Fuzhi Wang

Conductive mesh based flexible dye-sensitized solar cells

Conductive meshes are used to replace transparent conducting oxides (TCOs), which are commonly used in electrodes of dye-sensitized solar cells (DSSCs). The TCO-less flexible working electrode could be sintered under 400–500°C. A preliminary result that open-circuit voltage (VOC)=650mV, short-circuit current density (ISC)=4.5mA∕cm2, and efficiency (ηAM1.5)=1.49% (100mW∕cm2) is obtained from the liquid-type DSSC. The incident light could be dispersed uniformly inside the electrode. Testing results of the double-counterelectrode cell indicate that the transmission of electrolyte is not the rate-determining step. The dense TiO2 layer is critical in improving the cell’s performances.

Fibrous flexible solid-type dye-sensitized solar cells without transparent conducting oxide

We have explored a type of all-solid fibrous flexible dye-sensitized solar cells without transparent conducting oxide based on a CuI electrolyte. The working electrode’s substrate is a metal wire. Cu wire counterelectrode is twisted with the dye-sensitized and CuI-coated working electrode. The cell’s apparent diameter is about 150μm. The cell’s current-voltage output depends little on the incident angle of light. A 4-cm-long fibrous cell’s open-circuit voltage and short-circuit current generate 304mV and 0.032mA, respectively. The interfacial interaction between the two electrodes has a significant influence on the inner charge transfer of the cell.

YBaCuO superconducting thin films with zero resistance at 84 K by multilayer deposition

YBaCuO superconducting thin films were prepared by multilayer deposition on different kinds of substrates. High Tc with an onset of 94 K and a zero resistance at 84 K has been obtained by deposition on pure ZrO2 substrates. The nature of zero resistance as well as the dR/dT characteristic above Tc and the influence of substrates are discussed.

Density effect on relativistic electron beams in a plasma fiber

Intense short-petawatt-laser driven relativistic electron beams in a hollow high-Z plasma fiber embedded in low-Z plasmas of different densities are studied. When the plasma is of lower density than the hollow fiber, resistive filamentation of the electron beam is observed. It is found that the electron motion and the magnetic field are highly correlated with tens of terahertz oscillation frequency. Depending on the material property around the hollow fiber and the plasma density, the beam electrons can be focused or defocused as it propagates in the plasma. Relativistic electron transport and target heating are also investigated.

Voltage-controlled multicolor emitting devices

Voltage-controlled multicolor emitting devices were fabricated by combining an organic light-emitting diode and a solid-state electrochemiluminescent device. Though the device has a simple-stacking structure with Ru(II) complex, tris(8-hydroxyquinolinato) aluminum, 4,4′-bis(2,2′-diphenylvinyl)-1,1′-biphenyl, and N,N′-bis(naphthalen-1-yl)-N,N′-bis(phenyl)-benzidine as basic materials, it is able to stably emit different colors, from pure green to pure red or from pure blue to pure red, under different driving biases. Its luminance can reach up to 1836cd∕m2 with current efficiency reaching 1.84cd∕A. The Ru(II) complex is considered to play a dominant role in this kind of device due to its unique reversible redox property.

Thermally activated flux motion in epitaxial YBCO films

Abstract We systematically studied the resistive transition and the voltage-current characteristics of well epitaxially grown single-crystalline YBCO films and found two important features of magnetic-flux motion in high T c superconductors: 1. 1) Isothermal V-I curves can show both positive and negative curvatures simultaneously. This inflecting behavior may be explained by some nonlinearity effects in flux creep. 2. 2) The activation volume of the flux creep is temperature-dependent as [T-T c ] −3v with v~0.6 This behavior strongly hints that flux creep is related to the fluctuation below critical point of secondary phase transition. A modified model for flux motion is proposed.

Ultrafast electron diffraction with megahertz MeV electron pulses from a superconducting radio-frequency photoinjector

We report ultrafast relativistic electron diffraction operating at the megahertz repetition rate where the electron beam is produced in a superconducting radio-frequency (rf) photoinjector. We show that the beam quality is sufficiently high to provide clear diffraction patterns from gold and aluminium samples. With the number of electrons, several orders of magnitude higher than that from a normal conducting photocathode rf gun, such high repetition rate ultrafast MeV electron diffraction may open up many new opportunities in ultrafast science.

Critical current density and flux creep in epitaxial YBa2Cu3O7−x thin films

Abstract The superconducting transition and critical current density were studied for epitaxial YBa 2 Cu 3 O 7−x thin films as a function of temperature, magnetic field and electric voltage gradient. A linear section of the curve of the logarithm of apparent voltage versus transport current density, ln(E)-J, was discovered in a region of low electric voltage gradient. According to the Anderson–Kim flux creep model a linear dependence is expected, as E = E 0 exp[− ( U 0 − JD )/ k B T ]. From the linear fits in the set of ln(E)-J curves, the value of D was obtained at different temperatures in variable magnetic fields. JD is a direct measurement of the dissipation energy caused by flux creep. The activation energy, U 0 , was estimated from these measurements. The behaviour of the parameter D is discussed in terms of the flux creep model.

Extended power law of nonlinear transport properties of superconducting materials

Publisher Summary This chapter explores the extended power law of nonlinear transport properties of superconducting materials. The nonlinear transport properties of superconductors near tile transition are usually described by the so called power law E/E c = (J/J c ) n . A wide-range resistive transition equation with the form of an “extended power law” is presented. This equation fits the experimental data of MgB 2 and high T c cuprates. For designing superconducting magnets, fault current limiters, cables and many other devices thorough knowledge of the electromagnetic response near the critical state is necessary. In principle this should be determined by tile Maxwell equations combined with a proper materials equation J(E,T,B). At present, power law E(J) characteristics of the form E = E c [J/J co (T, B)] n are often used. In this study it is showed that the E(J) isothermal characteristics for wider range including the crossover to Ohmic-like regimes have the general form of extended power law which well fits experimental data.

Hall effect in the mixed state of superconducting MgB2

Abstract On the basis of a theoretical model for the Hall effect within the framework of BCS superconducting mixed state and considering our longitudinal nonlinear response equation, we derived an analytical expression for the mixed state Hall resistivity of MgB2. This equation enables one to compare quantitatively the experimental data with the theoretical model. We also propose some possible scaling relations for the temperature and field dependencies of the Hall resistivity of MgB2.