Arrangement of dendrite crystals grown along the bottom of Si ingots using the dendritic casting method by controlling thermal conductivity under crucibles

Dislocations in Si multicrystals strongly affect the efficiency of solar cells, and are usually generated from random grain boundaries during crystal growth. The low density of random grain boundaries and the coherency of random grain boundaries are very important in suppressing dislocations. Controlling arrangement of dendrite crystals grown along the bottom of ingots is effective for decreasing the density of random grain boundaries and for improving the coherency of random grain boundaries. A method of controlling thermal conductivity under crucibles to control the arrangement of dendrite crystals was proposed. Graphite plates with different thermal conductivities were used all over the bottom surface of crucibles. Two types of graphite plates, one with a line-shaped highly cooled part and the other with a ring-shaped one, were used. Using the graphite plates, the distribution of dendrite crystals was well arranged, and dendrite crystals were controlled to be fairly parallel to each other.