2D Ruddlesden–Popper (RP) perovskites, upon inclusion of a chiral amine, exhibit chirality-induced spin selectivity (CISS). Although alloying at the halogen site in MBA-based RPs (MBA: methylbenzylammonium) is one of the suitable routes to tune the CISS effect, the mixed-halide RP perovskites exhibited complete suppression of chirality when probed through circular dichroism (CD). Here, we present the CISS effect in a series of mixed-halide RP perovskites. We show that photoinduced halide segregation is the origin for the apparent chirality suppression. The spin-dependent charge transport was evidenced through magnetic-conducting atomic force microscopy (mc-AFM) studies and magnetoresistance (MR) measurements. The mc-AFM results show that in (R/S-MBA)₂PbI_4(1–x)Br_4x, the CISS effect decreases with bromide inclusion, nonmonotonically; the microstrain developed in the lattice and the spin-polarized charge transport are found to be correlated. Such a behavior has been explained through an inhomogeneity in the strength of the hydrogen bond between the organic moieties and halogens in the inorganic framework of the compounds. Our results further inferred that the hydrogen-bond-induced coupling transfers the chirality from the amine to the inorganic sublattice. The work explains the weakened CISS effect in mixed-halide chiral RP perovskites and provides a strategy to tune the spin-polarized charge transport as well.

中文翻译：

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为什么 2D 手性钙钛矿中的混合卤化物会削弱手性诱导的自旋选择性


2D Ruddlesden-Popper （RP） 钙钛矿在包含手性胺后，表现出手性诱导的自旋选择性 （CISS）。尽管基于 MBA 的 RP （MBA： 甲基苄基铵） 中卤素位点的合金化是调节 CISS 效应的合适途径之一，但当通过圆二色性 （CD） 探测时，混合卤化物 RP 钙钛矿表现出完全抑制手性。在这里，我们展示了一系列混合卤化物 RP 钙钛矿中的 CISS 效应。我们表明光诱导卤化物偏析是明显手性抑制的起源。通过磁传导原子力显微镜 （mc-AFM） 研究和磁阻 （MR） 测量证明了自旋依赖性电荷传输。mc-AFM 结果表明，在 （R/S-MBA）₂PbI_4（1–x）Br_4x 中，CISS 效应随着溴化物的包含而减弱，非单调;发现晶格中产生的微应变和自旋极化电荷传输是相关的。这种行为可以通过化合物无机框架中有机部分和卤素之间的氢键强度的不均匀性来解释。我们的结果进一步推断，氢键诱导的偶联将手性从胺转移到无机亚晶格。这项工作解释了混合卤化物手性 RP 钙钛矿中减弱的 CISS 效应，并提供了一种调整自旋极化电荷传输的策略。