Interfacial reinforcement relieves mechanical mismatch for stable perovskite photovoltaics

Long-term operational durability under realistic day-night cycling remains a critical bottleneck for the commercialization of perovskite solar cells (PSCs). While significant progress has been made in managing thermo-mechanical stress within the perovskite layer, day-night cycling tolerance remains far from real-world applications, as cycling-induced interface degradation at adjacent functional layers has largely been overlooked. Here, we identify a failure mechanism at the C60/atomic layer deposition (ALD)-SnO2 interface in inverted PSCs, where a severe mismatch in mechanical properties leads to substantial internal stress accumulation, readily causing interfacial delamination and accelerating device degradation. To address this, we introduce graphitic carbon nitride (g-C3N4) as a multifunctional buffer layer between C60 and ALD-SnO2. This two-dimensional material acts as a compliant mechanical bridge, effectively alleviating stress and suppressing microcrack formation, while simultaneously facilitating electron transport across the interface. As a result, the target PSCs achieve a remarkable efficiency of 27.05% and exhibit superior robustness. Notably, the devices retain over 90% of their initial efficiency after 1056 h of maximum power point tracking under day-night cycling. Our findings advance the understanding of interfacial failure mechanisms and provide a practical strategy to support the commercialization of durable PSCs. The day-night cycling durability remains a bottleneck for the commercialization of perovskite photovoltaics. Li et al. introduce g-C3N4 as a buffer layer between C60 and SnO2 to alleviate stress and suppress microcrack. The resulting device achieves a power conversion efficiency of 27.05%.