Radiation induced defects in Cu(In,Ga)Se2 solar cells-comparison of electron and proton irradiation

The authors report on irradiation experiments of ZnO/CdS/Cu(In,Ga)Se₂ heterojunction solar cells with high doses of 1 MeV electrons, 10 MeV (omni-directional) and 4 MeV (uni-directional) protons. Electron irradiation up to 10¹⁸ cm ^-2 is necessary to cause a power conversion efficiency loss of 20-30%. Electrical analysis of irradiated devices shows that the degradation is essentially due to the introduction of (relatively shallow) acceptor-like defects by a rate of approximately 0.02 cm^-1 . The decrease of effective doping density is quantified by a rate of 0.045 cm^-1. The degradation upon irradiation with 10 MeV (4 MeV) omni- (uni-)directional proton starts at fluences of 10¹³ cm^-2 (10¹² cm^-2). The remaining efficiency factor is 50% after a 4 MeV-proton fluence of 10¹⁴ cm^-2. Proton irradiation affects the open circuit voltage and the fill factor. All irradiated samples exhibit a continuous recovery at room temperature