Cyclic Structured Ionic Molecules Formulating Multi-Dimensional Perovskite Structures of Highly Stable and Efficient Perovskite Solar Cells

Perovskite solar cells (PSCs) achieve power conversion efficiency (PCE) above 26% but remain reliant on inert-atmosphere processing and toxic antisolvents, hampering scale-up. Here, ambient-condition (RH <50%) fabrication of PSCs is reported using an ethyl acetate antisolvent modified with ring-size-tunable N-heterocyclic ammonium ionic liquids (ILs): 1-(2-ethoxyethyl)-1-methylpyrrolidinium (PYR⁺) and 1-(2-ethoxyethyl)-1-methylpiperidinium (PIP⁺). Comparative analysis reveals that the PYR⁺ cation with the smaller ring size not only fosters an ultrathin interfacial low-dimensional perovskite layer, enhances (100) α-phase orientation, and suppresses trap states, but also induces beneficial in-plane compressive lattice strain, collectively yielding high-quality films with superior crystalline order. In situ GIWAXS under one-sun illumination and electrical bias demonstrates that IL treatment prevents α→δ phase transitions and PbI₂ formation, directly correlating with stable photocurrent output. PSCs incorporating PYR⁺ achieve a champion PCE of 24.7% and retain over 90% of their initial efficiency after 1000 h of damp-heat (85 °C/85% RH) stress. These findings establish ring-size-tunable N-heterocyclic ammonium ionic liquids as scalable, multifunctional additives for ambient-processed, high-performance, and durable PSCs.