Recycling solar-grade silicon from end-of-life photovoltaic modules by Al-Si solvent refining.

Abstract

The development of the solar market has been fast in the past decades, and the number of photovoltaic module installations is large. The photovoltaic modules have a lifetime of about 25 years and need recovery after that. The aluminium-back surface field (Al-BSF) module is the first kind of large-scale installed module and will come to its end of life in the next few years. The recycling of silicon material in the Al-BSF module is investigated in this work. The components of the module are separated, and the silicon material in the module is collected and then purified by (aluminium-silicon) Al-Si solvent refining for reuse. It is found that Al-Si solvent refining removed key impurity elements, namely boron and phosphorus, in the collected silicon. Kinetics has a great effect on boron and phosphorus removal, and boron and phosphorus contents in purified silicon decrease with decreasing cooling rate. The boron and phosphorus contents in silicon are lowered to 0.28 and 0.03 ppmw, respectively, after two times of Al-Si solvent refining with the cooling rate of 5.55 * 10^-4 K second^-1, and it meets the requirement of solar-grade silicon.