Electroluminescence efficiency degradation of crystalline silicon solar cells after irradiation with protons in the energy range between 0.8 MeV and 65 MeV

Standard crystalline silicon homojunction solar cells have been irradiated with high energy protons at variable energies between 0.8 MeV and 65 MeV. As one possible criterion for the evaluation of the radiation induced degradation, we compared the supression of the bandgap electroluminescence at a wavelength around 1150 nm for the solar cells, irradiated at different energies. The lowest electroluminescene efficiency has been observed for an intermediate proton energy of 1.7 MeV. At this energy value however crystalline silicon solar cells are not homogeneously damaged as shown by the defect profiles, calculated by the SRIM code. We propose therefore a irradiation at a high energy in order to obtain a relative homogeneous defect profile. At 65 MeV the projected range of the protons in silicon is about 2 cm and we obtain a nearly constant defect distribution in the solar cell and the irradiation can be performed in air. Subsequently we compared the fluence dependence of the degradation of the solar cell parameters after 65 MeV irradiation with other material by the quantum yield spectra and the effective excess charge carrier lifetime, as measured on silicon wafers by the contactless TRMC-technique. Similar degradation has been found for the short circuit current, solar cell efficiency and electroluminescence efficiency and a good agreement between diffusion length and excess charge carrier lifetime changes.