It is found that the degradation rate of the open-circuit voltage is remarkably larger than that of the short-circuit current in silicon solar cells damaged by 40keV protons. The reduc-tion in the minority carrier lifetime of the diffused layer of a cell thus damaged is estimated by fitting the curve of the observed change in spectral response to the calculated one. Bom-bardment with a total flux of 1.71×10
15 protons/cm
2 of 40keV protons reduced the n-type diffused region lifetime by a factor of 5 in a particular case. The spectral response change by #2000 Al
2O
3 lapping on the surface of the silicon solar cell extends to a longer wave length region than that by #4000 Al
2O
3 lapping in which the degradation of the spectral response is observed mainly in the region of wavelength shorter than 600mμ. This result is due to the decrease of the carrier lifetime in the diffused layer as shown by numerical analysis.
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