**4. Summary**

**4. Summary** 

**4. Summary** 

This study investigated the effects of two typical beam conditions in a space solar cell radiation test, the fluence rate, and beam-area expansion techniques (scanning and defocusing) on radiation degradation. Both high-efficiency silicon and InGaP/GaAs/Ge triplejunction solar cells were employed in this study. The 10 MeV protons and 1 MeV electrons were applied with different fluence rates. In addition, low-energy (50–150 keV) protons were irradiated to the triple-junction solar cell to understand the effects of localized damage on its stacked structure. All the results confirmed that the fluence rate did not affect This study investigated the effects of two typical beam conditions in a space solar cell radiation test, the fluence rate, and beam-area expansion techniques (scanning and defocusing) on radiation degradation. Both high-efficiency silicon and InGaP/GaAs/Ge triplejunction solar cells were employed in this study. The 10 MeV protons and 1 MeV electrons were applied with different fluence rates. In addition, low-energy (50–150 keV) protons were irradiated to the triple-junction solar cell to understand the effects of localized dam-This study investigated the effects of two typical beam conditions in a space solar cell radiation test, the fluence rate, and beam-area expansion techniques (scanning and defocusing) on radiation degradation. Both high-efficiency silicon and InGaP/GaAs/Ge triple-junction solar cells were employed in this study. The 10 MeV protons and 1 MeV electrons were applied with different fluence rates. In addition, low-energy (50–150 keV) protons were irradiated to the triple-junction solar cell to understand the effects of localized

damage on its stacked structure. All the results confirmed that the fluence rate did not affect the degradation of output performance of the two kinds of solar cell. However, cell temperature during the irradiation influenced the degradation of the silicon solar cell, a greater degradation arising from higher temperatures. Thus, sample temperature is an essential factor to be controlled in irradiation tests. High- (10 MeV) and low-energy (50 and 100 keV) protons were used with the two beam-area expansion techniques. The two sets of results proved that the radiation degradation is same regardless of the beam-area expansion technique. The obtained information will be reflected in the international standard on radiation test methods for space solar cells.

**Author Contributions:** Conceptualization, M.I., T.O. and Y.I.; methodology, M.I., Y.Y., K.S. and Y.I.; validation, M.I. and K.S.; formal analysis, M.I.; investigation, M.I. and T.O.; resources, M.I.; data curation, M.I.; writing—original draft preparation, M.I.; writing—review and editing, T.O., Y.Y. and K.S.; visualization, M.I. and Y.Y.; supervision, T.O. and K.S.; project administration, M.I.; funding acquisition, M.I. All authors have read and agreed to the published version of the manuscript.

**Funding:** This research received no external funding.

**Acknowledgments:** We would like to express our sincere appreciation to M. Saito of the Advanced Engineering Services Co., Ltd. for his tremendous contribution to the irradiation experiments. We would also like to thank the members of the space photovoltaics community for many fruitful discussions.

**Conflicts of Interest:** The authors declare no conflict of interest.
