Effect Of Oxygen And Metal Impurities In Crystal Silicon On The Performance Of Solar Cells

The effect of oxygen precipitates and Cu,Fe and Ni impurities in crystal silicon on performance of solar cell was studied. The experimental results showed that few oxygen precipitates formed in the wafers which have been subjected to single-step annealing. But a large amount of oxygen precipitates were produced in the bulk after l0w-high two-step annealing, simultaneity the efficiency of cells decreased sharply. The decline of cells efficiency became slowly when prolonging annealing time. Weather pre-annealing or not, few oxygen precipitates formed in silicon after high temperature annealing. Pre-annealing temperature has a great influence on the producing of oxygen precipitates, pre-annealing at 650℃enhances the producing of oxygen precipitates mostly in silicon. The performance of cells was improved after high-low-high three-step annealing.Most of oxygen precipitates are concentrated at grain boundaries and dislocations in multycrystalline silicon. When the density of precipitates is high enough, it will decay the p-n junction dramatically. The performance of cells decreases less after annealing at middle temperatures, but it will drop greatly after high temperature annealing. Pre-annealing did not enhance the oxygen precipitates in multicrystalline silicon. The performance of multicrystalline silicon cells was not improved after high-low-high three-step annealing.The decay of Cu,Ni and Fe impurities on the performance of solar cell is mainly because the impurities destroy on the p-n junction when the concentration of metal impurities is small. And the introducing of recombination ceters in the bulk reduced the decrease of cell efficiency when the concentration became higher. Generally, there is a critical density of metal impurity, the performance of cells changed slowly when the density of impurities is less than the critical density and decreased sharply when density of the impurities goes beyond the critical density.