Li Xiao-Wei

Characteristics of Photoelectron Decay of Silver Halide Microcrystal Illuminated by a Short Pulse Laser

A YAG supershort pulse laser (355nm, 35ps) is used as an exposure source and the microwave dielectric spectrum technique is used to quickly detect the photoelectron decay process in AgX microcrystals, because the free photoelectron lifetime and decay process can decide the sensitivity and other efficiencies of silver halide material. The result shows that the free photoelectron average lifetimes of Kodak-100 and Fuji-100 colour film samples are 8.5 and 9.5 ns, respectively.

Effect of Aluminium Nanoparticles on the Performance of Bulk Heterojunction Organic Solar Cells

Al nanoparticles (NPs) are incorporated in the active layers to enhance the performance of organic solar cells (OSCs). The improved short circuit current Jsc and power conversion efficiency (PCE) for OSCs with Al NPs are observed. A final PCE of 3.66wt% is achieved, which is an improvement of more than 30wt% compared to a standard cell with a PCE of 2.84wt%. When the mass of Al NPs is 10wt% of OSCs, the device performance is best. The optical performance of OSCs reveals that the absorption from sunlight increases. The external quantum efficiency spectra suggests that the Al NPs in the active layers influence the efficiency of converting photons into electrons, which leads to the improvements in the photocurrent. The enhanced photovoltaic performance induced by incorporating Al NPs in the active layer is discussed in the terms of increasing charge separation at the donor-acceptor interface and the effectively decreasing transmission distance of charge in polymer.

The influence of trapping centres on the photoelectron decay in silver halide

Photoelectron is the foundation of latent image formation, the decay process of photoelectrons is influenced by all kinds of trapping centres in silver halide. By analysing the mechanism of latent image formation it is found that electron trap, hole trap and one kind of recombination centre where free electron and trapped hole recombine are the main trapping centres in silver halide. Different trapping centres have different influences on the photoelectron behaviour. The effects of all kinds of typical trapping centres on the decay of photoelectrons are systematically investigated by solving the photoelectron decay kinetic equations. The results are in agreement with those obtained in the microwave absorption dielectric spectrum experiment.

Influence of substrate bias voltage on the microstructure of nc-SiOx:H film*

Amorphous silicon oxide containing nanocrystalline silicon grain (nc-SiOx:H) films are prepared by a plasma-enhanced chemical vapor deposition technique at different negative substrate bias voltages. The influence of the bias voltage applied to the substrate on the microstructure is investigated. The analysis of x-ray diffraction spectra evidences the in situ growth of nanocrystalline Si. The grain size can be well controlled by varying the substrate bias voltage, and the largest size is obtained at 60 V. Fourier transform infrared spectra studies on the microstructure evolutions of the nc-SiOx:H films suggest that the absorption peak intensities, which are related to the defect densities, can be well controlled. It can be attributed to the fact that the negative bias voltage provides a useful way to change the energies of the particles in the deposition process, which can provide sufficient driving force for the diffusion and movement for the species on the growing surface and effectively passivate the dangling bonds. Also the larger grain size and lower band gap, which will result in better photosensitivity, can also be obtained with a moderate substrate bias voltage of 60 V.

Measurement of the time-resolved spectrum of photoelectrons from ZnS:Mn, Cu luminescent material

The process of decay of photoelectrons in the conduction band of ZnS:Mn, Cu luminescent materials after excitation with a short-pulse laser has been investigated in this paper by means of measurements made using the microwave absorption dielectric spectrum detection technique. Exponential decay processes were observed for the electrons in the conduction band and the shallow-trapped electrons; the lifetimes of the electrons were found to be 1177 and 1703 ns, respectively. The processes of decay of the luminescence from ZnS:Mn, Cu were investigated and exponential decay processes were found for blue Cu+, green Cu+ and Mn2+ luminescent centres with lifetimes of the excited state of 139, 140 and 680 µs, respectively.

Low-Temperature Deposition of nc-SiOx:H below 400?C Using Magnetron Sputtering

Silicon oxide films containing nanocrystalline silicon (nc-SiOx:H) are deposited by co-sputtering technology at low temperatures (<400°C) that are much lower than the typical growth temperature of nc-Si in SiO2. The microstructures and bonding properties are characterized by Raman and FTIR. It is proven that an optimum range of substrate temperatures for the deposition of nc-SiOx:H films is 200–400°C, in which the ratio of transition crystalline silicon decreases, the crystalline fraction is higher, and the hydrogen content is lower. The underlying mechanism is explained by a competitive process between nc-Si Wolmer–Weber growth and oxidation reaction, both of which achieve a balance in the range of 200–400°C. We further implement this technique in the fabrication of multilayered nc-SiOx:H/a-SiOx:H films, which exhibit controllable nc-Si sizes with high crystallization quality.

The Effect of Using 1-Dodecanethiol as a Processing Additive on the Performances of Polymer Solar Cells

We introduce 1-Dodecanethiol (DT) to poly(3-hexylthiophene) (P3HT)/[6,6]-phenyl-C61-butyric acid methyl ester based polymer solar cells as a processing additive. When the amount of DT is 1vol%, the device performance is best. A final power conversion efficiency of 3.1% is achieved, which is an improvement of more than 40% compared to the reference solar cell without DT. To investigate the causes of improvement of the PCE, UV-vis spectroscopy, external quantum efficiency (EQE) is measured and an AFM is used. The enhanced photovoltaic performances are discussed in terms of optical properties and the film morphology.

The influence of K4Fe(CN)6 on the photosensitivity of cubic AgCl microcrystal

The influence of K4Fe(CN)6 at various doping concentrations on the photosensitivity of cubic AgCl microcrystals has been investigated by using the microwave absorption and phase-sensitive measurement technique. The time behaviour of free photoelectrons in AgCl microcrystals is analysed by using computer simulation as a function of three parameters of shallow electron trap (SET) including doping concentration, trap depth and capture cross-section (CCS). It is found that the three parameters of SET play different roles on the free photoelectron decay time (FDT). After considering the threshold effects of the three parameters and their collective effects, the trap depth value, the CCS value and the optimal doping concentration of the SET introduced by the dopant K4Fe(CN)6 in cubic AgCl microcrystals can also be determined and the best photosensitivity of cubic AgCl can be obtained.

Coherence effects in S/I/N/I/FS tunnel junctions

The dc Josephson effect in superconductor / insulator / normal metal / insulator /ferromagnetic superconductor junctions has been studied. We calculate the dc Josephson current based on the Bogoliubov de Gennes equation. The Josephson current is derived as a function of exchange field in ferromagnetic superconductor, normal metal thickness and insulating barrier strength. It is found that there exists an oscillation relation between the critical Josephson current and the normal metal thickness. The oscillation amplitude decreases as the thickness of the normal metal increases or the exchange field augments.

The research of photoelectron characteristic on Photoelectric Information material adsorbing green-sensitizing dye

The photoelectron time-resolved spectrums of silver halide, which adsorbed the green-sensitive cyanine dyes, are measured. The photoelectron lifetime of silver halide adsorbing dye is shorter than that of the pure silver halide.