Papers by Author: Zhi You Zhong

Abstract: Al-doped ZnO (ZnO:Al) thin films were deposited on glass substrates by rf magnetron sputtering technique. The effect of discharge power on the structural, optical and electrical characteristics of ZnO:Al films was investigated by X-ray diffraction (XRD), four-probe meter and optical transmission spectroscopy. The results show that the films are polycrystalline with a hexagonal wurtzite structure and preferentially oriented in the (002) crystallographic direction. The highest figure of merit of 5.58×10-3 -1 is obtained from the film prepared at the discharge power of 200 W. The average optical transmittance in the visible range of the films is over 78.2%.

Abstract: Transparent conductive ZnGa₂O₄ thin films were prepared by magnetron sputtering. The chemical state of O, Zn and Ga in the deposited films was investigated by X-ray photoelectron spectroscopy (XPS), and the optical properties were characterized by optical transmittance spectra. The XPS studies reveal that no metallic Zn and Ga were detected in the ZnGa₂O₄ thin films, and Zn and Ga exist only in oxidized state. The optical bandgap was calculated by Tauc's theory and the optical constants were determined using Swanepoel's method. Furthermore, the dispersion behavior of the refractive index was studied by means of single-oscillator model, and the physical parameters and the refractive index dispersion parameter were obtained. The results provide some useful references for the potential application of the ZnGa₂O₄ thin films in optoelectronic devices.

Abstract: Based on the analysis of the equivalent circuit model of organic photovoltaic (OPV) cells, the explicit expression of current, short-circuit current and open-circuit voltage was obtained by means of W-function, and the effects of internal resistances and diode quality factor on the output characteristics of OPV cells were studied. The results demonstrate that the series resistance can effect short-circuit current but not open-circuit voltage, and the shunt resistance and diode quality factor can influence open-circuit voltage but short-circuit current unchanged. The decrease in series resistance and the increase in shunt resistance and diode quality factor can enhance the fill factor and energy conversion efficiency of OPV cells. This conclusion is essential in preparing OPV cells and improving device performance.

Abstract: Thin films of transparent conducting aluminum-doped zinc oxide (ZnO:Al) were grown by rf magnetron sputtering technique using a sintered ceramic target of ZnAl₂O₄. The microstructure and optoelectrical properties of the deposited films were characterized wiyh XRD, four-point probe and spectrophotometer. The results show that the polycrystalline ZnO:Al films consist of the hexagonal crystal structures with c-axis as the preferred growth orientation normal to the substrate, and that the substrate temperature significantly affects the crystal structures and optoelectrical properties of the thin films. The ZnO:Al films deposited at the substrate temperature of 670 K has the relatively well crystallinity, the largest crystal grain, the highest transmittance and the highest figure of merit.

Abstract: Organic semiconductor thin films of bis-(2-methyl-8-quinolinolato)-4-(phenyl-phenolato) -aluminium-(III) (BAlq), N,N′-bis(naphthalen-1-yl)-N,N′-bis(phenyl)benzidine (NPB), and tris-(8- hydroxyquinoline) aluminum (Alq) were prepared by the vacuum sublimation technique. The optical properties in the UV-visible region of the thin films were investigated by optical transmittance and absorbance spectra. The optical energy gaps were obtained from direct allowed transitions at room temperature by Tauc’s law. The Urbach energy and the slope of Urbach edge were estimated by the Urbach-edges method, respectively. Furthermore, the current-voltage characteristics of organic thin films were analyzed, and the different slopes in the lower and higher voltage regions were observed. From the experimental studies, the effective carrier mobility, free carrier density, and electrical conductivity were also evaluated respectively.