Realizing stable and scalable perovskite solar cells (PSCs) under real-world outdoor conditions remains a challenge for deployment. Here we report a strategy to improve the resilience of the grain boundary, achieving simultaneous improvement in the power conversion efficiency and long-term operational durability under realistic light cycling and ultraviolet exposure of PSCs. By integrating photoswitchable isomers at grain boundaries, we suppress lattice bond rupture and defect accumulation during repeated light cycling through light-triggered dynamic damage release. This approach stabilizes the triple-cation lead-based perovskite lattice against photoinduced distortions and degradation pathways. As a result, the PSCs retain over 95% of their initial performance after 2,000 h of ultraviolet-containing light cycling at 65 °C and 500 thermal cycles between –40 °C and 85 °C, and deliver a power conversion efficiency of 27.2% (certified as 26.9%). Our strategy improves the operational stability and commercial viability of triple-cation perovskite photovoltaics.