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)₂MA_n−1Pb_nI_{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 PEA₂MA₉Pb₁₀I₃₁ (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).