Root cause analysis of solar cell cracks at shingle joints

In this work, we report a cracking mechanism occurring on shingle solar cells in PV modules subjected to thermal cycling. Experimental investigations of six different ECAs show that the positions of cracks are precisely limited to the applied ECA in the joint and the occurrence confined to the rear side of the solar cells. Structural mechanic simulations based on the Finite Element Method (FEM) obtain maximum stresses of up to 400MPa on the rear surface of the solar cell orientated towards the back sheet. On the opposing surface, orientated towards the glass, the stresses are on a far lower level at around 230MPa. We measured the characteristic fracture stresses and found values of 96MPa on the rear and 265MPa on the front side of the separated shingle solar cells. The lower values on the rear originate from microfractures at the solar cell edges caused by the laser scribe and mechanical cleave process.