Directional growth method to obtain high quality polycrystalline silicon from its melt

We propose a new concept for growing a polycrystalline silicon (poly-Si) ingot suitable for solar cells by the casting method. Usually, poly-Si ingots grown by casting method have many crystal grains with different orientations and different sizes, and have many grain boundaries because such polycrystalline structures have not been controlled during casting. In this study, we found that to induce a dendrite growth in the initial stage of directional growth was useful for controlling a polycrystalline structure such as grain orientation and grain size of each grain. In fact, we obtained a poly-Si ingot which had large-size crystal grains with same orientation to the growth direction by inducing dendrite growth along the crucible wall in the initial stage of growth. The solar cell property of such a structure-controlled poly-Si was higher than that of structure-uncontrolled poly-Si. This growth method is very promising in the field of the poly-Si solar cells.