Mechanical and thermomechanical assessment of encapsulated solar cells by finite-element-simulation

Within the following work mechanical and thermo-mechanical studies on embedded solar cells were carried out. Temperature dependant material properties such as shear modulus and coefficient of thermal expansion of an EVA encapsulant were determined by dynamic mechanical analysis (DMA) and thermo mechanical analysis (TMA). Those parameters were integrated into various simulation models such as the lamination process starting from the curing temperature at 150 °C and thermo cycling. Parameter studies were carried out concerning the cell thickness to assess the thermo-mechanical behavior of the cell string and the stress distribution in the silicon. Within a second study the mechanical behavior of the laminate was investigated. As a result it is shown that the solar cells have a significant impact on the deflection of the laminate, whose behavior over a temperature range is dominated by the stiffness properties of the encapsulant. By means of a combination of global models and submodels it was possible to assess the stress distribution in the solar cells with particular interest in the interconnection region between the cells. The magnitude of the stress depends strongly on the stiffness of the encapsulant. Especially for thin cells the stress can increase critically.