Measurements of Physical Parameters Characterizing ESDs on Solar Cell and Correlation Between Spectral Signature and Discharge Position

Electrostatic discharges (ESDs) on solar cells are a possible cause of dramatic consequences such as secondary arcs responsible for definitive power losses. To cope with these significant implications, different approaches are followed such as design rules reducing voltage between the adjacent cells, conductive layers, or grouting to try to reduce discharges triggering. However, ESDs on solar cells cannot be completely avoided and having a good knowledge of their characteristics is essential for prevention, prediction, and modeling. In this paper, we describe how the plasma emitted during an ESD on a solar cell can be analyzed with dynamic tools such as triple probes and time-resolved optical spectroscopy. These techniques are used to obtain the results on plasma density and electron temperature that can be compared with outputs from ESD and flashover propagation models. While time-resolved optical spectroscopy is used on a single point (the point where optical fiber is focused on), triple probe is also used for spatial measurements. With this technique, electron density is measured at several distances from the discharge point providing both temporal and spatial information. In a second time, the optical signature measured by optical spectroscopy is correlated with scanning electron microscope observations showing the existence of two kinds of triple points at cell's edge. These two kinds of discharges have different optical signatures showing either elements from the active junction or from the substrate and rear electrode. These discharges are also distinguished by microscopic observations and images of cell's edges confirm the previous results. These results show the importance of the silver back electrode and also of the eventual presence of covering glue on the position of the discharge. They provide information for models but let us also imagine the possible mitigation methods.