Yang Shao-Peng

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.

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.

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.

Dynamics of Exciton Diffusion in PVK:Phosphorescent Materials/Al Hetero-Structures

Exciton quenching dynamics in a polymer PVK doped with FirPic, Ir(piq)2(acac) and Ir(ppy)3 phosphorescent guest materials, respectively, due to the presence of metal films is analyzed using time-resolved photoluminescence. The quenching is directly governed by radiationless energy transfer to the metal and is further enhanced by diffusion of excitons into the depletion region of the exciton population at the polymer/metal interface. The influence of polymer layer thickness on the luminescence decay is described by a one-dimensional diffusion model. The energy transfer distance and exciton diffusion length are 10 nm, 9 nm, 15 nm and 29.3 nm, 30.1 nm, 30.9 nm for PVK doped with phosphorescent guest materials FirPic, Ir(piq)2(acac) and Ir(ppy)3, respectively. This can disentangle the contributions from direct energy transfer to the metal and exciton migration to the exciton quenching process. The lengths of the exciton quenching region of the three doping systems are 39.3 nm, 39.1 nm and 45.9 nm, respectively.

Kinetics study of ultrafast electron transfer from sensitized dyes to silver halide microcrystals

Spectral sensitization micromechanism of cyanine dyes J-aggregate adsorbed on the tabular and cubic AgBr microcrystals with different dye concentrations is studied by using picosecond time-resolved fluorescence spectroscopy and the dependences of electron transfer and spectral efficiency sensitization on different conditions are analysed in detail. With the steady spectroscopy, the wavelengths of absorption and fluorescence of J-aggregate adsorbed on AgBr microcrystals are found to shift to red relative to dye monomer. The spectrum of fluorescence has a red shift relative to the absorption peak. With the time-resolved fluorescence spectroscopy, the fluorescence decay curves of cyanine dyes J-aggregate adsorbed on the tabular and cubic AgBr grains are found to be fitted well by a double-exponential decay function. The fitting curves consist of a fast and a slow component. Because of the large amplitude of the fast component, this fast decay should be attributable mainly to the electron transfer from J-aggregate of dye to a conduction band of AgBr.

Photoluminescence Mechanism of ZnO:Zn Investigated by Microwave Dielectric Spectrometry

We investigate the decay process of photoelectrons from a luminescent material of ZnO:Zn using a microwave dielectric spectrometry. Electrons in the conduction band are found to decay exponentially and the lifetime is 781 ns, while the time interval of decay from the maximum to half of this value is 470 ns. ZnO:Zn is a green luminescent material at its central wavelength of 510 nm. Compared to the decay of electrons in the conduction band, the decay process of the luminescence is faster, and the time interval of decay from the maximum to half of the maximum is about 100 ns. We believe that the mechanism of the ZnO:Zn visible luminescence is recombination luminescence, and find that our theoretical simulation is in agreement with the experimental results.

Investigation of photoelectron action in cubic AgCl emulsion doped with formate ions

In recent years, the formate ion (HCO2−) as a kind of hole-to-electron converter has attracted much attention of photographic researchers. The formate ions can trap photo-generated holes, eliminate or reduce the electron loss caused by electron–hole recombination in latent image formation process. Through the hole-to-electron conversion, it can also release an extra electron or electron carrier, improving photosensitivity. In this paper the microwave absorption and dielectric spectrum detection technique is used to detect the time evolution behaviour of free photoelectrons generated by 35ps laser pulses in cubic AgCl emulsions doped with formate ions. The influence of different doping conditions of formate ions on the photoelectron decay kinetics of AgCl is analysed. It is found that when the HCO2− content is 10−3mol/mol Ag and the doping position is 90% the electron decay time and lifetime reach their maxima due to the efficient trap of holes by formate ions.