Methoxy‐Based Passivator 4‐Methoxyphenethylammonium Iodide as Multifunctional Passivator for High‐Efficiency 3D/2D Flexible Perovskite Solar Cells over 23%

As is well known, the interface of perovskite solar cells (PSCs) is rich in deep‐level carrier traps, which act as non‐radiative recombination centers and limit the open‐circuit voltage ( V OC ) and power conversion efficiency (PCE) of PSCs. Defect chemistry and surface passivation agents have been extensively studied, primarily focusing on the neutralization of non‐coordinated lead or anion defects. Herein, a novel methoxy‐based passivator 4‐methoxyphenethylammonium iodide (p‐MeOPEAI) is introduced for a multifunctional passivation effect at the perovskite interface. It is susceptible for p‐MeOPEAI to form 2D perovskite on top of 3D perovskite, and it interacts with the surface of 3D perovskite in multiple ways, forming a 3D/2D structure that facilitates charge transfer and p‐MeOPEAI passivates the uncoordinated Pb 2+ ions of the perovskite film surface. The interface defects in the PSCs are well passivated, minimizing non‐radiative recombination and enhancing device performance. As a result, a champion PCE of 23.3% is achieved for flexible PSCs with a high V OC (1.2 V). In addition, modified devices also show enhanced operational mechanical stability (retention of >80% initial PCE after 10 000 bending cycles).