Two-dimensional halide perovskites (2D-HPs) are of significant interest for their applications in optoelectronic devices. Part of this increased interest in 2D-HPs stems from their increased stability relative to their three-dimensional (3D) counterparts. Here, the origin of higher stability in 2D-HPs is mainly attributed to the bulky ammonium cation layers, which can act as a blocking layer against moisture and oxygen ingression and ion diffusion. While 2D-HPs have demonstrated increased stability, it is not clear how the structure of the ammonium ions impacts material stability. Herein, we investigate how the structure of ammonium cations, including three n-alkyl ammoniums, phenethylammonium (PEA) and five PEA derivatives, anilinium (An), benzylammonium (BzA), and cyclohexylmethylammonium (CHMA), affects the crystal structure and air, water, and oxygen stability of 2D tin halide perovskites (2D-SnHPs). We find that stability is influenced by several factors, including the molecular packing and intermolecular interactions in the organic layer, steric effects around the ammonium group, the orientation distribution of the 2D sheets, and the hydrophobicity of the perovskite film surface. With superior hydrophobicity, strong interactions between organic molecules, and a high extent of parallel oriented inorganic sheets, the 2-(4-trifluoromethyl-phenyl)-ethylammonium (4-TFMPEA) ion forms the most stable 2D-SnHP among the 12 ammonium cations investigated.

中文翻译：

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A'位阳离子结构对二维卤化锡钙钛矿稳定性的影响


二维卤化物钙钛矿 （2D-HPs） 因其在光电器件中的应用而受到重大关注。人们对 2D-HP 的兴趣增加，部分原因是它们相对于 3D （3D） 对应物的稳定性更高。在这里，2D-HPs 中较高稳定性的来源主要归因于大块的铵阳离子层，它可以作为阻止水分和氧气进入以及离子扩散的阻挡层。虽然 2D-HP 已显示出更高的稳定性，但尚不清楚铵离子的结构如何影响材料稳定性。在此，我们研究了铵阳离子的结构，包括三种正烷基铵、苯乙基铵 （PEA） 和五种 PEA 衍生物、苯胺 （An）、苄基铵 （BzA） 和环己基甲基铵 （CHMA），如何影响 2D 卤化锡钙钛矿 （2D-SnHPs） 的晶体结构和空气、水和氧稳定性。我们发现稳定性受多种因素影响，包括有机层中的分子堆积和分子间相互作用、铵基周围的空间效应、2D 片材的取向分布以及钙钛矿薄膜表面的疏水性。2-（4-三氟甲基苯基）-乙基铵 （4-TFMPEA） 离子具有优异的疏水性、有机分子之间的强相互作用以及高度平行取向的无机片，在所研究的 12 种铵阳离子中形成最稳定的 2D-SnHP。