Sustainable KCl-assisted PbI₂ recycling for high-performance quantum dot solar cells

Lead-based semiconductors play a critical role in emerging high-performance optoelectronics. For scalable, cost-effective fabrication, recycling lead waste from spent lead-acid batteries has proven a promising strategy. Nevertheless, achieving device-grade semiconductor quality from recycled sources remains a critical unresolved challenge. Here, we present the first additive-assisted lead recycling strategy, in which trace amounts of KCl are introduced during the recycling process to enable the formation of high-purity PbI₂. The incorporated KCl enhances crystallization and removes impurities, while residual KCl further improves the colloidal stability and photophysical properties of PbS quantum dots (QDs), addressing key challenges in their direct synthesis. The resulting PbS QD solar cells with KCl additive achieved a power conversion efficiency of 13.3%, surpassing those fabricated with commercial PbI₂ (12.1%) and recycled PbI₂ without the additive (11.0%). Moreover, CsPbI₃ QDs synthesized from KCl-assisted PbI₂ exhibited enhanced surface integrity, stronger photoluminescence, and longer carrier lifetimes, and the resulting solar cells delivered a superior efficiency of 16.6%, outperforming devices fabricated from commercial PbI₂ (15.4%), demonstrating the universality of this approach across different lead-based QD systems. This work establishes a sustainable, additive-assisted metallurgy-semiconductor coupling strategy, providing an energy-efficient pathway to convert lead waste into high-purity semiconductor precursors for advanced optoelectronic devices.