Organic-inorganic metal halides exhibit excellent compositional flexibility. When an ideal perovskite structure is adopted, they have the general formula ABX3, where A+ can be an organic or inorganic cation, B 2+ is an inorganic cation and X- is a halide anion. By changing the A, B, and X sites, the crystal structure, electronic structure and band gap can be tuned for a variety of optoelectronic applications, such as solar cells, light-emitting diodes, and photodetectors. However, the toxicity of lead in these materials is undesirable for practical applications. Thus, lead-free organic-inorganic metal halides are being extensively explored.In this study, we explored organic-inorganic metal halides based on the meta-xylylenediammonium (MXD) cation and a variety of trivalent metals. MXD contains an aromatic ring and is expected to improve stability in ambient conditions [1]. We succeeded in synthesising single crystals via a solution-based approach [2][3]. Based on single crystal X-ray diffraction, the structures were found to consist of isolated octahedra (or groups of octahedra) and are commonly referred to as zero-dimensional materials. We also investigated the tunability of the band gap due to halide substitution. As shown in Fig.1, the colours of samples change depending on the halogen content. Also, diffuse reflectance UV-visible spectroscopy clearly shows that the optical band gap is tunable. Here, we show the results of single crystal and powder diffraction, photoluminescence, scanning electron microscopy and ambient pressure photoemission spectroscopy to link the structure and optical properties of these new materials.
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