Key Engineering Materials Vols. 602-603

Abstract: The double-perovskite La_0.4Sr_1.6CoNbO_6-δ (LSCN) powders were synthesized by the solid-state reaction method. The electrical conductivities of LSCN samples were tested in air and 5 vol%H₂/Ar. The results show that the conductivity of LSCN in 5 vol%H₂/Ar (8.12 Scm^-1) at 850 °C was higher than that in air (7.03 Scm^-1). The activation energy obtained from the Arrhenius function was 0.821 eV in air and 0.707 eV in 5 vol%H₂/Ar. The analysis of XPS shows that there exit three valence states of Co (Co⁺², Co⁺³, Co⁺⁴) and two of Nb (Nb⁺⁴, Nb⁺⁵). The loss of lattice oxygen in LSCN not only produces oxygen vacancies, but also generates excess electrons, which contributes to the electrical conductivity of the LSCN samples.

Abstract: LSGM(La0.9Sr0.1Ga0.8Mg0.2O3-δ)-carbonate composite electrolyte was prepared by molten salt infiltration method and its properties were analyzed by scanning electron microscope (SEM), X ray diffractometer (XRD) and A.C. impedance. LSGM-carbonate composite electrolyte showed the same phase patterns as pure LSGM which suggests carbonates exist in an amorphous state. SEM images of porous LSGM pellet indicated all of the pores are uniformly distributed and nearly all of them are connected with each other. The A.C conductivity measurements showed composite electrolyte possessed a much higher ionic conductivity than LSGM electrolyte at a temperature within the range of 450-650 oC. Conductive highways for oxygen ions and multi-ions conduction were employed in explaining the improved property of composite electrolyte.

Abstract: In this work, the vacuum-assisted thermal deposition platinum (Pt) film was prepared and used as a counter electrode (CE) in dye sensitized solar cell (DSC). The films were characterized by scanning electron microscopy (SEM). Electrochemical catalytic activities of the films were also characterized by cyclic voltammetry (CV) and electrochemical impedance spectroscopy (EIS). The effects of the Pt loading amount on the fluorine-doped tin oxide (FTO) glass and titration time on the performance of the DSC were investigated. The optimal performance of the DSC was obtained when using the three-time titration with 1.69 mg/cm² Pt loading amount vacuum-assisted thermal deposit CE. The DSC showed a high efficiency of 7.20%. The short-circuit current density (Jsc), open circuit voltage (Voc) and fill factor (FF) were 13.79 mA·cm^-2, 0.73 V and 0.71, respectively.

Abstract: In this study, ZnO films, prepared by Chemical Bath Deposition (CBD), are applied as the conductive layers for thin film solar cells. Zinc acetate is used as a source of zinc, and different proportions of ammonia solution are added and well mixed. The growth of zinc oxide films in reaction solutions is taken place at 80°C and then heated to 500°C for one hour. In this study, the different ammonia concentrations and deposition times is controlled. The thin film structure is Hexagonal structure, which is determined by X-ray diffraction spectrometer (XRD) analysis. Scanning electron microscopy (SEM) is used as the observation of surface morphology, the bottom of the film is the interface where the heterogeneous nucleation happens. With the increase of deposition time, there were a few attached zinc oxide particles, which is formed by homogeneous nucleation. According to UV / visible light (UV / Vis) absorption spectrometer transmittance measurements and the relationship between/among the incident wavelength, it can be converted to the energy gaps (Eg), which are about 3.0 to 3.2eV, by using fluorescence spectroscopy analysis. The emission of zinc oxide films has two wavelengths which are located on 510nm and 570nm. According to Based on the all analytic results, the ammonia concentration at 0.05M, and the deposition time is 120 minutes, would obtain the conditions of ZnO films which is more suitable for applications of conductive layer material in thin film solar cell.

Abstract: The study of dye-sensitized solar cells (DSCs) based on nanocrystalline films of high band gap semiconductors is a progressive field of research that is being carried out by scientists in a wide range of laboratories. Of the many semiconductor materials utilized for conversion of solar energy into electricity, SnO₂ is a high band gap semiconductor that has been used extensively. However, its efficiency is at a relatively lower level when compared to other semiconductor materials such as TiO₂ working under similar circumstances. To improve the conversion efficiency of the DSCs, the SnO₂ nanorots photocurrent is prepared via the hydrothermal method, and characterized by XRD, FESEM, BET and Absorption spectrum. Though analysis the results, SnO₂ nanocrystalline were successfully synthesized using a hydrothermal method by certainly experimental parameters. The SnO₂ nanocrystalline is the rod-shape with length for 100nm and diameter for 5nm as pH=11. the specific surface area is 86.3412m²/g, which lay base for reaching the high conversion efficiency of the DSCs.

