Solar PV Silicon Recycling via Chemical and Vacuum Refining Techniques

The rapid expansion of global photovoltaic (PV) installations will inevitably result in large quantities of silicon-rich waste as early-generation modules reach their end of life. Recovering this silicon is critical for maintaining a sustainable solar value chain and reducing dependence on high-energy primary production. However, solar-grade silicon requires a purity level of 99.9999 wt% (6N), posing a significant challenge for recycling processes. Within the framework of the Apollo project, a combined chemical and vacuum refining route has been developed to recover and purify silicon from spent PV wafers. The integrated process sequence—acid leaching, alkaline leaching, and vacuum refining—reduces total impurity levels from 33,000 ppm in untreated material to 16 ppm in the final refined silicon. Chemical leaching steps remove adherent glass and metal contaminants, while vacuum refining efficiently eliminates volatile elements such as Ag and Cu. The final material reaches approximately 5N purity, with remaining impurities dominated by Ca and Zn. Minor carbon diffusion from the graphite crucible was detected but not included in the purity assessment. The results demonstrate the complementarity of the processes and suggest that further optimization of refining conditions could enable closed-loop silicon recycling for next-generation PV manufacturing.