Understanding and mitigating interfacial defects in tin‑lead perovskites for robust photovoltaics

Tin‑lead (SnPb) hybrid perovskite solar cells (PSCs) have attracted considerable attention due to their lower bandgaps, enabling higher Shockley-Queisser (S-Q) limit efficiencies and promising applications in all-perovskite tandem solar cells. However, SnPb perovskites suffer from abundant defect states, particularly at the interfaces, which primarily stem from the chemical instability of Sn (II) and the inherent weaknesses of the crystal structure. These defects induce severe non-radiative recombination at grain boundaries/film surfaces that hinder charge transport and accelerate film degradation, ultimately limiting the device's efficiency and operational stability. This review systematically discusses the surface/interfacial defect types and their formation mechanisms in SnPb perovskites, followed by an in-depth analysis of defect passivation mechanisms. We further summarize the latest advancements in passivation strategies and analyze their impact on device performance. Finally, we outline key challenges and future research directions for achieving high-performance and robust SnPb PSCs, which are crucial for shaping the evolution of next-generation perovskite photovoltaic technologies.