Jiquan Huang

Dye-sensitized solar cells based on nanoparticle-decorated ZnO/TiO2 core/shell nanorod arrays

Nanoparticles (NPs) decorated ZnO/TiO2 core/shell nanorod arrays were fabricated on transparent conductive glass substrates by sequential plasma deposition and post-annealing processes for dye-sensitized solar cells (DSSCs) applications. The NPs decorated ZnO/TiO2 nanorods were composed of single-crystalline ZnO nanorods, homogeneously coated thin TiO2 shells and entirely covered anatase TiO2 NPs. The photocurrent density of the composite electrode was largely enhanced due to the enlarged surface area, the dark current was suppressed and the open-circuit voltage was increased because of the energy barrier formed at the interface between the ZnO core and the TiO2 shell. The increased photocurrent and open-circuit voltage led to an improvement of twice the energy conversion efficiency.

Ag-Ba0.75Sr0.25TiO3 composites with excellent dielectric properties

The percolative ceramic composites of Ba0.75Sr0.25TiO3∕Ag (BST/Ag) with dense microstructure were sintered at a low temperature of 960°C. Excellent dielectric properties, such as high dielectric constant (er∼24000), low dielectric loss, and high dielectric tunability, were reported. The dielectric constant is found to be nearly temperature and frequency independent. It is essential to introduce the low-melting-point metal of silver into BST ceramics for significantly enhancing the dielectric properties of the composites. The superproperties make it potential to be used for electronic devices such as high charge-storage capacitors and tunable filters.

Luminescence properties of YAG:Ce, Gd phosphors synthesized under vacuum condition and their white LED performances

Modified YAG:Ce, Gd phosphors were synthesized by vacuum solid-state reaction. With the increase of Gd3+ concentration, the emission spectra of YAG:Ce, Gd phosphors shifted greatly to longer wavelength. At 400 K, YAG:Ce, Gd phosphors with 20 at.% Gd3+ could maintain 78% of room temperature intensity. Within the maximum junction temperature of a high brightness LED (around 400 K), the color coordinates of phosphors changed very little. In addition, white LEDs with a color rendering index of 82, luminous efficiency of 109 lm/W and color temperature of 5656 K were achieved by using optimized YAG:Ce, Gd phosphors.

The effects of shell characteristics on the current-voltage behaviors of dye-sensitized solar cells based on ZnO/TiO2 core/shell arrays

The ZnO/TiO2 core/shell structure was formed through deposition of a TiO2 coating layer on the hydrothermally fabricated ZnO nanorod arrays through radio frequency magnetron sputtering. The effects of the TiO2 shell’s characteristics on the current-voltage behaviors of the core/shell-based dye-sensitized solar cells (CS-DSSC) were investigated. As the rates of injection, transfer, and recombination of electrons of such CS-DSSC were affected significantly by the crystallization, morphology, and continuity of the TiO2 shells, the photovoltaic efficiency was accordingly varied remarkably. In addition, the efficiency was further improved by enhancing the surface area in the core/shell electrode.

Percolative ceramic composites with giant dielectric constants and low dielectric losses

Percolative composites with significant dielectric properties have been synthesized from Ba0.8Sr0.2TiO3 matrix, Ag particles and a PbO-B2O3 glass dopant by a traditional ceramic method. Such composites possess a high dielectric constant (er ∼ 24 000), which is stable with frequency and temperature, and very low loss (tan δ ∼ 0.035). The results demonstrate that the insulating glass dopant can serve as an electron barrier to restrict the electron transport between metallic particles, thus leading to a stable dielectric constant and low dielectric loss. Besides improving the dielectric properties, the presence of glass dopant further lowers the sintering temperature, being compatible with the current preparation of electronic elements. The proposed approach is generic and provides a new avenue to obtain percolative composites with excellent dielectric properties, which make it a promising material to be used in high dielectric constant components.

Spectroscopic properties and energy transfers in Cr, Tm, Ho triple-doped Y 3 Al 5 O 12 transparent ceramics

Highly transparent Cr, Tm, Ho triple-doped Y3Al5O12 (YAG) ceramics were prepared using advanced ceramic technology and their spectroscopic properties were studied for infrared laser applications. 2.09 μm emission was observed by exciting at 430 nm, which indicated the realization of energy transition from Cr3+ to Ho3+ with Tm3+ acted as an intermediate media. The efficiency between the energy transfer (Tm3+) 3F4→ (Ho3+) 5I7 and its back-transfer process was 7.87, which was comparable to that of YAG single crystal and YLF. Studies on the optical gain and stimulated emission characteristics suggested that this triple-doped YAG ceramic could be an appropriate material for 2.09 μm laser application.

Investigation on transition behavior and electrical properties of (K0.5Na0.5)1-xLixNb0.84Ta0.1Sb0.06O3 around polymorphic phase transition region

(K0.5Na0.5)1-xLixNb0.84Ta0.1Sb0.06O3 (KNLNTS) lead free ceramics with different Li concentration were fabricated by conventional solid-state reaction method. By increasing Li ions in KNLNTS, the grains grow up and the crystal structure changes from orthorhombic to tetragonal. When 0.03 ≤ x ≤ 0.05, the ceramics structure lays in PPT region. Polarization versus electric field (P-E) hysteresis loops at room temperature show good ferroelectric properties and the remnant polarization decreases by increasing Li content while coercive electric keeps almost unchanged. In PPT region, taking x = 0.04 as an example, the sample shows excellent dielectric properties: the dielectric constant is 1159 and loss tangent is 0.04, while the piezoelectric constant d33 is 245 pC/N and kp is 0.44 at room temperature, it is promising for (K0.5Na0.5)1-xLixNb0.84Ta0.1Sb0.06O3 with 4 at. % Li to substitute PZT.

Microstructure and Properties of Ni0.5Zn0.5Fe2O4-BaTiO3 Ceramic

Ni0.5Zn0.5Fe2O4-BaTiO3 composites were prepared by calcining Ni0.5Zn0.5Fe2O4 with BaTiO3 at 1220°C for 3 h. Both μ′ and μ″ of the composites decrease rapidly, but the cut-off frequency shifts to higher level with increasing BaTiO3 content. The dielectric constant of the composites increases quickly with increasing BaTiO3 content below 50% and keeps a high and nearly unchangeable value with increasing BaTiO3 above 50%. The composites with BaTiO3 content between 20% and 40% are suitable to use for the magneto-electric devices under high applied frequency due to its high permeability and low dielectric loss.