Investigations on crack development and crack growth in embedded solar cells

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Abstract
In recent investigations using various analysis methods it has been shown that mechanical or thermal loading of PV modules leads to mechanical stress in the module parts and especially in the encapsulated solar cells. Cracks in crystalline solar cells are a characteristic defect that is caused by mechanical stress. They can lead to efficiency losses and lifetime reduction of the modules. This paper presents two experiments for systematic investigation of crack initiation and crack growth under thermal and mechanical loading using electroluminescence. For this purpose PV modules and laminated test specimens on smaller scales were produced including different cell types and module layouts. They were exposed to thermal cycling and to mechanical loading derived from the international standard IEC 61215. Cracks were observed mainly at the beginning and the end of the busbars and along the busbars. The cracks were analyzed and evaluated statistically. The experimental results are compared to results from numerical simulations to understand the reasons for the crack initiation and the observed crack growth and to allow module design optimization to reduce the mechanical stress.

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