The Study On Dislocation In Casting Multicrystalline Silicon And It's Eliminating By Heating Treatment

Multicrystalline silicon cells predominate in solar cell industry, High-density dislocations and grain boundaries play an important role in influencing the electrical and photovoltaic properties of mc-Si solar cells. In this paper we report on dislocation in casting multicrystalline silicon and it's eliminating by heating treatment. It can be expected to reduce the dislocations of silicon. Consequently, the technology can improve the conversion efficiency of polycrystalline silicon cells.The main contents include:The dislocation density and dislocation distribution of cast multicrystalline silicon; the effect of dislocation on the electrical properties of multicrystalline silicon; the influence of annealing temperature and cooling method on the dislocation density in silicon wafers (thickness<0.2mm) and bricks (thickness>10mm). The results show that:the dislocation density of casting multicrystalline silicon was about 105/cm, and the dislocation density of silicon ingot from the bottom to the top showed a decreasing trend. We also found that the dislocation is one of the important influencing factors on electrical properties of materials. Namely, in the areas of high dislocation density, the minority carrier lifetime was low, and vice versa. High temperature annealing at 1000～1400℃and various subsequent cooling experiments for multicrystalline silicon wafers have been carried out. We found that the wafers were annealed at 1320℃or at higher temperature, and then cooled slowly (cooling rate≦7℃/min), the dislocation density of the wafers decreased remarkably, when the annealing temperature reached to 1340℃, the dislocation density of silicon wafers could be reduced 51.7%. But we also found that the dislocation density of silicon bricks increased when the bricks were annealed at 1340℃and cooled slowly (cooling rate was 2℃/min). Combing computational simulation and analysis, this paper discussed the experimental results and its reference value of productive practice.