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System voltages can cause significant degradation in photovoltaic modules. Polarization-type potential-induced degradation (PID) is accompanied by decreases in the short-circuit current density and the open-circuit voltage. The system voltage causes a polarization and surface charge accumulation, increasing the interface recombination. The surface passivation and the emitter doping concentration and gradient are considered to have large impacts. However, a systematic study on these effects has not yet been performed. In this paper, the effects of the front surface structure of n-type passivated emitter and rear totally diffused cell modules were investigated by accelerated PID tests. Standard cells with thin silicon dioxide/80 nm silicon nitride (SiN_x) antireflection/passivation layers, refractive index (RI) of 2.0, exhibited typical polarization-type PID. Cells with increased RI = 2.4 for the bottom 20 nm SiN_x showed no degradation at all. This may be caused by reduced charge accumulation in the SiN_x layer near the interface due to the higher electrical conductivity of the Si-rich bottom layer. Secondly, cells with both a highly distorted interface, due to nitrogen insertion in the silicon surface, and an emitter with a high surface doping concentration have excellent resistance to PID. Cells with either the highly distorted interface or the higher emitter-surface doping concentration show no to minor improved resistance to PID. These findings improve the understanding of the effects of the front surface structure of cells on the polarization-type PID and may contribute to the implementation of these measures to reduce PID., identifier:https://dspace.jaist.ac.jp/dspace/handle/10119/18204

n-type crystalline-silicon (c-Si) photovoltaic (PV) cell modules attracts attention because of their potential for achieving high efficiencies. The market share of n-type c-Si PV modules is expected to increase considerably, with wide use in PV systems, including large-scale PV systems, for which the system bias is set as markedly high. Such a high system bias leads to performance losses known as potential-induced degradation (PID). By virtue of many researchers’ efforts, the PID behaviors, PID mechanisms, and preventive measures against PID have been well documented in conventional p-type c-Si modules. Researchers recently started to investigate PID in high efficiency c-Si solar cells including n-type c-Si PV modules. Yet, the understanding of PID phenomena remains incomplete. Herein, a literature review of PID in high-efficiency n-type c-Si PV modules is provided as a resource elucidating the current status of related research and remaining unresolved issues. This report mainly presents discussion of PID in several kinds of n-type c-Si PV modules in terms of materials science. PID phenomena are described as divided into some degradation modes. Details present a review of their respective degradation modes, degradation behaviors, proposed mechanisms, and potential measures against degradation. Remaining open issues and anticipated future studies are also summarized.

Influences of both high-voltage stress and hygrothermal stress were studied for homojunction and heterojunction crystalline Si photovoltaic (PV) modules. In order to separately access the influence of these stresses, these PV modules were subjected to the sequential test with hygrothermal stress and high-voltage stress for various stress durations of each test. It was found that for p-type homojunction crystalline Si PV modules hygrothermal stress applied in advance much enhances potential-induced degradation (PID) by high-voltage stress. High-voltage stress applied in advance also accelerates finger-electrode degradation by hygrothermal stress. It was also clarified that hygrothermal stress for short duration applied in advance much enhances PID by high-voltage stress for n-type heterojunction crystalline Si PV modules. Possible mechanism for these accelerated degradation phenomena by combined stresses will be presented., identifier:https://dspace.jaist.ac.jp/dspace/handle/10119/18012

We investigate the effect of silicon nitride (SiN_x) films in n-type front-emitter (n-FE) crystalline Si (c-Si) solar cells on the potential-induced degradation (PID) of n-FE photovoltaic (PV) modules. A negative-bias PID test for a few min does not degrade the performance of PV modules with n-FE cells without SiN_x/silicon dioxide (SiO_2) stacks, unlike in the case of PV modules with cells with SiN_x/SiO_2. This is because of the absence of polarization-type PID. After a longer PID test, the PV modules with n-FE cells without SiN_x/SiO_2 show a slower decrease in fill factor (FF), originating from Na introduction into the depletion layer of a p–n junction, than the modules with cells with SiN_x/SiO_2. The mitigation of PID by eliminating SiN_x is partly consistent with the results of PV modules with p-type conventional cells without SiN_x in which no PID occurs. SiN_x thus has a function of enhancing Na introduction into c-Si., identifier:https://dspace.jaist.ac.jp/dspace/handle/10119/18016

Potential-induced degradation (PID)-test results of modules fabricated from the rear- and front-emitter silicon heterojunction (SHJ) solar cells were compared to clarify the influence of the emitter position of SHJ photovoltaic (PV) cell modules on their PID behaviors. The PID tests were performed by applying a bias of −2000 V to the shorted interconnector ribbons from the front surface of the cover glass, at 85 °C. In the initial stage, both modules showed the same degradation characterized by a reduction in the short-circuit current density (J_). After the firststage degradation, the rear-emitter SHJ PV modules exhibited subsequent degradation characterized by a significant reduction in the J_ and open-circuit voltage (V_), due to the enhancement of the minority-carrier recombination in the front surface region of the n-type crystalline silicon base. The front-emitter SHJ PV modules, on the other hand, showed a reduction in the fill factor (FF), in addition to moderate reductions in J_ and V_. The FF reduction of the front-emitter SHJ PV modules is considered to be caused by the enhancement of the recombination in the front surface region of the n-type crystalline-silicon base as the region corresponds to the pn junction interface of the front-emitter configuration. The moderate reductions in both J_ and V_ may be due to further progression of the first-stage degradation. These findings are essential for understanding the mechanism of PID in SHJ PV cell modules., identifier:https://dspace.jaist.ac.jp/dspace/handle/10119/18072