Interfacial Molecular Engineering for Stable Lead-Free Tin Perovskite Solar Cells: A Paradigm Shift in Buried Interface Optimization
The advancement of lead-free perovskite photovoltaics, particularly tin-based devices, has been hindered by interfacial instability and energetic mismatches at the buried interface. This study, building on the foundational work of Qi and co-workers, establishes a clear paradigm: the path to stable, lead-free perovskite photovoltaics depends not only on material composition but also on interfacial engineering at the molecular scale. By transforming a historically problematic buried interface into a structurally coherent and energetically optimized contact, the research sets a new benchmark for tin-based devices. The work demonstrates that molecular design of self-assembled monolayers (SAMs) on nickel oxide (NiOx) hole transport layers can significantly enhance device performance and stability. Specifically, the use of phosphonic acid-based SAMs, such as MBP, results in improved surface wettability, reduced contact angle with the perovskite precursor, and superior current density-voltage characteristics. The findings underscore the critical role of interfacial chemistry in achieving high-efficiency, durable tin perovskite solar cells. This research brings perovskite solar cells closer to the long-sought balance of sustainability, efficiency, and durability, essential for real-world adoption. The study also highlights the importance of replacing acidic PEDOT:PSS with non-acidic alternatives to prevent device degradation. Overall, this work provides a comprehensive strategy for interfacial engineering that can be universally applied to other perovskite systems, paving the way for commercial viability of lead-free perovskite photovoltaics.