Uncovering Multiple Intrinsic Chiral Phases in (PEA)₂PbI₄ Halide Perovskites

Two-dimensional (2D) halide perovskites offer a unique platform for investigating the ground state of materials possessing significant anharmonicity. In contrast to three-dimensional perovskites, their 2D counterparts offer substantially fewer degrees of freedom, resulting in multiple well-defined crystal structures. In this work, we thoroughly investigate the anharmonic ground state of the benchmark (PEA)2PbI4 compound, using complementary information from low-temperature X-ray diffraction (XRD) and photoluminescence spectroscopy, supported by density functional theory calculations. We extrapolate four crystallographic configurations from low-temperature XRD. These configurations imply that the ground state has an intrinsic disorder stemming from two coexisting chiral sublattices, each with a bioriented organic spacer molecule. We further show evidence that these chiral structures form unevenly populated ground states, portraying uneven anharmonicity, where the state population may be tuned by surface effects. Our results uncover a disordered ground state that may induce intrinsic grain boundaries, which cannot be ignored in practical applications.二维（2D）卤化物钙钛矿为研究具有显著非简谐性的材料基态提供了独特的研究平台。与三维卤化物钙钛矿相比，其二维对应物的自由度显著更少，因此可形成多种结构明确的晶体构型。 本研究中，我们结合低温X射线衍射（X-ray Diffraction, XRD）与光致发光光谱的互补信息，并辅以密度泛函理论（Density Functional Theory）计算，对基准化合物(PEA)₂PbI₄的非简谐基态开展了全面研究。我们从低温XRD数据中推导得到四种晶体构型，这些构型表明基态存在由两种共存手性子晶格引发的本征无序，每种手性子晶格均对应一种双取向有机间隔分子。 我们进一步证实，这类手性结构会形成占据比例不均的基态，呈现出非均匀的非简谐性，且该基态的占据比例可通过表面效应进行调控。本研究结果揭示了一种可能诱发本征晶界的无序基态，该现象在实际应用中不容忽视。