Crystallization Pathway Optimization and High‐Index Facet Stabilization for Perovskite Photovoltaics

Perovskite solar cells (PSCs) face a critical challenge in balancing high power conversion efficiency (PCE) with operational stability, largely governed by the crystallization kinetics and facet configuration of perovskite films. Here, we report a kinetically segmented crystallization strategy mediated by a conformationally preorganized macromolecular regulator, cellulose 2,4,6-trichlorophenylcarbamate (3Cl-NC). Through multidentate coordination, 3Cl-NC establishes localized precursor-rich microenvironments that promote heterogeneous nucleation. During thermal annealing, this association transitions into a thermally activated dynamic coordination state that retards long-range precursor transport while maintaining local availability for controlled crystal growth. This segmented regulation suppresses metastable δ-phase accumulation and facilitates photoactive α-phase formation. Furthermore, 3Cl-NC thermodynamically stabilizes the high-Miller-index (210) orientation, establishing a synergistic architecture that intrinsically enhances lattice structural stability. Consequently, the resulting perovskite films exhibit higher phase purity, relieved residual stress, and suppressed ion migration, enabling devices to achieve a champion PCE of 26.59% (certified 26.29%) with improved long-term stability.