Solar Grade Silicon Refining and Silicide Production Processes

The process of upgrading silicon from metallurgical grade to solar grade has great potential for reducing the price of silicon supply in the photovoltaic industry. Boron removal is crucial in the refinement process. We developed several methods using novel gas injection and slag treatment to remove boron effectively. Furthermore, we are in the process of optimizing these methods by studying their thermodynamic mechanisms and kinetics.

Titanium silicide (Ti₅Si₃) is a promising new material for very-high-temperature structural applications. We propose a pyro-metallurgical method to synthesize Ti₅Si₃ from titanium bearing slag and molten silicon at high temperature for reducing the production cost and elevating the quality of it. Thermodynamic properties of titanium bearing slag and kinetics of the process was studied. And the effects of slag compositions and reaction temperature were explored.

B and P are frequently difficult to remove completely by means of metallurgical refining methods to achieve solar grade Si. Thanks to compensation, which can be defined as the concurrent presence of donor and acceptor species in comparable amounts, it is possible to tolerate high concentrations of B and P for solar grade Si.

Due to the difference of segregation coefficient, the Si containing both P and B always shows a non-uniform net doping and hence poor electrical properties after crystallization. In order to overcome this issue, I deliberately added controlled amount of Al to P and B doped Si. Al with low segregation coefficient coupled with B effectively counterbalanced the increased P during crystallization resulting in a uniform net doping and good properties.