Mechanism of phosphorus removal from Si–Al melt by hydrogen

Abstract

Phosphorus is a critical impurity in solar cell that deteriorates the photovoltaic convection efficiency of solar cell. Phosphorus removal from metallurgical grade silicon by injecting H2 and Ar-50%H2 mixture during the Al–Si solvent refining was investigated. With gas injecting into the Al–Si melt, the phosphorus concentration in the refined Si decreased with an increase of the injecting time. When the gas injecting time was 2.5 h, the removal fraction of phosphorus increased to 93%, an improvement of 63% compared with 57% without Ar–H2 injection. The effects of H2 proportion, gas refining temperature, and Si proportion in the alloy were investigated. The kinetics of phosphorus removal with Ar–H2 injection were clarified. The mass transfer coefficient of phosphorus was 9.07 × 10−9 m/s during the Ar–H2-assisted solvent refining process. Three mechanisms of phosphorus removal were discussed for this gas-solvent composite refining process. These results demonstrate that H2 or Ar–H2 gas injecting treatment is an effective strategy to further improve the phosphorus removal and reduce the cost during Al–Si solvent refining.