Impact of illumination and encapsulant resistivity on polarization‐type potential‐induced degradation on n‐PERT cells

Abstract

Power loss caused by polarization-type potential-induced degradation (PID-p) in a variety of high-performance photovoltaic cell types has been observed to be recoverable via subsequent illumination and in some cases preventable via simultaneous illumination. In this report, we describe the results of a study in which the front faces of n-PERT cells encapsulated in polymers with a broad range of electrical resistivity were exposed to varying and controlled irradiance during PID testing. For a low resistivity ethylene-vinyl acetate copolymer encapsulant, no reduction in the rate or extent of power loss was observed for irradiance as high as 1,000 W/m 2 , whereas for high and intermediate resistivity polyolefin encapsulants, 100 and 300 W/m 2 , respectively, prevented power loss. We introduce a simple model based on charge accumulation that facilitates interpretation of these results whereby degradation via charge accumulation under voltage stress and recovery due to light exposure are opposing and interdependent phenomena that describe the susceptibility of a module to power loss.

Electrochemical degradation modes in bifacial silicon photovoltaic modules

“…(2) greater bulk conductivity as well as ionic transport of species such as Na+ for EVA encapsulants compared to POE, resulting in stronger PID effects. 8,[36][37][38] Indeed, Section S6 shows 1,000Â greater volumetric resistivity for the POE (2.6 Â 10 15 Ωcm) compared to the EVA 39 These results suggest that the PID degradation modes that we observe were likely unaffected by extended exposure to damp heat for POE modules, while moisture uptake by the encapsulant could worsen PID effects in EVA.…”

“…Typically, Na+ transport occurs in EVA encapsulants and likely contributes to PID-p, while POE encapsulants are found to be an effective barrier to Na+ transport. 37,38 Despite blocking of Na+ in POEs, PID-p has been observed to a lesser extent in POE-containing modules, and the severity of the polarization effect scales with the encapsulant's resistivity. 38 This suggests that charged species other than Na+ can contribute to PID-p.…”

“…37,38 Despite blocking of Na+ in POEs, PID-p has been observed to a lesser extent in POE-containing modules, and the severity of the polarization effect scales with the encapsulant's resistivity. 38 This suggests that charged species other than Na+ can contribute to PID-p. In particular, recent work describes a PID-p mechanism without Na+ caused by a change in charge state of K-centers in the silicon nitride layer.…”

Degradation in photovoltaic encapsulant transmittance: Results of the second PVQAT TG5 artificial weathering study

“…Polyolefins may also feature increased volume resistivity and decreased Na + mass transport, which may prevent potential induced degradation (PID). [32][33][34][35][36] Although EVA and polyolefins are both semicrystalline polymers, polyolefins typically have a greater crystalline content. Crystalline content can reduce optical performance, whereas EVA can offer better front side transmittance.…”

“…The industry continues to examine alternative encapsulants, including polyolefins (“POs”), which cannot produce acetic acid because no acetate side groups are present. Polyolefins may also feature increased volume resistivity and decreased Na + mass transport, which may prevent potential induced degradation (PID) 32–36 . Although EVA and polyolefins are both semicrystalline polymers, polyolefins typically have a greater crystalline content.…”