Researchers from Ningxia University and Helanshan Laboratory have developed a molten-salt approach to detach silver wires directly from crystalline silicon solar cells
The process achieved up to 97.11% silver recovery, while silicon loss was reported at 2.62% under a separate set of conditions
The method removes the silicon nitride layer beneath the silver grid, avoiding the need for prior cell crushing or silver dissolution
Researchers from Ningxia University and the Institute of New Energy Materials at Helanshan Laboratory in Yinchuan, China, have developed a molten-salt etching process to recover silver grid lines from end-of-life (EoL) solar cells. The research also involves the Ningxia Key Laboratory of Photovoltaic Materials at Ningxia University.
The method uses a mixture of sodium hydroxide (NaOH) and potassium hydroxide (KOH) to detach the silver wires from the solar cell. This approach avoids crushing the metal or dissolving it into solution before recovery.
The study, titled Sustainable recovery of silver wires from crystalline silicon solar cells, was published in the Journal of Cleaner Production. It addresses a key challenge in photovoltaic (PV) recycling: recovering valuable silver while minimizing damage to the silicon cell.
Conventional recovery methods often rely on acid leaching, which dissolves metallic silver into solution before it is extracted. Although effective, this approach requires additional processing to recover the metal and manage the resulting chemical waste.
The researchers instead investigated a molten NaOH-KOH mixture to separate silver from aluminum back-surface-field (Al-BSF) solar cells. The process targets the silicon nitride (SiNₓ) passivation layer beneath the silver grid lines. By removing this layer, the treatment weakens the interface between the silver and the underlying surface, allowing the metal wires to detach without first being dissolved into silver ions.
Thermodynamic calculations indicated that the silicon nitride and exposed silicon react with the alkaline mixture to form sodium silicate (Na₂SiO₃) and potassium silicate (K₂SiO₃). Results showed that silver recovery reached 94.34% at 230°C after 150 seconds. The researchers reported a maximum recovery rate of 97.11%. Once the silicon nitride layer is removed, hydroxide ions in the molten salt can attack the exposed silicon, converting it into silicates and limiting silicon loss to 2.62% at 230°C after 100 s.
The work adds to efforts to develop acid-free routes to recover silver from EoL solar cells. In an earlier study covered by TaiyangNews, researchers at Australia's University of Newcastle used mechanical crushing and grinding, followed by froth flotation, to separate silver-bearing material (see Acid-Free Process Recovers Nearly 100% Silver From End-Of-Life Solar Panels).
The two approaches differ in how they separate the metal. The Newcastle process first breaks the cells into particles and then concentrates the silver-bearing fraction through flotation. The molten-salt method, by contrast, targets the silver-passivation layer interface to detach the grid lines directly from the cell surface. Both aim to reduce reliance on conventional acid-based recovery, but the molten-salt study focuses particularly on balancing silver recovery with silicon-substrate loss.
