Effects of argon flow on impurities transport in a directional solidification furnace for silicon solar cells

A global simulation including coupled oxygen and carbon transport was carried out to study the argon flow effects on the impurities transport in a directional solidification furnace for silicon solar cells. The simulation is based on a fully coupled calculation of the thermal and flow fields in a furnace including argon gas flow and melt convection. Five chemical reactions are considered in the impurity transport model. The effects of both the argon flow rate and the furnace pressure were examined. It was found that the argon flow has an important effect on the silicon melt convection, which will further influence the evaporation characteristic of SiO at the melt free surface. The amount of SiO carried away by the argon flow increases with increase in the argon flow rate while the CO gas can be prevented from being transported to the melt free surface. There exists a peak value for the concentration of impurities in the furnace chamber regarding argon flow rate due to the correlation among SiO evaporated, reacted and taken away. The pressure also influences the impurity transport in the furnace by modifying the pattern of argon flow. The numerical results demonstrate a method to control the oxygen and carbon transport in a directional solidification furnace by adjusting the argon flow rate and the furnace pressure.