Dielectric polymer nanocomposites with a high breakdown field and high dielectric constant have drawn significant attention in modern electrical and electronic industries due to their potential applications in dielectric and energy storage systems. The interfaces of the nanomaterials play a significant role in improving the dielectric performance of polymer nanocomposites. In this work, polydopamine (dopa)-functionalized TiO2–BaTiO3–TiO2 (TiO2–BT–TiO2@dopa) core@double-shell nanoparticles have been developed as novel nanofillers for high-energy-density capacitor applications. The hierarchically designed nanofillers help in tailoring the interfaces surrounding the polymer matrix as well as act as individual capacitors in which the core and outer TiO2 shell function as a capacitor plate because of their high electrical conductivity while the middle BT layer functions as a dielectric medium due to high dielectric constant. Detailed electrical characterizations have revealed that TiO2–BT–TiO2@dopa/poly­(vinylidene fluoride) (PVDF) possesses a higher relative dielectric permittivity (εr), breakdown strength (E b), and energy density as compared to those of PVDF, TiO2/PVDF, TiO2@dopa/PVDF, and TiO2–BT@dopa/PVDF polymer nanocomposites. The εr and energy density of TiO2–BT–TiO2@dopa/PVDF were 12.6 at 1 kHz and 4.4 J cm–3 at 3128 kV cm–1, respectively, which were comparatively much higher than those of commercially available biaxially oriented polypropylene having εr of 2.2 and the energy density of 1.2 J cm–3 at a much higher electric field of 6400 kV cm–1. It is expected that these results will further open new avenues for the design of novel architecture for high-performance polymer nanocomposite-based capacitors having core@multishell nanofillers with tailored interfaces.

For a variety of mechanical energy harvesting as well as biomedical device applications, flexible energy devices are useful which require the development of environment-friendly and robust materials and devices. In this manuscript, we demonstrate a lead-free, facile, low-cost, sol–gel-processed reduced graphene oxide (rGO)/P­(VDF-TrFE) nanocomposite with multipurpose capability demonstration as a piezoelectric nanogenerator (PENG) and hybrid piezoelectric triboelectric nanogenerator (HPTENG) devices. The structural analysis of the materials shows that the interactions between the rGO and P­(VDF-TrFE) matrix help in breaking the centrosymmetry of rGO, resulting in a strong enhancement in the piezoelectric, ferroelectric, and triboelectric properties of composites over pristine P­(VDF-TrFE) films. In the case of PENG, the composite devices showed >22 times improvement in the piezoelectric output voltage over the pristine P­(VDF-TrFE) PENG device with the highest output voltage of 89.7 V for the 0.5 wt % rGO composite. Also, HPTENG devices based on composite films generated an average V OC of 227 V, much higher than the pristine P­(VDF-TrFE)-based devices. Maximum output power densities measured were 0.28 W/cm3 and 0.34 mW/cm3 for hybrid piezoelectric–triboelectric and piezoelectric devices, respectively. The triboelectric devices demonstrated lighting of 45 blue light-emitting diodes directly, connected in series, by harvesting mechanical energy generated by repeated finger tapping. The study highlights the promise of rGO/P­(VDF-TrFE) composites for PENG and HPTENG devices with dramatically improved electrical output.

a All solution processed transparent thin films of graphene oxide (GO) and zinc oxide (ZnO) with different compositions prepared by simple two-step chemical synthesis method have been studied for their UV detection properties. The preparation of GO through oxidation of graphite flakes is followed by sol-gel spin coating deposition of the GO-ZnO composite films on glass substrates. The surface morphology, microstructure and composition of the samples have been studied to confirm the formation of composite thin films comprising of wurtzite-ZnO nanocrystallites and GO flakes. Optical study demonstrates that both the transparency and optical band gap of the samples as estimated from wavelength dependent transmittance curves decrease with the increase of GO content in the films, while the charge carrier concentration increases by 5 fold. The in-plane current-voltage (I-V) measurement with two silver electrodes on the GO-ZnO film shows significant enhancement of photosensitivity in comparison to ZnO films when they are exposed to UV light of different intensities. The response time (t90-response) is nearly three times smaller for GO-ZnO composite films as compared to that of pure ZnO. This improvement is attributed to the defect state modulation and carrier density improvement of the thin films with incorporation of GO which is encouraging to propel optical, electrical and hence optoelectronics applicability of ZnO composite based transparent devices.

Conventional ceramic based piezoelectric materials are brittle, which restricts their use in energy harvesting where flexibility is required. Polymer counterparts are flexible but exhibit comparatively reduced electrical output. Here, we provide a method that overcomes these challenges through design of composites comprised of a piezoelectric polymer matrix (PVDF-TrFE) and filler nanoparticles (niobium-doped Pb­(Zr,Ti)­O3). Nanoparticles were functionalized with trimethoxysilylpropyl methacrylate (TMSPM) that promotes linkage between filler and the matrix to achieve effective local dipole–dipole interaction. An enhanced remnant polarization of 9.1 μC/cm2 at 100 Hz and high longitudinal piezoelectric coefficient of 101 pm/V are obtained. Using this composite, a piezoelectric nanogenerator (PENG) is demonstrated that delivers an output of 10 V in response to mechanical bending. Our composite devices show an output which is greater than 200% in comparison to polymeric PVDF-TrFE film based devices. These composites were also implemented in a triboelectric nanogenerator (TENG) device that can power 10 commercial red LEDs. This novel hybrid piezoelectric and triboelectric nanogenerator device has promise for powering wireless sensor nodes and wearable medical devices.

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