Influence and mitigation of interference by LID and LETID in damp heat and thermal cycling tests on PV modules

Abstract

Accelerated aging tests as defined in testing standards such as IEC 61215 are important to assure the 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 in IEC 61215:2021. However, positive performance deviations due to BO LID, as well as the general influence of LETID, are still not excluded. Variations of damp heat and thermal cycling tests on mini-modules built from the 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.