Pseudo Shunts Interfering Lock-In Thermography Investigations of Solar Cells: Characterization and Prevention

Pseudo shunts are artifacts, which may occur during lock-in thermography (LIT) measurements of solar cells. They are caused at the interface between the solar cell and the sample holder or at current feed-in points and may affect LIT investigations detrimentally, leading to misinterpretation of LIT images. The apparent current density-voltage ( J-V) characteristics of pseudo shunts show a significantly steeper slope than that of real shunts, and even of good parts of the cell, and cannot be fitted by the common one- or two-diode models. The cause of pseudo shunts is found to be a local contact on the backside of wafer-based silicon solar cells to the chuck, surrounded by a noncontacted region. A method is proposed to prevent the appearance of pseudo shunts.