Crystallographic Insights into the Structural Heterogeneities of 2D Ruddlesden‐Popper Perovskite Films

Abstract 2D Ruddlesden‐Popper phase perovskites (RPPs) offer significant potential for next‐generation photovoltaics owing to their excellent intrinsic stability. Fully understanding the crystalline configuration of 2D perovskite films is essential for further enhancing the power‐conversion‐efficiency (PCE) of 2D perovskite solar cells (2D‐PSCs). Herein, the structural heterogeneities, including the profiles of crystal orientation and defect distribution, at both the microscopic and mesoscopic scales for 2D perovskite films are investigated. Empty voids are observed in the buried interface of 2D perovskite films associated with Brownian tree‐shaped dendritic structures, and the crystal orientations of 2D RPPs in the upper and lower parts of these areas are mismatched. This configuration hinders charge carrier transport along the vertical direction and is likely responsible for the lower PCE of 2D‐PSCs compared to their 3D counterparts. The formation mechanism of these voids and the crystalline mismatching are revealed based on compositional and structural analysis. The results suggest that synchronizing the rate of crystallization in different film areas may eliminate these voids and thereby reduce the PCE gap between 2D‐ and 3D‐PSCs. This work provides a comprehensive understanding of the crystallographic heterogeneities of 2D perovskite films, highlighting new pathways to design more efficient 2D‐PSCs based on 2D RPP films.