Synchrotron-based microprobe investigation of impurities in raw quartz-bearing and carbon-bearing feedstock materials for photovoltaic applications

Using synchrotron-based analytical microprobe techniques, we determine micrometer-scale elemental composition, spatial distribution, and oxidation state of impurities in raw feedstock materials used in the photovoltaic industry. Investigated Si-bearing compounds are pegmatitic quartz, hydrothermal quartz, and quartzite. Micrometer-scale clusters containing Fe, Ti, and/or Ca are frequently observed at structural defects in oxidized states and in bulk concentrations equivalent to inductively coupled plasma mass spectroscopy measurements. Investigated C-bearing compounds are pine wood, pine charcoal, and eucalyptus charcoal. Clustered metals are observed only in the charcoal samples. Impurity clustering implies that industrial processing could be adapted to take advantage of this "natural gettering" phenomenon, expanding the usable range of raw feedstock materials to dirtier, cheaper, and more abundant ones, currently underexploited for solar-grade silicon production.