Comparison of magnetic field imaging (MFI) and magnetic field simulation of silicon solar cells

Abstract

In solar cells, electric currents are generated by electric injection or light flow distributed over the whole area. Each flowing current generates a magnetic field depending on the strength and the direction of the electric current. Recently, a new measuring technology, called magnetic field imaging (MFI) was presented showing the potential to measure the electric current strength and direction by imaging the resulting magnetic fields. The method was applied to various defects, e.g. missing or defect solder point between solar cell interconnector and cross-connector. Here, MFI measurements of various solar cell configurations and solar cell defects are compared with a finite elemental magnetic field simulation. The results are qualitatively and quantitatively interpreted and discussed. The model is used to obtain limits in resolution depending on measuring height and measurable defects (connector brakeage or defect soldering point) of the MFI method. The variation of geometry and material parameters (within reasonable boundaries) on the current flow and the corresponding magnetic field distribution show negligible influence of manufacturing tolerances regarding layer thicknesses and ribbon/connector width as well as material fluctuations resulting in variation of electrical resistance. Measuring height and electrical current have the biggest influence on magnetic field strength and are therefore starting points for process and product optimization.