Influence of hygrothermal stress on potential-induced degradation for homojunction and heterojunction crystalline Si photovoltaic modules

Abstract

The 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 sequential tests 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 considerably 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 considerably enhances PID by high-voltage stress for n-type heterojunction crystalline Si PV modules. The possible mechanisms for these accelerated degradation phenomena by the combined stresses are presented.

Potential‐Induced Degradation in High‐Efficiency n‐Type Crystalline‐Silicon Photovoltaic Modules: A Literature Review

“…In SHJ PV modules, corrosion‐type PID is the main PID mode. [ 40–43 ] It must also be emphasized that corrosion‐type PID is a Na‐related phenomenon. Section 6 specifically addresses corrosion‐type PID.…”

“…[ 41 ] Actual PV systems are typically limited both by technology and by regulations to 1000 or 1500 V. For that reason, Na‐penetration‐type PID is not regarded as easily occurring in actual PV systems. However, Masuda et al [ 42 ] demonstrated that the PID in SHJ cell modules is accelerated considerably by moisture ingress. It is also possible that SHJ cells with damaged TCO layers are more susceptible to Na‐penetration‐type PID.…”

“…As, based on this mechanism, H 2 O participates in the chemical reaction (), moisture has a strong effect on this corrosion‐type PID. Masuda et al [ 42 ] reported that moisture accelerates the corrosion‐type PID in SHJ PV modules to a marked degree. The above corrosion‐type PID is expected to occur in cells of other types that involve In 2 O 3 TCO layers, for example, carrier‐selective contact cells.…”

“…Some reports have described PID in PV modules fabricated from n‐type c‐Si cells, such as passivated emitter and rear totally diffused (PERT) cells, [ 16–30 ] passivated emitter and rear locally diffused (PERL) cells, [ 31 ] TOPCon cells, [ 32 ] rear‐emitter c‐Si PERT cells (with the junction not at the front‐glass side), [ 18,33,34 ] IBC cells, [ 15,35–39 ] and Si heterojunction (SHJ) cells. [ 40–43 ] According to these many studies, n‐type c‐Si PV cell modules show PID with different mechanisms from those in p‐type cells. This point has also been reported from some comparative studies.…”

Reliability Improvement and Remaining Issues on Photovoltaic Cells and Modules

“…For example, UV irradiation accelerates degradation by hygrothermal stress (9), on the other hand, delays degradation by potential difference (10). It was also found that hygrothermal stress accelerates the degradation by potential difference (11). Figure 2 shows materials and components used in photovoltaic modules and also degradation factors.…”