Universal 3D/2D Surface Heterojunction‐Based Piperidine Derivatives for Efficient Inverted Perovskite Solar Cells

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The 3D/2D perovskite heterostructure has emerged as a promising strategy to simultaneously enhance both the efficiency and stability of perovskite solar cells (PSCs). This work introduced a fluorinated piperidine derivative, 4‐trifluoromethylpiperidine (p‐CF 3 PiP), as a precise surface reconstruction agent for 3D perovskite. By harnessing the strong hydrophobicity of the ─CF 3 groups and the coordination interaction between the piperidine ring and lead iodide, this approach promotes the growth of high‐n‐value ( n = 4) 2D perovskite, resulting in significantly improved film stability. The 3D/2D structure significantly facilitates the extraction and transport of electrons, effectively reducing the density of defect states at the interface, leading to suppressed carrier recombination. The resulting inverted PSC (with a 1.55 eV bandgap) achieved a remarkable power conversion efficiency (PCE) of 26.17%, along with a high open‐circuit voltage ( V OC ) of 1.194 V. This strategy demonstrates broad applicability, as flexible devices reached a PCE of 24.26%, and wide‐bandgap (1.68 eV) systems achieved 22.72%. Notably, the 3D/2D heterojunction exhibits exceptional long‐term stability, maintaining 99% of its initial PCE after 1730 h under ISOS‐L‐1 protocols at 25 °C, and displaying only 20% PCE degradation after 423 h of maximum power point (MPP) tracking under 85 °C.