A poly-crystalline silicon ingot having a bottom and defining a vertical direction includes a plurality of silicon grains grown in the vertical direction, in which the plurality of the silicon grains have at least three crystal orientations; and a nucleation promotion layer comprising a plurality of chips and chunks of poly-crystalline silicon on the bottom, wherein the poly-crystalline silicon ingot has a defect density at a height ranging from about 150 mm to about 250 mm of the poly-crystalline silicon ingot that is less than 15%.