Influence Of Micro-Defects And Eletronic Structure In The Silicon-Based Semiconductor On Photoelectric Property Of The Materials

The effects of positron annihilation radiation,light illumination and heat treatment on the micro-defect and electricity output character of the single crystal of silicon solar cell have been studied by positron annihilation techniques. Positron lifetime and coincidence Doppler broadening spectra for porous silica monoliths calcined at different temperatures from 900 to 1500℃,single crystal of SiO₂ and Si have been measured.The results show that:(1)When positron annihilation radiation served as a source of light illuminating on the surface of the solar cell,there is no output of current and voltage from the solar cell.The IU characteristics of the solar cell before and after positron annihilation radiation are basically the same.The damage due to positron annihilation radiation is limited,which didn't change the basic IU output characteristics.(2)The conversion efficiency of single crystal of silicon solar cell decreases with the light exposure time increasing,and will remain basically unchanged when dropped to some extent.After annealed at about 150℃and 200℃,the conversion efficiency increases.The 200℃tempering is better for the recovery of the solar cell conversion efficiency than treating in 150℃.(3)The conversion efficiency of the solar cell decreased gradually with the light exposure time increasing,and then reached a constant value after the light exposure time longer than 12 hours.After light irradiation,the height of the peak of the ratio curve obtained from coincidence Doppler broadening spectrum measurements decreases,and the peak position,or the momentum of annihilation electron,increases.After annealed at temperature of about 200℃, the conversion efficiency of the solar cell will increase.The height of the peak of the ratio curve increases(lower than that of the solar cell without light illuminating),and the peak position,or the momentum of annihilation electron, decreases.(4)The decomposed rate of boron- and oxygen-related defects of the solar cell depend on the annealing temperature:the higher annealing temperature,the higher decomposed rate and lower oxygen content in defects.Correspondingly, the height of the peak of the ratio curve of the solar cell annealed at 150℃is lower than that annealed at 200℃;the electron momentum in the solar cell annealed at 150℃is higher than that annealed at 200℃.(5)In the SiO₂ samples,the momenta of 2p electrons of O atom is higher than that of 3p electrons of Si atom.There is a relatively high peak at 11.8×10^-3m₀c on the ratio curve of SiO₂.(6)The height of the peak of the ratio curve of the as-received SiO₂ is lower than that of the single crystal of SiO₂ indicates that the concentration of defect in the as-received SiO₂ is larger than that in the single crystal of SiO₂.(7)At sintering temperatures lower than 1000℃,the height of the peaks of the ratio curves decrease with,whileτ₃ increase with the sintering temperatures increasing.This may be due to the exclusion of the gas and the organic substance out of the cavities in the samples.The existence of cavities in the samples leads to the decrease of the height of the peaks of the ratio curve and the increase ofτ₃.(8)At sintering temperatures from 1000℃to 1250℃,some of the microdefects and cavities were recovered,the grains of low quarts appearing and growing.This gives rise to the increase of the height of the peak of the ratio curve,and the decrease of lifetime(τ₁,τ₂ andτ₃).(9)At sintering temperature from 1250℃to 1500℃,the height of the peaks of the ratio curves decrease,and the lifetime increase due to the phase transition of low quarts to cristobalite and the increase of the phase interface.