/06
Times Cited Count：3 Percentile：78.38(Energy & Fuels)Quantum Dot (QD) solar cells are regarded as promising candidate for solar cells with superior high efficiency. For space application, it is important to understand radiation effects in such QD solar cells. However, radiation response of QD solar cells has not yet been clarified. In this study, we irradiate QD solar cells with electrons, and investigate change in the electrical performance of the QD solar cells. PiN structure solar cells with self-organized InGaAs QD layers grown on GaAs (001) substrates by MBE were used in this study. The efficiency for the 30 QD layer solar cells without anti-reflector coating is 7.0% under AM 1.5 at 25 
C. The samples were irradiated with electrons at 1 MeV at room temperature. The current-voltage characteristics under AM0 and the quantum efficiency (QE) were measured before and after irradiations. Electron irradiation effects on single junction GaAs solar cells fabricated under the same process were also studied for comparison. The value of QE for both the GaAs solar cells with and without QD layers slightly decreases due to the irradiation at 1
10
/cm
, and no remarkable decrease in the increment of the QE in a long wavelength region due to the existence of QDs is observed.
Elfiky, D.*; Yamaguchi, Masafumi*; Sasaki, Takuo*; Takamoto, Tatsuya*; Morioka, Chiharu*; Imaizumi, Mitsuru*; Oshima, Takeshi; Sato, Shinichiro; Elnawawy, M.*; Eldesuky, T.*; et al.
Proceedings of 35th IEEE Photovoltaic Specialists Conference (PVSC-35) (CD-ROM), p.002528 - 002532, 2010/06
Times Cited Count：6 Percentile：87.7(Energy & Fuels)Proton energy dependence of radiation damage to GaAs/Ge solar cells irradiated with protons with various energies (50 keV, 200 keV, 1 MeV and 9.5 MeV) were analyzed by using PC1D simulation together with SRIM simulations to investigate their electrical properties. The degradation of the open-circuit voltage is highest for 50 keV irradiation and lowest for 9.5 MeV irradiation. According to SRIM simulations the above changes in electrical properties are mainly related to damage in different regions of the solar sells.
Sato, Shinichiro; Miyamoto, Haruki*; Imaizumi, Mitsuru*; Shimazaki, Kazunori*; Morioka, Chiharu*; Kawano, Katsuyasu*; Oshima, Takeshi
Solar Energy Materials and Solar Cells, 93(6-7), p.768 - 773, 2009/06
Times Cited Count：75 Percentile：90.65(Energy & Fuels)Degradation modeling of InGaP/GaAs/Ge triple-junction (3J) solar cells subjected to proton irradiation is performed with the use of a one-dimensional optical device simulator, PC1D. By fitting the external quantum efficiencies of 3J solar cells degraded by 30 keV, 150 keV, 3 MeV, or 10 MeV protons, the shortcircuit currents (
) and open-circuit voltages (
) are simulated. The damage coefficients of minority carrier diffusion length (
) and the carrier removal rate of base carrier concentration (
) of each subcell are also estimated. The values of and obtained from the calculations show good agreement with experimental values at an accuracy of 5%. These results confirm that the degradation modeling method developed in this study is effective for the lifetime prediction of 3J solar cells.
Morioka, Chiharu*; Imaizumi, Mitsuru*; Sato, Shinichiro; Oshima, Takeshi; Kibe, Koichi*
Proceedings of the 8th International Workshop on Radiation Effects on Semiconductor Devices for Space Applications (RASEDA-8), p.215 - 218, 2008/12
Radiation resistance of (Al)InGaP solar cells was examined in this study. The epitaxial structure, such as aluminum contents or carrier concentration (CC) in the base layer, is varied, whereas the base layer thickness is maintained at 1 
m. The cells are irradiated with 3 MeV protons up to the fluence of 110
/cm
. Remaining factors of short-circuit current and open-circuit voltage show no significant difference between Al
In
Ga
P and InGaP cells. The graded CC structure in the base layer is ineffective to improve radiation resistance in the case of (Al)InGaP cells with a thick base layer, which implies that radiation degradation is not primarily attributable to the decrease in minority-carrier diffusion length.
