A Lead-Free Ferroelectric 2D Dion-Jacobson Tin Iodide Perovskite.

Two-dimensional (2D) hybrid organic-inorganic halide perovskites have emerged as a new class of 2D semiconductors with the potential to combine excellent optoelectronic properties with symmetry-enabled properties such as ferroelectricity. Although many lead-based ferroelectric 2D halide perovskites have been reported, there is yet to be a conclusive report of ferroelectricity in tin-based 2D perovskites. Here, we report the structures and properties of a new series of 2D Dion-Jacobson (DJ) Sn perovskites: (4AMP)SnI 4 , (4AMP)(MA)Sn 2 I 7 , and (4AMP)(FA)Sn 2 I 7 (4AMP = 4-(aminomethyl)piperidinium, MA = methylammonium, and FA = formamidinium). Structural characterization reveals that (4AMP)SnI 4 is polar with in-plane spontaneous polarization whereas (4AMP)(MA)Sn 2 I 7 and (4AMP)(FA)Sn 2 I 7 are centrosymmetric. Furthermore, (4AMP)SnI 4 displays second harmonic generation (SHG) and polarization-electric field hysteresis measurements confirm it is ferroelectric with a spontaneous polarization of 10.0 µC cm -2 at room temperature. (4AMP)SnI 4 transitions into a centrosymmetric structure above 367 K. As the first direct experimnetal observation of the spontaneous ferroelectric polarization of a Sn-based 2D hybrid perovskite, this work opens up environmentally friendly 2D tin halide perovskites for ferroelectricity and other physical property studies. This article is protected by copyright. All rights reserved.