Mechanical characterization of wafer equivalent substrate materials from alternative silicon feedstock

The epitaxial wafer equivalent concept promises to reduce the cost for photovoltaic conversion. For this purpose, less expensive substrate silicon materials are used as a mechanical support for the epitaxial cell. In the presented paper the mechanical strength of different substrate materials was researched. The investigation of mechanical strength was performed depending on the relative ingot height in order to investigate the influence of contaminants and dopants segregation. The materials were tested with the ring on ring bending test. To interpret the results optical microscopy an impurity concentration measurements were done on selected wafers. It could be shown that impurities and dopants have a strong influence on the final material microstructure and thus on the mechanical strength. An increase in mechanical strength was found in certain parts of a highly Boron doped mc-Si block. Upgraded metallurgical Silicon showed less mechanical strength than industrial standard mc-Si. The quantity and the distribution of metallic impurities, mainly Aluminium, had a decisive influence on the mechanical strength of upgraded metallurgical Silicon.