Consideration on Na diffusion and recovery phenomena in potential-induced degradation for crystalline Si photovoltaic modules

Abstract

Potential-induced degradation (PID), which brings about a large rapid decrease in output power has been observed in megawatt-scale photovoltaic power plants. Na diffusion from a cover glass to a cell through an encapsulant is possibly the direct origin of PID for p-type crystalline Si photovoltaic modules. On the other hand, PID is suppressed when using an ionomer encapsulant instead of a conventional ethylene vinyl acetate encapsulant. Some researchers consider that the reason is the suppression of Na diffusion when using an ionomer encapsulant. However, there has been no direct observation of Na diffusion behavior to the best of our knowledge for the modules prepared using an ionomer encapsulant. In this study it was found for the first time that Na diffuses in p-type multicrystalline Si photovoltaic modules prepared using an ionomer encapsulant without PID, suggesting that Na diffusion is not a sufficient condition for PID to occur. Another feature of PID is the recovery phenomenon induced by applying reverse voltage after PID occurs. In this study it was also found that reverse voltage application in the initial stage is effective for suppressing PID.