Effect of HF and HNO₃ Concentration on Etching Rate of Each Component in Waste Crystalline Silicon Solar Cells

Abstract

In order to maximize the recovery of silicon wafer in waste crystalline silicon solar cells, chemical treatment has been carried out by using the mixed solution of hydrofluoric acid (HF) and nitric acid (HNO₃). The effect of HF and HNO₃ concentrations on etching rates of several components such as silver (Ag), aluminum (Al), anti-reflection film made of silicon nitride (AR) and silicon (Si) in the solar cells has been made clear. The etching rates of Ag, Al and Si are held almost constant with time and become larger with the increasing HF concentration and the etching temperature. All of the etching rates of Al, AR and Si have peaked at the HF mole fraction of about 0.8. The dependency of HF concentration on Al, AR and Si etching rates becomes larger than that of HNO₃. As the best solution composition for the Si recovery yield, the following relation has been found in this study: (number of AR moles)/(number of Al moles) = 7.62 × 10⁻⁴ C_HNO3^0.59C_HF^0.74 where C_HNO3, C_HF: HNO₃, HF concentration (kmol/m³).