Light Induced Degradation (LID) and Light and Elevated Temperature Induced Degradation (LETID) manifest with carrier injection due to light or forward bias and can lead to performance losses during the first months or years of operation in the field. We are investigating the effects of common LETID indoor test conditions and the module temperature under outdoor exposure on the evolution of BO LID and LETID over time. The investigations are based on experimental data from twelve structurally identical mono-crystalline and two multi-crystalline PERC PV modules, which underwent a detailed experiment including five different indoor test sequences and an outdoor test. Changes in the module performance are discussed based on the current knowledge on state transitions of the BO defect and LETID. Temporary recovery of the LETID defect was used to distinguish LETID from other degradation mechanisms. Our results confirm the importance of BO stabilization prior to LETID tests as it is included in the current IEC TS draft for LETID detection. We also show that too strong acceleration of the processes can lead to misinterpretation of LETID test results. Under dark storage conditions, destabilization of BO defects was found to already evolve at temperatures as low as 75 °C and a likely alteration of subsequent LETID was observed. The performance changes under outdoor exposure can be explained with the same mechanisms as investigated under indoor experiments and reveal reversible seasonal recovery effects. Furthermore, the influence of different module operating temperatures on the evolution of both, BO LID and LETID is presented and evaluated.

This paper reports the results of an international interlaboratory comparison study on light‐ and elevated temperature‐induced degradation (LETID) on crystalline silicon photovoltaic (PV) modules. A large global network of PV module manufacturers and PV testing laboratories collaborated to design a protocol for LETID detection and screen a large and diverse set of prototype modules for LETID. Results across labs indicate the reproducibility of LETID testing is likely within ±1% of maximum power (PMP). In intentionally engineered LETID‐sensitive modules, mean degradation after the prescribed detection stress is roughly 6% PMP. In other module types the LETID sensitivity is smaller, and in some we observe essentially negligible degradation attributable to LETID. In LETID‐sensitive modules, both open‐circuit voltage (VOC) and short‐circuit current (ISC) degrade by a roughly similar magnitude. We observe, as do previous studies, that LETID affects each cell in a module differently. An investigation of the potential mismatch losses caused by nonuniform LETID degradation found that mismatch loss is insignificant compared to the estimated loss of cell ISC, which drives loss of module ISC. Overall, this work has helped inform the creation of a forthcoming standard technical specification for LETID testing of PV modules, IEC TS 63342 ED1, and should aid in the interpretation of results from that and other LETID tests.

No abstract

Accelerated aging tests as defined in testing standards such as IEC 61215 are important to assure quality and safety of photovoltaic (PV) modules. The test conditions often contain high temperatures and sometimes carrier injection, which can cause light induced degradation (LID) effects, such as boron-oxygen LID (BO LID) or light and elevated temperature induced degradation (LETID). These effects can interfere with the interpretation of results or produce false fails or passes in certification tests. To address the most severe cases, an option for a regeneration procedure for BO LID after damp heat was recently included into IEC 61215:2021. However, positive performance deviations due to BO LID, as well as general influence of LETID are still not excluded. Variations of damp heat and thermal cycling tests on mini-modules built from monocrystalline passivated emitter and rear cells (PERC) are performed and combined with latest approaches for BO LID regeneration, BO degradation and LETID temporary recovery. The results show that LETID can superimpose procedures applied for BO LID regeneration but can be easily temporary recovered by one additional step. A combined stabilization procedure, which can exclude influences from both BO LID and LETID on accelerated aging test results, is proposed.

No abstract