Model of Cracked Solar Cell Metallization Leading to Permanent Module Power Loss

We measure the progression of resistances of cell cracks in laminated multicrystalline silicon solar cells and study the impact of the crack width and the number of loading cycles. The resistance of the front fingers increases by a factor larger than 1000 during loading. The resistance increase always recovers to its initial value of 0.2 Ω under unloaded conditions. This holds for up to 10
⁵
bending cycles. In contrast, the rear resistance of the aluminum paste shows a fatigue behavior. During the first 100 bending cycles, the unloaded rear resistance increases continuously from 0.03 to 2 Ω. Afterwards, it starts to scatter in the range of 0.1 Ω to more than 4000 Ω after 10
³
cycles. The rear resistance of a sample without rear encapsulation degrades 24 000 times slower compared with an encapsulated sample. After 10
⁵
cycles, the rear resistance is still less than 0.2 Ω. We introduce a model for the development of the crack resistance, which qualitatively explains the measured resistance values.