Jun Liu

Structural and optical properties of CdS thin films prepared by chemical bath deposition at different ammonia concentration and S/Cd molar ratios

CdS thin films were prepared by chemical bath deposition technique using the precursors of SC(NH2)2, CdCl2, NH4Cl, NH3·H2O and deionized water. The obtained thin films were characterized by scanning electron microscopy, X-ray diffraction, energy dispersive spectrometer, UV–VIS specrophotometry and photoluminescence spectroscopy. The morphology, structural and optical properties of CdS thin films were investigated as a function of ammonia concentration and S/Cd molar ratios in precursors. The results reveal that morphology of CdS films change from flake like into spherical particle like, crystal structure from wurtzite structure to zinc blende structure, S/Cd atom ratios in CdS thin films increase and optical band gap Eg decrease with increasing ammonia concentration in precursors. The room temperature photoluminescence spectrum of CdS thin films shows a strong peak at about 500xa0nm and a weak peak at about 675xa0nm.

Effect of stacking type in precursors on composition, morphology and electrical properties of the CIGS films

The copper-indium-gallium (CIG) metallic precursors with different stacking type (A: CuGa/CuIn/CuGa/glass and B: CuInGa/CuIn/CuInGa/glass) were prepared onto glass substrates by magnetron sputtering method. In order to prepare Cu(In1−xGax)Se2 (CIGS) thin films, the CIG precursors were then selenized with solid Se powder using a three-step reaction temperature profile. The influence of stacking type in precursors on structure, composition, morphology and electrical properties of the CIGS films is investigated by X-ray diffraction, energy dispersive spectrometer, scanning electron microscope and Hall effect measurement. The results reveal that the stacking type of the precursor has a strong influence on composition, morphology and properties of the CIGS thin films. The atomic ratios of Cu/(In+Ga)/Se of the CIGS films A and B are 1.61:1:2.11 and 1.39:1:2.04, respectively. The better quality CIGS thin films can be obtained through selenization of metallic precursor of CuInGa/CuIn/CuInGa/glass. The CIGS films are p-type semiconductor material. The hole concentration, resistivity and hole mobility of the CIGS thin films is 2.51xa0×xa01017xa0cm−3, 3.11xa0×xa0104xa0Ωxa0cm and 19.8xa0cm2xa0V−1xa0s−1, respectively.

Investigation of the ZnSxSe1-x thin films prepared by chemical bath deposition

The ZnSxSe1−x thin films were prepared by chemical bath deposition technique on glass substrates. The composition ‘x’ was varied from 0 to 1 by changing the concentration of thiourea and sodium selenosulphate in the precursors. The morphology, structural and optical properties of the ZnSxSe1−x thin films were characterized by energy dispersive spectrometer, scanning electron microscopy, X-ray diffraction and UV-Vis spectrophotometer. The results reveal that the ZnSxSe1−x films are cubic zinc blende structure for xxa0=xa00, 0.19, 0.25, and amorphous for xxa0=xa00.75, 1. The optical band gap of the ZnSxSe1−x films increase from 2.88 to 3.76xa0eV when the value of ‘x’ increases from 0 to 1. The growth mechanism of the ZnSxSe1–x films was discussed.

Growth of TiO2 nanowire bundle arrays and their application in dye-sensitized solar cells

Highly oriented single-crystalline TiO2 nanowire bundle arrays on transparent conductive fluorine-doped tin oxide substrates are prepared by hydrothermal method using the precursors of titanium butoxide, deionized water and hydrochloric acid. The structure and morphology characteristics of all the samples have been analyzed by X-ray diffraction (XRD), scanning electron microscopy and transmission electron microscopy. Results show that the diameter, length, and density of the nanowire bundle arrays can be varied by changing the growth parameters, such as growth time, initial reactant concentration and acidity. The enhanced (002) peak in XRD patterns indicate that the nanowire is well crystallized and grow perpendicular to the substrate. The high resolution transmission electron microscope images and selected-area electron diffraction patterns confirm that there are approximately 10–30 nanowires in each bundle. The nanowire is single crystalline. Dye-sensitized solar cells assembled from oriented TiO2 nanowire bundle arrays as the photoanode are studied. The light-to-electricity conversion efficiency is about 2.17xa0%.

