Study On Cast Multicrystalline Silicon Wafer Gettering

The research progress,future and unsolved problems of gettering on multicrystalline silicon is systematically reviewed in this paper from the fact that phosphorus diffusion and BSF formation are the necessary processes in solar cell's fabrication.The influences of phosphorus gettering, aluminium gettering and P/Al cogettering on multicrystalline silicon lifetime and electrical performance are mainly studied. And the best parameters of the three gettering methods are concluded. At the same time the effect of the concentration of oxygen, carbon and metal impurity, its existing state and the dislocation as well as microdefect density on the multicrystalline gettering is analysed. The simulation of gettering is also discussed primarily. These experimental results offered helpful reference and guide for improving the multicrystalline silicon efficiency by gettering.By experiments it can be concluded P/Al co-gettering is better than single phosphorus gettering or aluminium gettering. Though they can improve the wafer's lifetime at proper temperature and proper gettering time, phosphorus gettering and aluminium gettering can't improve the whole solar cell's electrical performance which perhaps results from the ununiformity of multicrystalline silicon. It also finds that minority carrier lifetime decreases rapidly on the condition of high gettering temperature and long gettering time, while the optimum parameters of phosphorus gettering is close to the pn junction formation. Thus it needn't to be introduced extra process for phosphorus gettering.Analyse of gettering mechanisms and gettering simulation is very helpful for researchers to understand the gettering thoroughly and serach for optimum gettering parameters.