Sustainable Valuable Materials from Waste Heterojunction Solar Cells: A Focus on the Purification of Indium

The expansion of silicon heterojunction (SHJ) solar cell production has prompted concerns regarding the rising consumption of indium. To address the issue of indium scarcity, the use of benign hydrometallurgical conditions for the recovery of indium—a rare noble metal—from the transparent conductive oxide (TCO) layer of the cells was investigated. The results showed that due to the insufficient adhesion between the silver fingers and the TCO layer, the complete recovery of the silver fingers could be accomplished without damaging the cell by the etching process involving 10% NaOH at 90 °C for 10 min. The optimal chemical treatment conditions were adjusted to ensure the efficient dissolution of indium metal from the cell into solution. The subsequent solvent extraction stripping process yielded an indium concentration of 6232 mg/L, a 24-fold increase over the initial leach solution concentration. Finally, a 12-h replacement reaction using aluminum plates was employed to achieve higher indium purity. The final recovery of indium from SHJ cells was determined to be approximately 85%, and an approximate cost analysis was conducted to assess the potential future of SHJ cell recycling.