Reduced Dimensionality of Perovskite Films Combined with 3D Configuration for Stable Carbon‐Based Perovskite Solar Cells

Constructing 3D/Low‐dimensional (3D/LD) hybrid perovskite structures has emerged as a promising route to enhance environmental tolerance due to the steric effect from the LD perovskite counterpart, while how to properly choose the LD perovskites remains a big obstacle in terms of the uncertain layer number n values formed in the perovskite precursor solution. In order to purposely form an efficient perovskite 3D/LD film, herein, a series of quasi‐2D perovskite (PEA) 2 MA n−1 Pb n I 3n + 1 solutions with varying n‐values ( n = 1, 3, 10, 20, 30, and 60) are prepared and incorporated into the bulk phase of methylammonium lead iodide precursors to construct 3D/LD hybrid structures. The introduction of the quasi‐2D phases with appropriate n values effectively regulated the crystallization of perovskite films, optimized film morphology, and reduced defect density. With the increase of the n value, the grain size and the diffraction peak intensity of the perovskite gradually increased, reaching the optimum at n = 10. Among them, the 3D/LD PSCs based on PEA 2 MA 9 Pb 10 I 31 ( n = 10) exhibited the highest power conversion efficiency (PCE) of 15.27%, primarily due to their excellent short‐circuit current density ( J SC ) and fill factor (FF), which indicates more efficient carrier transport. When the n value is further increased to 60, the device exhibited a lower PCE, possibly due to the excessively thick organic spacer layer limiting carrier transport. Furthermore, the intrinsic stability of the quasi‐2D phase endowed the devices with superior durability. Under environmental conditions (room temperature, 35–45% relative humidity), the unencapsulated 3D/LD devices retained approximately 90% of their initial PCE after 30 days, whereas the control devices retained only 60%. These results provide valuable insights into the role of quasi‐2D phase engineering in 3D/LD perovskite systems and offer an effective strategy for advancing the performance and durability of carbon‐based perovskite solar cells (C‐PSCs).