Unveiling the failure mechanism of electrical interconnection in thermal-aged PV modules

The electrical interconnection is the most decisive current transportation pathway in photovoltaic (PV) modules. However, thermal stresses, induced by temperature variation, can reduce the mechanical properties of the electrical interconnection and lead to the performance degradation of PV modules. The present study aims to investigate the influence of thermal stress on the failure mechanism of the electrical interconnection. The mechanical integrity of current transmission layers and interfaces is measured by peeling tests and evolution of defects and failure process is observed by in-situ electroluminescence (EL) imaging and scanning electron microscopy (SEM). Under repeated thermal stress, the defects initiated at the end of the soldering track and, then, expanded to the adjacent cell regions. Initially, the silver-glass interface was more vulnerable to separation under the action of the peeling force. However, the disruption between the silver busbar and silicon wafer increased with increasing thermal cycling. In addition, a possible failure mechanism has been proposed for electrical interconnection by SEM observation and defect analysis. Lastly, we have demonstrated that the reliability of the interconnection structure can be improved by increasing the edge distance of the PV modules or using an anti-overpressure device.