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Nickel cobalt sulfides (Ni-Co-S) have been extensive developed as platinum-free counter electrode (CE) materials for dye-sensitized solar cells (DSCs). However, the power conversion efficiency (PCE) of DSCs with Ni-Co-S CEs needs to be further improved by changing crystalline structure of Ni-Co-S. Herein, Ni-Co-S with amorphous structure have been synthesized on fluorine-doped tin oxide (FTO) glass by a potential reversal electrodeposition technique. The morphology of Ni-Co-S films can be controlled through adjusting the molar ratio of Ni and Co ions in the electroplating solution. Ni-Co-S films can be directly applied as low-cost CEs of DSCs. The results demonstrate that Ni-Co-S CEs exhibit excellent electrocatalytic performance for I3− reduction, owing to the synergistic effect and amorphous structure of Ni-Co-S films. Particularly, the DSC based on Ni-Co-S CE with the optimized Ni/Co ratio has achieved the high PCE of 8.18%, which is larger than that of the DSC with platinum (Pt) CE (6.33%).

Nickel selenide with the single-phase structure has been widely studied as counterelectrode nanomaterials for dye-sensitized solar cells (DSCs). However, the effect mechanism of the crystalline structure on the electrocatalytic activity is still needed to be explored and analyzed in nickel selenide with hybrid structure. Therefore, NiSe/NiSe2 hybrid nanomaterials are synthesized via a simple solvothermal approach in this work. NiSe/NiSe2 counterelectrodes are constructed by spraying NiSe/NiSe2 hybrid nanomaterials onto fluorine-doped tin oxide glass. The hybrid nanostructure of NiSe/NiSe2 counterelectrodes exhibits the more catalytic active sites, strong charge separation, and transfer ability for the reduction of triiodide owing to the well-controlled crystalline structure of nickel selenide. Therefore, the results from electrochemical measurements prove that the electrocatalytic activity of the optimized NiSe/NiSe2 counterelectrode is higher than that of platinum electrode. As a result, the DSC with the optimized NiSe/NiSe2 counterelectrode yields a remarkable photoelectrical conversion efficiency of 7.78%, which is larger than that of the DSC based on platinum electrode (7.09%). Our research work provides the insight into design and construct of nickel selenide counterelectrodes of DSCs.

Based on the transverse Ising model and using decoupling approximation to the Fermi-type Green's function, we study the phase transition properties of the epitaxial ferroelectric film with one substrate. A general recursive equation of the ferroelectric thin film with two n-layer materials is obtained, which enables us to study the phase transition properties for any number layers for epitaxial ferroelectric thin film. With the help of this equation, we analyze the effect of the exchange interaction and the transverse field in the phase diagram, the influence to the polarizations and Curie temperature numerically. The results show that epitaxial ferroelectric film are able to induce a strong increase or decrease of Curie temperature to different exchange interactions and transverse fields within the epitaxial film layers. The theoretical results are in reasonable accordance with experimental data of different ferroelectric thin film.

An ultra-thin metamaterial triple bandpass filter with high quality-factors is presented. This proposed structure consists of a periodic array of three concentric circle ring resonators at the top layer and a metallic mesh at the bottom layer, which are separated by a thin dielectric substrate. The investigations on the distribution of the electromagnetic field and surface current are made for explaining the filtering mechanism. The structure is also demonstrated to be flexibly and independently tunable of the pass-band resonance frequencies. Moreover, this simple structure with ultra-thin thickness is also a symmetric design which is insensitive to the polarization and incident angles. Experimental measurement of the manufactured sample show good agreement with the numerical simulations. Therefore, such a metamaterial triple bandpass filter is of great importance in some practical applications.

A novel flexible metamaterial narrow-band-pass filter is designed and proved to be reliable by both numerical simulations and experimental measurements. The unit cell of the designed structure consists of circle ring resonators on top of a thin dielectric layer backed by a metallic mesh. The investigations on the distribution of the surface current and magnetic field as well as the analysis of the equivalent circuit model reveal that the magnetic resonance response between layers induced by the reverse surface current contributes to the high quality factor band-pass property. Importantly, it is a flexible design with a tunable resonance frequency by just changing the radius of the circle rings and can also be easily extended to have the multi-band-pass property. Moreover, this simplified structure with low duty cycle and ultra-thin thickness is also a symmetric design which is insensitive to the polarization and incident angles. Therefore, such a metamaterial narrow-band-pass filter is of great importance in the practical applications such as filtering and radar stealth, and especially for the conformal structure applications in the infrared and optical window area.