In this article, low density polyethylene was used as a matrix polymer. The ZnO particles with diameters of 30 nm and 1 μm were used as inorganic filler. The nano-ZnO particles after surface modification would disperse in the matrix uniformly. The nano-, micro-, and micro-/nano-ZnO/LDPE were prepared by melt blending. During the experiment, the microstructures of different composites were characterized and discussed by SEM and DSC. Besides, the micro- and nano-ZnO/LDPE underwent a breakdown test, conductance test, and dielectric spectrum test. The microscopic experimental results showed that the ZnO particles dispersed uniformly in the LDPE matrix. The crystallinity of composites was higher than that of pure LDPE. Among them, the maximum crystallinity was 39.77% when the nano-ZnO particle size was 30 nm. It was 16.1% higher than pure LDPE. The macroscopic experimental results showed that the effect of micro- and nano-ZnO particle doping on breakdown properties of polymers was different. Among them, the breakdown field strength of nano-ZnO/LDPE was the highest at 138.0 kV/mm, which was 8.24% higher than that of pure LDPE. The micro-/nano-ZnO/LDPE took second place, which was still higher than pure LDPE. As the thickness of samples increased, the thermal breakdown was the dominant factor in the breakdown test. The AC breakdown field strength of all composites tended to decrease, and the reduction of micro-ZnO/LDPE was lower than that of nano-ZnO/LDPE. Besides, the dispersion of the breakdown became better. Moreover, the micro- and nano-ZnO particle doping could improve the conductivity characteristic of polymer effectively. The dielectric constant and dielectric loss of composites increased with the increase of the particle size.

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With the rapid development of power, energy, electronic information, rail transit, and aerospace industries, nanocomposite electrical insulating materials have been begun to be widely used as new materials. Polymer/inorganic nanocomposite dielectric materials possess excellent physical and mechanical properties. In addition, numerous unique properties, such as electricity, thermal, sound, light, and magnetic properties are exhibited by these materials. First, the macroscopic quantum tunneling effect, small-size effect, surface effect, and quantum-size effect of nanoparticles are introduced. There are a few anomalous changes in the physical and chemical properties of the matrix, which are caused by these effects. Second, the interaction mechanism between the nanoparticles and polymer matrix is introduced. These include infiltration adsorption theory, chemical bonding, diffusion theory, electrostatic theory, mechanical connection theory, deformation layer theory, and physical adsorption theory. The mechanism of action of the interface on the dielectric properties of the composites is summarized. These are the interface trap effect, interface barrier effect, and homogenization field strength effect. In addition, different interfacial structure models were used to analyze the specific properties of nanocomposite dielectric materials. Finally, the research status of the dielectric properties of nanocomposite dielectric materials in the electrical insulation field is introduced.

Binary nanoparticle inks comprising Ag 2 Se, In 2 Se 3 , and Ga 2 Se 3 were fabricated via a wet ball-milling method and were further used to fabricate AgInGaSe 2 (AIGS) precursors by sequentially spraying the inks onto a Mo-coated substrate. AIGS precursors were annealed under a Se atmosphere for 1 h at 570 • C. Na 2 Se thin layers of varying thicknesses (0, 5, 10, and 20 nm) were vacuum-evaporated onto the Mo layer prior to the AIGS precursors being fabricated to investigate the influence on AIGS solar cells. Sodium plays a critical role in improving the material properties and performance of AIGS thin-film solar cells. The grain size of the AIGS films was significantly improved by sodium doping. Secondary ion mass spectroscopy illustrated slight surficial sodium segregation and heavy sodium segregation at the AIGS/Mo interface. Double-graded band profiles were observed in the AIGS films. With the increase in Na 2 Se thickness, the basic photovoltaic characteristics of the AIGS solar cells were significantly improved. The highest solar cell conversion efficiency of 6.6% (open-circuit voltage: 775.6 mV, short-circuit current: 15.5 mA/cm 2 , fill factor: 54.9%, area: 0.2 cm 2 ) was obtained when the Na 2 Se thickness was 20 nm.Nanomaterials 2020, 10, 547 2 of 13 and 12.6% [12]. Herein, AIGS thin films were fabricated via a non-vacuum method to reduce the associated costs.Sodium has been widely adopted to improve device performance and the material properties of CIGS-related materials [13][14][15]. Numerous reports have demonstrated the positive influence of sodium on the chalcopyrite absorber layer properties and solar cell performance. There are research efforts that have assigned the improvement associated with sodium on the chalcopyrite-related film grain size [16], while other reports have focused on the mechanism of how sodium doping influences the electronic and material properties [17]. Sodium is observed to passivate defects in CIGS-related films, resulting in improved solar cell performance [18][19][20].In this work, a new non-vacuum method was adopted to fabricate low-cost AIGS absorber layers. Ag 2 Se, Ga 2 Se 3 , and In 2 Se 3 nanoparticle inks fabricated via a wet ball-milling method were used to further fabricate AIGS substrate precursors. The AIGS precursor structure is shown in Figure 1. Such structure types ensure double-graded bandgap structures in the AIGS precursors, which are important for improving solar cell performance [21]. To study the influence of Na on the properties of AIGS films and solar cell performance, Na 2 Se layers of various thicknesses were vacuum-evaporated onto Mo-coated soda-lime glass (SLG) substrates prior to the deposition of the nanoparticle layers. The Na 2 Se thicknesses were selected as 0, 5, 10, and 20 nm. Thereafter, the AIGS precursor was annealed in a continuously pumped two-zone furnace under a Se atmosphere to improve the grain size, crystallization, and electronic properties. Se flux was continuously supplied to prevent decomposition of the AIGS film because ...

Polyethylene, a thermoplastic resin made by ethylene polymerization, is widely used in electrical insulation. In this study, low-density polyethylene (LDPE) is used as a matrix with micro- and nano-ZnO particles as a filler to produce different proportions of micro- and nano-ZnO composites by melt blending. These samples are characterized by Polarized Light Microscopy (PLM) and FTIR tests, with their conductance measured under different field strengths. The current density vs. electric field strength (J-E) curve of micro- and nano-ZnO composites under different field strengths are measured and analyzed. The J-E curves of different composites at different temperatures are measured to explore conductance with temperature. The results of these tests showed that nano-ZnO composites successfully suppressed conductivity at elevated temperatures and electric field strengths, while micro-ZnO composites increased the conductivity relative to pure LDPE.