Two-Factor Phase Separations in Mixed-Halide Quasi-2D Perovskite LEDs: Dimensionality and Halide Segregations

Yang, Seok Joo; Wang, Kang; Luo, Yanqi; Park, Jee Yung; Yang, Hanjun; Coffey, Aidan H.; Ma, Ke; Sun, Jiaonan; Wieghold, Sarah; Zhu, Chenhui; Dou, Letian

doi:10.1021/acsenergylett.3c01009

We present a combined experimental and density functional theory study that characterizes the charge and spin density in NiX₂(3,5-lutidine)₄(X= Cl, Br and I). In this material, magnetic exchange interactions occur via Ni²⁺–halide...halide–Ni²⁺pathways, forming one-dimensional chains. We find evidence for weak halide...halide covalency in the iodine system, which is greatly reduced whenX= Br and is absent forX= Cl; this is consistent with the reported `switching-on' of magnetic exchange in the larger-halide cases. Our results are benchmarked against density functional theory calculations on [NiHF₂(pyrazine)₂]SbF₆, in which the primary magnetic exchange is mediated by F–H–F bridging ligands. This comparison indicates that, despite the largely depleted charge density found at the centre of halide...halide bonds, these through-space interactions can support strong magnetic exchange gated by weak covalency and enhanced by significant electron density overlapping that of the transition metal centres.

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