Exploring a lead-free organic-inorganic semiconducting hybrid with above-room-temperature dielectric phase transition

Recently, organic-inorganic hybrid lead halide perovskites have attracted great attention for optoelectronic applications, such as light-emitting diodes, photovoltaics and optoelectronics. Meanwhile, the flexible organic components of these compounds give rise to a large variety of important functions, such as dielectric phase transitions. However, those containing Pb are harmful to the environment in vast quantities. Herein, a lead-free organic-inorganic hybrid, (C₆H₁₄N)₂BiCl₅ (CHA; C₆H₁₄N⁺ is cyclohexylaminium), has been successfully developed. As expected, CHA exhibits an above-room-temperature solid phase transition at 325 K (T _c), which was confirmed by the differential scanning calorimetry measurement and variable temperature single crystal X-ray diffraction analyses. Further analyses indicate the phase transition is mainly governed by the order-disorder transformation of organic cyclohexylaminium cations. Interestingly, during the process of phase transition, the dielectric constant (ε') of CHA shows an obvious step-like anomaly, which displays a low dielectric constant state below T _c and a high dielectric constant state above T _c. Furthermore, variable temperature conductivity combined with theoretical calculations demonstrate the notable semiconducting feature of CHA. It is believed that our work will provide useful strategies for exploring lead-free organic-inorganic semiconducting hybrid materials with above room temperature dielectric phase transitions.