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Luminescence images of silicon solar cells contain information about local recombination properties and local series resistance. It is difficult to separate the information and interpret single images correctly and quantitatively though, which greatly limits the use of single luminescence images, in particular for the application as an in-production characterization tool. We therefore developed a fast method based on photoluminescence imaging for a spatially resolved coupled determination of the dark saturation current and series resistance (C-DCR)

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. 300 M. KASEMANN ET AL.Figure 7. ILIT (top) and PL (bottom) measurements of an intentionally shunted solar cell under open-circuit conditions. Shunts on grid lines are labeled by letters A-E in the ILIT image, while shunts between grid lines are labeled by numbers 1-7 in the PL image. Shunts appear as high values in ILIT and low values in PL imaging. The shunts have been introduced by laser firing

Solar cells in modules are reverse biased when they are shaded. This can lead to diode breakdown and eventually to the occurrence of hot spots, which may, in the extreme case, destroy the module by thermal degradation. We observed at least three different types of diode breakdown in multicrystalline silicon solar cells. One of them is found to be related to the recombination activity of defects. This type is indicated by a slow increase in the reverse current with reverse bias and a relatively low breakdown voltage around -10 V. The local breakdown voltage depends significantly on the level of contamination of the material. When the solar cell is reverse biased, the breakdown sites emit bright light which shows a broad spectral distribution in the visible range with a maximum at 700 nm