Finger and interconnect degradations in crystalline silicon photovoltaic modules: A review

The research and developments in the field of defects and degradations (D & D) in crystalline silicon photovoltaic (PV) modules have been on the forefront, to ensure reliable long term operation of solar power plants worldwide. Thereby, to maintain the overall electrical integrity and performance of cells and modules, it is essential to improve the reliability of cell metallization (i.e., busbar and fingers) and interconnects against D & D in the outdoor field conditions. This paper presents a comprehensive review and analysis on the reported D & D in conventional screen printed metallization and soldered interconnects. The review has been presented on the basis of operating modes of degradation induced via thermo-mechanical fatigue, chemical mechanisms, manufacturing fallacies, and system voltage. Furthermore, for increased understanding of the underlying defect mechanisms, these D & D have been investigated for the respective modes of electrical loss, and sensitivity to common variable parameters like position, orientation and number of defects by electrical stimulation. The use of common characterization techniques for defect detection and analysis have also been presented, wherein, the effective use of imaging techniques is advised. Also, standard environmental tests, specified under IEC 61215 were found to induce finger and interconnect D & D like in field, however, defect specific tests may be devised for a detailed analysis. Finally, the precautions performed during the manufacturing processes, especially the soldering process are identified to be key in prevention of D & D in finger and interconnects.