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High-intensity illumination treatments against LeTID - Intensity and temperature dependence of stability and inline feasibility

: Vahlman, H.; Roder, S.; Nekarda, J.; Rein, S.


Solar energy materials and solar cells 223 (2021), Art. 110978
ISSN: 0927-0248
Journal Article
Fraunhofer ISE ()

We study the mitigation of light- and elevated temperature-induced degradation (LeTID) with high-intensity illumination treatments, placing special emphasis on inline feasibility. After the treatments, we investigate the stability upon degradation conditions close to the recently suggested standard, which allows estimating the LeTID behavior during the operating lifetime of solar modules in the field. Subsequently, we map the stability at different treatment intensities and temperatures achievable with an air-cooled tool. We show that, when applying short treatment times, the stability improves with increasing treatment intensity and deteriorates steeply with rising temperature above an optimum region around 250 °C. However, these intensity- and temperature-dependent differences largely vanish when increasing the treatment time sufficiently. We also investigate the significance of darkness/illumination during the cooling ramp from the treatment temperature in view of the LeTID stability. We discuss our results based on suggested defect models of LeTID, and provide hypotheses of the origin of the instabilities observed at the high treatment temperatures. After identifying optimal treatments, we demonstrate that the energy yield loss due to LeTID reduces by over 60% after an inline-feasible process consisting of only 30 s of high-intensity illumination, combined with cooling of the samples from the process temperature under a lower-intensity illumination.