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Excess PbI2 has been deemed as indispensable component to boost the efficiency of perovskite solar cells (PSCs). However, the random aggregation of PbI2 crystals seriously disturbs the transport behavior of the carrier and accelerates the degradation of perovskite film. Herein, an effective strategy to in situ disperse excess PbI2 crystals via the columnar liquid crystal (T6TE) is developed. Rapid self‐assembly induced by intermolecular π–π interaction enables T6TE to form the ordered columnar phase with "edge‐on" orientation in perovskite. The columnar T6TE can efficiently disperse excess PbI2 crystals with the merits of strong negative electrostatic potential and highly steric hindrance. Target perovskite deserves preferable crystallization and reconstructed surface, leading to reduced defects density, less residual stress, and efficient carrier transport. Besides, the T6TE significantly impedes the degradation of perovskite film and the formation of Pb0 defects. Resultant T6TE‐assisted PSCs achieve the champion power conversion efficiency (PCE) of 24.27% for mixed Cs+‐FA+‐MA+ perovskite. The PCE of a larger area (1 cm2) device reaches to 21.50%. The unencapsulated device maintains ≈85% of the initial PCE after 1500 h storage in the atmosphere with 40–60% relative humidity. This work provides a new strategy to in situ disperse excess PbI2 by incorporating columnar liquid crystal for the first time. [ABSTRACT FROM AUTHOR]

α‐phase formamidine lead iodine (α‐FAPbI3) as a competitive candidate to pursue high‐performance perovskite solar cells (PSCs) suffers from the weakness of random nucleation and disordered growth in chasing high‐grade polycrystalline films. Here, single‐crystal seeds crystallization (SCSC) method is proposed to obtain high‐quality α‐FAPbI3 perovskite films for the first time. Six single‐crystals seeds (CsPbBr3, CsPbI3, FAPbBr3, FAPbI3, MAPbBr3, and MAPbI3) are employed to regulate α‐FAPbI3 perovskite crystallization. These seeds act as nucleation sites and allow the perovskite to grow directly. The rapid crystallization significantly improves the crystallinity of perovskite films with uniform morphology, large grain size, and less defects. Of particular note, FAPbBr3 seed prefers to grow α‐FAPbI3 epitaxially from FAPbBr3@PbI2 heterostructure through a halogen anion exchange process. The average grain size of FAPbBr3‐perovskite film is boosted to 2.6 µm, and the trap density reduced by 11 times. The resultant FAPbBr3‐PSCs achieve a maximum power conversion efficiency (PCE) of 23.84% with a high open‐circuit voltage of 1.18 V. The unencapsulated PSC retains 91% of the initial PCE after 3000 h of storage at ≈30–50% relative humidity and preserves 98.5% of the original value after 155 h illumination with maximum power point tracking. [ABSTRACT FROM AUTHOR]