Cell Metallic Contact Resistance of Field-Retrieved PV Modules

It is well known that the series resistance of photovoltaic (PV) modules increases over time in the field. Depending on the stress level and duration of local field/climatic conditions (e.g., temperature, humidity), the extent of series resistance increase can vary. To reduce the overall increase of the series resistance, it is crucial to determine and understand the extent of resistance increase in the individual components (i.e., cell metallization and interconnect solder bonds) of the field exposed modules. The cell metallization resistance is caused by both line resistance of the gridlines and the contact resistance between gridlines and semiconductor. This paper analyzes the increase of gridline resistance and contact resistance of the cells in the PV modules of same construction/type retrieved from two different high stress level climatic conditions, hot-dry (Arizona) and hot-humid (Florida). To correlate the contact resistance data with other studies, both retrieved-modules and extracted-cells have been characterized by current-voltage, UV fluorescence, reflected light microscopy and X-ray photoelectron spectroscopy measurements.