Prevention of Potential-Induced Degradation With Thin Ionomer Film

Significant power loss has been observed in photovoltaic (PV) modules resulting from high voltage bias experienced in the field. This type of failure has been called potential-induced degradation (PID). Encapsulant materials provide protection and electrical isolation of the solar components in PV modules. Several researchers have shown that the type of encapsulant can directly affect the severity of the PID. Ionomers, in particular, were amongst the first encapsulants identified as having the ability to prevent this degradation mechanism. In this study, we introduce an ionomer/EVA bilayer encapsulant to the module to determine the effect of ionomer on PID and sodium ion migration in minimodules. We determined that the encapsulant's volume resistivity is temperature independent with the presence of ionomer. Results confirm that the module's volume resistivity at elevated temperature inversely correlates with leakage current and that ion enrichment at the cell/encapsulant interface correlates with power degradation of a PV module. The rate of sodium ion migration to the cell was also investigated. An analytical method was refined for this application using laser ablation and mass spectrometry to observe the sodium migration within the module. Sodium ion profiles were obtained by elemental mapping of the encapsulant and solar cell cross section after the module had been exposed to a simulated PID test. Results show that sodium ion accumulation at the encapsulant/solar cell region increases linearly with PID testing time when only EVA encapsulant is used and is significantly different when an ionomer/EVA encapsulant is used in the module.