Polycrystalline ZnO/CdS/Cu(In,Ga)Se-2 heterojunction solar cells display a very high radiation resistance under 1-MeV electrons. We irradiated high-efficiency Cu(In,Ga)Se-2 solar cells with 1-MeV electron fluences up to phi (e) = 5 X 10(18) cm(-2). The loss in the conversion efficiency, starting at phi (e) = 10(17) cm(-2), was caused by the open circuit voltage loss. An analytical model for the open circuit voltage describes the loss by considering the increase in space charge recombination via deep defects introduced by electron irradiation. A reduction of the doping density in the Cu(In,Ga)Se, absorber layer upon irradiation was analyzed by capacitance voltage measurements. The rate at which the net doping density decreased was 0.045 cm(-1). Accumulative irradiation shows that partial recovery of the radiation induced damage occurred during our analysis cycle well below 100 degreesC.