Sato, Shinichiro; Miyamoto, Haruki; Imaizumi, Mitsuru*; Shimazaki, Kazunori*; Morioka, Chiharu*; Kawano, Katsuyasu*; Oshima, Takeshi
Proceedings of 33rd IEEE Photovoltaic Specialists Conference (PVSC-33) (CD-ROM), 5 Pages, 2008/00
Degradation modeling of InGaP/GaAs/Ge triple-junction (3J) solar cells due to proton irradiation is performed with the use of a one-dimensional optical device simulator; PC1D, and the degradation level in each sub-cell is evaluated. By fitting external quantum efficiencies of the 3J solar cells degraded by proton irradiation, the short-circuit currents () and open-circuit voltages () are simulated. The validity of this model is confirmed by comparing the results of both and to the experimental data. The carrier removal rate of base layer () and the damage coefficient of minority carrier diffusion length () in each sub-cell are also estimated. In addition, NIEL (Non-Ionizing Energy Loss) analysis for both radiation degradation parameters and is discussed.
Sato, Shinichiro; Miyamoto, Haruki; Imaizumi, Mitsuru*; Shimazaki, Kazunori*; Morioka, Chiharu*; Kawano, Katsuyasu*; Oshima, Takeshi
Proceedings of 17th International Photovoltaic Science and Engineering Conference (PVSEC-17) (CD-ROM), p.502 - 503, 2007/12
Degradation modeling of InGaP/GaAs/Ge triple junction (3J) solar cells with the use of a one dimensional optical device simulator, PC1D, is performed for cell lifetime prediction. By fitting the quantum efficiencies of 3J solar cells degraded by 30 keV, 150 keV, 3 MeV, or 10 MeV proton irradiation, the short circuit currents (Isc) and open circuit voltages (Voc) are simulated. The damage coefficient of minority carrier diffusion length () and carrier removal rate () of base carrier concentration of each sub cell are also estimated. The values of Isc and Voc obtained using the calculations show good agreement with experimental values. These results confirm that the degradation modeling method is effective for lifetime prediction of 3J solar cells.
Miyamoto, Haruki; Sato, Shinichiro; Oshima, Takeshi; Morioka, Chiharu*; Imaizumi, Mitsuru*; Kawano, Katsuyasu*
Proceedings of 17th International Photovoltaic Science and Engineering Conference (PVSEC-17) (CD-ROM), p.961 - 962, 2007/12
InGaP and Si solar cells are irradiated with 10 MeV protons at fluences up to 
cm at room temperature (RT) and low temperature (LT). Results show that the remaining factor Voc irradiated at LT is higher than that at RT, and vice versa for Isc. The temperature coefficient of Voc after irradiation is greater than that before irradiation, although the coefficients of Isc are the same before and after irradiation. This degradation of the output performance of these solar cells can be interpreted in terms of a decrease in minority-carrier diffusion length.
Morioka, Chiharu*; Imaizumi, Mitsuru*; Sugimoto, Hiroki*; Sato, Shinichiro; Oshima, Takeshi; Tajima, Michio*
Proceedings of 17th International Photovoltaic Science and Engineering Conference (PVSEC-17) (CD-ROM), p.504 - 505, 2007/12
Radiation resistance of (Al)InGaP solar cells was examined in this study. The epitaxial structure, such as aluminum contents or carrier concentration (CC) in the base layer, is varied, whereas the base layer thickness is maintained at 1 m. The cells are irradiated with 3 MeV protons up to the fluence of 
cm. Remaining factors of short-circuit current and open-circuit voltage show no significant difference between AlInGaP and InGaP cells. The graded CC structure in the base layer is ineffective to improve radiation resistance in the case of (Al)InGaP cells with a thick base layer, which implies that radiation degradation is not primarily attributable to the decrease in minority-carrier diffusion length.
