Characterization of a 75 kg multicrystalline Si ingot grown in a KRISTMAG ® -type G2-sized directional solidification furnace

Abstract A 75 kg solar-grade boron-doped silicon (Si) ingot has been directionally solidified in a Vertical Gradient Freeze (VGF)-type G2-sized furnace equipped with KRISTMAG® Heater Magnet Module (HMM). Alternating Magnetic Fields (AMFs) were used to enhance melt stirring and to control the growth interface morphology and shape. This as-grown multicrystalline (mc)-silicon ingot of 384×384×230 mm3 in volume was cut into 4 bricks and in Vertical Cuts (VC) to analyze the material and to produce solar cells. Numerical simulations have been performed in order to optimize mass transport processes. Information about the curvature of the liquid–solid interface, the distribution of carbon (C) and oxygen (O), the content of Silicon Carbide (SiC) and Silicon Nitride (Si3N4)-particles and the electrical activity of defects were obtained from the ingot core. Except for the last-to-freeze part, a primarily inclusion-free ingot was solidified. Minority carrier lifetimes of τ~4 µs were measured on the grinded as-cut surface. The concentrations of C and O were determined by Fourier Transform Infrared (FTIR) spectroscopy to (0.4–7.9)×1017 atoms/cm3 and (0.3–5.4)×1017 atoms/cm3, respectively. Solar cells were produced from wafers at the Meyer Burger Roth & Rau Technology and Research Centre using the Meyer Burger Roth & Rau Passivated Emitter Rear Cell (PERC) process. Solar cell efficiencies were achieved between 17.7% and 18.0%.