Seira Yamaguchi

Potential-induced degradation of Cu(In,Ga)Se2 photovoltaic modules

Potential-induced degradation (PID) of Cu(In,Ga)Se2 (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.

Progression of rapid potential-induced degradation of n-type single-crystalline silicon photovoltaic modules

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.

Behavior of the potential-induced degradation of photovoltaic modules fabricated using flat mono-crystalline silicon cells with different surface orientations

This paper deals with the dependence of the potential-induced degradation (PID) of flat, p-type mono-crystalline silicon solar cell modules on the surface orientation of solar cells. The investigated modules were fabricated from p-type mono-crystalline silicon cells with a (100) or (111) surface orientation using a module laminator. PID tests were performed by applying a voltage of −1000 V to shorted module interconnector ribbons with respect to an Al plate placed on the cover glass of the modules at 85 °C. A decrease in the parallel resistance of the (100)-oriented cell modules is more significant than that of the (111)-oriented cell modules. Hence, the performance of the (100)-oriented-cell modules drastically deteriorates, compared with that of the (111)-oriented-cell modules. This implies that (111)-oriented cells offer a higher PID resistance.

Behavior of the potential-induced degradation for photovoltaic modules fabricated using flat mono-crystalline silicon cells with different surface orientations

This paper deals with the behavior of the potential-induced degradation (PID) of photovoltaic modules fabricated using p-type flat mono-crystalline silicon cells with (100) and (111) surface orientations. PID tests are performed by applying a voltage of −1000 V to connected interconnector ribbons of the modules. A decrease in the normalized maximum power of the modules with (100)-oriented cells is more significant than that with (111)-oriented cells, implying that the (111)-oriented cells have the higher PID resistance.

Potential-induced degradation behavior of n-type single-crystalline silicon photovoltaic modules with a rear-side emitter

This paper deals with the behavior of the potential-induced degradation (PID) of n-type single-crystalline silicon photovoltaic (PV) modules with a rear-side emitter. The n-type rear-emitter modules were fabricated by encapsulating n-type bifacial solar cells with the p+-emitter side down. The modules show degradation mainly characterized by decreases in the open-circuit voltage (Voc) and the fill factor (FF), under negative bias. The degradation is saturated within 1 h, and normalized Voc decreases to approximately 0.96. Their dark current density-voltage (J-V) data and external quantum efficiencies (EQEs) indicate that the drop in Voc is caused by an increase in the saturation current density due to the enhanced surface recombination of minority carriers. The degree of the degradation of PV performance is not, however, considerably severe in the n-type rear-emitter c-Si PV modules, and they are relatively resistant to PID compared to other types of PV modules. This may become an advantage of the n-type rear-emitter c-Si PV modules particularly for the usage in very large-scale PV systems.

Multistage performance deterioration in n-type crystalline silicon photovoltaic modules undergoing potential-induced degradation

Abstract This study addresses the behavior of n-type front-emitter (FE) crystalline-silicon (c-Si) photovoltaic (PV) modules in potential-induced degradation (PID) tests with a long duration of up to 20 days. By PID tests where a negative bias of −1000 V was applied at 85 °C to 20 × 20-mm2-sized n-type FE c-Si PV cells in modules, the short-circuit current density (Jsc) and the open-circuit voltage (Voc) started to be decreased within 10 s, and strongly saturates within approximately 120 s, resulting in a reduction in the maximum output power (Pmax) and its saturation. After the saturation, all the parameters were almost unchanged until after 1 h. However, the fill factor (FF) then started to decrease and saturated again. After approximately 48 h, FF further decreased again, accompanied by a reduction in Voc. The first degradation is known to be due to an increase in the surface recombination of minority carriers by the accumulation of additional positive charges in the front Si nitride (SiNx) films. The second and third degradations may be due to significant increases in recombination in the space charge region. The enhancement in recombination in the space charge region may be due to additional defect levels of sodium (Na) introduced into the space charge region in the p–n junction. We also performed recovery tests by applying a positive bias of +1000 V. The module with the first degradation completely recovered its performance losses, and the module with the second degradation was almost completely recovered. On the contrary, the modules with the third degradation could not be recovered. These findings may improve the understanding of the reliability of n-type FE c-Si PV modules in large-scale PV systems.