Controlling Top‐Interface Reconstruction in Perovskite Solar Cells via Molecular Design of Dual‐Functional Ammonium Salts

Surface defects on perovskite films induce non‐radiative charge recombination, which remains a primary factor limiting the open‐circuit voltage ( V OC ) and overall performance of perovskite solar cells (PSCs). Herein, we introduce a passivation strategy employing two amine hydrochlorides, N‐(2‐aminoethyl)maleimide hydrochloride (AEMCl) and N‐(2‐aminoethyl)phthalimide hydrochloride (AEPCl), which yield distinctly different interfacial phase behaviors on the perovskite top surface. Intriguingly, AEPCl promotes the formation of n = 1 Ruddlesden–Popper (RP) phases at the interface, whereas AEMCl suppresses such low‐dimensional phases and effectively passivates residual PbI 2 . Consequently, the AEMCl‐treated device achieves a superior power conversion efficiency (PCE) of 26.14% with a V OC of 1.164 V, outperforming both the control (24.72%) and AEPCl‐treated devices (25.46%). Furthermore, unencapsulated AEMCl‐modified devices exhibited excellent durability, retaining 89.78% of their initial PCE after 4500 h of storage in N 2 atmosphere. Under continuous one‐sun illumination and maximum power point tracking (MPPT) in N 2 at room temperature, the device maintained 85.01% of its initial efficiency after 1000 h. At the molecular level, this work demonstrates how molecular structure dictates the phase behavior of perovskites.