Although batteries possess high energy storage density, their output power is limited by the slow movement of charge carriers, and thus capacitors are often required to deliver high power output. Dielectric capacitors have high power density with fast discharge rate, but their energy density is typically much lower than electrochemical supercapacitors. Increasing the energy density of dielectric materials is highly desired to extend their applications in many emerging power system applications. In this paper, we review the mechanisms and major characteristics of electric energy storage with electrochemical supercapacitors and dielectric capacitors. Three types of in-house-produced ferroic nonlinear dielectric thin film materials with high energy density are described, including (Pb_0.97La_0.02)(Zr_0.90Sn_0.05Ti_0.05)O₃ (PLZST) antiferroelectric ceramic thin films, Pb(Zn_1/3Nb_2/3)O_3-Pb(Mg_1/3Nb_2/3) O_3-PbTiO₃ (PZN-PMN-PT) relaxor ferroelectric ceramic thin films, and poly(vinylidene fluoride) (PVDF)-based polymer blend thin films. The results showed that these thin film materials are promising for electric storage with outstandingly high power density and fairly high energy density, comparable with electrochemical supercapacitors.

Simple strain enhancement: Piezoelectric materials are important as sensors and transducers for applications such as ultrasonics. Liu et al. discovered nanopillar regions in a sodium-niobium-oxide film that substantially improve the piezoelectric properties (see the Perspective by Bassiri-Gharb). These nanopillar regions reverse where the cations and anions are located in the crystal structure, with a distinctive boundary in between. This difference in structure results in a strain-sensitive polarity that enhances the piezoelectric properties in a chemically simple material. Science this issue p. 292 ; see also p. 252

Nanocomposites comprising a P(VDF-HFP) polymer matrix and core–shell structured nanoparticle fillers were prepared, in which a crystalline, ultrathin TiO₂ shell layer encapsulates BaTiO₃ nanoparticles. A large dielectric constant (>110) was obtained, which was unexpectedly more than 3 times higher than that of the nanocomposite without the TiO₂ shell layer. The significant improvement in electric polarization is attributed to the highly interactive interfaces among the multiple dielectric materials with the introduction of the intermediate TiO₂ layer, which also improves the breakdown field (>340 MV m⁻¹). Thus a resulting dielectric energy density of 12.2 J cm⁻³ is achieved, among the highest energy densities for polymer–ceramic composites.

We present a study on the bulk photovoltaic effect (BPVE) in ferroelectric thin films, in which the photocurrent is measured with symmetric electrodes in the plane perpendicular to the ferroelectric polarization to eliminate the effect of the depolarization field and interfacial energy barriers. We show evidence of a strong BPVE in epitaxial BiFeO3 (BFO) films as thin as 40 nm. By taking into account the nonuniform absorption of incident photons, we obtain the bulk photovoltaic tensor coefficient $\beta${}22 for BFO thin films. Remarkably, it is about five orders of magnitude larger than that of other typical ferroelectric materials for visible wavelengths. The results indicate that the BPVE in ferroelectric BFO thin films could be further explored for solar light photovoltaic applications.

It was discovered that the dielectric constant of the electrodes substantially determines the photovoltaic output in (Pb0.97La0.03)(Zr0.52Ti0.48)O3 ferroelectric thin films. With the screening charges distributed extensively away from the electrode interfaces, the use of the electrodes with a high dielectric constant gives rise to dramatically enhanced magnitude of photocurrent in photovoltaic thin films, and extremely high photovoltaic efficiency is theoretically predicted to be possible in ferroelectric ultrathin films or nanostructures.