The effects of light illumination and heat treatment on the micro-defect and electricity output character of Cz-silicon solar cells have been studied by using coincidence Doppler broadening spectra of positron annihilation.The results showed that the conversion efficiency of solar cell decreased gradually with the light exposure time increasing

and then reached a constant value after irradiating more than 12 hours.When irradiated samples annealed at 200℃ for 2 hours

the conversion efficiency would recover gradually.The metastable boron-and oxygen-related defects center in samples which activated by light illumination and inactivated by thermal treatment caused the change of conversion efficiency and the variation of ratio curves.