For simulating space environmental radiation a 2×1.7 MV tandem accelerator was used. GaAs solar cells with and without MQW were irradiated using 2 MeV protons with fluences of 1×109—2×1013 cm-2

and the I-V char- acteristics and the spectral response of GaAs solar cells were measured. The results show that the degradation of Isc

Voc and Pmax of the two kinds of solar cells increases as the irradiation fluence rises. But the degradation for the GaAs solar cells with MQW is more serious than that for the GaAs solar cells without MQW at the same irradiation fluence. After irradiation with a fluence of 2×1013 cm-2

the spectral response of GaAs solar cells with MQW drops in the whole wavelengths (400—1000 nm)

and the quantum well characteristics in the long wavelengths (900—1000 nm) disappear. Thus

the addition of MQW structure to GaAs solar cells results in the degradation of its radiation tolerance.