Phosphorous Gettering Of Crystalline Silicon For Solar Cells

In recent years, it was becoming more and more important to utilize solar energy through solar cells. As one of the key processes, phosphorous gettering treatment has been widely applied to improve the electrical properties of crystalline silicon which is the main photovoltaic material. In the paper, variable temperature and rapid thermal phosphorus gettering were put forward to better the quality of crystalline silicon. On the basis of experiments, the mechanism of phosphorus gettering for crystalline silicon were suggested.The optimized process was found to exist when using constant temperature phosphorous gettering to fabricate crystalline silicon solar cells, which suggests that phosphorous gettering effect depends strongly on the dislocation, diffusion as well as the segregation of transitional metals. Through Orthogonality Experiment, we also found the optimal parameter of variable temperature phosphorus gettering, it was 900℃/lh+750℃/2h for Cast Multi-crystalline Silicon and 900℃/1.5h+750℃/1.5h for Solar Cell's CZ.Furthermore, the gettering effect strongly depends on the forms of iron in the silicon. Once contaminated by iron, the electrical properties of crystalline silicon were degraded in despite of the annealing termperature. If the iron-contaminated temperature is lower than 900℃, the quality of crystalline silicon could be improved by using the isothermal-temperature phosphorous-gettering treatment at 900℃ for 2 hours. However, if iron precipitated formed, it was hardly to better the quality of materials. This is due to the different form of iron exist in silicon matrix—precipitated iron, interstitial iron and FeB pairs.In cmparison with the constant temperature phosphorous gettering, rapid thermal phosphorous gettering was found to almost have no effect to better the qulity of crystalline silicon. It is well known that the gettering dwell time of rapid thermal phosphorous gettering is too shorter to dissolved impurities and precipitate of transitional metals in the silicon matrix and diffused to the gettering sites.Precipitated iron was more worse than interstitial iron and iron complexes to degrad the electrical properties of crystalline silicon. It was found that the material electrical properties was enhanced for phosphorus gettering after iron contamination at mid and low temperature(under 900℃) anneal treatment, especially recombining with hydrogen passivation after phosphorus gettering. Moreover, hydrogen passivation is beneficial to improve electricalproperties of cast multicrystalline silicon only after metallic impurities was gettered c...