Hardening of Solar Cells against Low-Energy Rear-Incident Protons

The damage mechanisms resulting from normally incident low-energy proton irradiation on the back side of standard n/p silicon solar cells have been investigated, and an evaluation was performed of cells modified to better withstand back irradiation. The damage effects produced by the low-energy rear-incident protons resulted in the formation of an additional junction at the back contact and an increase in effective series resistance, indicating the removal of majority carriers at the damaged region. The proton irradiation caused an injection level dependence of the spectral response; the spectral response degradation at high injection levels was greater than at low injection levels. The results of the evaluation of the modified cells indicate that the n/p solar cells with a p+-doped-back surface are less sensitive to normally rear-incident low-energy proton irradiation. Sensitivity to this type radiation also decreases with increasing cell thickness.