Lead-free solder alloys for PV modules: Life cycle assessment for environmental impact and toxicity

• Comparison of (lead-free) solder alloys for six LCA impact categories. • Avoiding Pb does not automatically decrease toxicity related environmental impacts. • Rare Elements (Ag, In, Ge) cause high impacts due to economic value and effort. • Impacts of solder alloys are minor compared to the LCA of a complete PV module. • Recycling materials, renewable energies, reduced material consumption limits impacts. This study presents a comprehensive life cycle assessment (LCA) of interconnection materials utilized in photovoltaic (PV) module manufacturing, focusing on the environmental impacts from raw material extraction to the production stage (cradle-to-gate). The primary objective is to complement the existing research of technological comparisons of different solder alloys for PV modules by ecological aspects, such as climate change, toxicity and resource use. The conducted LCA refers to the impacts of different alloys for manufacturing one state-of-the-art full-size glass-backsheet PV module, employing the Environmental Footprint 3.1 for the life cycle impact assessment method. To identify suitable (lead-free) solder materials for future high-efficiency PV modules, the analysis includes solder alloys for the interconnection of tunnel oxide passivated contact (TOPCon) as e.g. SnAgCu or SnZn and for low-temperature soldering of silicon heterojunction (SHJ) solar cells as e.g. SnBiAg or InSn. A key finding is the dominant influence of raw materials, rather than solder alloy production itself. Scarce materials like Ag, In and Ge cause high environmental impacts if used in solder alloys. The exact material composition of the alloy plays a minor role. Avoiding toxic materials such as Pb does not automatically lead to a module with improved environmental impact. To address future PV module layouts with different amounts of solder needed, the LCA is extended to various module designs, also evaluating the influence of the Cu wires. Our results complement the technological rating for interconnection materials of PV module manufacturing by environmental arguments for a sustainable product design.