A Hybrid Organic-Inorganic Bismuth Iodine Material Showing High Phase Transition Point and Low Bandgap

Recently, hybrid organic-inorganic lead halide materials have attracted great attention for their applications in the fields of light-emitting diodes, photovoltaics, photodetector. However, these hybrid materials usually suffer from environmental and human health issues because of the toxic lead moieties. Herein, we report a novel lead-free bismuth iodide phase transition material, [NH3(CH2)(7)NH3][BiI5] (1), which undergoes a reversible phase transition at high temperature 351.7 K and exhibits a step fashion dielectric anomaly. The structural phase transition of 1 is mainly originated from the order-disorder transition of the 1,7-heptanediamine cations. Besides, the solid-state UV-vis spectrum of 1 displays an intense adsorption at around 658 nm; which gives an indirect bandgap of 1.89 eV. Such a small bandgap value is comparable to most of the organic-inorganic hybrid lead halide type semiconductors. We believe this study will shed light on the exploration of lead-free organic-inorganic hybrid metal halide semiconductors toward future device applications.