Determination of local minority carrier diffusion lengths in crystalline silicon from luminescence images

In 2007 Wuumlrfel [J. Appl. Phys. 101, 123110 (2007)] introduced a method to determine spatially resolved minority carrier diffusion lengths in silicon solar cells from electroluminescence intensity ratios. The key feature of this method was the exploitation of reabsorption of luminescence within a solar cell through optical short pass filters. The first part of this work deals with some experimental challenges which we encountered with the practical application of this method. A procedure of removing an artifact due to typical lateral filter inhomogeneities is introduced. Moreover, temperature dependence of luminescence is discussed and incorporated into the underlying model. The second part of this work aims at a determination of spatially resolved carrier diffusion lengths from photoluminescence (PL) on silicon wafers. The shortcomings of a diffusion length determination from PL intensity ratios are discussed. A straightforward method to determine spatially resolved integral excess charge carrier density from single PL images is introduced, thereby rendering a calibration with another measuring technique unnecessary. We show that quantitative information about recombination properties, such as minority carrier diffusion length, can be directly extracted from single PL images of silicon wafers.