Stability of Lead‐Free Perovskite Solar Cells

ABSTRACT Lead‐free perovskite solar cells (PSCs) have emerged as sustainable alternatives to toxic lead‐based counterparts, offering environmental compatibility and tunable optoelectronic properties. However, achieving long‐term stability remains a major bottleneck hindering commercialization. Among lead‐free systems, tin‐based perovskites have received the greatest attention owing to their structural and electronic similarity to Pb‐based analogs and their potential for high efficiencies, yet they remain limited by intrinsic Sn ^{2 +} oxidation, ion migration, and rapid degradation under ambient conditions. In contrast, antimony‐, bismuth‐, and germanium‐based perovskites exhibit superior chemical and environmental stability but suffer from wide bandgaps, localized electronic states, and low carrier mobility, resulting in modest power conversion efficiencies. This review provides a comprehensive, stability‐centered analysis of lead‐free PSCs, emphasizing intrinsic degradation mechanisms, extrinsic stress factors, and the role of fabrication, interfacial, and additive engineering in improving device stability. Advanced in‐situ and operando characterization techniques are discussed to elucidate defect dynamics and degradation pathways. While Sn‐based systems are analyzed in greater detail due to the availability and depth of mechanistic studies, equal attention is given to recent developments in Bi‐, Sb‐, and Ge‐based perovskites to present a balanced perspective. Finally, key challenges, mitigation strategies, and future research directions are outlined to guide the design of stable, efficient, and environmentally benign lead‐free perovskite photovoltaics.