Stereoelectronic effect of ionic liquids as carrier filter in perovskite optoelectronics

Abstract

Carrier transport in perovskite solar cells (PSCs) can be tuned by optimizing charge transport layers (CTLs) or introducing interfacial interlayers. Ionic liquids (ILs) exhibit high ionic conductivity, which enables their use in various energy and electronic applications. In this study, 1-allyl-3-methylimidazolium iodide (AMIZI) is introduced as an IL at the buried interface of PSCs. The iodine in AMIZI not only passivates both the perovskite and the electron transport layer (ETL), but also contributes to phase stabilization, while the imidazole ring adopts an equatorial conformation that promotes stereoelectronic effects, acting as a carrier filter to enhance charge transport. To highlight the carrier-filtering effect of AMIZI, we examined carrier dynamics at both the material and device levels. By systematically varying the strength and direction of the applied electric field, the associated magnetic fields, and the induced Lorentz force, we revealed bias-dependent filtering behavior and stable device operation after the incorporation of AMIZI. Owing to its unique stereoelectronic, passivation, and phase-stabilizing properties, AMIZI enables the fabrication of high-quality films and devices, achieving a power conversion efficiency (PCE) of 22.08 % and retaining over 90 % of the initial efficiency after 1400 h under harsh conditions (air, heat, and light).