High-Power Light-Emitting Diodes Package With Phase Change Material

We report the fabrication and charaterization of high-power light-emitting diodes (LEDs) package with phase change material. Paraffin wax with melting point of 49.6 °C was inserted between the LED die and silicone encapsulant. The phase changing of embedded wax in a working LED is observed by studying its output flux and junction temperature. With a driving current density of 443 mA/mm

Influence of Deposition Parameters on the Morphology, Structural, and Optical Properties of ZnSe Nanocrystalline Thin Films

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Dye-Sensitized Solar Cells Based on the Composites Photoanodes of ZnO Microrods/TiO2 Nanoparticles

, LED sample demonstrates a decreasing of junction temperature by 19 °C and an increasing of light flux by 25% with the insertion of 6-mg paraffin wax. Optical and thermal simulations are employed to analyze the improved performance of LED package. Higher thermal conductivity of paraffin wax compared with silicone resin is considered to be reason for LEDs reduced junction temperature. The high refractive index of paraffin wax is considered to be the dominant mechanism of LEDs enhanced emission.

Synthesis of Cu 2 ZnSn(S x Se 1−x ) 4 thin films directly on transparent conductive glass substrates by solvothermal method

Zinc selenide (ZnSe) nanocrystalline thin films were prepared by using chemical bath deposition at different ammonia concentrations and different deposition temperatures. The structural and optical properties of ZnSe nanocrystalline thin films were investigated as a function of the ammonia concentration in precursors or the deposition temperature using scanning electron microscopy, energy-dispersive spectrometry, x-ray diffraction measurements, and ultraviolet (UV)–visible spectrophotometry measurements. The results reveal that the ZnSe thin films are composed of a large number of uniform spherical particles. Each spherical particle contains several nanocrystals 5xa0nm to 7xa0nm in crystallite size. An increase in both the average diameter of the spherical particles and the crystallite size of the nanocrystals occurs with an increase in ammonia concentration and/or deposition temperature. The Se/Zn atom ratios in the ZnSe thin films increase and the optical band gaps, Eg, of the ZnSe thin films decrease with an increase in ammonia concentration or deposition temperature. The kinetics and reaction mechanism of the ZnSe nanocrystalline thin films during deposition are discussed.

Fabrication and study on anode of dye-Sensitized solar cells

Dye-sensitized solar cells (DSSCs) were fabricated based on the composites of ZnO microrods and TiO2 nanoparticles. The ZnO/TiO2 composites photoanode was prepared on FTO with slurry of different mass ratios of ZnO microrods to TiO2 nanopowders by doctor-blade method. The effect of the relative microrods/nanoparticles ratio on the performance of DSSCs was systematically investigated by I-V curve and electrochemical impedance spectroscope. The results showed that the solar conversion efficiency of DSSCs with the addition of ZnO microrods (50 wt%) was increased by about 30% compared to that without ZnO microrods. Therefore, the application of ZnO/TiO2 composites represents a promising approach for further improving the efficiency of DSSCs.

Synthesis and characterization of CdSe nanocrystalline thin films deposited by chemical bath deposition

In this paper, the single-step solvothermal method was proposed to grow directly Cu2ZnSn (SxSe1−x)4 (CZTSSe) thin films on FTO substrates. The composition ‘x’ was varied by changing the molar ratios of thiourea to selenourea in the precursor solutions. The effects of the molar ratios of thiourea to selenourea on the structure, morphology and optical properties of CZTSSe thin films were investigated by X-ray diffraction, Raman spectroscopy, scanning electronic microscopy, energy dispersive spectrometry and UV–Vis spectrophotometry. The results indicated that CZTSSe thin films are composed of a large number of uniform sphere-like particles, and the diameter of particles varies from 600 to 280xa0nm when the molar ratios is changed from 1 to 0. The major XRD diffraction peaks shift towards lower diffraction angles, the Raman peak position of A1 mode of CZTSSe thin films moves consecutively towards the lower frequency due to the S replacement by Se. CZTS and CZTSe thin films are single kesterite structure, however, CZTSSe thin films are mixture structure of kesterite and wurtzite. By varying the molar ratios of thiourea to selenourea in the precursor solution, the atom ratios of S/Se in CZTSSe NCs thin films can be well controlled over the whole range, resulting in tunable optical band gap from 1.54 to 1.38xa0eV.