Analysis for the degradation mechanism of photovoltaic ribbon wire under thermal cycling

For assurance more than 25 year lifetime of photovoltaic module, the reliability of components and material should be guaranteed. This study draws a conclusion of ribbon wire degradation mechanism among the materials under thermal cycling. The main degradation mechanism of ribbon wire the crack caused by coefficient of thermal expansion (CTE) mismatch between the module material and the ribbon wire solder. To demonstrate the degradation mechanism, thermal cycle test was designed and conducted with small photovoltaic module. The temperature cycle condition was (-) 45°C ~ (+) 85°C and the dwell time was 20 minutes. Measurement was carried out every 100 cycles monitoring the series resistance (R_s) through dark I-V. The result shows that R_s increases. After 1,000 cycles, the characteristics of Dark I-V and illuminated I-V were compared and analyzed. Failure mechanism analysis was conducted for the modules which decreased 20 % of P_max. Water-jet techniques for cross-section and SEM were used to analyze the factor of resistance change and efficiency degradation. The degradation mechanism of ribbon wire was proved.