We have demonstrated the effect of oxygen precipitation on the performance of Czochralski (CZ) silicon solar cells. The oxygen precipitates in silicon substrates were formed by a low-high two-step annealing. With the increase of oxygen precipitation, the minority carrier diffusion length of CZ silicon solar cells decreases and, meanwhile, the leakage currents due to the carrier recombination at the defect states get increased. The external quantum efficiency (EQE) measurement shows that the decrease of the solar cell efficiency due to oxygen precipitates mainly takes place in the long wavelength range of light. The short-circuit current and open-circuit voltage of solar cells both become smaller, while the fill factor does not significantly change. The efficiency of solar cells is reduced to 12.7% from an original value of 17.5%. All these results suggest that the oxygen precipitation is a limitation factor for the improvement of solar cell efficiency, which should be strictly controlled during the crystal growth and cell fabrication. (C) 2011 Elsevier B.V. All rights reserved.