High-Energy Electron and Proton Irradiation of Cu(In,Ga)Se2 Heterojunction Solar Cells

Abstract

ABSTRACTWe investigate radiation-induced defects in high-efficiency Cu(In,Ga)Se2/CdS/ZnO heterojunction solar cells after 1-MeV electron and 4-MeV proton irradiation. We use electron and proton fluences of more than 1018 cm−2 and up to 1014 cm−2, respectively. The irradiation experiments performed at three independent electron irradiation facilities consistently prove the superior radiation resistance of these Cu(In,Ga)Se2 devices compared to other types of solar cells. The reduction of the solar cell efficiency in all experiments is predominantly caused by a loss ΔVOC of the open circuit voltage VOC. An analytical model describes ΔVOC in terms of radiation-induced defects enhancing recombination in the Cu(In,Ga)Se2 absorber material. From our model we extract the defect introduction rates for recombination centers in Cu(In,Ga)Se2 for the respective particles and energies. Isochronal annealing steps fully recover VOC of the irradiated Cu(In,Ga)Se2 solar cells. Exposure to temperatures of approx. 400 K are sufficient to restore the initial VOC within less than 5 %, even after excessive irradiation. The annealing process displays an activation energy of EA = 1.1 eV. Admittance spectroscopy directly reveals the generation and the annealing of radiation-induced defects.