Resource-efficient demetallization of silicon solar cells by alkaline etching: Silver recovery and solution reutilization

This study compares two methods for recovering metals from Al-BSF solar cell fragments: alkaline etching and acid leaching. Etching experiments were carried out in an installation processing six fragments simultaneously. A 35% KOH + 5% ethanol aqueous solution completely removed the metal contacts, yielding high-quality silicon substrates for reuse, as confirmed by carrier lifetime tests; the etching solution could be reused up to three times before silica precipitation occurred. Large differences in Ag and Al particle sizes enabled efficient sieving and high recovery rates (75% pure Ag recovery). The methodology was further extended to bifacial PERC cells. In this case, a 25% KOH + 5% ethanol aqueous solution also removed the contacts, but similar Ag and Al particle sizes made separation by sieving difficult. In both Al-BSF and PERC, acid leaching achieved comparable Ag recoveries (i.e., Ag mg per gram of cell) of 4 mg/g and 3.7 mg/g, respectively, but required precipitation steps to increase the recovery of pure silver. These findings highlight the efficiency of alkaline etching, particularly for Al-BSF cells, and demonstrate that particle size distribution strongly influences the separation efficiency in metallurgical recovery from solar cells.