A Two-component Ferroelectric containing Amino-Phosphonium Cations and Organo-Phosphinate Anions and Its Piezoelectric Energy Harvesting Applications

Abstract

Ferroelectric phosphate-based materials are known for their biocompatibility, proton conductivity, dipole switching, and high thermal stability. In this context, we report a new family of organic ferroelectric material, tetrakis(phenylamino)phosphonium diphenylphosphinate (PANI·DPPi), which crystallizes in the non-centrosymmetric polar tetrahedral space group P4₁. The ferroelectric nature of PANI·DPPi was confirmed by the observation of a rectangular P–E hysteresis loop, yielding a saturated polarization value of 0.6 μC cm⁻². Ferroelectric polar domains of PANI·DPPi, along with bias-dependent amplitude butterfly and phase hysteresis loops, were visualized by piezo response force microscopy (PFM). Furthermore, polydimethylsiloxane (PDMS) composites of PANI·DPPi enabled the fabrication of humidity-resistant piezoelectric nanogenerators (PENGs) with energy harvesting and mechanical-to-electrical sensing capabilities. The top-performing 10wt% PANI·DPPi–PDMS device achieved a peak output voltage of 21.6 V. Differential scanning calorimetry (DSC) analysis of PANI·DPPi exhibited thermal transitions around 445 K, classified as a significant phase change, with crystallization occurring at 436 K. Dielectric studies confirmed the presence of a thermally driven phase transition at ~430 K, accompanied by a substantial change in dielectric behaviour, reinforcing its potential for phase-transition-driven dielectric applications. Additionally, we present a refined method for calculating the output work efficiency (OWE) parameter, which quantifies the ratio of harvested electrical energy to the maximum elastic energy stored in the composite device, considering key parameters during PENG measurements. For the 10 wt% PANI·DPPi–PDMS composite, an OWE of 37.4% was achieved, demonstrating both its current performance and potential for optimization. This metric provides a standardized approach for evaluating PENGs, addressing a critical gap in assessing mechanical-to-electrical energy conversion efficiency.