Xu Wei-Wei

Dye-Sensitized Solar Cells Based on ZnO Films

In order to improve the performance of the dye-sensitized solar cells based on ZnO films, ZnO nanoparticles of different sizes were prepared by two methods. Some surfactants were added into the particles to form three types of ZnO pastes. Electrodes of various thickness applied to dye-sensitized solar cell were prepared starting from each of those pastes by the screen-printing method. The performance of dye-sensitized solar cells was optimized via both the selected particle size and film thickness. The reason of the inefficiency was explained by the infrared and ultraviolet-visible absorption spectra.

Influence of Yb-Doped Nanoporous TiO2 Films on Photovoltaic Performance of Dye-Sensitized Solar Cells

Yb-doped TiO2 pastes with different Yb/TiO2 weight ratios are prepared in the sol-gel process to obtain dye-sensitized solar cells (DSCs). The nanocrystalline size of Yb-TiO2 becomes smaller and the lattice parameters change. Lattice distortion is observed and dark current is detected. It is found that a part of Yb existing as insulating oxide Yb2O3 state acts as barrier layers at the electrode–electrolyte interface to suppress charge recombination. A Yb-doped TiO2 electrode applied in DSCs leads to a higher open-circuit voltage and a higher fill factor. How the Yb-doped TiO2 films affect the photovoltaic response of DSCs is discussed.

A Polymeric/Inorganic Nanocomposite for Solid-State Dye-Sensitized Solar Cells

A novel nanocomposite consisting of poly (3, 4-ethylenedioxythiophene)/poly (styrenesulfonate) (PEDOT/PSS) and CuI was synthesized via the reduction of CuCl2 by NaI in an aqueous PEDOT/PSS solution. The CuI in the composite was pure γ-phase, as was characterized by means of x-ray photoelectron spectroscopy (XPS), x-ray diffraction (XRD) and transmission electron microscopy (TEM). The dye-sensitized solar cell with PEDOT/PSS-CuI (15% in wt) nanocomposite as hole-transport electrolyte exhibited a considerable photocurrent, photovoltage and energy conversion efficiency (i.e. Jsc = 0.50 mAcm-2, Voc = 0.44 V, η = 0.1%).

The Electric Mechanism of Surface Pretreatments for Dye-Sensitized Solar Cells Based on Internal Equivalent Resistance Analysis

Based on the optimization of dye-sensitized solar cell (DSC) photoelectrodes pretreated with different methods such as electrodeposition, spin-coating and TiCl4 pretreatment, theoretical calculations are carried out to interpret the internal electric mechanism. The numerical values, including the series resistance Rs and the shunt resistance Rsh corresponding to the equivalent circuit model, are well evaluated and confirm that the DSC has good performance with a high Rsh and a low Rs due to good electrical contact and a low charge recombination after the different modifications. The I-V curves are fitted in the case without series resistance, and account for the role of Rs in the output characteristics. It is found that when Rs tends to the infinitesimal, the short-circuit current Isc, the open-circuit voltage Voc and the fill factor can be improved by almost 0.8–1.4, 2.9 and 2.1–6.8%, respectively.

A Study on Porosity Distribution in Nanoporous TiO2 Photoelectrodes for Output Performance of Dye-Sensitized Solar Cells

Porosity as one of the crucial factors to film morphology affects the overall electrical current-voltage characteristics of dye-sensitized solar cell (DSC). We search for the short-circuit current density, the open-circuit voltage and the maximum power output as the main functional parameters of DSC closely related to porosity under different film thickness. The theoretical analyses show some exciting results. As porosity changes from 0.41 to 0.75, the short-circuit current density shows the optimal value when the film thickness is 8–10 μm. The open-circuit voltage presents different variation tendencies for the film thicknesses within 1–8 μm and within 10–30 μm. The porosity is near 0.41 and the film thickness is about 10 μm, DSC will have the maximum power output. The theoretical studies also illustrate that given a good porosity distribution, DSC can obtain an excellent short-circuit current characteristic, which agrees well with the experimental results reported in previous literature.

Correction of PMT position effect for a lead-scintillating fiber electromagnetic calorimeter

The position effect of the photoelectron multiplier tube (PMT) of the electromagnetic calorimeter (ECAL) of Alpha Magnetic Spectrometer-02 (AMS-02) has been studied with beam-test data. The reconstructed deposited energy in a layer versus incidence position in the cell can be described by Gaussian distribution, maximum and minimum value can be obtained when the particle passes across the center and the edge of a cell respectively. The distribution can be used to correct the effect of incidence position on energy reconstruction. Much better energy resolution was acquired be got with the correction, for 100 GeV electrons, energy resolution improved from 3% to 2%.

Discrimination of converted photons and neutral pions at high energies

In the LHC experiment, the H → γγ channel provides a clean final state with an effective mass peak that is reconstructed with great precision, despite the small branching ratio. As a consequence, the H → γγ channel is one of the most promising channels for the Higgs discovery in the very low mass region. In order to increase the sensitivity of the Higgs search, background rejection rate is very important, so γ/π0 discrimination is one of the key points in the analysis. At least 40% of photons will convert with the experience of ATLAS and CMS. We constructed electromagnetic calorimeter (ECAL) in GEANT4 simulation, using 6 variables which have different shapes between converted γ and π0, with the TMVA (Toolkit for Multivariate Data Analysis) to do the separation. With this method we can get 30% to 60% π0 rejection efficiency when keeping 90% converted γ efficiency, in the region of transverse momentum 15 GeV to 75 GeV, not only in MC sumulation but also in real data.

Influence of TiCl 4 nanoporous TiO 2 films on the performance of dye-sensitized solar cells

The mechanisms of electron transport and back-reaction in dye-sensitized solar cells (DSCSs) are investigated by intensity-modulated photocurrent spectroscopy (IMPS) and intensity-modulated photovoltage spectroscopy (IMVS). The DSCSs with and without TiCl 4 -treated nanoporous TiO 2 films are measured by IMPS/IMVS. The results indicate that the electron lifetime ( τ n ), the diffusion coefficient ( D n ), the diffusion length ( L n ), the incident photon to current efficiency (IPCE) and the photoinduced charge ( Q oc ) increase markedly, while the dark current and the electron transit time ( τ d ) decreases for the TiCl 4 -treated nanoporous TiO 2 films. The influence of TiCl 4 -treatment of nanoporous TiO 2 film on the electron generation, the transport and the recombination processes is investigated at a microscopic level.

A study of hadronic shower development in the ECAL of the alpha magnetic spectrometer II

In this paper, we studied the development of hadronic shower in an electromagnetic calorimeter of Alpha Magnetic Spectrometer II. Two parametrized empirical formulae were proposed to describe the hadronic shower shape in calorimeter. Using 100 GeV proton beam incident on the center of the ECAL, detailed plots of lateral and longitudinal hadronic shower behavior were given and we found the formulae can describe the development of the hadronic shower with the test beam data. The possible application of the parametrized formulae including e?-?? discrimination and tau jet reconstruction was discussed.