Controlling Crystallization Dynamics of the Perovskite by Restricted Assembly Strategy Enables High‐Performance Solar Cells

Abstract Multifunctional polymer materials are extensively applied to regulate the crystallization process of perovskite films. However, a comprehensive understanding of the correlations among spatial structure of polymers, crystallization modulation, and device performance is still lacking. Here, a restricted assembly strategy is proposed to prepare high‐quality perovskite films by systematically studying the effect of space configurations of polymers on modulating the crystallization of cesium lead triiodide (CsPbI 3 ) perovskite. The results confirm the importance of high backbone coplanar space configurations in promoting nucleation, accelerating phase transitions, and enhancing crystalline orientation. The polymer with the high backbone coplanar structure not only facilitates the formation of uniform and dense nucleation sites by precisely controlling the spatial distribution of colloidal particles but also enhances the crystal orientation through the orientational growth induced by the coplanar structure. As a result, the efficiency of the CsPbI 3 solar cells increases from 17.84% to 20.39%. Additionally, the unencapsulated devices show excellent storage and operational stability.