ABSTRACT
SnO2/TiO2 type II heterojunctions are often introduced to enhance the separation efficiency of photogenerated carriers in photoelectrochemical electrodes, while most of these heterojunctions are of core-shell structure, which often limits the synergistic effect from the two components. In this work, dissymmetric SnO2/TiO2 side-by-side bi-component nanofibers (SBNFs) with tunable composition ratios have been prepared by a novel needleless electrospinning technique with two V-shape connected conductive channels (V-channel electrospinning). Results show that this V-channel electrospinning technique is more stable, controllable and tunable for the large-scale preparation of SBNF materials compared to the traditional electrospinning using two side-by-side metal needles. And these SnO2/TiO2 SBNFs are dissymmetric and comprised of a tiny SnO2 NF (tunable diameter within 20-80 nm) and a Sn-doped TiO2 NF (diameter of ~ 250 nm) with a side-by-side structure. Moreover, the dye-sensitized solar cells (DSSCs) based these dissymmetric SnO2/TiO2 SBNFs show the maximum power conversion efficiency (PCE) of 8.3%, which is 2.59 times that of the ones based on the TiO2 NFs. Series of analyses indicate that the enhancements in PCE could mainly be due to the improved electron transport via SnO2 NFs and the enhanced carrier separation via dissymmetric SnO2/TiO2 heterojunction interface. This research will give some new insight in the preparation of SBNFs for high-performance photoelectrochemical devices.
ABSTRACT
Well-crystallizedß-SiC nanorods grown on electrospun nanofibers were synthesized by carbothermal reduction of Tb doped SiO2(SiO2:Tb) nanofibers at 1,250 °C. The as-synthesized SiC nanorods were 100-300 nm in diameter and 2-3 µm in length. Scanning electron microscopy (SEM) results suggested that the growth of the SiC nanorods should be governed by vapor-liquid-solid (VLS) mechanism with Tb metal as catalyst. Tb(NO3)3particles on the surface of the electrospun nanofibers were decomposed at 500 °C and later reduced to the formation of Tb nanoclusters at 1,200 °C, and finally the formation of a Si-C-Tb ally droplet will stimulate the VLS growth at 1,250 °C. Microstructure of the nanorod was further investigated by transmission electron microscopy (TEM). It was found that SiC <111> is the preferred initial growth direction. The liquid droplet was identified to be Si86Tb14, which acted as effective catalyst. Strong green emissions were observed from the SiC nanorod samples. Four characteristic photoluminescence (PL) peaks of Tb ions were also identified.
ABSTRACT
The structure and characteristics of CdTe thin films are dependent on the working atmosphere states in close-spaced sublimation. In the present paper, CdTe polycrystalline thin films were deposited by CSS in mixture atmosphere of argon and oxygen. The physical mechanism of CSS was analyzed, and the temperature distribution in CSS system was measured. The dependence of preliminary nucleus creation on the atmosphere states (involving component and pressure) was studied. Transparencies were measured and optic energy gaps were calculated. The results show that: (1) The CdTe films deposited in different atmospheres are cubic structure. With increasing oxygen concentration, a increases and reaches the maximum at 6% oxygen concentration, then reduces, and increases again after passing the point at 12% oxygen concentration. Among them, the sample depositing at 9% oxygen concentration is the best. The optic energy gaps are 1.50-1.51 eV for all CdTe films. (2) The samples depositing at different pressures at 9% oxygen concentration are all cubical structure of CdTe, and the diffraction peaks of CdS and SnO2:F still appear. With the gas pressure increasing, the crystal size of CdTe minishes, the transparency of the thin film goes down, and the absorption side shifts to the short-wave direction. (3) The polycrystalline thin films with high quality deposit in 4 minutes under the depositing condition that the substrate temperature is 550 degrees C, and source temperature is 620 degrees C at 9% oxygen concentration.
