Carboxyl-Functionalized Perovskite Enables ALD Growth of a Compact and Uniform Ion Migration Barrier

Integrating mixed-halide wide bandgap (WBG) perovskite solar cells (PSCs) into tandem architectures offers pathways to surpass the efficiency limits of single–junction cells. However, the long–term stability of these devices is hindered by halide migration, which degrades performance. In this work, we address halide migration by developing a novel interface engineering approach using atomic layer deposition (ALD). Specifically, we functionalize the perovskite surface with 5–ammonium valeric acid iodide (5–AVAI), enabling uniform Al₂O₃ growth at 100°C–a significant improvement over the conventional 60°C limit.
The ALD–grown Al₂O₃ layer effectively suppresses halide ion migration, as confirmed by time–of–flight secondary ion mass spectrometry (ToF–SIMS). Iodine penetration into the electron transport layer (C₆₀) is reduced by over 10x compared to unmodified devices. The stabilized WBG PSCs (1.78 eV) demonstrate exceptional operational durability, achieving a T₉₉ lifetime of 615 hours under maximum power point tracking at 25°C. Furthermore, these cells retain 90% of their initial efficiency after 1000 hours of continuous operation at 55°C. This study highlights the promise of ALD–engineered interfaces for overcoming stability challenges in WBG PSC-based tandems and advancing high-efficiency photovoltaics.