Solder Bond Degradation of Fielded PV Modules: Correlation between Performance, Series Resistance and Electroluminescence Imaging
Archana Sinha1, Viswa Sai Pavan Buddha1, Eric J Schneller2,3, Dylan J Colvin2,3, Kristopher O Davis2,3, GovindaSamy TamizhMani1
1Photovoltaic Reliability Laboratory, Arizona State University , Mesa, AZ, United States
/2Department of Materials Science and Engineering, University of Central Florida, Orlando, FL, United States
/3Florida Solar Energy Center, University of Central Florida, Cocoa, FL, United States

One of the most dominant degradation modes in the field deployed modules is degradation of interconnect-metallization system, which significantly affects modules’ degradation rates and service lifetime. The effect of solder bond degradation on the performance of three 10-year-old modules installed at a Florida site has been quantified through the cell series resistance (Rs) acquired from dark current-voltage (I-V) curves, which has been correlated with performance loss and electroluminescence (EL) intensity. The regions of poor solder joints are identified in EL image through the high luminescence spots at interconnect ribbons because of current crowding. Each individual cell of the tested modules was accessed by cutting off a small segment of backsheet and soldering at cell interconnect. A spatial distribution of Rs in the modules is mapped, which demonstrated a good correlation with fill factor and output power as identified by two parallel trendlines. This implies that the performance loss of these fielded modules is significantly dictated by the solder bond degradation. Further, the ultraviolet fluorescence images showed an identical browning pattern of encapsulant over the cells, indicating uniform current loss in all the cells of the module.