Reduction of the initial defects generated during casting of quasi-single crystalline silicon by reserving gaps between seed crystals

Abstract

The presence of dislocation is a significant impediment to enhancing the quality of quasi-single crystalline silicon cast by seed-assisted directional solidification. A novel approach was proposed to reduce dislocations in G7 166-type silicon ingots, especially in the region of seed crystal seams, by reserving seed crystal gaps during loading. We calculated that the seed crystal's linear thermal expansion after heating from 298.15 to 1683.15 K was 0.9 mm. However, in consideration of the actual deviation in seed processing and measurement, we increased the gap between seeds to 1.2 mm to prevent compressive stress on all 49 seed crystals. The actual residual seed gap measured after ingot casting was approximately 0.325 mm, which is relatively close to the calculated value. It was discovered that the average defect ratio in the silicon blocks decreased from 26.95% (without gaps) to 6.79% (with 1.2 mm seed gaps) for the proposed method. This indicates that a portion of the dislocation source was reduced by reducing compressive stress caused by linear expansion between adjacent unmelted seeds. The average conversion efficiency of the solar cells prepared using the gapless seed method for p-type polycrystalline cells is 22.03%, whereas the novel approach resulted in an average cell efficiency of 22.22%, featuring a higher proportion of high-efficiency sections.