Ferroelectricity and Piezoelectric Energy Harvesting of Hybrid A2BX4‑Type Halogenocuprates Stabilized by Phosphonium Cations

Perovskite-structured compounds containing organic cations and inorganic anions have gained prominence as materials for next-generation electronic and energy devices. Hybrid materials possessing ferro- and piezoelectric properties are in recent focus for mechanical energy harvesting (nanogenerator) applications. Here, we report the ferroelectric behavior of A2BX4-type halogenocuprate materials supported by heteroleptic phosphonium cations. These lead-free discrete Cu­(II) halides [Ph3MeP]2[CuCl4] (1) and [Ph3MeP]2[CuBr4] (2) exhibit a remnant polarization (Pr) of 17.16 and 26.02 μC cm–2, respectively, at room temperature. Furthermore, flexible polymer films were prepared with various weight percentage (wt %) compositions of 1 in thermoplastic polyurethane (TPU) and studied for mechanical energy harvesting applications. A highest peak-to-peak voltage output of 25 V and power density of 14.1 μW cm–2 were obtained for the optimal 15 wt % 1-TPU composite film. The obtained output voltages were utilized for charging a 100 μF electrolytic capacitor that reaches its maximum charging point within 30 s with sizable stored energies and accumulated charges.含有机阳离子与无机阴离子的钙钛矿结构化合物（Perovskite-structured compounds）现已成为下一代电子与能源器件的热门材料。兼具铁电性与压电性的杂化材料是当前机械能收集（纳米发电机，nanogenerator）应用领域的研究焦点。本研究报道了由杂配位鏻阳离子（heteroleptic phosphonium cations）稳定的A₂BX₄型卤代铜酸盐材料的铁电行为。这类无铅分立型Cu(II)卤化物[Ph₃MeP]₂[CuCl₄]（化合物1）与[Ph₃MeP]₂[CuBr₄]（化合物2）在室温下的剩余极化强度（remnant polarization, Pr）分别为17.16 μC·cm⁻²与26.02 μC·cm⁻²。此外，我们将不同质量分数（weight percentage, wt%）的化合物1掺入热塑性聚氨酯（thermoplastic polyurethane, TPU）中制备柔性复合聚合物薄膜，并针对其机械能收集应用开展研究。针对最优配比的15 wt%化合物1-TPU复合薄膜，测得其最高峰峰值输出电压为25 V，功率密度达14.1 μW·cm⁻²。所得输出电压可用于为100 μF电解电容器充电，该电容器可在30秒内达到满充状态，储存可观的电能并积累足量电荷。