Axisymmetric Crystallization‐Guiding Agent Directs Perovskite Films Toward Densification for High‐Performance Solar Cells

Crystallization management and defect passivation are essential for fabricating high‐performance perovskite solar cells. However, structural decomposition and grain loosening of perovskite arising from additive side effects remain critical barriers to device advancement. Herein, we design and synthesize a series of axisymmetric multifunctional molecules based on silicon phthalocyanine to regulate both the crystallization and stability of perovskite films. The axial molecular engineering of silicon phthalocyanine effectively suppresses disordered aggregation and preferential crystallization of macromolecular additives within the precursor perovskite film. By optimizing the type and strength of interactions between silicon phthalocyanine and perovskite, highly compact and uniform perovskite films with reinforced interfacial connections in the resulting solar cells are achieved. These modified perovskite films exhibit superior optoelectronic properties, enabling a champion power conversion efficiency of 23.18%. Benefiting from the rational multisite passivation, defect‐induced perovskite decomposition is substantially inhibited. In situ Fourier transform infrared spectroscopy further reveals that the modified perovskite resists thermally induced structural decomposition and mitigates the loss of organic components. Remarkably, the modified devices retain approximately 75% of their initial efficiency after 1000 h of aging at 85°C in a nitrogen atmosphere, demonstrating significantly enhanced stability compared to reference devices.