Mechanical Investigations on Metallization Layouts of Solar Cells with Respect to Module Reliability

Abstract

This case study deals with the assessment of different metallization layouts on the reliability of encapsulated solar cells. Six different metallization layouts were modelled by means of finite- element- modelling. In a first step cooling after soldering was simulated and the mechanical stress field in the silicon determined. In a second step mechanical bending of a module laminate consisting of one string was simulated. Prior to bending stresses from soldering were imported into the model. Two different load setups were realized applying the bending perpendicular or parallel to the busbars. The probability of failure was calculated by means of a probabilistic approach for brittle materials. Results show that the load direction strongly influences the probability of failure, which is in good agreement with literature. Different metallization layouts have a large effect on the reliability of solar cell in particular with an orientation of the busbars parallel to the main load direction. Although the stresses from soldering may be comparably small to the stress from bending but they guide the fracture characteristic of a cell. The results show that an understanding of the intrinsic stresses in the silicon after processing is important for interpretations on module level.