Contactless Electroluminescence for Shunt-Value Measurement in Solar Cells

In recent years, there have been many new applications of PhotoLuminescence and ElectroLuminescence for use in silicon wafer, solar cell, and module characterization. This paper will present data and modeling for a contactless electroluminescence measurement of shunt values on solar cells. In this scheme, a large fraction of the free-standing solar cell is illuminated. A small fraction of the cell area is shadowed to be dark, and “viewed” by an electroluminescence photodetector. The sensor sees a “dark” region of the cell, largely indicative of the PN-junction voltage everywhere on the solar cell due to the gridlines on a finished cell. At low illumination, the gridlines can maintain a nominally constant voltage across a solar cell because the lateral currents are small. An analysis analogous to the standard Suns-Voc technique is used to extract shunt values. A simple interpretation of Suns-EL data is also demonstrated. The measurement represents a simplification over a PL method, yet avoids the electrical contacting usually associated with EL measurements. Some artifacts associated with PL shunt detection are avoided in this method since the excitation is dark injection from the junction, which depends directly on the voltage present on the cell gridlines.