Defect generation in Cu(In,Ga)Se2 heterojunction solar cells by high-energy electron and proton irradiation

We investigate irradiation-induced defects in high-efficiency Cu(In,Ga)Se-2/CdS/ZnO heterojunction solar cells after electron irradiation with energies of 0.5, 1, and 3 MeV and after 4 MeV proton irradiation. We use electron and proton fluences of more than 10(18) cm(-2) and up to 10(14) cm(-2), respectively. The reduction of the solar cell efficiency in all experiments is predominantly caused by a loss DeltaV(OC) of the open circuit voltage V-OC. An analytical model describes DeltaV(OC) in terms of radiation-induced defects enhancing recombination in the Cu(In,Ga)Se-2 absorber material. From our model, we extract defect introduction rates for recombination centers in Cu(In,Ga)Se-2 for the respective particles and energies. We directly monitor the defect generation of these radiation-induced defects by admittance spectroscopy. The decrease of effective doping density in the Cu(In,Ga)Se-2 absorber layer under particle irradiation is analyzed with capacitance voltage measurements at low temperatures. Furthermore, data on the relative damage coefficients for high-energy electron irradiation in Cu(In,Ga)Se-2 solar cells are presented. All data, from electron as well as proton irradiations, merge to a single characteristic degradation curve. (C) 2001 American Institute of Physics.