Chiral two-dimensional (2D) perovskites are a promising material class for the next generation of spintronic and chiroptical devices. Despite their promise, many aspects related to film formation and crystallization remain elusive. When chiral ammonium-based organic cations such as methylbenzylammonium (MBA) are employed in the preparation of chiral 2D perovskites, their interaction with the halide species in the inorganic perovskite network often introduces substantial steric hindrance, leading to the formation of one-dimensional (1D) phase impurities within the 2D matrix. Here, we demonstrate that this 1D phase manifests itself in the photoluminescence (PL) spectra of the 2D perovskite film as an additional weakly emissive, thermally activated state with a self-trapped excitonic character, leading to an asymmetric PL response. We demonstrate that the strategic introduction of a methoxy (OMe) group on the para position of the MBA cations can mitigate the formation of the 1D phase. As a result, the emission band becomes narrower and more symmetric and the 2D perovskite film has a higher PL quantum yield at room temperature. Our findings elucidate the origins of asymmetry and broadband emission of MBA-based chiral 2D perovskites and highlight the indispensable role of molecular design in chiral organic cations in controlling phase purity and attaining the desired optical properties.

中文翻译：

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了解和控制手性甲基苯甲基铵基阳离子二维钙钛矿的光致发光线形状

手性二维（2D）钙钛矿是下一代自旋电子和手性光学器件的有前途的材料类别。尽管前景广阔，但与成膜和结晶相关的许多方面仍然难以捉摸。当手性铵基有机阳离子如甲基苄基铵（MBA）用于制备手性二维钙钛矿时，它们与无机钙钛矿网络中卤化物的相互作用通常会引入大量的空间位阻，导致形成一维（1D） ) 二维矩阵内的相杂质。在这里，我们证明这一一维相在二维钙钛矿薄膜的光致发光 (PL) 光谱中表现为一种额外的弱发射、热激活状态，具有自俘获激子特性，从而导致不对称的 PL 响应。我们证明，在 MBA 阳离子的对位上战略性引入甲氧基 (OMe) 基团可以减轻一维相的形成。结果，发射带变得更窄、更对称，并且二维钙钛矿薄膜在室温下具有更高的PL量子产率。我们的研究结果阐明了基于 MBA 的手性二维钙钛矿的不对称性和宽带发射的起源，并强调了手性有机阳离子分子设计在控制相纯度和获得所需光学性能方面不可或缺的作用。