In this study, we investigated progression of potential-induced degradation (PID) in photovoltaic modules fabricated from n-type-based crystalline-silicon cells with front p+ emitters. In PID tests in which a bias of −1000 V was applied to the modules, they started to degrade within 5 s and their degradation saturated within 60 s. This behavior suggested that the PID was caused by positive charge accumulation in the front passivation films. Performing PID tests with a bias of −1500 V revealed that the degradation rate strongly depended on the applied bias whereas the saturation value was independent of the applied bias. Regeneration tests on degraded modules previously subjected to PID tests for durations of 5 and 10 min were performed by applying a positive bias of +1000 V. All the degraded modules completely recovered their performance losses within 60 s regardless of the degradation test duration. On the basis of these results, we proposed that these positive charges originate from positively charged K centers formed by extracting electrons from neutral and negatively charged K centers. This model readily explains the observed degradation and regeneration behavior. To test our model, we determined the fixed positive charge densities (Qf) of a silicon nitride passivation film before and after PID, for which it was found that Qf showed similar saturation behavior. Additionally, the saturated Qf value was of the same order as K center density. These results support our model involving a charging process of K centers.

This study addresses progression of potential-induced degradation (PID) of photovoltaic modules using n-type single-crystalline silicon cells. In a PID test in which a voltage of −1000 V was applied to the cells, the modules started to degrade within 10 s and the degradation saturated within 120 s, suggesting that PID is caused by positive charge accumulation in the front passivation films. We propose that these positive charges originate from positively charged K centers formed by extracting electrons from the K centers, which explains the rapid degradation and its saturation behavior. We obtain simulated and experimental results supporting this hypothesis.

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Potential-induced degradation (PID) of Cu(In,Ga)Se 2 (CIGS) photovoltaic (PV) modules fabricated from integrated submodules is investigated. PID tests were performed by applying a voltage of %1000 V to connected submodule interconnector ribbons at 85°C. The normalized energy conversion efficiency of a standard module decreases to 0.2 after the PID test for 14 days. This reveals that CIGS modules suffer PID under this experimental condition. In contrast, a module with non-alkali glass shows no degradation, which implies that the degradation occurs owing to alkali metal ions, e.g., Na + , migrating from the cover glass. The results of dynamic secondary ion mass spectrometry show Na accumulation in the n-ZnO transparent conductive oxide layer of the degraded module. A CIGS PV module with an ionomer (IO) encapsulant instead of a copolymer of ethylene and vinyl acetate shows no degradation. This reveals that the IO encapsulant can prevent PID of CIGS modules. A degraded module can recover from its performance losses by applying +1000 V to connected submodule interconnector ribbons from an Al plate placed on the test module.

Accelerated tests were used to study potential‐induced degradation (PID) in photovoltaic (PV) modules fabricated from silicon heterojunction (SHJ) solar cells containing tungsten‐doped indium oxide (IWO) transparent conductive films on both sides of the cells and a rear‐side emitter. A negative bias of −1000 V was applied to a module with respect to the cover glass surface in a chamber maintained at 85°C, which significantly reduced the cell's short‐circuit current density (Jsc) within several days. Based on dark current density‐voltage and external quantum efficiency measurements, the reduction in the Jsc was attributed to optical losses rather than carrier recombination. X‐ray absorption fine structure spectroscopy showed the formation of metallic indium (In) in the IWO layers of a degraded cell, which suggests that the root cause of the optical loss was a darkening of the front IWO layers caused by the precipitation of metallic In. In extremely severe PID tests, the SHJ PV modules exhibited not only a further reduction in the Jsc but also a moderate reduction in the open‐circuit voltage (Voc). These Jsc and Voc reductions were probably caused by sodium being introduced into the base region of the cells. A comparison of the PID test results of the SHJ PV modules with those of other types of PV modules indicates that SHJ PV modules have a relatively high resistance to PID. As a module with an ionomer encapsulant exhibited little degradation, their high resistances to PID may be further improved by using encapsulants with high electrical resistances.