Improved testing of soldered Busbar interconnects on silicon solar cells

The expected life of a PV solar cell is 20-25 years. To ensure this the quality and reliability of the material and process parameters of solder joints that connect single cells into strings has to be assured. A standardized test method or clearly defined good-bad-criteria are not available for PV products. Thus a product, manufacturer or joining technology comparison is not possible. Due to the lack of standards and commercial available test equipment PV module manufacturers often implement their own test solutions and specifications. However, these mostly have limited scientific proof, are difficult to interpret and lack optimisation. Because there is no standardization these solutions cannot be used for comparative characterization of different manufacturers, cell types, base- and joining materials or joining technologies. The most commonly used test for solar cell ribbon interconnects is the Pull test, as used in micro-electronics. For thin, brittle, large area silicon solar cells substantial modifications of the test equipment and methodology are required to realize a suitable metrology. In addition the factors influencing the defect conditions in multi crystalline material, high strains around the solder connect, inhomogeneous contact interfaces has to be considered. Results show the development, optimization and evaluation of a test method for soldered bus bar interconnects on silicon a solar cell that is independent of product, manufacturer and cell assembly. A comparison between this new method, its results and the previously mentioned issues is made. The test method demonstrates how cell breakage during a test can be avoided by optimising how it is mounted and guided.