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Benchmarking Light and Elevated Temperature Induced Degradation (LeTID)
M. Pander, M. Turek, J. Bauer, T. Luka, C. Hagendorf, M. Ebert, R. Gottschalg
Degradation, PERC, PV Module, LID, LeTID
Photovoltaic Modules and BoS Components
Subtopic: PV Module Design, Manufacture, Performance and Reliability
Event: 35th European Photovoltaic Solar Energy Conference and Exhibition
Session: 5CV.1.46
1265 - 1268
ISBN: 3-936338-50-7
Paper DOI: 10.4229/35thEUPVSEC20182018-5CV.1.46
0,00 EUR
Document(s): paper


Light Induced Degradation (LID) is a well-known cell effect, impacting in the first hours of testing or first months of operation. All c-Si device types are affected, typically with less than 5% degradation. The known mechanisms (Boron Oxygen complex formation and Iron Boron pair dissociation) are identified during certification by IEC 61215:2016 standard stabilization procedures carried out at around 50°C. Unfortunately, there is a second degradation mode which is only apparent at higher temperatures. This Light and Elevated Temperature Induced Degradation (LeTID) is not identified during certification. Typically, there is no specific information commonly available for system planners to estimate the magnitude of the losses due to this effect. Testing at higher temperatures of PERC devices resulted in much higher degradation levels (up to 10 %), but slower degradation rates than BO. Therefore, this new type of degradation was termed Light and elevated Temperature Induced Degradation (LeTID). Initially LeTID was thought to only affect multi-PERC but recent studies have shown that mono-PERC may be affected equally. LeTID is not fully understood but can virtually be eliminated in production. Currently there is no generally accepted standard to test for LeTID degradation on cell and module level. Thus it is not possible to identify modules susceptible to LeTID. The question arises to what extent currently available modules contain LeTID-susceptible cells, and the magnitude of long-term yield losses. For this purpose, nine module types from different manufacturers were procured from different suppliers and subjected to a LeTID-specific test procedure. Power losses up to 6 % were found during the LeTID-Test. The three multi-Si modules tested show moderate degradation or are even stable. Some of the commercially available mono-Si PERC modules show high LeTID.