The failure of photovoltaic modules in high-temperature and high-humidity tests is generally caused by the loss of electrical contact between the cell emitter and finger metallization, due to the corrosion of the glass layer by the acetic acid which is generated by the hydrolysis of the ethylene vinyl-acetate copolymer that is used as the encapsulant. In this study, a high-temperature high-humidity test was conducted on a photovoltaic module—namely, a solar cell with reduced output—to examine the metallization–Si wafer interface. The results confirmed that Pb was eluted from the glass layer to form an alteration layer that inhibits electron movement from the emitter layer to the metallization, thereby decreasing the output of the module. The corrosion products generated from the eluted Pb indicated that the front-side metallization was statically exposed to the same environment inside the PV module as that in an aqueous solution of acetic acid.

This study investigated how the SiN x refractive index (RI) and SiO 2 thickness, d ox , of stacked SiN x /SiO 2 passivation layers of the front p + emitters of n-type crystalline-silicon (c-Si) photovoltaic (PV) cells affect their polarization-type potential-induced degradation (PID) behaviors. We prepared six n-type c-Si PV cells with an RI of 2.0 or 2.2 and with d ox of 9, 2, or 1 nm. Then PV modules fabricated from the cells were subjected to PID tests during which a bias of −1000 V was applied to cells with respect to the front cover glass surface.For d ox of 9 or 2 nm, rapid polarization-type PID was observed, irrespective of the RI. However, for d ox of 1 nm, the RI markedly affected the degradation behavior, and cells with an RI of 2.2 showed no degradation. These findings are attributable to carrier transport between the high RI (Si-rich) SiN x and the c-Si substrates, which can readily occur only when the SiO 2 layer is sufficiently thin for electrons to tunnel through the SiO 2 layer. These results are important for elucidating polarization-type PID mechanisms and for developing preventive measures against polarization-type PID.

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This study investigates the effect of corrosion of the metallization containing lead tellurite glass frit used in solar cells due to acetic acid. When the c-Si photovoltaic (PV) module is operating in the new degradation mode, the electroluminescence (EL) dark area showed an increase in the series resistance that spreads around the bus bars. To understand metallization corrosion, a high-temperature and high-humidity test was conducted using PV modules. The metallization was observed with a scanning electron microscope. Observation of the metallization of the degraded module confirmed the generation of voids and gaps near the interface between the metallization and the Si wafer in the EL dark area. It was also observed that Te and Pb were mostly eluted from the glass frit components in the metallization during the acetic acid leaching test. The results suggest that the elution of Te by the acetic acid generates voids and gaps in the metallization.

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