The First Improper Ferroelectric of 2D Multilayered Hybrid Perovskite Enabling Strong Tunable Polarization‐Directed Second Harmonic Generation Effect

Abstract 2D organometallic halide perovskites are recently emerging as a robust family of ferroelectrics, of which their inherent spontaneous polarization ( P s ) endows fascinating quadratic nonlinear optical properties. However, up to date, few studies are reported to tune and control the second harmonic generation (SHG) effect in this ferroelectric branch. Herein, the first improper ferroelectric of 2D multilayered hybrid perovskites, (IA) 2 (EA) 2 Pb 3 Br 10 ( 1 , where IA is isoamylammonium and EA is ethylammonium), which exhibits a high Curie temperature ( ≈ 371 K) and biaxial ferroelectricity with P s of 2.2 µ C cm −2 is reported. Strikingly, its unique in‐plane ferroelectricity allows strong tunable SHG properties under the polarized‐light. That is, the maximum SHG signals are observed with polarized‐light parallel to P s , while the minimum SHG appears along the vertical direction. This SHG anisotropy creates an extremely large dichroism ratio of ≈ 12, as visualized by 2D color mapping, which is the record‐high merit for this type of SHG systems. To the best knowledge, this is the first time to achieve tunable SHG effects through ferroelectric polarization. As a pioneering study, the coupling between the SHG effect and ferroelectricity paves a new direction of 2D hybrid perovskite ferroelectrics toward smart optical device applications.