Material limits of multicrystalline silicon from state-of-the-art photoluminescence imaging techniques

This work reports on state-of-the-art silicon material characterization by calibrated photoluminescence ( PL) imaging. PL imaging techniques allow for a characterization of a large variety of material properties, ranging from bulk and surface recombination properties of bare silicon ingots, to crystal structure, dopant concentration, and bulk lifetime of silicon wafers up to material limiting impurities. In combination with solar cell simulations, injection-dependent PL imaging of processed wafers provides a method for determining the material's efficiency potential. In this contribution, we present two methods for imaging the concentration of interstitial iron at passivated silicon slices and at unpassivated silicon ingots. The latter is achieved by our latest progress in PL-based charge carrier bulk lifetime measurements with highest sensitivity, giving access to the bulk recombination properties of the ingot. Additionally, we present an improved analysis of specific loss mechanisms in silicon based on de-smeared injection-dependent lifetime images of processed wafers, which is demonstrated on the example of the bulk-related efficiency limitations in n-type high-performance multicrystalline silicon. This latest progress rounds off the established techniques, enhancing the potential of PL-based imaging techniques for a comprehensive assessment of silicon material quality, from limitations in bare silicon ingots to efficiency loss mechanisms in processed samples. Copyright (C) 2016 John Wiley & Sons, Ltd.