Methoxyl‐Substitution of Phenylethylammonium Strengthened 2D/3D Heterogeneous Structures for Inverted Perovskite Solar Cells with Enhanced Efficiency and Stability

ABSTRACT Two‐dimensional (2D) perovskites are widely introduced into formamidinium (FA ⁺ ) based three‐dimensional (3D) perovskites due to their major benefits of: (i) stabilizing the α‐phase of FA ⁺ ‐based perovskites; (ii) regulating the crystallization process; (iii) mitigating interface defects. However, knowledge regarding how the configuration of bulky ammonium cations influences the formation and performance of 2D/3D heterogeneous structures are still scarce. Here, we report that substituting phenethylammonium with methoxyl (MeO‐PEA ⁺ ) can decrease its solubility in polar solvents and enhance the α‐phase stability for both the FA‐based perovskite crystallization nuclei and final polycrystalline films. Adding a minimal concentration (0.3%) of p‐methoxyphenethylammonium chloride (MeO‐PEACl) in the perovskite precursor can achieve both a grain boundary wrapping and an in situ formation of buried 2D/3D perovskite structures, leading to solar cells with increased open‐circuit voltage from 1.11 to 1.16 V and power conversion efficiency (PCE) from 21.1% to 23.1%. The resulting 2D/3D heterogeneous film can maintain its black phase after 3380 h of exposure at 65 ± 10% relative humidity, and the corresponding solar cells preserved 98% of their initial PCE after 1850 h of heating at 65°C.