Scientists from India’s KPR Institute of Engineering and Technology have developed a new technique to recycle pure silicon from solar cells at the end of their lifecycle.
Unlike other conventional methods to recycle silicon from PV devices, the new technique is not based on the use of highly toxic chemical hydrofluoric acid, which is commonly utilized in the PV industry for both quartz cleaning and wafer etching. In solar module recycling, the corrosive acid is used for separating silicon from the cell by removing the anti-reflecting coating, silver, lead, and p-n junction.
The corrosive acid was replaced by the Indian group with three different chemicals: a 10 M solution of sodium hydroxide (NaOH) was applied to the aluminum layer for five minutes at 63 degrees Celsius; a 6 M solution of nitric acid (HNO3) was used to remove the silver electrodes and lead; and a solution of 90% phosphoric acid was used to remove the antireflecting coating based on silicon nitride (Si3NA4) for 45 minutes at 70 degrees Celsius.
The outer parts of a solar panel such as glass, ethylene-vinyl acetate glass, copper, steel, aluminum, and plastic were previously removed through thermal degradation.
According to the scientists, the proposed technique is able to deliver recycled silicon with a purity of up to 99.9984%. The recycling cost for 1 kg solar cell with this process is estimated at $68.9 and the total profit after recycling a 1 kg solar cell is calculated to be $185.4. The recovered silicon can be used to manufacture new solar cells or electronic components such as diodes, transistors, and microchips, they explained.
The recycling technique is also said to enable the recovery of aluminum, silver, and lead as aluminum hydroxide, silver chloride, and lead oxide, respectively. It is described in the paper “Recovery of Pure Silicon and Other Materials from Disposed Solar Cells,” published in the International Journal of Photoenergy.