Homogenizing out-of-plane strain distribution for high-performance flexible perovskite photovoltaics

Flexible perovskite solar cells (PVSCs) are promising for next-generation photovoltaic due to their lightweight and flexibility. However, nonuniform out-of-plane strain from heterogeneous A-site doping and residual stress from PbI₂-rich surfaces limits their long-term stability and mechanical robustness. Here, we demonstrate that optimized A-site doping reduces defect density and microstrain, improving compositional homogeneity. Advanced visualization of out-of-plane strain reveals key pathways for strain homogenization. Additionally, an in situ-formed 2D perovskite layer on PbI₂-rich surface effectively relieves residual stress, promotes interfacial carrier transport, and strengthens the mechanical property of perovskite film. Consequently, we achieve champion power conversion efficiencies of 26.59% for rigid and 25.88% (certified 25.55%) for flexible PVSCs. Furthermore, large-area flexible modules obtain impressive efficiencies of 21.77% (25 square centimeters) and 19.23% (100 square centimeters). Unencapsulated flexible devices retain 97.8% initial efficiency after 2000 hours of operation tracking (ISOS-L-1) while also demonstrating outstanding durability in damp-heat, thermal cycling, and mechanical tests. This work provides critical foundation for advancing the commercialization of flexible PVSCs.