@inproceedings{oai:jaxa.repo.nii.ac.jp:00007993,
 author = {豊田, 裕之 and 小林, 大輔 and 田島, 道夫 and Toyota, Hiroyuki and Kobayashi, Daisuke and Tajima, Michio},
 book = {宇宙エネルギーシンポジウム, Space Energy Symposium},
 month = {Jun},
 note = {第28回宇宙エネルギーシンポジウム(2009年3月9日, 宇宙航空研究開発機構宇宙科学研究本部相模原キャンパス), The twenty-eight Space Energy Symposium (March 9, 2009. Institute of Space and Astronautical Science, Japan Aerospace Exploration Agency, Sagamihara), Electroluminescence (EL) imaging diagnosis of space silicon solar cells and its simulation analysis is demonstrated. Diagnosis technique using luminescence from semiconductor devices is a powerful tool to evaluate impurities and defects. When sunlight impinges on a solar cell, it induces excess carriers (free electrons and holes). They diffuse in the crystal and result in generation of electricity when they reach to the electrodes. At the same time, a portion of the careers recombine radiatively, which is called band-edge emission. The intensity of band-edge emission reflects the crystalline quality, since it is proportional to the lifetime of minority carriers. When we perform EL imaging, we pass current to a solar cell in the forward direction to inject carriers and observe band-edge emission using a cooled CCD camera with a band-pass filter. Since various kinds of defects appear in EL images, it is occasionally difficult to identify what the patters in the images reflects especially in case of multi-junction solar cells. For deeper understanding of EL images, we analyzed them by computer simulation. In this paper, analysis of a space silicon solar cell damaged after an electrostatic discharge (ESD) test is presented. After an ESD test in a plasma environment, current and voltage (IV) characteristics of one of the cells indicated decreased shunt resistance. In an EL image of the cell, a tapered dark area expanding from the edge was found. In order to investigate the relation between the decreased shunt resistance and the tapered dark area in the EL image, we obtained IV characteristics and EL images of a solar cell with a variable resistor which connects the end of a grid electrode and the back electrode to simulate the reduced shunt resistance. IV characteristics of the cell showed decreased shunt resistance, and a tapered dark area expanding from the point that the resistor was connected appeared in the EL image in the same manner as the damaged cell. Though it has been confirmed that the dark area in the EL image is associated with the reduced shunt resistance, it is still not clear what causes the dark area expand along the grid electrode and determines its tapered shape. In order to clarify the reason, we performed computer simulation using a device simulator "Sentaurus Device" from Synopsys, Inc. We made a three dimensional model of the silicon solar cell based on its actual material parameter such as the doping profile. A mixed mode simulation was done using the solar cell model and an ideal circuit model of a variable resistor and power sources. We performed two kinds of simulations: measurement of IV characteristics and EL imaging diagnosis. For the simulation of IV measurement, a variable resistor to simulate the reduced shunt resistance and a voltage source to sweep the voltage between the electrodes were connected to the cell model. Monochromatic light which had a wavelength of 1 micro m and an irradiance of 1 kW/m2 was used to simulate the sunlight. Decreased shunt resistance was indicated in the obtained IV characteristics in the same manner as the measurement described above. For the simulation of EL imaging diagnosis, a variable resistor to simulate the reduced shunt resistance and a current source were connected to the cell model. We calculated the distribution of radiative recombinations as the parameter that corresponded to the intensity of the EL. A low-radiative recombination area appeared in a tapered shape in the same manner as the measurement described above. It was found to be determined by the distribution of the electrostatic potential on the cell surface. The distribution of the electrostatic potential was determined by the geometric arrangement of the finger electrodes. Therefore, the geometric arrangement of the finger electrodes was found to be the cause of the tapered dark area in the EL image., 資料番号: AA0064295002},
 publisher = {宇宙航空研究開発機構宇宙科学研究本部, Institute of Space and Astronautical Science, Japan Aerospace Exploration Agency (JAXA)},
 title = {太陽電池セルELイメージングのシミュレーション分析},
 volume = {28},
 year = {2009}
}