Dielectric Relaxation Mechanism in the Phase-Transition Region of a Chiral Hybrid Perovskite and Its Piezoelectric-Energy-Harvesting Properties

Chiral halide perovskites are being extensively studied due to their promising spintronic and optoelectronic properties, where the organic chiral ligands introduce chirality into halide perovskites. Right-handed and left-handed chiral materials are mirror images of one another and break the inversion symmetry, which produces ferroelectricity. In this work, we study the dielectric, piezoelectric, and ferroelectric properties of (R)-(-)-1-cyclohexylethylammonium)PbI3 (R-CYHEAPbI3), a chiral, one-dimensional perovskite. We performed and analyzed complex impedance spectroscopy; ac conductivity; and the complex electric modulus using the Maxwell-Wagner equivalent circuit model, the universal power law, the Havrilliak-Negami (HN) model, and the Kohlrausch-Williams-Watts (KWW) model to understand the transport and relaxation mechanism in the chiral R-CYHEAPbI3 perovskite over wide temperature (313-473 K) and frequency (4 Hz-8 MHz) ranges. The dc conductivity is almost constant in the paraelectric-to-ferroelectric phase-transition region (PTR) but increases below and above this region. The activation energy of this region is very low, about 0.09 eV, while below the PTR, the activation energy is about 0.85 eV, and above the PTR, it is about 0.90 eV. We further note that the conduction mechanism changes from overlapped large polaron tunneling to correlated barrier hopping due to the ferroelectric-to-paraelectric phase transition. The activation energy derived from the relaxation time (using HN and KWW models) agrees with that obtained from the dc conductivity. In addition, we measured the saturation polarization of 0.01 μC/cm2 at a 4-kV/cm applied electric field and a piezoelectric constant (d33) of about 36 pm/V at the maximum applied bias voltage of 10 V. Finally, we fabricated a polyvinylidene fluoride and 3-wt % R-CYHEAPbI3 chiral perovskite composite film for the development of high-performance energy-harvesting nanogenerators.