Recovery of Metal Contacts and Reutilization of Silicon Substrates from Recycled Solar Cells

As the installed capacity of photovoltaic (PV) systems increases, so does the need to address the accumulation of waste from decommissioned modules, a challenge that requires the development of cost-effective and efficient recycling strategies. This work presents the main results in the research carried out within the RESILIENS project (funded by the Spanish National Research Agency) to develop a cost-effective and environmentally meaningful technological recycling process for silicon solar cells, that allows the recovery of precious metals and the reutilization of silicon substrates. On the one hand, three methods were evaluated for metal recovery: (i) acid leaching, for which 3 M HNO₃ was found to be the most effective, and an organic acidic medium, with Fe³⁺ as an oxidant and Cl- to avoid Fe precipitation, was also explored; (ii) alkaline etching with KOH/ethanol/water, that allowed the separation of metal contacts and the removal of anti-reflection coatings with minimal silicon loss; and (iii) acidophilic and halotolerant bacteria, that effectively performed the bioleaching. On the other hand, p-type monocrystalline ingots with suitable electrical properties were obtained from the Czochralski growth of fragments of old boron-doped multicrystalline silicon wafers. Phosphorus gettering treatments were applied to p-type recrystallized wafers, achieving lifetimes in excess of 250 µs. Cells fabricated on recrystallised silicon showed only 5.2 % relative lower efficiency than reference ones, attributable to processing, not to the material quality. Conversion to n-type silicon was demonstrated when phosphorus emitters were present in the recrystallized material, Conversion to n-type silicon was demonstrated when phosphorus emitters were present, although challenges due to excessive doping were identified. The RESILIENS project has contributed to the reduction of the environmental footprint associated with solar photovoltaic energy, supporting the transformation of PV technology into a true example of circular economy.