Ferroelectricity and Piezoelectric Energy Harvesting of Hybrid A 2 BX 4 -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 A 2 BX 4 -type halogenocuprate materials supported by heteroleptic phosphonium cations. These lead-free discrete Cu(II) halides [Ph 3 MeP] 2 [CuCl 4 ] ( 1 ) and [Ph 3 MeP] 2 [CuBr 4 ] ( 2 ) exhibit a remnant polarization ( P r ) 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.