Short process recovery of silver and purification mechanism of crystalline silicon deep etching from end-of-life photovoltaic cells

Photovoltaic (PV) devices, which are representative tools for generating renewable energy, have experienced record growth in terms of installed capacity, with crystalline silicon (c-Si) PV modules accounting for up to 95 % of all installed devices. A large amount of waste is generated when PV modules reach the end of their life. This paper investigated the recovery of Si from end-of-life c-Si solar cell wafers by immersing the wafers in a single reagent sodium hydroxide (NaOH) solution, which recovered Si while realizing the direct recovery of Ag. The conditions for the separation of the Al backsheets and Ag grids on the solar cell surfaces were optimized, and recovered 96.45 % of Si with a purity of 99.98 wt%, which meets the standard of industrial-grade Si, at the same time, 99.87 % of Ag was directly recovered. Moreover, in order to obtain higher purity silicon, we investigated the effect of different acids on the etching of silicon nitride (SiNx) and chose to use 60 wt% H3PO4 for the etching of SiNx, and combined with DFT calculations, we investigated the mechanism of H3PO4 removal of SiNx from the surface of the solar cell wafers. Finally, the experimental parameters for removing the emitter layer from the surface of silicon wafer by NaOH solution were optimized and the efficient recovery of Si by controlled etching was achieved, yielding Si with 6 N purity and meeting the requirements of commercial virgin Si wafers.