Luminescence imaging for the detection of shunts on silicon solar cells

Luminescence imaging is a non-destructive, fast, and versatile imaging method for spatially resolved solar cell and material characterization. In this paper, we investigate its ability to detect shunts on silicon solar cells. We give a detailed description of the relation between local junction voltage and local luminescence signal. This relation is important because shunts drain majority currents causing voltage drops across the surrounding series resistances and that way affect luminescence images. To investigate effects related to majority currents, we describe and apply a simulation model that allows the simulation of lateral voltage distributions on solar cells. This model, and a comparison to illuminated lock-in thermography, helps to discuss some practical aspects about shunt detection by luminescence imaging. We will discuss a procedure to distinguish between ohmic and diode-like shunts and finally present simulations and measurements showing that luminescence imaging is only weakly sensitive to shunts under the metallization. However, we also show its high sensitivity for remote shunts and propose a possible application where this high sensitivity could be especially helpful.