Simulation of Series Resistance Increase through Solder Layer Cracking in Si Solar Cells under Thermal Cycling

In solar cell modules, thermal cycling stresses can cause cracking in the ribbon wire, leading to an increase in series resistance and a drop in the power output of the module. Quantitative analysis was conducted to study the increase in series resistance, considering two cracking models: continuous and random. In the continuous model, it was expected that if all the ribbon wires on the front side of the module cracked, the current would decrease linearly from 0 to 100%, and the series resistance would increase exponentially to infinity. In the random crack model, the current dropped slowly, and the series resistance increased less compared with that in the continuous one. A mathematical model based on the bypass mechanism of the currents was proposed to explain the differences between the two models. The study found that cracking in the solder layer under thermal cycling can be described by a combination of continuous and random models, which can represent the upper and lower levels of the series resistance increase. When the solar cell power dropped to 80%, the increase in series resistance was expected to be in the range of 200 to 250% using the continuous and random models, respectively.