Fraunhofer Center for Silicon Photovoltaics CSP
Resource recovery from PV modules at the end of their life-cycle will move more and more into focus for the responsible consumption of raw materials and the energy efficient use of renewable feedstock. The Fraunhofer CSP develops new procedures for the refinement and the reuse of wafer and cell scrap, with the final goal to feed the PV silicon back into the value chain. High temperature melting furnaces are available, inductive heating allows fast heating-up and cooling down cycles. Wet chemical processes are under development to etch off surface coatings and to dissolve metallic impurities. New methods are investigated for segregation based refinement steps. Furthermore, the use of getter processes or the application of inductive vacuum melting, or the treatment of liquid silicon with gas bubbling and with active stirring are techniques offered to remove impurities. Modern equipment for trace analysis gives a direct feedback with respect to the efficiency of the refinement process and a quantification of the material purification. The refined silicon might then be crystallized in our state-of-the-art industrial size crystallization equipment, like the Czochralski-pullers or the directional solidification furnace.