A reliability study of silicon heterojunction photovoltaic modules exposed to damp heat testing

In this paper, we report on the reliability of silicon heterojunction (SHJ) solar cell mini-modules. The output of a photovoltaic module is degraded because of moisture ingress from the encapsulated polyvinyl butyral (PVB). Moisture ingress starts on the edge of a module and gradually progresses towards the interior, which delaminates the encapsulant to form a haze. This haze makes a reduction in current. Therefore, we analyzed the haze ratio using a haze spectrophotometer and the increased haze ratio leads to the decrease in the current. The predicted mechanism of the module by the moisture ingress is described from the analysis of the sheet resistance and contact resistivity, respectively. Therefore, we monitored different encapsulant materials— both ethylene vinyl acetate (EVA) and olefin-based—for 1000 h under damp heat (DH) conditions to determine how to minimize moisture penetration in the module. The PV module based on olefin is better than that based on EVA, which has an error range within 3.46%. It was found that, in terms of maximum module power output, the olefin-based module was more resistant to moisture ingress than the EVA-based module.