Solar energy, especially the photovoltaic (PV) technology, currently holds a quite important position in the renewable energy market. The global demand for PV power has increased from 1 GW in 2004 to 57 GWs in 2015; the annual growth rate is more than 20%, which is much higher than that of any other industry, including other emerging renewable energy industries.
Crystalline silicon panels are the most widely used commercial solar panel materials and account for about 90% of the global PV market.As shown in Fig., a typical crystalline silicon panel has a structure made of multilayer panels, which include an aluminium alloy outline border, a TPT backboard and a piece of tempered glass in the outer sphere.
The inner layer comprises a silicon wafer as the core structure, which is fixed with a poly(ethylene-co-vinyl acetate) (EVA) binder layer. It is known that silicon wafers are the most expensive materials in the PV modules and have drawn significant attention from research institutions.
Reclaimed silicon wafers can be obtained from EoL PV modules as broken or unbroken wafers. The broken silicon wafers can be crushed into powder and used as raw materials for PV production. Moreover, it has been reported that the unbroken wafers are almost identical to commercial virgin wafers.
So far, most research works have focused on the chemical leaching method to recycle clean silicon wafers by removing silver, aluminum, the anti-reflection (AR) coating and n–p connector. However, in the silicon recycling process, the aluminium alloy outline border, the TPT backing materials, the junction box and the tempered glass should be removed from the crystalline silicon solar panel beforehand. The reason is that different materials are glued together, and this kind of sandwich structure would interfere with the silicon wafer recycling process. As a matter of fact, the aluminium alloy frame and the junction box can be artificially dismantled and are easy to recycle. However, the tempered glass, the solar cell panel, and the TPT backing materials are stuck together by the EVA binder, and such specific structure makes the separation and recycling processes quite difficult.