Heterointerface Growth Equilibration Enables High‐Efficiency and Mechanically Robust Flexible Perovskite Solar Cells

Abstract Flexible perovskite solar cells (FPSCs) exhibit significant potential for applications in wearable and portable electronics, yet they are inherently constrained by insufficient mechanical deformation tolerance and suboptimal charge transport properties. Despite diverse strategies pursued to address these challenges, fundamental solutions have remained elusive. In this study, these limitations are overcome through a ligand‐assisted heterointerface growth equilibration (HGE) strategy that synchronizes nucleation and extends the growth window across heterointerfaces, leading to synergistic perovskite crystallization. This approach contributes to high‐quality films characterized by reduced buried voids, enhanced fracture energy, significantly lowered residual stress, and improved elastic compliance, thereby intrinsically toughening the perovskite material and substantially boosting mechanical durability. The resulting FPSCs achieve an impressive power conversion efficiency (PCE) of 25.76%, alongside exceptional flexibility, retaining over 90% of their initial PCE after 30 000 bending cycles at a 4 mm radius. Notably, this represents the best bending performance reported to date for ≥25.5% perovskite‐based flexible photovoltaics. The application of the ISOS‐LM‐1 standard is also pioneered under light‐mechanical coupling conditions to evaluate operational stability in FPSCs. This work highlights the critical importance of intrinsic crystallinity and mechanical modulations in perovskites, providing a viable pathway toward highly efficient and mechanically robust flexible photovoltaics.