Recovery of crystalline silicon from waste solar cells by a green deep eutectic solvent–hydrogen peroxide system

Abstract

With the rise in installed capacity of photovoltaic systems, the growing generation of waste crystalline silicon solar cells has become an important issue. Silicon is one of the most valuable materials in cells; recyclable treatments with green techniques must be developed for it. A new strategy for the recovery of silicon wafers has been proposed using choline chloride and oxalic acid-based deep eutectic solvent–hydrogen peroxide (DES–H₂O₂) aqueous solution systems. With the synergistic effect of DES and H₂O₂, the leaching efficiency of silver from cells reached 89.19%, along with complete aluminum leaching. Compared with only the DES control, the leaching efficiency of silver was enhanced by as high as 97.45%. Subsequently, reusable silicon wafers were obtained with 97.47 wt% surface purity, and 99.41% of silicon retention rate (169 μm) after removing Si₃N₄. Favorable results were mainly attributed to the higher concentration of H⁺ due to a boost by oxalic acid-based DES compared to concentrations in an oxalic acid aqueous solution, which could provide stronger oxidizing power, and besides, lower oxidation activation energy for silver in H₂O₂. In this work, high-purity silicon wafers were obtained with high leaching efficiency of metals in a short time (2 h) at a low temperature (80 °C) without using strong acids; among solvents, the DES showed great potential for reuse. It is concluded that the DES–H₂O₂ aqueous solution system provides an environmentally friendly process for green and nearly lossless recovery of silicon wafers from silicon solar cells.