Abstract: In this paper, the inverse opal structures used in dye-sensitized solar cells were prepared by Sol-Gel method. The TiO₂ inverse opal photonic crystal was formed by coating glass slices using dip-coating process. The structure, surface morphology and the optical properties were characterized by x-ray diffraction (XRD), scanning electron microscopy (SEM) and ultraviolet spectrograph (UV-is). The structural characteristics of the films were investigated by the SEM showed that inverse opal titanium dioxide could trap electrons, thus enhance the photoelectric current in the dye-sensitized solar cells. By use of the inverse opals into TiO₂ photo anodes with the screen printing method, I-V testing measurement showed that the highest photoelectric conversion efficiency is 1.2%. And the best preparation process of inverse opal titanium dioxide is using Ti (OC₄H₉)₄ as precursor, ethanol as the solvent, nitric acid as inhibitor, and dipping-lift number for 3 times. The result of the test showed that this inverse opals structure has the most appropriate thickness and the optimal performance. Based on the research, the results indicate that the TiO₂ inverse opals structure could apply in dye-sensitized solar cells.

Abstract: In order to improve the photoelectric conversion efficiency of dye-sensitized solar cells (DSSC), the photoanode process conditions were optimized in this work. The effects on photoelectric conversion efficiency of three methods were mainly investigated, including magnetron sputtering barrier layer, printing scattering layer and post-treatment with TiCl₄. The microstructure of TiO₂ thin films was measured by scanning electron microscope (SEM). The results showed that porous photoanode benefited to electronic transmission. The photoelectric conversion efficiency and performance of DSSC were measured by I-V testing instrument. The results indicated that the short circuit current and photoelectric conversion efficiency were improved. Finally, the best result was obtained by combining the three optimal conditions. A high photoelectric conversion efficiency of 7.31% was achieved under illumination of simulated AM 1.5 sunlight (100mW/cm²). Compared to the previous result of 5.48%, the improvement of 33.4% was achieved.

Abstract: Titanium dioxide (TiO₂) nanotubes film was deposited on conducting glass oxide (FTO) by using ZnO nanorods as template, and the TiO₂ nanotubes film was applied in DSCs. First, ZnO nanorods were fabricated on ZnO-doped TiO₂ seed layer coated substrates by the hydrothermal method. Second, the obtained ZnO nanorods were used as a template to synthesize ZnOTiO₂ coreshell structure through the immersion method. Third, the ZnO nanorods template was removed by etching method to obtained TiO₂ nanotubes film. The thickness of ZnO-doped TiO₂ seed layer is about 200nm and the crystalline size of nanoparticles are about 5~10nm. The length of the ZnO nanorods are about 1~3μm. The TiO₂ nanotube was composed of TiO₂ nanoparticles. The short-circuit current density (Jsc), open-circuit voltage, fill factor (FF) and efficiency of TiO₂ nanotubes DSC were 4.63 mA·cm^-2, 0.74V, 62% and 2.15%, respectively.

Abstract: In this paper, a series of xLiFePO₄·yLi₃V₂(PO₄)₃/C (x/y = 1:0, 7:1, 5:1, 3:1, 1:1, 1:3 and 0:1, ratio of mol) nanosized composite cathode materials were prepared by solid reaction method. Influence of x/y ratio on the composition, microstructure and electrochemical properties of the materials were characterized by X-ray diffraction (XRD), transmission electron microscopy (TEM) and electrochemical measurements, et al. XRD patterns showed that most of iron (Fe) and vanadium (V) in raw materials tended to form the LiFePO₄ and Li₃V₂(PO₄)₃ phases, while small amounts of them were as the dopant and entered into the lattice of Li₃V₂(PO₄)₃ and LiFePO₄, respectively. TEM images exhibited that the 7LiFePO₄·Li₃V₂(PO₄)₃/C composite shows good dispersion and the size ranging in 50-150 nm, which was coated uniformly with the carbon layer. The value of the first discharge specific capacity of the composites was 145.6 mAh/g and its capacity retention was 99.8% after 50 cycles at 0.1 C. Compared with the single LiFePO₄ and Li₃V₂(PO₄)₃, its cycle performance was also remarkable improved.

Abstract: Zirconia fiber separator is one of the important materials of nickel-hydrogen battery .In this paper,we studied the factors affecting the properties of zirconia fiber separator used as nickel-hydrogen battery separator, which prepared by precursor process, including the precursor fibers,fibrous cloths,concentration of the precursor solution and the heating rate before 500oC.The results show that, because the gully structure copied the precursor fibers, as well as smaller diameter of the fiber has larger specific surface area, so the zirconia cloth has the higher absorption capacity and retention ability of alkal. In the same way as woven, the low fabric areal density is beneficial to the absorption ability. When the concentration of the precursor solution is 1.36g/ml, the properties of the zirconia fiber separator is the best. If the heating rate is too fast, will cause a decrease in performance of zirconia fiber separator. The diameter of the fibers in the zirconia fiber sepatator is about 4-5μm, the main phase of the separator is tetragonal zirconia.