Radiation response of dual-junction GayIn1-yP/Ga1-xInxAs solar cells

The radiation response of dual-junction Ga_yIn_1-y P/Ga_1-xIn_xAs solar cells grown with 0.35<y<0.51 and 0.01<x<0.17 is presented. These lattice-mismatched structures were grown by metal-organic-vapor-phase-epitaxy on GaAs or Ge substrates. Measurement of the photovoltaic output of the cells made under simulated one-sun, AM0 spectral conditions shows that the new dual-junction Ga_xIn_1-xP/Ga_yIn_1-yAs cells perform as well or better than commercially available multijunction cells. Measurement of the quantum efficiency gives insight into which subcell determines the total cell degradation under proton irradiation. As has been found previously for the Ga_yIn_1-yP/GaAs tandem cell, degradation of the new Ga_yIn_1-yP/Ga_1-xIn_xAs material combination is controlled by the bottom solar cell. Analysis of the irradiation data is used to determine the basic mechanisms governing the radiation response of these devices, including the effect of stoichiometry, lattice-mismatch and cell structure