Cracks in Solar Cell Metallization Leading to Module Power Loss under Mechanical Loads

We investigate the mechanisms leading to electrically insulated cell parts in a photovoltaic module under mechanical load. For this we measure the resistances across a crack in a laminated solar cell during bending that is typical in the field. The cracks in the solar cell are detected with electroluminescence imaging. The resistance over the aluminum paste increases continuously by negligible 30 mΩ whereas the front finger resistance increases by 15.4 kΩ stepwise. This difference is the result of the higher ductility of the aluminum paste in comparison to the front finger metallization. We associate the steps in the front finger resistance measurement to breakage of single fingers with an equivalent circuit model. Furthermore we found that a silicon crack widths lower 2 μm has no influence on the resistances. Crack widths higher than 7 μm leads to a complete front finger interruption. We determine that the specific resistance of such a crack causes nearly 100% of the power loss, which is caused by a completely electrically insulating crack in a photovoltaic module.