Columnar Liquid Crystal Enables In‐Situ Dispersing of Excess PbI2 Crystals for Efficient and Stable Perovskite Solar Cells

Abstract Excess PbI 2 has been deemed as indispensable component to boost the efficiency of perovskite solar cells (PSCs). However, the random aggregation of PbI 2 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 PbI 2 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 PbI 2 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 Pb 0 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 cm 2 ) 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 PbI 2 by incorporating columnar liquid crystal for the first time.