Inverted metamorphic triple-junction solar cell and its radiation hardness for space applications

Abstract

In recent years, with the development of solar cell technology, the conversion efficiency of the lattice-matched Ga0.51In0.49P/In0.01Ga0.99As/Ge triple-junction solar cell has achieved 30% under AM0 spectrum. As is well known, it is difficult to further improve the efficiency due to the limited bandgap combination. Therefore, an inverted metamorphic triple-junction solar cell is designed by replacing the Ge subcell with a 1.0 eV InGaAs subcell. The efficiency could be increased with the open-circuit voltage increasing, while the short circuit current maintains a similar value.#br#In this paper, the inverted metamorphic GaInP/GaAs/In0.3Ga0.7As triple-junction solar cells are grown on 4-inch GaAs substrates via metal organic chemical vapor deposition. Optimizing the epitaxy process, AlInGaAs graded buffer shows nearly 100% relaxation by the reciprocal space mapping of the high-resolution X-ray diffraction and low average threading dislocation density~5.4×106/cm2 evaluated from the cathodoluminescence image. Finally, the inverted metamorphic triple-junction solar cell with 24 cm2 area shows a conversion efficiency of 32% with an open-circuit voltage of 3.045 V and a short-circuit current of 404.5 mA under one sun, AM0 spectrum, 25℃ conditions, which is 5% higher than the lattice-matched GaInP/InGaAs/Ge triple-junction solar cell. Under 1 MeV electron irradiation test, the degradations of the external quantum efficiency and I-V characteristics of inverted metamorphic triple-junction solar cell are exhibited each as a function of fluence, and finally the end-of-life efficiency is 27.2% with a degradation of 15% under 1×1015/cm2 fluence. More experiments mainly focusing on the lattice quality of AlInGaAs graded buffer and the structure of In0.3Ga0.7As subcell, will be carried out to improve the efficiency and enhance the radiation hardness.