High-quality multi-crystalline silicon (mc-Si) grown by directional solidification using notched crucibles

We report on an idea for grain control during directional solidification using a crucible with notches at the bottom for mc-Si solar materials. It was observed that with a proper notch size, the initial grain competition could be controlled with a proper cooling rate. The notch could enlarge the grains induced by the spot cooling method and the grains became dominant at the later stage of solidification. Furthermore, the crystals grown from the notch showed a higher minority carrier lifetime and a larger area of twins, with a much lower dislocation density as well. The electron back scattered diffraction (EBSD) analysis for the controlled crystals further indicated that the region near the notch had almost the same {1 1 2} orientation from the notch. The proposed method can be easily implemented in commercial ingot production.