JAXA Repository / AIREX 未来へ続く、宙(そら)への英知

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Other TitleEvaluation of space triple junction solar cells by EL and PL imaging
Author(jpn)豊田 裕之; 田島 道夫; 今泉 充; 野崎 幸重
Author(eng)Toyota, Hiroyuki; Tajima, Michio; Imaizumi, Mitsuru; Nozaki, Yukishige
Author Affiliation(jpn)宇宙航空研究開発機構 宇宙科学研究本部; 宇宙航空研究開発機構 宇宙科学研究本部; 宇宙航空研究開発機構 総合技術研究本部; NEC東芝スペースシステム
Author Affiliation(eng)Japan Aerospace Exploration Agency (JAXA) Institute of Space and Astronautical Science; Japan Aerospace Exploration Agency (JAXA) Institute of Space and Astronautical Science; Japan Aerospace Exploration Agency (JAXA) Institute of Aerospace Technology; NEC TOSHIBA Space Systems Ltd.
Issue Date2008-05
PublisherInstitute of Space and Astronautical Science, Japan Aerospace Exploration Agency (JAXA/ISAS)
Publication title第27回宇宙エネルギーシンポジウム 平成19年度
The Twenty-seventh Space Energy Symposium
Start page39
End page43
Publication date2008-05
AbstractDiagnosis of space triple junction solar cells using ElectroLuminescence (EL) and PhotoLuminescence (PL) imaging techniques are demonstrated. Solar cells, which are essential satellites components, can be damaged easily because of their thin structure. Damaged cells are difficult to diagnose because the generating process is not visible. Evaluation of solar cells mostly depends on current and voltage (IV) characteristics. However, IV characteristics give little information other than the cells are damaged or not. A Triple Junction (TJ) solar cell, which has a complex structure consisting of three thin solar cells (subcells) stacking up with a thickness of 150 mu m, is even more difficult to evaluate. We have developed a diagnostic imaging technique employing EL and PL for analyzing semiconductor devices including solar cells. EL is light emission from solar cells under the forward bias condition as LEDs (Light Emitting Diodes). A TJ cell can be regarded as three diodes connected in series. PL is light emission from solar cells illuminated. When a solar cell is illuminated by light with energy larger than the bandgap, excess careers are generated. If the careers recombine radiatively, PL emission can be observed. When we perform EL and PL imaging, we use a cooled CCD (Charge Coupled Device) camera to detect the light emission and band-pass filters to select the appropriate wavelength from the respective subcell. This technique allows us to diagnose each subcell noncontact and nondestructively. TJ cells damaged after thermal cycling test and ElectroStatic Discharge (ESD) test were examined using EL and PL imaging technique as well as IV characteristics measurement. The thermal cycling test was performed in the range of -180 C to +180 C for 558 cycles. IV characteristics of a TJ cell after the test suggested only the existence of a current leakage but the location or the condition of the leakage point. In the EL and PL images of the cell, dark areas appeared and we could locate where the current leakage point was. In the EL images, dark areas tend to a form long and narrow shape affected by the grid electrodes, because the excess careers are injected through them. In the PL images, dark areas tend to form circular shape, because the excess careers are generated by the uniform light emission over the cell. A microscope photograph of the current leakage point, which was located by the EL and PL images, revealed micro cracks of about 10 micrometer. They seemed to be the cause of the current leakage. The ESD test was performed in a simulated LEO (Low Earth Orbit) plasma environment. Many flashovers were observed when the voltage between the strings equaled to 320 V and some cells were damaged severely. IV characteristics of one of the damaged cells suggested the existence of a current leakage again. So many discharge craters were left around the cells that which crater caused the current leakage was hard to tell. In the EL image of the cell, two neighboring current leakage points were located at a corner. In the PL image, an dark area was observed at the respective corner, but it was too large to distinguish the two points. A microscopic photograph showed two discharge craters where a portion of the cell was blown off. In both cases, IV characteristics suggests the cell is damaged but not showed which part of the cell was deteriorated. EL and PL images clearly located it.
Keywordssolar cell panel; triple-junction solar cell; spacecraft power supply; diagnosis; imaging technique; electroluminescence; photoluminescence; electrostatic discharge; thermal cycling test; evaluation; 太陽電池パネル; 3接合太陽電池; 宇宙機給電; 診断; 撮像技術; エレクトロルミネッセンス; フォトルミネッセンス; 静電気放電; 熱サイクル試験; 評価
Document TypeConference Paper
JAXA Categoryシンポジウム・研究会

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