A technique for fast and spatially resolved measurement of the effective series resistance of silicon solar cells from luminescence images is introduced. Without compromising the speed of existing luminescence based series resistance imaging methods, this method offers significant advantages in that it is more robust against variations in local diode characteristics. Lateral variations in the series resistance of an industrial screen printed multicrystalline silicon solar cell obtained from this method show excellent correlation with a Corescan measurement and are also shown to be unaffected by lateral variations in the diode properties.

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

A fast converging iterative procedure is proposed to calculate series resistance (Rs) and saturation current (j0) images from two electroluminescence (EL) images taken at two biases. It is not necessary here that for one bias the influence of the series resistance is negligible. Moreover, voltage series of EL images have been evaluated for calculating images of Rs, j0, and the parallel conductance Gp separately. However, it has been found that Rs variations cannot uniquely be separated from Gp variations. The reason for this is discussed. Thus, for quantitatively detecting weak ohmic shunts, EL imaging cannot replace lock‐in thermography. For strong ohmic shunts a formula for converting EL images into shunt images is given. (© 2010 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)

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