Defect generation in polycrystalline Cu(In,Ga)Se2 by high-energy electron irradiation

Abstract.

We investigate the degradation of ZnO/CdS/ Cu(In,Ga)Se₂ heterojunction solar cells for space applications and the defect generation in polycrystalline Cu(In,Ga)Se₂ thin films by irradiation with 1-MeV electrons with fluences φ_e up to φ_e=5×10¹⁸ cm^-2. Notable degradation of the solar cell performance starts at fluences of φ_e=10¹⁷ cm^-2 where the open circuit voltage decreases by about 5% while short circuit current and fill factor remain essentially unaffected. Thus, Cu(In,Ga)Se₂ solar cells withstand electron fluences which are higher by one order of magnitude or more when compared to other technologies. A model describes the absolute open circuit voltage loss considering the increase of space charge recombination by electron irradiation-induced defects. Defect analysis by admittance spectroscopy shows that acceptor defects with an energy distance of approximately 300 meV from the valence band are generated at a rate γ=0.017 (±0.01) cm^-1.