Surface Recombination Velocity Measurements of Metallized Surfaces by Photoluminescence Imaging

QSSPC-calibrated photoluminescence imaging (PLI) was used to determine the rear surface recombination velocity Srear,eff of p-type Si FZ wafers after processing of large area screen printed Al contacts with varying paste thickness and firing temperatures. The paste thickness was varied by changing the snap off in the screen printer, and the resulting back surface field (BSF) thickness was investigated by scanning electron microscopy. BSF thicknesses of between 1.4 and 6.2 μm were found. The BSF thickness saturated at high paste amounts combined with high firing temperatures while an increase in the eutectic layer thickness was observed. Several luminescence images were taken of each sample with different reference samples to assess the stability of the technique, and uncertainties are discussed.