Eco-friendly lead-free and low-lead perovskite solar cells

Driven by the demand for sustainable energy solutions, perovskite solar cells (PSCs) have recently emerged as a research focus owing to their rapid improvements in power conversion efficiency (PCE). However, environmental concerns associated with lead-containing perovskites have rendered the development of lead-free PSCs increasingly urgent. This review summarizes recent advances in lead-free and low-lead PSCs, focusing on material design, performance optimization, and stability enhancement. We first examine tin (Sn)-based perovskites, the most extensively investigated lead-free system. Although Sn-based PSCs have achieved power conversion efficiencies of up to 18%, their practical application remains constrained by Sn2+ oxidation, high background carrier density, and limited long-term stability. Tin-lead (Sn-Pb) mixed perovskites are then discussed as a promising low-lead strategy that balances environmental considerations with high performance, achieving certified efficiencies exceeding 24% in single-junction cells and over 28% in tandem devices. We further evaluate other metal-based perovskites, as well as double perovskites, by analyzing their electronic structure limitations and potential improvement strategies. Finally, key challenges and future research directions are outlined. Despite notable progress, commercialization remains limited by stability concerns, bandgap optimization, and scalable fabrication. This review provides a theoretical and strategic foundation for advancing efficient and sustainable lead-free PSCs.