Shimazaki, Kazunori*; Imaizumi, Mitsuru*; Kawakita, Shiro*; Morioka, Chiharu*; Oshima, Takeshi; Ito, Hisayoshi; Kibe, Koichi*
JAEA-Review 2006-042, JAEA Takasaki Annual Report 2005, P. 5, 2007/02
no abstracts in English
Oshima, Takeshi; Miyamoto, Haruki; Imaizumi, Mitsuru*; Morioka, Chiharu*; Kawakita, Shiro*; Shimazaki, Kazunori*; Kibe, Koichi*; Kawano, Katsuyasu*; Ito, Hisayoshi
JAEA-Review 2006-042, JAEA Takasaki Annual Report 2005, P. 6, 2007/02
no abstracts in English
Sato, Shinichiro; Miyamoto, Haruki; Oshima, Takeshi; Imaizumi, Mitsuru*; Morioka, Chiharu*; Kawano, Katsuyasu*; Ito, Hisayoshi
Proceedings of 7th International Workshop on Radiation Effects on Semiconductor Devices for Space Application (RASEDA-7), p.161 - 164, 2006/10
The performance recovery of III-V solar cells irradiated with protons by current injection was investigated. InGaP/GaAs/Ge triple-junction (3J) solar cells were irradiated with 50keV protons at 110
or 10MeV protons at 110
ions/cm at room temperature. Then, the recoveries of the electric (current-voltage: 
-
) characteristics of these samples were investigated by forward current (minority carrier) injection. As a result, the open circuit voltage (
) of these 3J solar cells was recovered although no significant change in their short circuit current (
) was observed due to current injection. In addition, the samples irradiated with 50keV protons were recovered compared to the ones irradiated with 10MeV protons.
Miyamoto, Haruki; Sato, Shinichiro; Oshima, Takeshi; Imaizumi, Mitsuru*; Morioka, Chiharu*; Ito, Hisayoshi; Kawano, Katsuyasu*
Proceedings of 7th International Workshop on Radiation Effects on Semiconductor Devices for Space Application (RASEDA-7), p.189 - 191, 2006/10
InGaP/GaAs/Ge triple-junction (3J) and Si single junction solar cells designed for space application were irradiated with 1.0 MeV- and 0.8 MeV-electrons at 110
510/cm in the atmosphere. The distance between the irradiation window and samples was changed from 20 to 50 cm. The accelerated electron energy changed from 1.0 to 0.93 MeV at the surface of samples with 20 cm below the irradiation window. This energy change caused by the energy attenuation of the Ti irradiation window and atmosphere. The electrical properties of solar cells were measured and compared before irradiation to after irradiation. No significant difference in the degradation of 3J solar cells due to electron irradiation was observed in energies range between 0.93 and 0.71 MeV. For Si solar cells, the value of degradation is the same in energies range between 0.93 and 0.87 MeV, however, the decrease in degradation was observed below 0.73 MeV.
Morioka, Chiharu*; Imaizumi, Mitsuru*; Oshima, Takeshi; Ito, Hisayoshi; Kibe, Koichi*
Proceedings of 7th International Workshop on Radiation Effects on Semiconductor Devices for Space Application (RASEDA-7), p.169 - 172, 2006/10
no abstracts in English
Oshima, Takeshi; Miyamoto, Haruki; Imaizumi, Mitsuru*; Morioka, Chiharu*; Kawakita, Shiro*; Shimazaki, Kazunori*; Kibe, Koichi*; Kawano, Katsuyasu*; Ito, Hisayoshi
Proceedings of 2006 IEEE 4th World Conference on Photovoltaic Energy Conversion (WCPEC-4) (CD-ROM), p.1818 - 1821, 2006/05
no abstracts in English
Morioka, Chiharu*; Imaizumi, Mitsuru*; Oshima, Takeshi; Ito, Hisayoshi; Kibe, Koichi*
Proceedings of 2006 IEEE 4th World Conference on Photovoltaic Energy Conversion (WCPEC-4) (CD-ROM), p.1846 - 1849, 2006/05
no abstracts in English
Miyamoto, Haruki; Oshima, Takeshi; Ito, Hisayoshi; Imaizumi, Mitsuru*; Morioka, Chiharu*; Kawakita, Shiro*; Shimazaki, Kazunori*; Kibe, Koichi*; Kawano, Katsuyasu*
no journal, ,
no abstracts in English
