Multisite Polymer Regulates Crystallization for Low‐Strain Perovskite Film

Defect‐induced lattice distortion represents a primary origin of lattice strain in perovskite films. Relieving this strain is essential for improving both the efficiency and stability of perovskite solar cells (PSCs), yet it remains a significant challenge. In this work, we introduce a multisite polyurea adhesive (MPUA) as an additive to regulate perovskite crystallization. The MPUA additive promotes rapid nucleation while prolonging the growth period, yielding films with higher crystallinity, enlarged grains, and fewer defects, thereby alleviating lattice strain. Notably, MPUA also converts residual tensile strain into compressive strain within the film. As a result, MPUA‐modified PSCs achieve a power conversion efficiency of 24.91% with substantially enhanced stability. This work demonstrates the potential of multisite polymers for strain regulation in perovskite films toward high‐performance PSCs.