2D organic–inorganic lead iodide perovskites have recently received tremendous attention as promising light absorbers for solar cells, due to their excellent optoelectronic properties, structural tunability, and environmental stability. However, although great efforts have been made, no 2D lead iodide perovskites have been discovered as ferroelectrics, in which the ferroelectricity may improve the photovoltaic performance. Here, by incorporating homochiral cations, 2D lead iodide perovskite ferroelectrics [R‐1‐(4‐chlorophenyl)ethylammonium]₂PbI₄ and [S‐1‐(4‐chlorophenyl)ethylammonium]₂PbI₄ are successfully obtained. The vibrational circular dichroism spectra and crystal structural analysis reveal their homochirality. They both crystalize in a polar space group P1 at room temperature, and undergo a 422F1 type ferroelectric phase transition with transition temperature as high as 483 and 473.2 K, respectively, showing a multiaxial ferroelectric nature. They also possess semiconductor characteristics with a direct bandgap of 2.34 eV. Nevertheless, their racemic analogue adopts a centrosymmetric space group P2₁/c at room temperature, exhibiting no high‐temperature phase transition. The homochirality in 2D lead iodide perovskites facilitates crystallization in polar space groups. This finding indicates an effective way to design high‐performance 2D lead iodide perovskite ferroelectrics with great application prospects.

中文翻译：

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首个二维手性碘化钙钛矿铁电体：[R-和S-1-（4-氯苯基）乙基铵] 2PbI4

二维有机-无机碘化铅钙钛矿由于其优异的光电性能，结构可调性和环境稳定性，最近成为太阳能电池有希望的光吸收剂，引起了极大的关注。然而，尽管已经付出了巨大的努力，但是尚未发现2D碘化铅钙钛矿作为铁电体，其中铁电性可以改善光伏性能。在这里，通过引入同手性阳离子，二维碘化铅钙钛矿铁电体[ R -1-（4-氯苯基）乙基铵] ₂ PbI ₄和[ S -1-（4-氯苯基）乙基铵] ₂ PbI ₄成功获得。振动圆二色性光谱和晶体结构分析显示出它们的手性。它们都在室温下在极性空间群P 1中结晶，并经历422 F 1型铁电相变，其转变温度分别高达483和473.2 K，显示出多轴铁电性质。它们还具有2.34 eV的直接带隙的半导体特性。然而，他们的外消旋类似物采用了一个中心对称的空间群P 2 ₁ / c在室温下，没有高温相变。二维碘化铅钙钛矿中的手性有助于在极性空间群中结晶。这一发现表明，一种设计高性能二维碘化钙钛矿型铁电体的有效方法具有广阔的应用前景。