An analysis of the spectral response of a solar cell is given which includes the effect of the electric field present in the diffused surface region. Results are presented which show the variation of response with junction depth and with carrier lifetime in both surface and bulk regions. By curve fitting, it is found that in a typical silicon cell the bulk lifetime is in the range 1–15 &mgr;sec, while the surface region lifetime is between 10−9and 10−10sec. Bombardment with a total flux of 3.3×1014electrons/cm2of 2‐Mev electrons reduced thenregion lifetime by a factor of 300, and thepregion lifetime by a factor of 6 in a particular case.