Radiation effects on luminescent coupling in III?V solar cells

Advances in the architecture of GaInP solar cells have recently lead to ~21% conversion efficiencies under the global spectrum due to high radiative efficiencies, and the resulting strong luminescent coupling in GaInP/GaAs tandems has lead to record dual-junction efficiencies. The suitability of these newer GaInP cells to space applications has not been examined, however. Here we present a study to compare the radiation hardness of rear-heterojunction and more traditional GaInP junctions and the resulting luminescent coupling. Pairs of GaInP/GaAs tandem cells were irradiated with 1 MeV electrons at fluences up to 1015 e/cm2. The cells were thoroughly characterized, before and after irradiation, by measuring the quantum efficiency, IV characteristics, electroluminescence and luminescent coupling. We find the luminescent coupling to be unchanged below ~1013 e/cm2, and to decrease to zero by 1015 e/cm2. For all fluence levels, the rear heterojunction structure had a higher coupling constant than the front junction structure. Despite these advantages, the efficiency degraded at the same rate for both structures.