The installations of photovoltaic (PV) solar modules are growing extremely fast. As a result of the increase, the volume of discarded solar modules that end up on the recycling market annually will grow at the same rate in the near future. Currently, the aluminum, glass, and copper of the discarded modules are reprocessed; however, the silicon solar cells are not.
Now, researchers from the Fraunhofer Center for Silicon Photovoltaics CSP and the Fraunhofer Institute for Solar Energy Systems ISE, together with the largest German recycling company for PV modules, Reiling GmbH & Co. KG, have built new PERC solar cells with 100% crystalline silicon recycled from end-of-life photovoltaic panels.
The team has developed a process for recovering the silicon material with funding from the German Federal Ministry for Economic Affairs and Climate BMWK. The technique is claimed to recycle silicon from different types of crystalline silicon PV modules, regardless of manufacturer and origin.
They separated and collected solar cell fragments from by-products of the already established mechanical recycling process. These cell fragments with sizes from 0.1 to 1 millimeter are first freed from the glass and plastic by various sorting processes. This is followed by the step-by-step removal of the backside contact, the silver contacts, the anti-reflective layer, and finally, the emitter by wet chemical etching. Later, the researchers processed the cleaned silicon into monocrystalline or quasi-monocrystalline ingots in standard processes and then into wafers.
The researchers then carried out the crystallization process with 100% recycled silicon without the addition of commercial ultrapure silicon. The wafers made of recycled silicon were fabricated into PERC solar cells. The performance of the first trial PERC cells was tested, and the devices were found to achieve a power conversion efficiency of 19.7%. “This is below the efficiency of today’s premium PERC solar cells, which have an efficiency of around 22.2%, but it is certainly above that of the solar cells in the old, discarded modules,” says Prof. Dr. Peter Dold, project manager at Fraunhofer CSP, putting the initial results into context.