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Objectives
The objectives of the current activity are:
- To acquire sufficient test data to allow appropriately accurate prediction of ‘relative damage coefficients’ (as input to the ‘equivalent damage’ method) for the following two types of triple-junction solar cells, developed by Azur:
- 3G28% class new generation solar cells, fully European,
- GAGET2 solar cells.
- To acquire complementary test data for ‘component’ top, middle and bottom cells for the two triple-junction solar cells.
- To construct a test database of the above measurements against which future models can be tested and validated by the space community.
- To analyse and compare performance prediction using data for component cells with prediction using data for complete triple-junction cells.
- To define a general process for the validation of future models, as an alternative to the ‘equivalent damage’ method and to apply this process to new models such as the ‘displacement damage dose’ model.
Challenges
The construction of a coherent database of solar cell main characteristics after irradiation is of major importance since it will improve the accuracy of the end-of-life prediction of satellite power budget.
The testing of the relevance of the ‘equivalent damage’ method for triple junctions is a key issue as this is the reference method, widely used throughout the solar cell community and in space industry.
The testing of new methods, such as the ‘displacement damage dose’ or Bourgoin?s ones, is a key issue as important benefits are expected from using in the future more theoretical and less time and money-consuming methods.
Plan
The pre-test phase consists in testing GAGET2 + 3G28:
- 300 keV protons (5×1010 /cm2) at Philips Research Laboratory (NL) -GAGET2-,
- 1 MeV electrons (5×1014 /cm2) at Delft University (NL) -GAGET2 + 3G28-,
- 6.5 MeV protons (2×1011 /cm2) at Isotron (UK) -3G28-.
The second phase includes five successive increasing fluences on both GAGET2 + 3G28 at following energies:
- 30 keV protons at Philips Research Laboratory,
- 100 keV protons at Philips Research Laboratory,
- 300 keV protons at Philips Research Laboratory,
- 750 keV protons at Philips Research Laboratory,
- 6.5 MeV protons at Isotron,
- 0.5 MeV electrons at Delft University,
- 1 MeV electrons at Delft University,
- 3 MeV electrons at Delft University.
Current Status
The pre-test phase is completed.
No problem was detected during irradiations, dose levels being controlled both by in-house dosimetry equipment and control samples. The foreseen schedule, based on successive periods of three weeks for irradiations and three weeks for electrical measurements seems realistic.
Before and after irradiation, standard I-V curves were recorded for all triple-junction cells and their degradation under both electron and proton irradiation is in line with previous results; a good fit is also obtained by using ‘displacement damage dose’ method. Concerning ‘component’ cells, before irradiation, standard I-V curves were also recorded, but after proton or electron irradiation, most of the I-V curves were degraded. The problem seems to be identified and should be corrected for second phase solar cells.
The second phase should start at the end of August with the purchase of solar cells, followed by their initial characterizations at Fraunhofer-Institut für Solare Energie Systeme, INTA-Spasolab, and Astrium GmbH. First round of irradiations is foreseen in the autumn.