Mechanisms and melting behavior study of Si-kerf agglomerates under inert and vacuum conditions to recover PV silicon

Abstract

The continued increase in usage of solar energy as the world moves towards a greener future means that there is even more PV waste each year than the previous. For every silicon wafer produced, about a third is lost as Si-kerf. Thus, the recovery and recycling of this material is a critical step to maximizing energy and material utilization. A study of the melting behavior of Si-kerf agglomerates under inert and vacuum conditions was carried out. It was found that the size of agglomerates does not play a major role in the melting behavior of kerf pellets within the size range 1 mm–10 mm, while the application of higher temperatures than 1600 °C is necessary. No single melt was produced under inert conditions between 1600 °C and 1700 °C, while a single melt with a shiny metallic luster was produced under vacuum conditions at the same temperature range. It is shown that the melting under inert gas occurs mostly via the joining of tiny silicon droplets surrounded by a thin oxide layer, and the formation of a silicon melt with an oxide layer around it. In the case of vacuum melting, however, the silicon oxide layer is eliminated via deoxidation through SiO gas formation, yielding a silicon melt.