German scientists develop PERC solar cells from recycled silicon

Circular economy

Germany – Scientists from the Fraunhofer Center for Silicon Photovoltaics CSP and the Fraunhofer Institute for Solar Energy Systems ISE, in collaboration with Reiling GmbH, developed a solution that allows for the industrial recycling of silicon from old modules and the subsequent production of new PERC solar cells.

During the first wave of photovoltaic expansion in Germany, most PV systems were installed between 2009 and 2011. With a silicon content of 150,000 tons in 2021, Germany had already installed five million tons of PV modules. Solar cells rely heavily on silicon, which is used as a semiconductor.

As a result, with support from the German Federal Ministry for Economic Affairs and Climate BMWK, a Fraunhofer CSP working group in collaboration with Reiling GmbH developed a process for recovering silicon material. All crystalline silicon photovoltaic modules can be recycled using this method, regardless of their manufacturer or place of origin.

Mechanical recycling

The mechanical recycling process by-products are used to separate and collect solar cell fragments for the process. Sorting processes at Fraunhofer CSP remove the cell fragments, which range in size from 0.1 to 1 millimeter, from the glass and plastic. Once the backside contact, silver contacts, anti-reflective layer and emitter are removed, wet chemical etching is used to remove the emitter. Standard processes are used to produce monocrystalline or quasi-monocrystalline ingots and then wafers from the thoroughly cleaned silicon.

Commercial ultrapure silicon is not used in the crystallization process because the recycled silicon is 100 percent pure. Fraunhofer ISE’s PV-TEC fabricated the PERC solar cells from the recycled silicon wafers. Conversion efficiency of 19.7 percent for the first trial of solar cells was used.