Thermo-mechanical degradation at finger-solder interface in a crystalline silicon photovoltaic module under thermal fatigue conditions
Sagarika Kumar& Rajesh Gupta
Indian Institute of Technology Bombay, Mumbai, India

The reliability of current carrying fingers in a photovoltaic (PV) cell is essential to the overall performance of a module. The thermo-mechanical performance of fingers is often discussed in the domain of solder layer degradation due to the close proximity, and vulnerability under transient temperature variations. This work utilizes a 3-D finite element model of a PV module simulated under accelerated thermal cycles to discuss the thermo-mechanical behavior at the finger-solder interface. Experimental TC cycles were run to support the simulated results by characterization of observed finger breakages using illuminated current-voltage and electroluminescence imaging technique. The finger-solder interface was established to be vulnerable to thermal cyclic conditions from both simulated and experimental findings. Further, the effect of variable solder geometrical parameters (solder thickness and width) on damage accumulation at the finger-solder interface was investigated. Solder thickness was found to be a crucial parameter for the maintenance of finger reliability. In addition, variable width simulation demonstrated increased damage accumulation due to the case of over-soldering. The findings from the investigation highlight the need to take precautionary measures during the soldering process of module manufacturing for enhanced finger reliability, which is essential for the overall PV module performance.