Encapsulant Selection for PID Resistant Modules Made with Heterojunction Solar Cells

Recent studies showed that SHJ solar cells can be prone to PID when encapsulated with a low volume resistivity encapsulant, such as ethylene vinyl acetate (EVA). These studies also demonstrated that their degradation mechanism is different from Al-BSF modules. It is well known that PID in Al-BSF cells can be prevented by a high volume resistivity encapsulant. In this work we perform PID tests in humid conditions (85°C/85% RH) on one-cell SHJ glass/glass modules with and without edge sealant. Seven different encapsulants are used: ionomer, three elastomer polyolefin (POEs), thermoplastic polyolefin (TPO), polyvinyl butyral (PVB) and EVA. Moreover, the effect of water ingress and the voltage polarization are also considered. The results indicate that PID can be prevented with the proper selection of encapsulants. Ionomer, POEs and TPO show beneficial effects on preventing degradation, both with and without edge sealant. Modules encapsulated with EVA do not suffer from PID when encapsulated with an edge seal configuration, even after extended tests (e.g. five times the 96 h of test duration foreseen in the IEC Technical Specification for c-Si modules).