Spatio‐Temporal Evolution of 2D Templates Enables Synchronized Crystallization and Efficient Charge Extraction in Perovskite Solar Cells

Achieving uniform crystallization across the entire film depth remains a critical challenge in the two‐step fabrication of perovskite films, where mismatched crystallization rates between the top and bottom regions often result in structural heterogeneity. Here, we develop a spatio‐temporally evolved 2D template‐assisted strategy by incorporating meta ‐fluorophenethylammonium iodide ( m ‐F‐PEAI) into the PbI 2 precursor solution to enhance the perovskite film quality via a two‐step solution method. The in situ formed ( m ‐F‐PEA) 2 PbI 4 2D perovskite redirects the thermodynamic phase transformation by providing a coherent crystallographic framework that synchronizes crystallization kinetics along the vertical direction. Furthermore, this 2D perovskite serves as a spatio‐temporal template: it directs monolithic grain growth during crystallization, while the residual 2D perovskite remains at grain boundaries in the final film. By modifying the local potential landscape, the 2D perovskite facilitates charge extraction, overcoming the charge‐blocking behavior associated with traditional passivating layers. It synergistically works with the monolithic grains to enable efficient macroscopic charge transport rather than merely passivating defects. As a result, the template‐assisted devices exhibit improvement in photovoltaic performance, achieving a power conversion efficiency (PCE) of 26.03% with an anti‐reflective film. Moreover, the unencapsulated devices demonstrate improved storage stability under N 2 and dry‐air conditions, along with enhanced operational stability.