Suppressing Interfacial Reactions in Perovskite/Silicon Tandem Solar Cells via an All‐ALD SnO x /AZO Bilayer

ABSTRACT Perovskite/silicon tandem solar cells have reached 35% certified efficiency, yet their operational stability remains a key commercialization barrier. Degradation often originates at interfaces, where charge accumulation under operational bias and light triggers redox reactions and ion migration, accelerating performance decay. Although low‐temperature atomic‐layer‐deposited (ALD) SnO x is widely used as an electron‐transport layer, its high resistivity exacerbates interfacial charge buildup. Here, we develop an all‐ALD bilayer comprising an ultrathin SnO x film and a conductive Al‐doped ZnO (AZO) overlayer. This design decouples functionality: SnO x ensures favorable band alignment, while AZO provides a low‐resistance pathway and a dense barrier against ion diffusion, collectively suppressing interfacial reactions. Wide‐bandgap perovskite cells with this bilayer achieve 23.47% efficiency. Monolithic perovskite/silicon tandem cells reach 33.25% and retain over 96% of their initial efficiency after 1000 h of continuous illumination, demonstrating a viable interface‐focused strategy for stable tandem solar cells.