Stress analysis of encapsulated solar cells by means of superposition of thermal and mechanical stresses

Within this contribution several 3D finite- element- models have been created in order to simulate processing of solar cells (lamination, soldering) as well as mechanical bending. The stress state for each load case was analysed with respect to magnitude and direction of principal stresses. For the process steps there are different mechanisms that induce stresses in the silicon. For soldering the mismatch in CTE is dominant. For lamination, bending around the ribbon is the dominant mechanism, which is due to the contraction of the encapsulant. Furthermore, it was found that cooling during lamination applies the highest loads into a solar cell. Mechanical bending was simulated and investigated experimentally by 4-point-bending with different load ramps. Due to strain-rate dependent properties of the encapsulant EVA there is a minor in fluence on the load deflection behaviour but a large influence on the reliability of a solar cell. By means of a parameter study the influ ence of the cell distance on mechanical reliability was investigates. It was shown that a small cell distance (here < 3mm) increases the probability of failure of the solar cell significantly.