Evaluation of the Contact Quality in Silicon Solar Cells and Modules Using LBIC Phase Mapping

Making good electrical contacts when interconnecting solar cells with no or very small busbars in a module can be challenging. Light beam induced current (LBIC) mapping reveals the contact quality with a high spatial resolution when evaluating the phase shift between the pulsating laser light and the current. In this research, we have fabricated solar modules with Sticky Solar Power’s “The Tape SolutionTM” and assessed the modules using LBIC phase mapping. Enhanced LBIC phase shifts correlate with smaller series resistances between the point of illumination and current extraction. The areas with abrupt changes in the phase shift were observed under optical microscope and revealed breakage or weakening along fingers. We also developed a cross-section preparation method to investigate the physical contact between the solar cell and the taped wires at the areas of interest. This method included cutting the laminated module using rotary diamond blades followed by grinding and polishing the surface to remove the damaging effects of cutting pressure. Optical microscopic and SEM/EDS images of the cross-section near the silver pads at areas with higher resistance showed low silver content in some parts and minor gaps between the silver and solder alloy.