Method For Producing Directionally Solidified Silicon Ingots

1 . Method for the production of directionally solidified Czochralski, float zone or multicrystalline silicon ingots or thin sheets or ribbon for making wafers for solar cells from silicon feedstock initially containing between 0.2 ppma and 10 ppma boron and between 0.1 ppma and 10 ppma phosphorous, characterized in that if the boron content in the silicon feedstock is higher than the phosphorous content, the boron content in the molten silicon is kept higher than the phosphorous content during the directional solidification process by adding boron discontinuously, continuously or substantially continuously to the molten silicon in order to extend the part of the directionally solidified ingot or the thin sheet or ribbon solidifying as p-type material, or if the content of phosphorous in the silicon feedstock is higher than the boron content, the phosphorous content in the molten silicon is kept higher than the boron content during the directional solidification process by adding phosphorous to the molten silicon discontinuously, continuously or substantially continuously in order to extend the part of the ingot or the thin sheet or ribbon solidifying as n-type material.