Flexible Composite Energy Harvesters from Ferroelectric A₂MX₄-Type Hybrid Halogenometallates

Two new molecular organic–inorganic hybrid halogenometallates [BnNMe2R]CdBr4 (Bn = benzyl; 1: R = Me; 2: R = n-Pr) have been synthesized and found to crystallize in the acentric crystal systems suitable for ferroelectric behavior. Both these compounds exhibit well-resolved rectangular polarization vs electric field (P–E) hysteresis loops at room temperature for their polycrystalline thin films. Compounds 1 and 2 exhibited fairly high remnant polarization (Pr) values of 18.59 and 14.24 μC cm–2, respectively. Moreover, flexible composite thin films of these halogenometallate salts with poly(dimethylsiloxane) (PDMS) were prepared and employed as mechanical energy-harvesting devices using an impact test setup operating at a frequency of 25 Hz and an applied force of 40 N. The maximum output voltages of 52.9 and 63.8 V have been recorded for the PDMS-fabricated devices of 5 wt % of 1 and 10 wt % of 2, respectively. Also, the obtained power densities of 13.8 and 37.1 μW cm–2 for the respective 5 wt % 1–PDMS and 10 wt % 2–PDMS devices are much higher than all known devices made up of organic–inorganic hybrid materials embedded in PDMS. The energy harvested from these devices was further utilized to charge a capacitor through a full wave-bridge rectifier.