Field failure mechanism study of solder interconnection for crystalline silicon photovoltaic module

This study investigates a solder interconnection failure of a 25-year-old crystalline silicon photovoltaic (c-Si PV) module and draws conclusions on the failure mechanism of the solder interconnection. The efficiency degradation of the 25-year-old c-Si PV module is –23%. Physical analysis of the solder interconnection failure finds solder to solder cracking and solder to Ag paste cracking. The main failure mechanism of the solder interconnection crack is caused by coefficient of thermal expansion (CTE) mismatch between the module material and the ribbon wire solder as shown by FMEA. To demonstrate the failure mechanism, a thermal cycle test is designed and conducted on a small c-Si PV module. The temperature cycle condition is −45 °C to 85 °C and the dwell time is 20 min. Measurements are carried out every 100 cycles monitoring the series resistance (Rs) through dark I–V. The result shows that Rs increases. After 1,000 cycles, the characteristics of dark I–V and light I–V are compared and analyzed. Failure mechanism analysis is conducted for the modules for which Pmax decreased with 20%. Water-jet techniques for cross-section and SEM are used to analyze the factor of resistance change and efficiency degradation. The failure mechanism of solder interconnection for c-Si PV Module is proved.