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.