Space Environments and Effects on CIGS Solar Cells and Modules
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Space Environments and Effects on CIGS Solar Cells and Modules Shirou Kawakita1, Mitsuru Imaizumi1 and Hiroaki Kusawake1 1
Japan Aerospace Exploration Agency (JAXA), Tsukuba, Ibaraki, 305-8505 Japan
ABSTRACT Cu (In, Ga) Se2 (CIGS) thin-film solar cells are optimal solar cells for spacecraft, since they have high efficiency, lightweight, flexible and high radiation tolerance. The CIGS solar module without a coverglass to prevent degradation in space has been demonstrated with a small satellite and its electrical performance indicates no degradation as predicted from ground tests. However, the cells need to prevent the damages from other effects in space. The paper introduces some space environment tests and how to improve performance in CIGS cells for spacecraft. INTRODUCTION Spacecraft have to be more compact, lightweight and economical and these requirements also apply to thin-film solar cells for solar paddles. In particular, flexible solar cells are needed for new type of satellites, for example, a space solar sail [1]. CIGS thin-film solar cells are suitable for such satellites. CIGS solar cells have great potential as future thin-film space solar cells, given the high conversion efficiencies exceeding 20% [2] they have shown. In addition, excellent radiation tolerance of CIGS thin-film cells has also been reported [3]. The cells have the potential to be low-cost, lightweight and flexible since they can be formed on polyimide or metal sheet substrates [4,5,6]. Accordingly, we have been studying the potential of using CIGS solar cells as flexible solar paddles in future. Radiation damage studies for CIGS thin-film solar cells reported that the electrical property of the cells does not degrade when exposed to high-energy electrons [3]. In this paper, we introduce the effects of the space environment and improvements of tolerance of CIGS solar cells against the environment. SPACE ENVIRONMENT and EFFECTS “Space Environment” means energetic particle radiation, plasma, atmosphere, microparticles, ultraviolet rays and extreme thermal cycles [7]. Figure 1 shows the space environment and its effects on spacecraft. Since all of them may cause severe damage on spacecraft, electrical devices, especially those on the surface of the spacecraft, must maintain their performance for an extended period in space. High-energy electrons and protons are the main factors causing space solar cells to degrade. In addition, charging and discharging interacted with space plasma can trigger severe damage on thin-film solar cells, including CIGS solar cells, due to the thin-film solar cell structure.
© JAXA
Figure. 1 Space environment and effects on spacecraft.
RADIATION EFFECTS on CIGS CIGS solar cells have excellent radiation tolerance to electrons. Conversely, cell performance is impaired with exposure to proton irradiation, similar to other solar cell types. Cells having radiation damage caused by proton irradiation gradually recover when the irradiated cells are kept even at room temperature and the recovery rate is temperature-d
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