The conversion efficiency of solar cells made from single crystalline Si is generally about 3–4% higher than those made from Si multicrystal by the casting method. In this paper, the single crystalline Si obtained by the Czochralski method using metallurgical grade silicon raw materials was characterised by minority carrier lifetime, optical microscopy, the concentration of impurities and the conversion efficiency. The influence of crystalline defects and impurity elements on the electrical property has been investigated. We can conclude that both defects and impurity elements play important roles in the deterioration of the minority carrier lifetime. The conversion efficiency of solar cell using the middle wafer can reach 11·39%.