1 MeV electron irradiation of monolithic, two-terminal InP/Ga0.47In0.53As solar cells

The effect of irradiating monolithic, two-terminal InP/Ga_0.47 In_0.53As tandem solar cells with 1 MeV electrons has been studied. These are the first solar cells of their kind to be produced. In addition, Ga_0.47In_0.53As single-junction cells with various base dopant levels grown to simulate the bottom cell of the tandem have been irradiated. The irradiation proceeded in incremental fluence steps from 6×10¹³ up to 10¹⁶ cm^-2. The 1 sun, AMO I-V curve of each cell was measured after each fluence step. Before irradiation, efficiencies as high as 20% were measured on the tandem cells. The radiation resistance of the tandem cells is shown to be as high as that of an InP homojunction for fluences less than 3×10¹⁴ cm ^-2. For fluences greater than this, the bottom cell was seen to limit the cell current and thus degrade the tandem cell efficiency. It was found that the high base dopant level in the bottom cell served to increase the resistance of V_oc but decrease the resistance of I_sc. The data suggest that a base dopant level of around 2-5×10¹⁶ cm^-3 in the bottom cell would significantly increase the resistance of I_sc without seriously affecting V_oc. In this way, a tandem cell can be designed which should remain current matched and produce efficiencies over 20% even after fluences well above 3×10¹⁴ cm^-2